Particulate Formation, Evolution, and Fate -Michelson Day 2 Part 3

Summary

The script discusses various diagnostic techniques used in sampling and analyzing particles in flames, focusing on the importance of careful sampling to avoid altering particle properties. It covers methods like photo ionization mass spectrometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and helium ion microscopy. The lecturer also explores particle sizing techniques, including Mobility particle sizers and aerosol mass spectrometers, along with spectroscopic methods like IR, Raman, and X-ray based analyses. The summary highlights the need for collaboration between different techniques for comprehensive understanding and touches on the potential issues with traditional sampling methods that could affect the interpretation of experimental results.

Takeaways

• 🔬 The script discusses various diagnostic techniques used in sampling and analyzing particles, emphasizing the importance of understanding what you want to measure before deciding on a sampling method.
• 🌡 It highlights the significance of parameters like temperature and pressure in particle measurement, noting how these can affect the behavior of particles, especially volatile ones.
• 💡 The speaker introduces different methods such as photo ionization mass spectrometry and transmission electron microscopy (TEM) for analyzing particle properties, including their size, structure, and composition.
• 🧬 High-resolution TEM is mentioned as a crucial technique for understanding the fine structure of particles, including the disordered center and ordered shells of aggregates.
• 📊 Atomic Force Microscopy (AFM) is discussed as a method for imaging incipient particles, providing insights into their physical properties like viscosity and shape.
• 🌟 Helium ion microscopy is introduced as an alternative to electron-based techniques, offering different information due to the use of helium atoms instead of electrons for sampling.
• 🔍 The script covers Mobility type measurements, such as the Scanning Mobility Particle Sizer (SMPS), which helps in obtaining particle size distributions by extracting particles from a flame and analyzing their mobility.
• 🌪️ The Aerosol Particle Mass Analyzer (APM) and the Centrifugal Particle Mass Analyzer (CPMA) are presented as techniques that measure particle mass independent of their shape or charge.
• 🌡️ The potential issues with sampling methods are discussed, including how the act of sampling can perturb the flame and affect the chemistry and particle properties being measured.
• 🔬 The importance of combining different diagnostic techniques is emphasized to gain a more comprehensive understanding of particle behavior and properties.

Q & A

What is the primary focus of the Diagnostics discussion in the script?

The primary focus of the Diagnostics discussion is on sampling techniques and the artifacts associated with sampling in the context of particle measurements and analysis.

Why is it challenging to measure highly volatile particles using certain techniques?

Measuring highly volatile particles can be challenging because if a technique requires a vacuum, the particles might vaporize, making it difficult to accurately measure them.

What factors should be considered when sampling particles for measurement?

Factors to consider when sampling particles for measurement include the properties of the particles, the desired parameters to measure, environmental conditions like temperature and pressure, and the potential need for techniques that do not perturb the sample or the surrounding environment.

What is photo ionization mass spectrometry and how is it used in the context of particle sampling?

Photo ionization mass spectrometry is a technique used to analyze particles by ionizing them with a laser and then analyzing the resulting ions using mass spectrometry. In the script, it is used to sample particles from a flame using a quartz probe, creating a beam of particles that are then ionized and analyzed.

How does transmission electron microscopy (TEM) contribute to understanding particle structure?

Transmission electron microscopy (TEM) allows researchers to send an electron beam through a sample, providing high-resolution images of the particle structure. This technique can reveal the morphology of particles and even allow for 3D imaging through tomography.

What is the significance of using a quartz probe for sampling in flames?

A quartz probe is used for sampling in flames because it can withstand high temperatures without melting and is less reactive than metals. This allows for the extraction of particles without significant alteration of their properties.

How does atomic force microscopy (AFM) differ from TEM and SEM in analyzing particles?

Atomic force microscopy (AFM) differs from TEM and SEM as it uses a mechanical mechanism with a physical tip that scans across the sample, detecting deflections as it encounters features on the surface. This allows for the imaging of particles and can provide information about their physical properties, such as viscosity or shape, on a nanoscale level.

What is the purpose of the skimmer in the sampling process described in the script?

The skimmer in the sampling process serves to create a supersonic expansion of the gas carrying the particles, which cools and dilutes the sample before it enters the vacuum chamber for analysis.

What are some of the limitations of using a TEM grid for sampling very small particles in flames?

Using a TEM grid for sampling very small particles in flames can be challenging because the real incipient particles, which are the smallest particles, are hard to sample accurately with this method. The grid may not capture these particles effectively, and larger aggregates are easier to sample.

How does the script suggest improving the understanding of particle formation and measurement?

The script suggests improving understanding by combining different measurement techniques and collaborating with others who have different expertise or access to various instruments. This multi-technique approach can provide more comprehensive insights into particle formation and properties.

Outlines

00:00

🔬 Particle Diagnostics and Sampling Techniques

The speaker introduces the topic of particle diagnostics, focusing on the challenges and methods associated with sampling particles for analysis. They discuss the importance of understanding various particle properties and how these properties influence the choice of measurement techniques. The speaker also touches on the difficulties of sampling highly volatile particles and the need to consider factors such as temperature and pressure in the sampling process.

05:01

🌐 Sampling and Particle Measurement Methods

This paragraph delves into specific techniques for sampling and measuring particles. The speaker discusses the use of photo ionization mass spectrometry and transmission electron microscopy (TEM) for analyzing particle growth. They explain how particles are extracted from a flame using a quartz probe and how different sampling techniques can affect the measurements. The paragraph also covers the use of substrates for capturing particles and the challenges of sampling very small particles.

10:02

📐 Advanced Particle Imaging and Analysis

The speaker discusses advanced imaging techniques such as TEM tomography for obtaining 3D images of particle aggregates and high-resolution TEM for examining the fine structure of particles. They also mention atomic force microscopy (AFM) for imaging incipient particles and helium ion microscopy for differentiating particle structures. The paragraph highlights the importance of these techniques in understanding particle morphology and structure.

15:04

🚀 Mobility Measurements and Particle Sizing

This section focuses on mobility measurements for determining particle size distributions. The speaker explains the scanning mobility particle sizer (SMPS) technique, which involves extracting particles from a flame, neutralizing them, and then sizing them based on their mobility in an electric field. They also discuss the challenges of dealing with multiple charges on particles and the use of aerodynamic aerosol classifiers for particle sizing.

