OK Well it's a pleasure to be here.

And tell you some fairly new results but

have that have a fairly
long history actually.

For a lot of.

People the early days of soft matter
physics was sponsored in large part by

NASA and so we had to find interesting
experiments that we could do which I

think we all did in those days I'm going
to tell you about some that started about

fifteen years ago but have evolved over
the years and we have new results.

And the main person who is
doing all of this of course

is Peter Lew who I'm sure
everybody here knows.

And so
this is a really his recent results and

this is talk where I also should
acknowledge a whole bunch of people

basically the crew on
the International Space Station and

you'll see what I mean when
I show you the results so.

Colloidal particles I probably don't
have to tell everybody in this audience

why we like to study them.

The main reason for
looking at them is that they're large and

they're relatively slow and
they're thermal equilibrium and so

they explore phase space
very simply because of.

Thermal effects but
they're large enough and

slow enough that you can follow
the individual particles and

again the phase behavior is fairly
well known if you have just.

Particles with no
interactions then packing

constraints dictate the phase behavior.

Buckley Prize this year was awarded for
understanding packing constraints and

particles among other things so
they go through.

An order.

Disorder transition they crystallize and

they can form crystal structures
they can form glasses a large

number of of interesting
behaviors if you add

an attractive interaction which can be
done in a very simple way by adding.

An inert polymer So you have
exclusively repulsive interactions

nevertheless because the because of
entropic effects the exclusion of the.

Polymer from the space between
the colloidal particles leads

to a weak attraction and

you can control that attraction can both
the link scale of the attraction and

the depth of the attraction by controlling
the concentration the size of the polymer

you can get attractive
colloidal particles.

And when you have attractive chordal
particles of phase be a viewer changes you

get a very complex are much more
complicated kind of behavior

where you can get different types of
phase separations into colored rich and

colored poor regions these are series of
calculated phase behaviors a function

of both the concentration of
the collards and the concentration of

the polymers depending on the range of
the interaction so this is the hard

fear interaction this is the colloidal
particles Here's the coexistence between

the fluid in the solid This is Crystal and
and you get these new.

Types of behavior.

Actually you also can get sort of hidden.

Kinds of face separation as well depending
where they are depending on the range of

the interaction and a simple way
of summarizing the sort of flows.

States is to understand how
the how delay tional curves.

And if you plot then the volume fraction

the interaction energy if you
have very low volume fraction.

But very very strong interaction then you
get these fractal like structures and

they can gel at arbitrarily small
volume fractions because the mass

of the structure is getting larger
faster than the than the volume so

they can expand overall volume
interesting observation is if you go to.

Relatively weak interactions you
actually shift the glass transition

to higher volume fractions
that is you can make things

unfreeze even though they
would otherwise be frozen.

In the.

In in the case of in the absence of
an interaction I won't talk about this I'm

going to focus on this region where you
can get different kinds of structures

ultimately get delays and
not an infinite attractions but

at fairly weak attractions and
as you control it as you watch what

happens in here you control both the
interaction and the volume fraction and

you get this wealth of
interesting behaviors basically

you will get some kind of face separation
the simplest type of face separation is

either some spin notable or
by notable kind of face separation and

exactly where that occurs
compared to where it freezes

depends on the length
of the interaction so

as you go from a short range interaction
to a longer range interaction it

shifts the face separation down and
you can cross over and

you can see it rather than jelling
the system you can actually see.

The.

A region where you can actually study
the face separation this Jallow

if I go back here in fact this
gel is essentially like freezing.

So it starts to spin notably composed but
it's frozen instead.

So the problem that that we are faced
is even if you if you really carefully.

Buoyancy match the particles and

we're getting better and
better at both buoyancy matching and.

And Index matching you want to index match
them so you can study them with some kind

of optical technique you want to buoyancy
match them so that they don't settle but

certainly fifteen years ago we weren't as
good at pointing matching now are fairly

good but still not that good and
eventually they will settle and

so how do you avoid settling well
you put them in microgravity So

you go into low Earth orbit and
you do experiments and

space so we did some experiments
from a historical perspective

we did some of the experiments at the be
at the beginning of this millennium

in the early two thousand and
we had a really beautiful.

Piece of apparatus that several
groups had samples and several groups

use it was a light scattering
apparatus Dave canal at U.C.S.B.

was really the primary driver
be behind the design so

you can see that there were eight
samples each sample fits on a big

hemispherical lens and that lens
focuses the light scattering onto.

The screen where you can capture
the light scattering with the C.C.D.

you had examples you could spin
the sample around and look at it and

you had a little camera here just.

To check when you.

