The objective of this proposal is to acquire and develop an ultra-fast femtosecond infrared-visible sum-frequency generation spectrometer (SFG) to probe the structure and dynamics of polymer molecules at moving interfaces encountered in the areas of friction, adhesion and dynamic surface tension. Past results using poly (dimethylsiloxane) (PDMS) lenses using Johnson-Kendall-Roberts technique and mica surfaces using surface force apparatus have found a relationship between friction, adhesion hysteresis and mobility of the molecules at the interface. Still, there is no direct information on the changes in the structure of molecules at moving or sliding interfaces. Recently, we have developed SFG in total internal reflection geometry to study hidden polymer interfaces and the preliminary results from the picosecond SFG system shows that it is possible to measure the changes in structure between two moving or sliding surfaces. The proposed broadband femtosecond system will provide the time resolution needed to measure rapid changes in structure at solid-solid, liquid-liquid and air-liquid contact interfaces to understand friction, adhesion and dynamic interfacial tension. The education and outreach activities will be offered to local schools in District 5 in order to promote an interest in science by encouraging students to undertake science projects and compete at district, state and international level.
Friction, adhesion and dynamic surface tension between surfaces are of utmost importance in a variety of technological and biological applications. Tires on roads, windshield wipers, and movement of human joints are some examples where friction and adhesion are experienced. This field, for a long time, has relied only on force measurements to interpret the molecular mechanism involved in these processes. This proposal provides a new experimental method based on nonlinear optics and contact mechanics to probe the molecular motion or deformation at the interface during sliding. The understanding and control of these phenomena will have a tremendous impact in conserving and using precious energy resources. This research will influence our design of surfaces, lubricants and micro or nano-actuators. The education and outreach activities will be offered to local schools in District 5 in order to promote an interest in science by encouraging students to undertake science projects and compete at district, state and international level.