20:05

🌡️ Particle Sampling Issues and Considerations

The speaker addresses potential issues with particle sampling, such as perturbation of the flame and the quenching of radicals, which can affect the accuracy of measurements. They highlight the importance of minimizing these effects to maintain the integrity of the reactive environment being studied. The paragraph raises questions about the validity of long-standing sampling techniques and the need for the scientific community to consider alternative methods.

25:05

🔬 In-Situ and Online Particle Analysis Techniques

The speaker explores the possibility of performing in-situ and online particle analysis, such as infrared (IR) spectroscopy and Raman spectroscopy, without the need for sample extraction. They discuss the benefits of these techniques, including the ability to continuously refresh the sample and the potential for coupling different methods to gain more comprehensive insights into particle properties.

30:08

🌟 Spectroscopic Techniques for Particle Analysis

This paragraph covers various spectroscopic techniques used for analyzing particles, including IR spectroscopy, Raman spectroscopy, and electron spin resonance (ESR). The speaker discusses the types of information these techniques can provide, such as bonding information from NMR and elemental composition from elemental analysis. They also mention the challenges associated with analyzing data from these methods.

35:09

💡 Optical and Acoustic Spectroscopies for Particle Study

The speaker introduces optical band gap and photoacoustic spectroscopies as methods for studying particles. They explain how these techniques can provide information about the maturity of particles and their interaction with light and sound. The paragraph also touches on the use of x-ray diffraction for understanding the structure of materials and the historical significance of these techniques in particle analysis.

40:19

🔍 Sampling Techniques and Their Impact on Flame Chemistry

This paragraph discusses different sampling techniques used in flame studies and their potential impact on the chemistry of the flame. The speaker describes thermophoretic sampling, where a cold grid is inserted into the flame to collect particles, and the use of probes with nitrogen jackets to minimize perturbation. They also mention the issues with using metal tubes, which can lead to oxidation of the sample. The speaker emphasizes the need to consider the effects of sampling methods on the accuracy of flame chemistry measurements.

Keywords

💡Diagnostics

Diagnostics in the context of this video refers to the process of analyzing and identifying characteristics of particles within a flame or similar environment. It's a key theme as the video discusses various methods and tools used to examine particle properties, such as size, structure, and composition. For instance, the script mentions 'Diagnostics' when introducing the topic and later when discussing different measurement techniques.

💡Sampling

Sampling is a fundamental concept in the video, which involves the collection of particles from a flame for analysis. The script discusses various techniques for sampling, such as using a quartz probe or a grid, and the importance of careful sampling to avoid altering the properties of the particles or the environment. The term is used multiple times, emphasizing its relevance to the diagnostic process.

💡Photo Ionization Mass Spectrometry

Photo Ionization Mass Spectrometry (PI-MS) is a technique mentioned in the script used to analyze particles by ionizing them with a laser and then analyzing the mass-to-charge ratio of the resulting ions. This technique is vital for understanding the chemical composition of particles and is highlighted in the script as a method for extracting information about the particles' properties.

💡Transmission Electron Microscopy (TEM)

TEM is a powerful imaging technique used to visualize the fine structure of particles. The script discusses its use for obtaining high-resolution images of particles, including their size and morphology. TEM is highlighted as a method that has contributed significantly to the understanding of particle structure, such as the disordered center and ordered shells of aggregated particles.

💡Scanning Electron Microscopy (SEM)

SEM is another imaging technique that allows for the observation of particle surfaces and morphology. The script mentions SEM as a tool for analyzing larger particles and for obtaining information about particle structure when high-resolution imaging is not required. SEM is often used in conjunction with TEM to provide a comprehensive analysis.

💡Particle Size Distribution

Particle Size Distribution is a key concept in the video that refers to the range of sizes that particles can have within a sample. The script discusses how different techniques, such as the Mobility Particle Sizer, can be used to measure this distribution, which is crucial for understanding the properties and behavior of particles in various environments.

💡Aerosol Particle Mass Analyzer (APM)

The APM, also known as the Centrifugal Particle Mass Analyzer (CPMA), is a device used to measure the mass of aerosol particles based on their centrifugal force and electrical mobility. The script describes how the CPMA operates and how it differs from other techniques like the Mobility Particle Sizer, emphasizing its reliance on mass rather than electrical charge.

💡Laser Induced Incandescence (LII)

LII is a technique used to measure the concentration of black carbon in aerosols. The script explains how LII works by heating particles with a laser to the point of incandescence and then measuring the emitted light. This technique is highlighted for its ability to analyze individual particles and its application in atmospheric science.

💡X-ray Diffraction

X-ray Diffraction is a method used to study the crystal structure of materials. In the script, it is mentioned as a technique that has been instrumental in understanding the structure of soot particles, including the spacing between graphene layers. The technique is used to identify the maturity of particles and their structural properties.

💡Sampling Perturbation

Sampling Perturbation refers to the changes or disturbances caused to the sample or the environment during the sampling process. The script discusses various ways in which different sampling techniques can affect the flame or the particles being studied, such as altering temperature, flow fields, or chemical reactions. This concept is crucial for understanding the limitations and potential biases introduced by sampling methods.

Highlights

Introduction to the importance of sampling and how to avoid artifacts.

Explanation of how temperature and pressure affect particle measurements.

Discussion on the challenges of measuring highly volatile particles.

Description of the photo ionization mass spectrometry technique.

Importance of using quartz probes in high-temperature environments.

Introduction to transmission electron microscopy (TEM) and its applications.

Comparison between TEM and scanning electron microscopy (SEM).

Details on high-resolution TEM and its ability to provide fine structural information.

Introduction to Atomic Force Microscopy (AFM) and its ability to image incipient particles.

Explanation of scanning tunneling microscopy for electron density mapping.

Overview of helium ion microscopy and its use in structural analysis.

Discussion on scanning mobility particle sizer (SMPS) for particle size distribution.

Description of aerosol particle mass analyzer (APMA) for mass-based measurements.

Introduction to laser-induced incandescence for single particle analysis.

Explanation of x-ray absorption spectroscopy (XAS) for compositional analysis.

Details on x-ray photoelectron spectroscopy (XPS) for surface composition analysis.

