The principal objective of the proposed research is to further the systematic investigation of the novel phenomenon of photodriven polymer mass transport in azo functionalized polymer films, at modest light intensities and substantially below their glass transition temperatures. All-optical holographic fabrication of large modulation depth (>6000A) surface relief gratings (SRG) have been achieved on azobenzene-functionalized polymer films, without any pre- and/or post-processing. A systematic investigation of this novel photodriven surface deformation and SRG formation process in a variety of azobenzene functionalized polymer systems has established a number of critical research findings and conclusions. This includes the fundamental understanding, the mechanism and identifying possible device applications of this all-optical process. The process is a result of polymer mass transport by optical field gradients and is initiated at the polymer film surface. A number of models and mechanisms for the driving force have proposed. The gradient force model developed by the PI describes the macroscopic behavior observed in this unique photofabrication process in amorphous azobenzene polymer film. This model utilizing a single viscoelastic parameter has presented the opportunity to further connect the experimentally established deformation behavior to molecular level processes and molecular structural details. The viscoelastic parameter of the photoplasticized deformation layer can be correlated with the molecular structural details by investigating the SRG process in tailored macromolecules under selected writing conditions.
The focus of this further explore the unusual light-driven transport phenomenon discovered under prior NSF funding. In this all-optical process, desired micro and nonopatterning may be carried out in practically all polymers with some azo functionalization, at modest light intensities without any post processing. Understanding the fundamental photophysical processes in this class of materials may lead to important devices and fabrication processes for photonic technologies. Direct inscription of desired patterns is expected to serve as a simple and dramatic demonstration and learning tool for the classroom using this unusual optical and polymer-physical phenomenon.
