Coherent x-ray beam

1. Structural and Dynamical Studies of Thin Polymer Films Using X-ray Scattering Sunil K. Sinha (UCSD) and Laurence Lurio (NIU)DMR-0209542 CCD Camera Polystyrene films supported on silicon substrates form an important model system for studying the effects of confinement on polymer flow. X-ray scattering is a useful tool for such studies. Coherent x-ray beam Scattered X-rays For thick polymer films the capillary wave dynamics is very well described by classical hydrodynamics. An important result of the present study is the observation of deviations from predicted hydrodynamic behavior when the film thickness approaches the size of the polymer coils. This behavior can only be explained as the combination of two effects. 1) For polymer films which are very thin the polymers are not as entangled as they are in the bulk material. This results in an increased mobility. 2) Parts of the polymer chain get stuck or adsorbed on to the bottom substrate. This gives the polymeric liquid a resistance to shear which normal liquids do not have. Si Substrate Polymer films are rough because thermal energy excites waves on their surfaces called capillary waves. The shape of the rough surface slowly changes over time. By following the motion of the surface, the hydrodynamic properties of the film can be studied. The figure on the right is a schematic of how a polymer surface fluctuates. On the left is a time sequence of measured x-ray scattering images from a polymer surface. Analysis of the changes in the x-ray patterns with time reveals the film dynamics

2. Structural and Dynamical Studies of Thin Polymer Films Using X-ray Scattering" Sunil K. Sinha (UCSD) and Laurence Lurio (NIU)  DMR-0209542 Education This work formed part of the Ph.D. thesis of UCSD graduate student Zhang Jiang. In addition, it was the basis of the Masters thesis of NIU graduate student Jarrett Stark, and formed part of the post-doctoral training of Dr. Xuesong Jiao. NIU undergraduate engineering student Yagnesh Trivedi, designed the vacuum and thermal enclosure used for parts of these studies. Dr Jiao is presently a staff scientist at the Advanced Photon Source. Jarrett Stark, after completing his Masters degree in 2005, is working in the semiconductor division of the United States Patent Office Societal Impact Understanding the mechanical, elastic, and flow properties of polymers at the molecular scale is important for applications such as coatings, insulation, adhesives, packaging material and in prosthetic devices. The results of the present work will provide a basis for an improved theoretical understanding these phenomena One example of possible applications is IBM’s millipede project, which aims to replace magnetic hard drives on computers with arrays of small holes melted in polymer films. The success of such a device would depend on understanding molecular scale polymer flow and melting.