Some of the most exciting work to come from Chris Johnson’s thesis was the ability to control the dimensions and contact mechanics of polyacrylamide hydrogels by simply starting with different recipes for the hydrogel in the first place. We already knew that the composition controlled the bulk structure, but now we know it controls the […]
I have started many posts this way, but in fact we keep discovering more reasons. I’m thrilled to share that our recent work shows how hydrogel surfaces have an innate structure that allows them to maintain robust low friction: a gradient layer. When you submerge a hydrogel into a water bath, the polymer chains want […]
Hydrogels are inherently slippery — we know this from touching jello and sliding on banana peels. It’s been shown in many of our prior publications, as well as publications from the Sawyer group (University of Florida), the Spencer group (ETH), the tribology group at Imperial College, and many others. However, making polyacrylamide hydrogels in the […]
Latch mechanisms are one of the most fun mechanical systems, yet we rarely teach about them, or research them. When the ketchup bottle is open and closed, the problem is solved. But what if that little snap didn’t just hold the lid closed, but was designed to snap open a huge structure? That’s what the […]
While we normally work with single-polymer hydrogels, we had the opportunity to work with the Grunlan group at Texas A&M to study their charged double-network hydrogels. These hydrogels are tough! Looking more like cartilage all the time. In this paper we present evidence that their lubrication behavior matches or exceeds that of native cartilage. Higher […]
Many researchers are aware that hydrogels, even a single kind of hydrogel (polyacrylamide) can be designed to have properties that range from brittle to viscoelastic. It’s truly a versatile material! As hydrogels are being considered as replacements for cartilage in the body, they need to be able to take a beating: they can’t break under […]
We had the nice chance to collaborate with Kyle Schulze at Auburn University to put together a review. Check it out to get some good resources for your next paper or proposal! https://rdcu.be/b9jwq
We usually think of hydrogels as slippery and wet — that’s their definition! But if a probe pushes on them to a higher pressure before applying lateral slip, that high pressure causes unstable friction, or stick-slip (just like the elastomer in our prior post!). So even inherently low-friction materials relieve interfacial strain in extreme ways. […]
Last year I had the privilege of hosting the now Dr. Chao Wang in my lab to use our optical in situ microtribometer to study the stick-slip behavior of seal elastomers. He obtained a supporting fellowship from the Austrian Marshall Plan Foundation, and used this work toward his PhD in Polymer Tribology from Montanuniversität Leoben. […]
We describe the resistance to slip of an interface as friction, and the origin of that friction can vary widely: roughness, plasticity, lubrication, temperature, etc. Some of those originating mechanisms can also change with time: asperities flattening, lubricating migration, or other things. The way that people have tried to quantify those changing mechanisms is to […]