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[Narrator:] Accurately measuring
and quantifying the adhesive properties of materials
to be used in, among many other applications,
things like Scotch Tape...Post-It Notes...and
sealants to keep moisture from getting behind auto headlights
or help car doors stick together,
is vital to providing products of highest quality.
Developing versatile, flexible tests
that evaluate the performance of such materials is part
of the mission of the Polymers Division
of the National Institute of Standards and Technology.
[Stafford:] Industry likes combinatorial methods
because it allows them
to conduct their experiments faster and more efficiently.
So, they can do in one day what it used
to take them multiple weeks to do.
So, in a fast paced research environment,
combinatorial methods are extremely valuable.
Combinatorial library is exactly what it sounds like.
It's every combination of a particular variable
in one sample and it looks like a library
because you have a whole row or an array
of samples on one substrate.
[Johnson:] My research concerns photopolymers
so what I'm looking at for the research is the adhesive
and time response capabilities of these photopolymers.
So, how well they stick to certain surfaces and what
that does, actually, over time.
[Narrator:] Screening the cure time and intensity
for UV coatings and adhesives arrays can be complex
and time consuming.
However, a gradient in UV cure allows for rapid analysis
of conditions all in one sample.
It also allows for rapid analysis
of sample conditions that, otherwise,
would be difficult to perform.
In short, new materials
and formulations may require optimization of cure protocols
that lie outside standard conditions.
Beyond that, existing technology cannot always be leveraged
toward effective solutions for a new application.
Library fabrication can often present a primary--
if not THE primary-- obstacle to implementing "combi"
for emerging material systems
for an increasingly fast-paced industrial research environment.
Furthermore, established workflows require flexible
techniques which can adapt when changes
in research are called for.
Given these challenges,
versatile library fabrication routes and instrumentation
that can be easily modified and applied to a variety
of applications are extremely valuable to polymer researchers.
Thus, the development
of gradient library fabrication approaches
by the Polymers Division of the National Institute of Standards
and Technology help speed the application
of advances in polymer science.
[Johnson:] For photopolymers what is really a big concern is
light dose, which is light intensity times exposure time
and what you can do is tailor both of those parameters
and you can use any kind of combination
which gives you a wide range of dose properties
that you can test and that's much easier
than doing a single experiment over and over again.
This is just our standard UV wand.
It has a fairly broad exposure area.
So, we place our sample here.
We're going to have exposure time be constant
in this direction while we're going
to have a varying exposure time gradient in this direction.
So, this wand is at a fixed intensity here.
And, the intensity actually varies
as a function of distance squared.
So, we can actually move this wand up and down.
So, if we turn this we can actually get it to raise
and you can actually see the light wand moves up
and the actual light broadens and it becomes less intense
because we've moved the stage up.
So, we can fix the light intensity at a specific position
and only change the exposure time.
The motor will step in slight increments dependent
on the exposure time that you are running.
So, in every single case here, it'll step slightly
and that step will take longer and longer to produce over time.
You can manipulate the exposure time gradient to whatever sort
of system that you want and we have this system
where we can configure it
to different sorts of function types.
So, we have an exponential function.
So, you have the case where, say, this would be
up to 60 seconds and then from 60 seconds
to two minutes you have this weird sub-optimal,
clearly coating and then you have the fully cured coating
where I can just rub my finger over it and nothing happens.
And, then, in the bottom here,
I can actually still wipe my finger through it
because it's still monomer.
And, that's sort of where you can actually see this being a
powerful technique.
[Stafford:] In this case,
we're going to change the UV intensity while keeping the UV
exposure time constant.
And, we're going to change the UV intensity by using a filter
that filters out the UV light in a very controlled fashion.
So, in this case, we have a neutral density filter
that can attenuate the UV light
by an absorbent coating that's formed
in a gradient across this sample.
And, we have step gradients.
On one end we are allowing all the light intensity
to transmit to the sample.
On the other end, all the light intensity is being absorbed.
So, you have a very clearly defined gradient
of light intensity that will be exposed on your sample.
And, so, in this particular demonstration we're putting this
neutral density filter in between the light source
and our sample so we're exposing the entire sample all at once
so it's highly parallel.
So, there's our light beam.
We're exposing our sample with UV light.
What we can do is choose a particular exposure time,
we're keeping that fixed, and the intensity will decay
from one side of the sample to the other
because of this neutral density filter.
[Johnson:] The practical reality is
that once industry makes a new monomer that is fantastic,
it has new properties, you have to integrate
that into your existing compositions.
And, so, when you do that you have
to pretty much run every single analysis that you did before.
And one of them is actually testing, well,
does this cure the same as it did before.
And that's one of the large bottlenecks because if you have
to run a sample for, say, 10 minutes
and you're changing the composition slightly every
single time, that time builds up.
So, it's mainly trying to speed up the process of discovery
so once you actually get this new chemical,
how can we integrate that into what goes
out to the end user faster?