Mix the sample So this is
a beautiful system it's soft you can

melt the sample just by sharing it so
you shake it up and

you start your experiment and so
we did some experiments and the person

is really driving this is art Bailey who's
now in Vancouver working a small company.

He was doing the experiments and
we set up to do light scattering and

we had one sample that we thought would
undergo Sparano the composition and

in fact collecting the lights
gathering data you saw exactly that

you saw the characteristic
peak that would develop and

would grow that means it shifts
this is a scattering function.

Only average it would grow it would shift
to longer and longer length scales as the.

Characteristic length of this but
no really composition set in and

started the course and started to grow and
you could scale all the data together

in a way that was consistent with what you
expect With been older composition but

we had set this up to do really small and
the light scattering but

we found that really now that we were in
space we had no effect of settling and

things kept evolving much
more than we expected so

Art very cleverly adapted the experiment
to something it was not meant to do and

he would start the experiment with
the light scattering and turn the whole.

Turntable around one hundred
eighty degrees to the camera and

then take pictures of it and that's
what the pictures were just meant to or

the camera was just meant to to monitor
the sample but in fact you turned out you

could get really interesting science with
it and so these are a series of image.

I'll show you over the course
of about a day and a half.

Where you can see this been notably
composition this is I think it's

pioneer has so or
pi centimeters by centimeters so

this is really macroscopic
face separation in

fact if you watch it right to the end you
can see that it completely face separates

you can learn lots of interesting physics
here it's wetting the surfaces you expect

that because the particles are slightly
more attractive to a flat surface so

you can see it what's the surface and
you can see the effects of surface tension

you can see all the effects of Spin Boldak
composition so now you can really follow

this all the way along and you can
plot say that peak of the scattering

vector as a function of time
over many decades of time and

it all actually fits very
nicely to some theory.

That you would that you could.

See the behavior
the interesting thing was that

you know the characteristic length scale
of the sample now is much larger but

the initial length scale of this is still
something of the order of a particle size

the particle size is Micron So
it's much larger than normally is but

it's what you might expect and you're
fairly far away from any critical point

with this who we haven't really intended
to be close to a critical point it was

really at that time difficult to find
exactly where the critical point was.

Because we couldn't do the experiment so
well on earth so.

This inspired us to try and
follow these this behavior

even more and for
that we needed longer periods of time

if we wanted to move closer to the
critical point because everything slowed.

Down so.

To move away from the shuttle
also the shuttle went away

didn't use this anymore instead
we moved to the space station and

there you could do experiments over
quite long periods of time and so

we put a sample together that
had a series of different.

Mixtures that would scan through or
we tried to scan through the critical

point to truly really trying to understand
can we understand this they separation and

something in a little
bit more more detail and

I thought this is the series of
samples and it was in Iraq and

we had a series of experiments
that were planned but then.

There was the one of
the shuttle disasters and

not only was it sort of a disaster for
everything that.

The fact that the the shuttle was lost but
also it meant for about a year year and

a half there was no ability to get
things into the space station this

it was no shuttles that were being
were taken off but they came to us and

said look these astronauts are there they
have lots of time on their hands because

there aren't any experiments
there can you do anything but

you have to do it without taking anything
up what we had these samples there and

so we looked around they gave us a list
of all the equipment that they had and

we found as a flashlight and
there was a camera there was some.

Sticky tape so we did some experiments you
know what do you do is experimentalist

you have to do experiments this is
the ultimate of doing experiments so

this is my fault this is early days you
can see the samples there's a flashlight

held together with with tape and he's
just taking pictures of it but you know

you can go a long way just doing this you
know that was a necessity as a mother and.

So we did this we could follow
the link scale here is the A series

of pictures these are different samples
this is the time and you know you.

Is Like many days and different they
separate you can start to build up

a bit of a phase behavior and this really
gave us confidence that we could even with

the samples that we have actually
learned some interesting physics so

slowly we went through
the the equipment was there and

we automated the expound we find a way
to put a timer on and we could hold

this down with a little bit more than
thinking tape but still the sticky

tape holding the whole experiment
together so it's automated like this.

And OK so then we could do a scan
of of experiments through this and

then the astronauts still had to.

Set things up get things going and they
were very diligent they enjoyed working

on this this is Dan Tani who did this
sample and he was ready to do it and so

you don't believe me that we're
in microgravity Well Harry is

setting up the experiment the experiments
are actually on the roof so.

He's the truth which is always so

we can see it is there up or
down where you don't know.

But he's careful so he sees that
there's some dirt on the Lambs so

you want to have dirt on the lands of what
you have to do you have to go down and

you have to go to where you keep
your lens cleaners right so

well they happen to be next door so
off you go to your lands clean earth.

And.

