Showing papers by "Jeffrey W. Kysar published in 2012"

Mechanical properties of thin glassy polymer films filled with spherical polymer-grafted nanoparticles

Abstract: It is commonly accepted that the addition of spherical nanoparticles (NPs) cannot simultaneously improve the elastic modulus, the yield stress, and the ductility of an amorphous glassy polymer matrix. In contrast to this conventional wisdom, we show that ductility can be substantially increased, while maintaining gains in the elastic modulus and yield stress, in glassy nanocomposite films composed of spherical silica NPs grafted with polystyrene (PS) chains in a PS matrix. The key to these improvements are (i) uniform NP spatial dispersion and (ii) strong interfacial binding between NPs and the matrix, by making the grafted chains sufficiently long relative to the matrix. Strikingly, the optimal conditions for the mechanical reinforcement of the same nanocomposite material in the melt state is completely different, requiring the presence of spatially extended NP clusters. Evidently, NP spatial dispersions that optimize material properties are crucially sensitive to the state (melt versus glass) of the polymeric material.

Heterogeneous nucleation of protein crystals using nanoporous gold nucleants

Abstract: We present a theory and experiments that help clarify the origin of the effectiveness of nanoporous substrates in the heterogeneous nucleation of protein crystals. The central idea tested here is that when a substrate (or “nucleant”) possesses pores of the order of the hydrodynamical radius of a protein, then the entropic penalty associated with nucleating a protein crystal on that surface may be alleviated. Model experiments using lysozyme and nanoporous gold (NPG) substrates suggest that there is indeed a reduction in the entropy associated with creating critical nuclei, but the magnitude of the reduction is small. Taken together with further examination of protein crystallization with NPG nucleants using four other proteins, our aggregate results suggest that surface chemistry and surface area effects play the dominant role in nucleation when using these nanoporous nucleants.

CHAPTER 5:Microfabrication of Nanoporous Gold

Abstract: Fabrication of microstructures comprising NPG requires precise control over selective corrosion of the precursor alloy. In many designs, the precursor alloy is constrained to a substrate, and complex surface reconstruction during dealloying potentially leads to a high overall stress in the newly formed NPG. Hence, constrained NPG thin films or suspended NPG structures often develop cracks in fabrication. Similarly, nanovoids in thin-film precursor alloys or low Au content in the precursor alloys may lead to fractures in the NPG thin films, which compromise the integrity and functionality of the resulting architecture. Recently developed scalable electrochemical methods for which the rate of removal of the less noble elements in the precursor alloy can be precisely controlled produce crack-free blanket films constrained to a substrate. In this chapter, conventional as well as newly developed NPG fabrication techniques are assessed from a microscale fabrication perspective, with regard to the NPG product quality, means of tailoring the final porous structure, and their compatibility with the standard microdevice fabrication techniques.

Thin glassy polymer films including spherical nanoparticles

Abstract: A method of forming a solid-state polymer can include grafting a graft polymer to nanoparticles to provide grafted nanoparticles, and dispersing the grafted nanoparticles in a polymer matrix to provide a specified loading of the grafted nanoparticles within the polymer matrix to form a solid-state polymer. A solid-state polymer can include grafted nanoparticles comprising a polymer graft grafted to nanoparticles, and a polymer matrix, in which the grafted nanoparticles are dispersed to form a solid-state polymer, the dispersion configured to provide a specified loading of the grafted nanoparticles within the solid-state polymer.