Discussion on sampling techniques and their potential to perturb flame environments.

Introduction to thermophoretic sampling and its application in flame studies.

Explanation of sampling issues and the impact of probe design on measurements.

Discussion on the challenges of interpreting data from different sampling techniques.

Emphasis on the importance of combining multiple techniques for comprehensive analysis.

Summary of how different spectroscopic methods can be applied to particle analysis.

Conclusion with an invitation to collaborate and combine techniques for better results.

Transcripts

all right are you coffeed up

ready to go for Diagnostics

um okay so let's do this

um

uh so let's talk about exit shoe

Diagnostics I moved it

um so this part is mostly about sampling

and all the artifacts associated with

sampling and how we might be able to get

around the artifacts

um laughs

okay let's see if uh maybe I have

protection

okay let me try this again

okay I'm gonna see if I can

one more

yes we're back okay

um

okay so um

yeah let's just get going

oh yeah this is

we're into Diagnostics

um and then tomorrow we'll talk about

atmospheric you'll probably finish

Diagnostics tomorrow and then talk about

atmospheric

um okay so you want to make measurements

you want to make a whole bunch of

different you want no different

properties of the particles and how you

do your measurements you know what will

depend on what you actually want to

measure right so uh there are a whole

bunch of different parameters you might

want to understand about your particles

or maybe you don't care about the the

some of these parameters and then you

can be a little bit more flexible about

what how you want to sample your

particles

um and it's not just sampling and

sampling and storing or you know or

putting like if you have a highly

volatile particle for instance it's

going to be hard to do a technique that

requires you have vacuum right because

you'll just vaporize your particles so

you so you have to think carefully about

how you're going to do these

measurements

um

then you'll want to probably do you know

if you're trying like say you're trying

to model

um so formation you're going to want to

also know and you're trying to compare

to data you're going to want to also

know all these other parameters

associated with the measurement

temperature for chemistry is hugely

important it's exponential with

temperature right so you want to know

temperature

um and you probably want to know like

you know if if you're under different

pressure conditions if your burner is

you probably want to know your burner

temperature there are all these

different parameters that we usually

need to to think about

so we'll talk a little bit about all uh

some of that as well okay so let's start

with

um some of the techniques that we've

already talked about just how they were

how these measurements were made and how

you might want to make them okay so

here's one a sampling

um we talked about this uh measurement

the photo ionization Mass spectrometry

on the the full particles that um the uh

growthier you know edel did

and remember we're this this is one of

the two modes and we're trying to figure

out you know what if those two modes

were different character or not

um so the way they sample from a flame

you see that they have a quartz probe

um so it's like a you know just like an

eyedropper almost that goes into

um their pre-mixed flame and often when

people do this type of measurement they

have the the quartz probe is sitting

above the burner you don't usually do

metal because it'll melt quartz will go

to higher temperature

and it's not highly reactive so you're

you're you're sitting there with your

quartz probe and you move the burner up

and down so you can get different

heights in the burner

um so in this case they extracted this

whole thing into a vacuum chamber and

they basically made a type of a beam

this is the beam of all the gas like all

the particles like straight into they

basically shot this into their vacuum

machine and then ionized with a laser

and then did a master

okay so the way they did their sampling

though is if you notice at the top in

that Circle that uh red circle of their

sampling

you see that

um

well so their sampling goes um right

directly from the flame they have they

use helium to carry the particles over

to their chamber and then they take the

whole thing helium and particles

directly into the chamber and how they

did that was

um through what they call a skimmer so

that all that helium pressed particle so

they do a dilution with helium they cool

with helium not the best gas to cool

with but we're doing a supersonic

expansion so they do a supersonic

expansion through this what you call is

what that cone shape

um

uh people call a skimmer for molecular

beams

um

your mechanical engineers most of you

right so you you know this technology

this makes a supersonic expansion into

their machine so that cools immediately

cools their whole sample

so they do a dilution and a cooling into

the machine and then they do the Mass

Spectrum Mass spectrometry

um

so this is um so then they do photo

ionization they don't vaporize in this

this machine

um

in this

um this is um transmission electron

microscopy so

um

so okay so I'm gonna let me instead of

talking about actually how you do

sampling right now let's talk about some

of these techniques so so that was how

you got Mass

um they they cool their beam there and

made a molecular beam a molecular beam

of their small

um of their molecules plus their small

particles

um and actually ionize the entire

particle so it didn't vaporize right

okay so here's another way of making

these

um small measurements of these small

particles

um with sampling so execute another exit

shoe technique this is um we and we saw

looked at this again uh earlier right

yesterday and earlier today you

basically take your sample

uh put it on

um a substrate so the way they um did

these measurements is they took a

substrate and they stuck it into the

flame and pulled it out and and then had

their sample on this they and it deuces

really fast you don't want to melt your

grid is usually a

um a carbon-coated gold

um often so you do this really fast like

it's a fast inject and we'll talk a

little bit about this later and then

they do transmission electron microscopy

so you send an electron beam through

your samples but your sample is is

sitting on a grid so the Electron Beam

can go through and um and collect the

electrons you also can look at the

electrons that are bounced off of the

sample so you have um this that's how

you get your scanning when you see

people say scanning electron microscopy

you'll see

um so that's that

um uh balanced like a beam and the one

that that goes through is the

transmission electron microscopy right

so you see both types the tem is

actually better for higher resolution

but if you have a big sample and you

don't and you don't need any resolution

better than a nanometer it's you a lot

of people use sem okay

okay so that's how they make that um

measurement

um

so this is

um tem of a particle oh yeah this is uh

coded

um uh particle that what collapsed us of

restructuring

um here's how people do

um so you can get aggregate size so you

can get so that a tiny particle size but

remember it's hard to sample the T the

real incipient particles are really the

smallest particles remember we we

weren't able to sample them it's really

hard to sample those really small

particle sizes using just a tem grid

inserted into that into the the flame

but it's really pretty easy to get these

um Aggregates okay and for Aggregates on

the size of you know 100 so nanometers

it's a really great technique just to do

regular tem put it into the machine

um this is a new technique you know this

um an interesting technique where they

do temography where they're able to like

rotate the sample and get a 3D image of

their aggregate this is really cool

because a lot of times we're trying to

understand the structure the morphology

of these Aggregates when they're sitting