You have a handy set of lands
cleaners don't bump your head.

You get the lens cleaners
where are they they are.

And now you have back come back and
then isn't this the way

you clean your lenses all the time when
you do experiments I mean these guys

the amazing thing is that you know they
actually did a really good job and

this is not what they normally do but
they're very inventive and Peter got VERY

got to know all of them very well so all
the lists of people he's friendly with.

So they did these experiments.

And this is a series of images
that they took over many days.

You'll notice I have a little arrow
sometimes all the time saying G.

and G.

is micro G.

but there is still
an average direction of G.

because you are going around
the circle and you shouldn't believe me

because you don't see any collapse but
I'll prove to you that there is a G.

eventually but you see this is
the same kind of face separation so.

Well those of you out here's a repeat
those of you who know Peter will

understand that things didn't happen
as fast as some people work but

eventually he got around to analyzing the
data it was actually a fairly difficult

analysis because the samples
weren't fixed it was still

you know wiggling wobbling you're
taking pictures every few hours but

everything would move a bit so
things would shake.

And so we had to first remove
all the spatial drift and

then he did a lot of image
analysis he corrected for

the background so you can start
seeing better contrast you can

remove all the effects of dust and
now you can see really very clearly and

you can get now really good data
from experiments like this and

really understand something about
the behavior of the face separation.

And so here's the thing I'm
imaging the analyzing it now you

can just pick out the length scale by
doing a two dimensional for your transform

averaging or intentionally averaging and
you can see the link scale grow and

you plot the growth of the late scale this
is the growth of the length scale that was

measured originally just by these hand
cameras these three points now we can do

a much better job and you can see you
get beautiful data this is the linear

growth in the only times that you're
looking at the data are repeatable

you do it several times you get
exactly the same behavior so

now Peter said well let's really try to
understand the physics of what's going on

so the first thing that he did was
if you go back and we understand

how the attractive interaction works
it works because of the polymer but

the polar itself is somewhat
flexible its radius

actually depends somewhat on concentration
that's not normally accounted for

in all of the simple theoretical work but
Peter went.

To fry Brewer and
work with book Hard really

renowned classic like
the classical light scatter and

did they did very very careful
measurements of the radius of gyration

with static light scattering of
the polymer as a function of concentration

to try and really sort out what
the effects of concentration were and

then he worked with the manual as a sack
a rally at in Rome who did simulations

using exactly the same parameters
that we had in the experiment and

really tried to determine
what the phase diagram is but

now since we absolutely
understand what the.

Behavior of the poller is you.

Can put this all in terms
of an interaction potential

that doesn't depend just on
the length of the polymer and

you can straighten everything out and make
it look like the kind of phase diagram

that you're more used to seeing where
everything is been accounted for

this is now a combination of
all of these experiments and

some simulations it's very
very flat at the bottom so

the very difficult to reach the critical
point we still work not with say

the really beautiful types of experiments
that Arjun and others do where they

can change the volume fraction by changing
the particle size by making slight

temperature depends here to change the
volume fraction just make a new sample.

And as inventive as these people
were making things work in space

it's actually fairly difficult to put
a new sample to take a new sample every

time you want to so we're limited to the
number of samples that we could use and

how close to the critical point
nevertheless we got much closer and

we could start seeing a really
interesting type of behavior

now you can see that we scale
things the way you really

want to how close you are to the critical
point and really try to understand it.

We then sent more samples up so
these samples were

not poignancy matched it was easier for

technical reasons if you have ever
tried to send something in space and

you realize how difficult it is to get all
the approvals it was easier to not send

buoyancy match samples at first because
not all the fluids were approved but

eventually we said look we really want to
make sure there's no buoyancy effects.

And so we buoyancy match them and so
now these are really perfectly pointed.

Match and in this case you can
start seeing even new behaviors and

that's shown by this growth
of the of the the peak

and what you see this is the linear
behavior and I didn't mention it but

what you saw with the full car with
the original behaviors at long times

the growth becomes linear and that's
just the standard coarsening of the.

Of the spin oldie composition is basically
where surface tension is pulling it in and

fighting the Scott City However if you

now really go to long
times in the sample gets.

Much larger and you are closer to
the critical point you start to see

different behaviors so this is the lier a
game and now you really start to see some

turn over some deviation of this behavior
and as best we can tell right now and

we're still trying to really sort this out
by comparing two different simulations as

best we can tell this is actually
a behavior that is predicted by some

simulations by my Kates and it suggests
that there is some inertial of facts

because you are really so
far away from the critical point and

this by the way this behavior
is supposed to be a slow

power law of two thirds This
is now plotted linearly but

if you plot this logarithmically and
subtract off where you see this

crossover you actually see something
that has this two thirds slope and

you see this quite persistently you
can see of a riot of different samples

all of them behave in the same
way except the sample that

is closest to the critical point and we
can come really quite close to or we did.

