Direct Observation of Shear-Induced Orientational Phase Coexistence in a Lyotropic System Using a Modified X-Ray Surface Forces Apparatus

Yuval Golan; Ana Martin-Herranz; Youli Li; Cyrus R. Safinya; Jacob Israelachvili

doi:10.1103/PhysRevLett.86.1263

Direct Observation of Shear-Induced Orientational Phase Coexistence in a Lyotropic System Using a Modified X-Ray Surface Forces Apparatus

Yuval Golan, Ana Martin-Herranz, Youli Li, Cyrus R. Safinya, and Jacob Israelachvili

Phys. Rev. Lett. 86, 1263 – Published 12 February 2001

Abstract

The second generation x-ray surface forces apparatus (XSFA-II) allows for the first time simultaneous in situ small-angle x-ray scattering and surface force measurements. We have used the XSFA-II to monitor shear-induced orientational transitions in a lyotropic model lubricant system. Upon applying small shear amplitudes ( $\sim 20 μ m$ ) to a relatively thick ( $\sim 800 μ m$ ) film, we observed evidence for the formation of an orientational boundary layer at the shearing surface. Time-resolved x-ray diffraction revealed the gradual transition to shear-favored orientation by growth of the boundary layer.

Received 2 August 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.1263

Authors & Affiliations

Yuval Golan^1,2,*, Ana Martin-Herranz^3,†, Youli Li^3,‡, Cyrus R. Safinya^3,§, and Jacob Israelachvili^1,∥

¹Materials Department, Chemical Engineering Department, and Materials Research Laboratory, University of California, Santa Barbara, California 93106
²Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
³Materials Department, Physics Department, and Materials Research Laboratory, University of California, Santa Barbara, California 93106

^*Electronic address: ygolan@bgumail.bgu.ac.il
^†Present address: Unilever Research Port Sunlight Lab, Wirral CH63 3JW, Merseyside, United Kingdom.Electronic address: ana.martin-herranz@unilever.com
^‡Electronic address: youli@mrl.ucsb.edu
^§Electronic address: safinya@engineering.ucsb.edu
^∥Electronic address: jacob@engineering.ucsb.edu