on the grid and you just get basically

this this image like you're looking

through like at what's ever fallen onto

the grid sometimes you'll be able to see

the little arms like moving a little bit

in the TM machine but it's really hard

to figure out what the three-dimensional

structure is but this is tomography you

don't see this very often I think it's

very

um computationally labor intensive to

get one of these images but but it's a

really cool technique and you can see

how that aggregate is structured versus

how it looks in in the 2D team Imaging

okay

um

and this is sem tomography so you can do

the same thing with sem as well rotate

your sample and get um some structure

okay and then you can take these tem

machines and do high resolution tem so

this is a a different machine where you

do high resolution tem where you

actually get the fine structure of the

particle people have actually think they

can see even how big these

um these like graphene like sheets are

and calculate like they and they even

calculate if it has a little bit of

curvature they can calculate how much

curvature it has so people have done

some really really beautiful work with

these high resolution tem machines where

you can get the fine structure of the

particle that's this is a technique that

we get almost everything we know about

you know the um disordered Center and

then the ordered shells on the outside

we know almost like this is the only

technique that's been able to give us

that kind of information

um

and and this is a type of information

all of this came from high resolution

tem okay

um

so and then remember we were talking

about Atomic Force microscopy right

where we could actually image the

incipient particles and figure out that

they were like seem to be squishing on

on the um our our

um our substrate

um because the if if the particles were

spherical

um then we were seeing it like like

wider than it was tall so AFM was helped

us actually see that these incipient

particles seem to be somewhat waxy or at

least some uh like

um or liquid like maybe but probably not

but um pretty viscous if they're liquid

like so kind of waxy type particles that

was all done with this AFM machine and

remember I was telling you yesterday the

way this this works is you have this tip

that goes across like it's actually a

mechanical type of a mechanism it's um

that you have this actual tip that goes

across your sim you drag across your

sample and when it hits something the

mirror on the top of the tip tilts a

little bit and your laser beam that's

reflected off that mirror

moves so you can watch the movement of

that laser beam and know when you have a

deflection of your tip it's a very

clever technique

um

and you can do so this is

um uh the

um TM the AFM we're talking about I was

just talking about where you could see

the position

um of that tip and that the that

particle smeared out

okay

um this is the high resolution version

of it remember we were like it actually

can see individual atoms

um this is really interesting work and

um this type of technique was invented

at IBM in the 90s and I think they these

people collaborated with people at IBM

in um

he was in Switzerland

um in Europe somewhere um to actually

map out the structures of these ph's so

you actually can see individual carbon

atoms it's so cool

okay

um this is and then even see radicals

you can see the extra little

um uh signal from radicals

and then scanning tunneling microscopy

is a way of looking at the electron

density as you scan across the surface

and and

um look at the electron Den as it

transmission as it goes across the

sample that's getting tunneling

microscopy because electrons are small

enough that they can tunnel through

materials right

um

and and you can see that uh gives you

electron density

um okay and then we have

um

let's see which one is this oh helium

ion microscopy where you actually

instead of do it using electrons you can

use helium atoms

um and that can give you information

um that's a little bit that's um

different from tem in that you're

actually now sending a a bigger particle

now and slamming it into your sample

right and then looking at it looking at

it reflect

so its resolution isn't quite as good as

electrons electrons are really really

useful at being able to

sample materials and um and and being

able to uh interact with electron

density now once you start to get

um to bigger particles like a helium

atom you're not so much sampling

electron density you're sampling more

like that the nucleus

right so but and you're actually you're

not at you're not so easily able to

um see the high resolution that you can

get with electron so this is

um

uh helium ion microscopy and this is

remember we use that's the technique

that we use to see these different

structures like that the particles

actually may not be spherical so and

it's the same burner remember the same

conditions where we with tem we saw the

spherical particles

okay

um we talked I know some of you actually

have been using these Mobility

type measurements this is a a scanning

Mobility particle sizer

so in this technique you extract your

particles from the flame so this allows

you to get particle size distributions

so you extract your particles from the

flame

um and then you uh uh they they

the terminology isn't something I really

like but you send those particles like

you're you extract your particles and

remember when when you do

um

uh when you when you take particles from

a flame the soot particles are actually

charged

um some of them are charged some of them

are neutral some of them are positively

charged some are negatively charged and

some are neutral okay so what you take

these particles out of the flame and

then you send them through something

called a neutralizer and what the

neutralizer does is it um gives you a a

known or an assumed uh um charge

distribution so it has a distribution of

single charges

um and you usually make this measurement

assuming that you have all like single

charged particles it doesn't charge all

of them

um it charges some subset of them so

it's hard to get quantitative but you

can actually make some assumptions about

how many particles are charged and and

see if you can um and and give it gives

you some kind of at least

reproducibility so you get this particle

size distribution and then the whole

thing acts almost like a mass

spectrometer for particles so you have

so you have a single charge on a

particle

um the particles and so it's a cylinder

so um where you have a a high voltage on

it's a

coannular two cylinders

um basically like electrodes so you have

a high voltage inner cylinder and then a

neutral outer cylinder and that puts a

field on inside the tube and the

particles drift through this field right

so now you have a charge drifting

through a field right electric field and

the charge the particles are going to be

diverted

based on what the field they're

experiencing how big they are and what

their charges right their Master charge

ratio basically

um and you actually sweep the voltage on

the inner rod and particles of a

particular size as you see the voltage

respond to that that field and go

through some of them the ones that are

in the The Sweet Spot of that field go

through this hole at the bottom and then

are extracted and you count them

usually count them with um

a condensation particle counter which is

just a laser

in order to count these particles

especially the small ones you have to

coat them with some kind of liquid and

there's usually like butanol

um you coat the particles and then you

can count them with this laser

and and as you sweep the voltage

different particles of different sizes

will go through and then you count how

many get through that's what gives you

the particle size distribution from a

skinny Mobility particle Sizer

um and this is a technique that like we

use all the time it's like been super

super helpful

um so this is an example okay so one

thing to note about a skinny Mobility

particle Sizer is that you can get

multiple charges so now

um if you you can actually use

um a part of this to select out and

