Shear-induced dilation of confined liquid films. Dhinojwala, Ali; Bae, Sung Chul; Granick, Steve. Department of Materials Science and Engineering University of Illinois, Urbana, IL, USA. Tribol. Lett. (2000), 9(1,2), 55-62. CODEN: TRLEFS ISSN: 1023-8883. Journal written in English. CAN 135:97844 AN 2001:363012 CAPLUS

Sheared molecularly-thin fluid films dilate at the point of stick-to-slip (which is the transition from static to kinetic friction), indicating that d. decreases when sliding occurs. This contrasts with incompressibility characteristic of bulk fluids when they are deformed. The magnitude of dilation was less than the size of the mol. and was larger in a polymer system (large mols.) than for small-mol. fluids. The expts. employed a surface forces app. modified to measure, using piezoelec. methods, sub-angstrom variations of film thickness during dynamic shear excitations that were performed at rates too rapid to allow fluid to enter and exit the zone of shear contact during the period of shear excitation. To demonstrate generality of the dilation effect, the specific systems studied included nonpolar fluids whose complexity was varied (a globular-shaped mol., OMCTS; a branched alkane, squalane; a tethered diblock copolymer, polyvinylpyridine-polybutadiene) and also an aq. electrolyte, MgCl2 dissolved in water. Extensive anal. is also presented of the piezoelec. methods that were employed to detect vol. changes too small to observe by the methods of multiple beam interferometry that are traditional for thickness measurement in a surface forces app.