Come quite close to the critical
point there you see

really what I think is qualitatively
different behavior I'll show you.

That here this is coursing
now it looks more or

less like what you see but eventually.

It seems to really break up.

And no longer become connected but
rather have these disconnected regions

I am still trying to figure out
what is really going on but

my intuition right now is
that the surface tension

the fluctuations of the surface
tension are really large scale there.

Of order.

A millimeter and I think that these
fluctuations are just starting to tear

it apart but that's just my own intuition
we're still truly trying to work out

what's happening but as you get close
to the critical point you see really

qualitatively different behavior it still
starts to move exhibit this deviation

of of the behavior but
now you really can barely see it and

this is over a very very long period of
time I did a simple calculation I just

wanted to make sure that it's not
the effects of gravity I just took it.

The the normal gravity or
the reduction of gravity as assumed some

buoyancy matching but not huge amounts of
pointing matching and you would have to go

to huge length scales before you would
have gravitational effects all I did was I

balance gravitational forces
with surface tension or or.

Plus pressure stresses to ask whether
that might be causing this ice so

I really don't think it's
gravitational effects even at this.

And we did a series of
different experiments and

I can just show you some of the kinds
of phase behavior that we would see.

This is just.

Looking not exactly at the critical point
now these are buoyancy match as well as we

can to really be able to look at this
this is just looking at as a function of

the concentration of the polymer remember
as you get closer as you go down and

concentration you get to the point
where the interaction is his weaker and

so you'll see behavior that that is
closer to the phase transition but

now we explored a series of them so
if we start here these

concentrations don't mean anything until
you convert them to the interaction or

just that's OK because I can show
you the qualitative behavior we can

convert them but you can see you will see
immediately just from the behavior that

that you observe what the nature
of the of the structure is so

here this one is where you
get the same kind of spin

oldie composition that we were seeing
before it's all just play this and

this looks exactly like we were seeing
before this been notably composition So

this is this intermediate value.

So if we go even closer to the.

Even lower concentration here we
weren't really close we're not really

near the critical point so we're off
to the side of the critical point but

in this case we see really very different
behavior and this is now over four months

and you can see it takes
it really takes forever and

it's not really clear
that you have a connected

by continuous region instead it almost
looks like you have a little drop so

this sort of implies we're
not really sure of this

the the analysis is still going
on that sort of implies this my.

B.

Actually by noting the composition
rather than spinal the composition

that's really close to the.

Critical point so you have these things
right in the middle in between of them

in between them you could imagine
that you would you would see this

if you go up in concentration here.

Then you see face separation but
now this is an attractive interaction and

what I hinted that but
didn't really emphasize is that the sample

sticks to the walls the reason six of
the walls by the way is simply that.

Surface is more favorable for

the depletion interaction
than a spherical surface so

there's a slightly stronger interaction
with the walls but it's not that high so

in this case you get the attraction but
the sample the bonds from the wall.

And so now you see Cinna rhesus
it just collapses in on itself

it's not held in place this is over
four weeks here's the same thing

over seven weeks ago remember
I told you there's gravity and

you didn't believe me because it's
microgravity this is a bubble.

Watch the bubble see it does appear

I can measure gravity perfectly by
measuring the velocity of the motion

of the bubble this is another sample that
center Riis's that the bond from the wall.

As we go up interaction energy
then we see other a fact.

So this is the more common thing if you
would go to a stronger interaction with

shorter range that is fairly widely
studied that's where you get delays and

well if you go to a stronger
interaction with longer range you

can get a frozen state which
essentially gels and that's shown here.

So now you see this been
all the composition but

eventually it just stops and Jelf.

And it just it won't change anymore
maybe over here changes to the bit.

And then finally if you go to even
larger interaction you get you're

starting to put push the particles because
they're attractive you're pushing them

together fairly strongly but still
it's a relatively Leake interaction so

now you push them together enough that
if you watch you see the speckles

you see you're actually forming colloidal
crystals as you push them together so

now the interaction is enough to
drive the particles into the range

where they'll begin to crystallize for
this particular interaction

before the interactions were not enough
they weren't driving the particles close

enough together that they could
start to crystallize now they do so

you have a whole wealth of different types
of behavior that you can assets now.

The unfortunate thing of course is
that the experiments are relatively

simple to do but
relatively difficult to to get to.

And so you're limited or

we're limited in the number of things that
we can actually measure OK with that.

Let me stop to leave some time for
questions and thank you for

your attention thank you.