particle like if you keep your voltage

in a single voltage your inner Rod is

single voltage

um you can select out one particle size

so if you want to do an experiments

where you're just looking at one

particle size

you send it through this thing and you

just collect the particles that come out

okay you

you say what size you want particles

come out but your neutralizer actually

gives you particles with one charge two

charge and three charged normally

um so when you send that distribution

back through an smps a different smps

you see one charge is the left two

charges the middle because the larger

Mass has two charges and it thinks it's

just one charge so the massive charge

ratio is the same as the first Peak same

and then then you have three charges and

that's um that's the distribution you

get after you send it back through okay

so you just have to be aware of that

when you're where you're doing this um

the uh the um and and okay so that is

that's

um dependent on the mobility diameter

right the mobility diameter actually

depends on for soot it's kind of

confusing because you um if you had a

spherical particle the mobility diameter

would be the same as that diameter with

soot you have this like aggregate right

this you know big floppy and it's like

you know not spherical so the mobility

diameter is kind of confusing because

this Mobility diameter of a big floppy

thing is going to be different from a

Mobility diameter of a spherical thing

and that and you know the the reason is

it's

um you're kind of drifting it's an

aerodynamic thing because you're

drifting through this field right with a

charge on on yourself and you go through

you know based on that

um as you're drifting through you're not

under vacuum you have a gas in there and

you're trying to make it through this

gas

um with this chart with this force on

you okay so all that like affects your

Mo how how you get measured but this um

uh aerosol particle Mass analyzer or

centrifugal particle mass and letters

are is based on charge is placed based

on mass so it doesn't matter how floppy

you are you have a mass right and this

um is kind of a cool I don't know I wish

I had brought a picture of of our our

cpma it's kind of this like uh

funky machine it looks like it should be

in an old in a little old um

cafe or something next to the Jukebox

it's like it it works and it spins and

what it is is it has two cylinders and

one of the cylinders is spinning and the

particles are kind of like whoa want to

fly out you know like with the spinning

cylinder and and you apply it um you do

the same neutralizer thing put a charge

distribution and then you apply this

field to pull the particles back so

you're fighting this centrifugal force

with this field and that's how you use a

centrifical mass analyzer and that is

dependent on Mass so it's all really

cool

um uh and and then you can compare so a

lot of people when they're looking at

um

at soot this is really common especially

for atmospheric scientists

um when they're trying to understand how

mature stood is or where it's come from

they cut they want to do this

measurement basically of how how um you

know what is fractal dementia like we

would put under a TM machine rate and

say okay the fracture mention is this it

looks like a regular aggregate from this

hasn't been processed blow up

um they'll often in the field take a a

mass measurement and a Mobility

measurement and compare them and say

okay the mass measurement says this but

the mobility measurement is not it's not

spherical right it doesn't give you know

so they have these relationships they've

done with different particles of

different

um shapes and and masses to and they

have these like correlations and stuff

and that's they they tell something

about is this a diesel particle based on

them the masked Mobility

ratio which I find fascinating

okay

um

and this is um the aerodynamic aerosol

classifier that does not actually even

depend on

um charging so this is kind of a new a

new technique that doesn't depend on

charging you don't actually have to

change you just do it aerodynamically

you send the particles in

aerodynamically and then

um you still have the rotating cylinder

um and you still have that centrifugal

force but it's everything's aerodynamic

instead of

um uh by charge by field charge and

field so this is actually a really nice

you don't have to worry about single

charges double charges triple charges

it's it's a really nice technique

um I've never used one though and I

don't so I don't know how how easy it is

to use the the thing with a cpma is it

takes like

um

so in terms of time scale if you've

never used any of these techniques like

you can make a laser-based technique and

you know whatever you have

uh 30 seconds

um and average whatever you know you're

doing 10 Hertz you can you know average

quite a bit in a few seconds

um

if you are using it a cpma it might take

five minutes to get one measurement

um so it's a it takes a long time for

you to go through

um and make one of these measurements

um I've never used one of these these

instruments

okay

if you want to extract this is a really

cool technique that um uh it's an

instrument that atmospheric scientists

have been using for uh years

um and it's kind of the Workhorse for

measuring black carbon in the atmosphere

trying to understand

um how should is emitted and distributed

in the atmosphere to try to understand

climate climate change so people carry

these instruments you know out into the

field they fly them on airplanes

um and it's it's kind of an interesting

instrument because it measures soot

using laser induced incandescence one

particle at a time but you have to

extract extract yourself from the flame

and send your sit through this

instrument so we haven't talked about

laser induced in essence that much yet

but

um if you've ever used laser induced

incandescence it's usually a post laser

um and it's usually a high-powered laser

enough to heat your soot up to a

sublimation point of 4 000 Kelvin so you

really need a nice

big laser and usually water cooled and

Flash lamp pumped yags

um this

um

how they get the particles to high

enough temperature with a tiny lace they

actually use just a small yeah Glazer

it's a CW laser so instead of being

pulsed it just is continuous so it your

particle and it's in the way they get

the particle hot is in the middle of the

laser cavity they have this stream of

particles you you take your particle one

at a time and let it go through your

laser beam

it takes about 20 microseconds

um for your laser instead of nanoseconds

where you normally do these posts things

like nanoseconds this goes through

microseconds like 20 microseconds so it

is sitting there for a long time just

absorbing all of that ir and heating up

hopefully to the sublimation temperature

though it's not always true

um and then it emits

um laser intestinecandescence and you

measure that single particle Li it's

sort of it's actually really clever you

also measure scatter from that single

particle so you can then then they have

these fancy ways of of comparing the

timing of the LI to the timing of the

scatter to tell if your particles are

coded you're vaporizing so it's they

actually will do vaporization

um measurements like they say okay if I

see scatter first and then Lai at at a

later time I know it's taking me longer

to heat up my particle so I know there's

a coating and then they've done all

these like you know characterizations of

this instrument to figure out what the

Coatings are it's a really kind of

fascinating technique

um uh yeah so so

um you can then see like the different

as a function of time you know the

different

um

parts of your distribution because you

see one particle at a time instead of a

whole distribution of particles

okay

oh yeah and then one of the drawbacks of

the instrument is the lower limit is

about half of a phentogram which is the

particle size for particles about 140

nanometers Mobility diameter so if you

work on diesel engines you know hmm

that's a little bit too low of a lower

too high of a lower limit to do a good

