Central Florida Future, Vol. 03 No. 33, July 23, 1971

University busing may not be joke; Six students approved for Com Grad Program; University of Florida sets visitation rules; GPS hiked for honors; FuTUre Editorials: The Joke\u27s on whom? Developmental center expanding in C dorm; Project physics stresses philosophical approach; Myrick joins sea researchers; WKIS\u27 Burns tells of broadcasting creativity (with photo of Gene Burns); Natural Sciences Asst. Dean named (with photo of Robert J. Laird); Supersonic wind tunnel used in pressure study; SG News: Activity fee budget approved by senate; Santry\u27s goal: commuter action; Future Sports News: Salerno appointed Clark\u27s assistant (with photo of Russ Salerno); Final enrollment hits 2,917 mark; FuTure\u27s Friday Girl: [Debbie Cusick].https://stars.library.ucf.edu/centralfloridafuture/1097/thumbnail.jp

Fluorescent molecular rotors: From working principles to visualization of mechanical contacts

In this thesis, we develop and characterize a method that enables us to visualize the real microscopic contact area between objects, using fluorescent molecules. Visualization and the ability to predict the real contact area between touching objects is a subject of a considerable interest, because the real contact area plays an important role in friction. In this thesis, a method that enables us to visualize mechanical contacts by using fluorescent molecular rotors is described, and photophysical characterization of such molecules is examined in detail by means of steady-state, time-resolved fluorescence and transient spectroscopy techniques. To visualize the real contact area between solid surfaces, we developed a method based on fluorescent molecular rotors immobilized on a solid glass substrate. Fluorescent molecular rotors are weakly fluorescent in low-viscosity solvents, because internal rotational motions result in a rapid decay of the excited state, such that the emission of a fluorescence photon is not fast enough to compete effectively. In high viscosity liquids and polymer matrices, however, such motions become severely hindered. Therefore, the molecules can remain in the excited state much longer, and become strongly fluorescent. A similar situation arises when molecular rotors are confined in contacts between objects, and this effect can be imaged and used to measure the real contact area with fluorescence microscopy

Molecular probes reveal deviations from Amontons' law in multi-asperity frictional contacts

Amontons' law defines the friction coefficient as the ratio between friction force and normal force, and assumes that both these forces depend linearly on the real contact area between the two sliding surfaces. However, experimental testing of frictional contact models has proven difficult, because few in situ experiments are able to resolve this real contact area. Here, we present a contact detection method with molecular-level sensitivity. We find that while the friction force is proportional to the real contact area, the real contact area does not increase linearly with normal force. Contact simulations show that this is due to both elastic interactions between asperities on the surface and contact plasticity of the asperities. We reproduce the contact area and fine details of the measured contact geometry by including plastic hardening into the simulations. These new insights will pave the way for a quantitative microscopic understanding of contact mechanics and tribology