Video Description for the Visually Impaired
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Visual: Dr. Chris Stafford on camera.
Text: Dr. Chris Stafford, PhD.
Research Chemist
National Institute of Standards & Technology
“We’re interested in combinatorial research and that involves not only generating combinatorial libraries that express key parameters that you’re interested in in one sample, but we’re also interested in developing combinatorial measurements which now we can use those libraries to measure a property across a gradient sample.”
Visual: Dr. Adam Nolte on camera.
Text: Adam Nolte, PhD.
Materials Research Engineer
National Institute of Standards & Technology
“This lab is dedicated, mainly, to adhesion research. So, the adhesion research is focused on examining how and why and how much things stick together.”
Text: Probe Tack Measurements of Combinatorial Libraries
Visual: examples of PSAs
Narrator:
Pressure-sensitive adhesives--or PSAs--are a class
of soft adhesives able to adhere to a surface by applying light contact pressure and short contact times, without a chemical
reaction or solvent evaporation.
Visual: computer screen illustrating what narrator is saying about “conformal contact”.
Narrator:
Such behavior originates from the ability of the material to create intimate conformal contact with a stiff surface along with a concomitant capacity to sustain a significant load before failure occurs.
Visual: illustrations of PSAs narrator mentions.
Narrator:
Among their wide range of applications, PSAs are used on Post-it notes, to adhere the year sticker to a car’s license plate, and around automobile headlights to keep moisture out.
Visual: a roll of Scotch Tape.
Narrator:
A perfect example is ordinary Scotch Tape!
Visual: Dr. Nolte on camera.
“It’s got a non-sticky film on the back and, then, on the surface is a very, very thin layer of a gooey-type substance and so Scotch Tape works because once you push the tape into contact with a surface that goo there on the film is soft enough to make conformal contact with an object and when you pull it off that layer is also cohesive enough to resist coming off the surface.”
Visual: computer screen showing the results of a PSA adhesive strength test.
Narrator:
There are several ways to test the adhesive
strength of PSAs. These include shear tests, peel tests, and probe-type tack tests. All serve to quantify adhesion levels.
Visual: Dr. Nolte on camera.
“The instrument behind me, for example, brings two surfaces into contact. One is a probe and it brings it onto a surface and the it very controllably pulls the surfaces apart and by measuring the forces during that experiment, you can get to measure adhesion energy back out.”
Visual: Dr. Nolte illustrates the demonstration he is describing.
“The first thing I do is mount the sample on this platform on the machine. This is an inverted optical microscope platform. So, what this allows us to do is take pictures of the contact area while the two surfaces are coming into contact.
This is my probe I’m going to attach to my motor. This is a linear motor assembly. This is a very precise motor called an inchworm-type motor. And, so, this motor allows me to very controllably move the probe into the surface with a resolution of distances much, much less than a human hair. On this motor assembly, here, this little square, down here, is the load cell. This allows us to very precisely measures the force on the probe in contact with the surface. And, these two wings coming out are two pieces of reflected silicon material that provide a surface for our distance sensors to reflect off of and measure the distance from the probe onto the surface.
Once I have the sample mounted and the motor assembly positioned over the sample, I’m then going to advance the motor slowly towards the surface until I have contact. So, once the sample has been mounted then it’s time to control and begin the instrument using the computer interface. We’re going to do this test at two microns per second. A micron is one one thousandth of a millimeter. We’re going to come to a maximum force of three grams and then the probe is going to retract from the surface until it pulls off.
On this monitor we’re watching the underside so we can see when the probe actually makes contact. The contact area of the probe is increasing in diameter as the probe is pushed into the surface. So, here we are above three grams. From now on the experiment is reversed and it’s pulling the probe back from the surface. This dark contact area is decreasing. So, once the force, actually, dips below zero on the probe, this means that the probe is actually in a tensile situation with the substrate. That means the system is trying to tug the probe off the surface--so those are adhesive surfaces.”
Visual: Dr, Nolte on camera.
“The performance of PSAs is tested because, obviously, say an industrial manufacturer or a researcher would want to know how well their material is performing. So, the main application of a pressure sensitive adhesive is adhesion, obviously--sticking things together. So, by measuring the adhesion, you’re basically making a measurement of how well the material performs.”
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