job with diesel particles because those

particles are smaller

okay aerosol Mass Spec that's another

one where we have to extract

here's our the instrument we use

um uh and the typical Mass Spectrum we

get for this is for particle composition

um so we extract

um and we send we'll talk about how we

extract it in a little bit send the

particles I think I described this

yesterday we send the particles through

an aerodynamic lens system which focuses

the being the particles into a beam

sucks away all the gas

um so we don't see the gas phase that

beam of particles hits a plate is

vaporized under vacuum and then we

ionize using the vuv from uh synchrotron

and then do a Mass Spectrum

uh and then we can tune the photon

energy and and get our photo ionization

efficiency

um

and then uh so this provides information

about

um species that are on the surface that

are vaporized or species that are part

of the particle that you can vaporize um

just by heating on that plate on under

uh vacuum

okay so here is a technique

um

that the uh that's uh x-ray based right

where you're extracting it's near Edge

x-ray absorption spectroscopy or x-ray

absorption spectroscopy

um there are multiple different names

that you can use

um there are different ways of doing

this technique

um and you usually take your sample to a

synchrotron and do these measurements

you can get a so basically you take your

X-ray beam

um and then you pull off an electron

right and then you can can actually

either do the technique by looking at

the electrons

um or you can do the technique by

um so what will happen you pull off an

electron

and you can either look at the

fluorescence of you know one of the

electrons will fall back down into that

hole right and you can look at that

fluorescence and when that electron that

second electron Falls at the excited

state falls back into the um hole you've

developed when you excited another

electron will fly off and you can

measure that electron or you can measure

the fluorescence so there are two

different ways of doing this technique

um and you can get compositional effects

information about the the uh

and it usually

um you'll have a peak that's related to

graphite so it's a pi to X star

transition so at that Photon energy

where you have the transition from the

ground state to the um the the 1s to Pi

uh excited state

um

you can either look at that and and try

to get understand about the how graphic

your sample is you can understand how

many

um the state over to the store it says

1s to Sigma star that's um for these

aliphatic you know side chain type

things you can get information about

oxygenated Peaks okay

um

thank you

and then XPS is also x-ray

um and you basically hit the particle of

your sample with an x-ray beam and then

look at the energy of the electron that

comes off

so that gives you also almost like very

very similar information to next house

but as very surface sensitive because

you have to count on the electrons

coming off and if they're buried your

sample if it's very deep in the sample

you're not going to see those electrons

coming off the surface

so that

what's hard about this technique and and

probably also next apps is

um doing the analysis and trying to

understand what you're seeing because if

you see there like here's an example

where

um you see this carbon binding energy so

this this technique can give you

information about so

um that 284 is where you will get it's

called the carbon K Edge it's where

you're going to get that excitation in

carbon

um

the what your carbon is bonded to

um that the energy will change depending

on what your carbon is bonded to so you

can get some information about the

bonding to carbon to whatever oxygen

another carbon whatever

um but you notice how hard it it is to

see all those little Peaks underneath

that carp that and then you're trying to

fit all these little Peaks it can be

really messy to try to analyze the data

okay

um

oh yeah so

um

this is this is really interesting the

um I haven't seen a lot from these

experiments but this is actually

fascinating where you do some of these

x-ray techniques with a beam of of like

where you you can extract from your

flame and send so I was just showing you

techniques where just now where you

would

sample by sticking a grid in the flame

I'm extracting the sample and then

carrying it over to the synchrotron and

and putting it up you know putting it in

an atmosphere well you get it over to

your vacuum at the synchrotron and

putting it in the machine and trying not

to let it contact oxygen and stuff

um this technique you actually can do

online so have a beam of of

um of uh particles that go into this

machine and then

on the fly in this beam actually do some

of these measurements of X-ray

absorption or this one is for x-ray

photore

um XPS x-ray photoelectron spectroscopy

like I was just talking to you

um on the previous slide so this is

actually really interesting that you can

do these measurements like on a beam of

of um of particles and and you can start

to think you know so this is an example

of where you're almost merging

um a technique that's

uh

uh really hard to actually kind of move

sort out right like move do all the

stuff to get to the machine

um

where you can almost start to exclude

the surface from your you know your

particles are just going right from the

sample into the machine

so you can start thinking about okay

how about IR spectroscopy could you have

a beam of of particles and do IR

spectroscopy on the Fly could you do the

same thing with Rama and spectroscopy

are there so then then you don't have to

worry about the sample sitting on

um a substrate or you can refresh your

sample you can actually continuously

refresh your sample and maybe change

something and then and do the

measurement while you're changing

something so these are the types of

things that we can start thinking about

right once you can do something like

this and get rid of some of the

complications maybe there are other

techniques we can do the same thing and

these would be types of things you could

do actually in your own lab rather than

going to a synchrotron

um

so this one is also on the Fly next

halfs and XPS

um where they make a beam of particles

and then do the measurement

um

as their as there you know can change

something change the height in the flame

where you're extracting okay so

um

okay so here are some kind of a

description of all the different types

of spectroscopies right you have

infrared you're absorbing right just

direct absorption

um you have you can do infrared overtone

like looking at multiple overtones of of

going from say uh uh the first

vibrational state to uh so the ground

vibrational state to the first or the

second or the third so that would be

overtone spec IR overtone spectroscopy

um

you can do a spectroscopy where

um you do get the same transition but

you do it by excite doing a ram on

transition so you excite and then relax

back to that state and look at the

difference in the photon energy

so that's another way instead of

um then then you can do this type of

spectroscopy so basically getting the

um energy of a vibrational State you can

do with actual visible light instead of

IR light so there are all these

different ways to use spectroscopy right

um so when we talk about Stokes you know

we that means that when you do the

transition you go up to an excited state

and down so you're going

um

you're going

to a higher state going to a low uh

going Andy Stokes yeah going to a higher

state and then anti-stokes is going to a

lower State okay so we're going to talk

about Stokes and anti-stokes in a little

bit when we do cars

um and then we can do different orders

of Raman so you'll see this and

different the second order of Raman

spectroscopy gives you more information

some other types of information related

to the conjugation length in in

subparticles

I know this is like a lot of just

dumping information that you

um

but this is like you'll be able to look

back and go okay oh yeah yeah

um

do you have

yeah previously

oh

um probably if I

