Development of a COIFM with Lateral Modulation for Studying Interfacial Water Byung I. Kim, Boise State University, DMR The cantilever-based optical interfacial force microscope (COIFM) with lateral modulation (CLM) was designed and constructed to study interfacial water confined between two surfaces. We observed remarkable oscillatory behavior in normal (red) and friction forces (blue) (see Figure 1) in the CLM force-distance curve, as the two silica surfaces approached one another at ambient relative humidity (33%). This is difficult to observe with currently available techniques (e.g. conventional atomic force microscopy techniques). The tip started to interact with interfacial water molecules at 17 nm away from the surface. Once the tip and sample came in contact, there was a very sharp change in normal force and an increase in friction force as well. The oscillatory amplitude in normal forces is 60–90 nN with a periodicity of nm and nm for valley- valley and for peak-peak distances, respectively. This periodicity is roughly three diameters of water molecules (diameter of single water molecule is ~0.3 nm). The periodicity of multiple water molecule diameters, instead of one water molecule diameter, suggests that the interfacial water structure in the ambient environment is possibly different from that at the (bulk) water-solid interface. Figure 1: Force-distance curves collected using COIFM with lateral modulation of 6 nm at RH 33%. Both normal and lateral forces show large oscillatory forces generated by interfacial water molecules confined between two hydrophilic surfaces in air*. *Reprinted with permission from B. I. Kim, J. A. Rasmussen, and E. J. Kim, Appl. Phys. Lett. 99, (2011). Copyright 2011, American Institute of Physics..

Education Activities: Through this NSF DMR support, more opportunities have been provided to students in physics, biology, chemistry, and engineering majors for interdisciplinary research. Nine undergraduate students and eight high school interns in the Boise area have been trained and involved in the research (Figure 2). Additionally, a graduate biophysics course (BMOL Biophysical Instrumentation) has been developed for the newly created Biomolecular Science Ph.D. courses to begin in fall of Dissemination Activities: We have disseminated and evaluated the research results in the following ways: (1) presenting at three international, two national, and fifteen Boise scientific conferences; (2) seven publications in peer-reviewed journals; and (3) submitting two patent applications. In addition to these activities, three other efforts are currently being prepared: (1) six publications in peer-reviewed journals have been submitted and are under review; (2) creation of an interactive physics lab website; and (3) demonstrations for lab visitors. Development of a COIFM with Lateral Modulation for Studying Interfacial Water Byung I. Kim, Boise State University, DMR Figure 2: Undergraduate and high school students involved in research.