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Jeong-Yun Sun's picture

Highly stretchable and tough hydrogels

Yuhang Hu's picture

Poroelastic relaxation indentation of thin layers of gels

We develop a method of poroelastic relaxation indentation (PRI) to characterize thin layers of gels.  The solution to the time-dependent boundary-value problem is obtained in a remarkably simple form, so that the force-relaxation curve obtained by indenting a gel readily determines all the poroelastic constants of the gel—the shear modulus, Poisson’s ratio, and the effective diffusivity.  The method is demonstrated with a layer of polydimethylsiloxane immersed in heptane.

Jeong-Yun Sun's picture

Inorganic islands on a highly stretchable polyimide substrate

For a flexible electronic device integrating inorganic materials on a polymer substrate, the polymer can deform substantially, but the inorganic materials usually fracture at small strains.  This paper describes an approach to make such a device highly stretchable.  A polyimide substrate is first coated with a thin layer of an elastomer, on top of which SiNx islands are fabricated.  When the substrate is stretched to a large strain, the SiNx islands remain intact.  Calculations confirm that the elastomer reduces the

Li Han's picture

Determining the elastic modulus and hardness of an ultra-thin film on a substrate using nanoindentation

Abstract – A data analysis procedure has been developed to estimate the contact area in an elasto-plastic indentation of a thin film bonded to a substrate. The procedure can be used to derive the elastic modulus and hardness of the film from the indentation load, displacement, and contact stiffness data at indentation depths that are a significant fraction of the film thickness. The analysis is based on Yu’s elastic solution for the contact of a rigid conical punch on a layered half-space and uses an approach similar to the Oliver-Pharr method for bulk materials.

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