um

let's go back to see

um oh let me see if I can do this

is it is this where

you're talking about yeah yeah yeah no

so the color actually

um I it's color-coded by temperature

which on the experiment was done so

these were individual experiments

measuring the particle size distribution

as a function of temperature of the

pyrolysis

does that make sense

yeah

oh yeah

yeah yeah yeah yeah actually

yeah yeah totally so any of these

techniques and I think that there's a

power in coupling techniques so I would

say instead of

um marrying yourself to one technique

um even if like say your lab only does

smps

um okay you're all here

um and you're meeting other people who

may have another technique and if you

collaborate putting two techniques

together can actually give you a

powerful way of finding out new

information

so I totally encourage you to talk to

each other or talk to me like you know

I've done lots of different techniques

maybe I could set you up with something

at a synchrotron if you want to do a

particular measurement you think that

would help with your your experiment

um this is exactly I I you know I I

definitely think it's it's worthwhile

thinking about combining techniques

yeah

yeah so so so keep meeting people okay

keep talking yeah thank you

okay

um

okay okay okay okay

um we're almost done with this part I

think

um

okay we talked about IR spectroscopy

right

um

and then

um RAM on spectroscopy those are two

exitu techniques that maybe you can

figure out a way to make them at least

online you know maybe in situ but that's

awfully hard because you have Luminosity

from the flame okay so that it was a

complicating Factor

um

uh so remember the GP because your

graphite Peak the DP gives you

information about and Raman Spectros

which gives you information about

defects so you can use that technique to

give you information about

um how how

um what's a fine structure of the

particle okay

um this technique is electron spin

resonance or electron paramagnetic

resonance spectroscopy gives you

information about radicals like okay so

can we find a technique that's like

sensitive radical you see yes this is it

um

but it has the big drawback is that you

have to have a huge magnet to apply a

big magnetic field and then that

magnetic field splits the energy related

to that remember that you have this in a

radical you have a lone electron it's

either spin up or spin down right so

depending on how your spin is aligned

with your magnetic field you're going to

have different energies of these um

States okay and you can do spectroscopy

um between these states and this is what

you can so there there would be two ways

of doing this you can either

scan your magnetic field strength right

or you can scan the

um the wavelength of your light your

light is going to be probably terahertz

right so your terahertz light so it's

nine gigahertz and you have a big

magnetic field so in this case I think

they keep the

um light the same and they scan the

magnetic field

um and then they get a signal for

um their radical species and as you

notice as a function of height in the

flame they get different signals for

Radicals I'm not sure how selective this

is without actually having a very fancy

epr machine I haven't seen it because no

one's done the experiment

um so it tells you that about the

radicals in the flame but you know this

the particles in the flame but I'm not

sure how much you can get from this

technique

okay

okay NMR nuclear magnetic resonance

similar to electron magnetic resonance

and now you're looking at the um the uh

carbon so this is a really really really

common technique that organic chemists

use

um again you need a big magnetic field

in this case so you're looking at the

hydrogens in your your sample

um so you can actually tell something

about the bonding of the hydrogens to

different carbon atoms but it's a very

and these are also huge machines but you

can usually have organic chemistry

friends that can help you do NMR

spectroscopy

and then we go to

Elemental analysis one of the oldest

techniques we have

um but that we need to do I think we

need to do more Elemental analysis where

we can distinguish how many carbons how

many hydrogens and maybe how many

oxygens and if you're doing something

else how you know other elements that

are involved in your particle formation

um okay so I think this might be the

last of the

oh yeah so um this is also

um an execute

um remember uh Optical band Gap gives

you information about let's see

um the majority of the particle so this

is uh where people have extracted

particles and looked at the maturity

using the optical band Gap technique

trying to sort out how big are their

species in the flea

um again that's remember that's related

to the um all the uh how how Broadband

your spectrum is the um and the uh

dispersion exponent it's very similar so

it basically gives you the transition

energy between your highest occupied

molecular orbital and the lowest

unoccupied molecular orbital

um

and then your dispersion exponent we

talked about that already and then photo

acoustic spectroscopy is kind of

interesting we I don't know anyone in

the field who uses it in combustion

science but I do know people use it in

atmospheric science to look at sip

particles in the atmosphere

um basically it's

um you send a laser in the the particle

absorbs and then it does you know it

generates a pressure wave as soon as it

absorbs you know it heats up quickly it

generates a pressure wave and you um you

put this into an acoustic cavity you put

your sample into your acoustic cavity

heat it do this

laser Heating and you look for the

acoustic wave

it has some issues like it's highly

sensitive it's it's uh you have to be

very careful about your the alignment of

your acoustic cavity but um but people

do use it in atmospheric science

um oh yeah so now let's look at we're

going to come back to this because we're

going to look at an in-situ version of

this but this is x-ray diffraction

spectroscopy very very old technique

also looking at the structure of

materials anyone who does Material

Science has probably come across this

technique

um where you basically look at the

correlations between different

um your your X-ray beam hitting

um different surfaces in a crystal or

different layers in a crystal and then

you have either

um

uh uh you have then they constructively

or destructively interfere with each

other the the the the beams the the as

if you think of the light as wavelength

um and you'll get resonances at

particular

um

um particular they're associated with

particular spacings in your Crystal so

um you look at for those resonances

and let's see here's an example

um oh yeah so and those can be

associated with the lay so for graphite

there would be layers in the graphite

right between the different layers but

it's also you can look at the spacings

and the six-membered Rings like you're

going to have repeated structures in the

six-membered Rings they're going to be

um constructively interfering to give

you a peak

um

and and and different ways have you like

they're they're so they're different

um uh resonances that are associated

with

um the different ways that the beam can

constructively interfere with different

parts of your sample

um oh yeah and here is

um Rosalind Franklin and her one of her

experiments looking at the X-ray

crystallography or x-ray diffraction of

this graphite sample

so uh

so here is a sample from a flame and you

can see the graphite Peak that's the 001

is the um

the interior spacing

um and then there's first uh soot

and this is one of the techniques that

actually was

um was very

um instrumental in telling us how far

space the graphing sheets are and soot

um so that gave us that answer and it's

it's been very consistent

yeah and then there's a 100 diffraction

Peak

which is commonly seen and I think

that's the spacing

um between the the uh

um in this in the plane the six-membered

Rings

um so it gives us information about the

maturity of the particle Okay so

um let's quickly talk about sampling

sampling issues

[Music]

um

okay so here are a whole bunch of um

these are these are Flames that we use

in our lab all of them give like

different

combustion conditions right

um so uh and here's what happens when

you put a probe in them so you can see

we actually do a lot of tech experiments

where we probe the flame

and they the probe perturbs the flame in

different ways okay and and we use

different types of probes depending on

the type of flame that we have

um and this is important not just for

for

um flames it's also important for any

reactive environment where you're trying

to probe the particles you're generating

okay so um this is one of the oldest

techniques that um people use for

extracting so from Flames

um it's uh basically it's

um where you take a grid and you

um it's it's like a rapid insertion

thermophoretic sampling where you take a

grid you insert it into a flame really

fast so this rapid insertion you have a

Pneumatic cylinder that like shoves that

grid into the flame and pulls it back

really fast or you shove it in

um wait for

a very short fraction of time to collect

something and pull it back but it

happens all that happens really fast you

wouldn't be able to do it yourself you

have to have this pneumatic cylinder

doing it

um the the grid tends to be on the order

of um like a couple or to three

millimeters when you're doing tem grid

sampling

um so your sample can be pretty big

compared to your flame

um and people have found that it's

better to have the the grid vertical

um in the flame but then you like mess

up the um the if you're interested in

what's happening as a function of height

in the flame and you have a three

millimeter grid you're going to mess up

your vertical resolution right

um so you anyway you inject this and the

the grid is cold compared to the flame

so you are preferentially having the

particles going towards your cold grid

and sticking there hopefully sticking

there right and um and then you pull it

out and then you you cool it off and you

put in your TM machine

or whatever machine you're using okay

that's thermophoretic sampling

um

uh

this is

so this is a tech okay

I think this is

oh yeah yeah sorry I I made these slides

a while ago and uh they needed them to

print out like three months ago or

something or two months ago so some of

these I'm like oh wait what did I don't

remember that

um so yeah this this is another like

where they um stuck it into the flame

but they applied a voltage to it and and

they think that this actually helps and

I would I would be interested to see

what happens if you apply a positive

voltage versus a negative voltage

because particles negatively or

positively charged or neutral

um so they collected and they they

um see more sample collected when they

actually put a voltage on their their

sampling their T their our

thermophoretic sampling system

I thought that was really interesting

um

so here's what happens so here's the you

know the kind of the downside of this

type of sampling is it can actually

perturb the flame quite a bit so it

perturbs the flow field

um here are a couple multiple papers

that have talked about how the sampling

perturbs the flow field this is

perturbing the temperature so this is a

calculation of how the probe could

perturb the temperature

um and then

um

uh this is like measurements of the

temperature as a function of where the

the probe is inserted in the flame so

you you see that you know there there

can be like a distribution of

temperatures so if you're inserting so

here's the question is and this is this

is true for all sampling you stick the

Grid in

um

if it's if you're cooling your flame a

few millimeters from your or your

sampling you're actually changing the

chemistry

where near where you're sampling and I'm

not actually I'm not sure what the

effect is but you also quench the

radicals so you're actually changing the

chemistry around your sampling so in

this case you know

um

it you know I'm concerned like we do

this we do this sampling but I'm kind of

concerned about this technique so um

uh

and here are some okay so this technique

remember is one of the first techniques

it's one of the most

um widely used technique for

understanding what looks like in a flame

this is how we've been sampling for

decades right using this thermophoretic

sampling so if it has some problems

is it affecting how we view the field

you know what we know about snow

formation so that's just a question I

just don't know the answer to it

um but it's something that we should be

thinking about as a community like are

there different ways we can do this okay

um

this is another way to sample

um you put a quartz probe or you know

into and remember

so here's a ques here's here's what we

want to do is like you want to extract

the you want to extract the particles

without perturbing your reaction your

system right you want to quen you want

to dilute them really quickly so they

don't interact with each other or with

the gas phase right and you want to cool

them really fast so that you quench all

chemistry when you sample right as you

get into that your probe so here are

some um attempts to do that so you take

a probe and in this case you you

um you have a jacket of nitrogen that

flows around the probe and then you

sample you suck into the probe and the

nitrogen goes up with the sample so it's

a club very clever way of of making a

probe the problem is the probe then gets

bigger because you have this jacket of

nitrogen around it

um there's another here's another way of

sampling through a tube with a hole in

it and you send nitrogen through so this

is like it cools and

um and dilutes in the tube as the

particles go into the tube you you

basically add vect them into your hole

in the tube and send them down

both of these probes have been shown to

um perturb like possibly perturb the

sample a little bit like particle size

distribution

um and we found that uh if we use a

metal tube

um and we we get oxygen like so if we if

we use a um a co-flow diffusion flame

and we were sucking from the flame if we

get a little bit we get to the closer to

the tip and we suck in some of the

oxygen from the co-flow

everything's hot enough to catalyze

um the tube gets really hot the Tomato

tube gets hot and we catalyze reactions

on the metal tube in the probe even

though we've diluted even though we've

cooled a little bit it's still hot

enough to get oxidation of the of the

sample in the tube so we don't use this

technique anymore with a metal tube

because we're we're really we're trying

to understand the chemistry and we we

get oxidation of the the sample

um

here's another way of of probing you you

stick up you know as talking about on

the very very beginning you stick a

quartz tube into the flame

we do this all the time

um and then you suck out of the flame so

people have done these are measurements

showing the change to the temperature so

that the probe is um over there on the

right hand side

um let me see if I marked it

so the the probe is on the right hand

side and you see how it cools the whole

region around the probe in the flame

um that's really disturbing because

that's basically cooling the whole

region you're really perturbing the

chemistry on the left hand side people

have also shown that it really perturbs

the radical concentration near the probe

so that's something that we have to

worry about when we're doing this type

of probing

um so

um I think I'll stop here

um and because it's the end of our day

and you must be exhausted sitting here

for so many hours so go get some sleep

and

um I'll see you tomorrow and we'll

finish up the diagnostic section then

jump into atmospheric and have fun