Optorheological studies of sheared confined fluids with mesoscopic thickness

Iwao Soga, Ali Dhinojwala, Steve Granick

Research output: Contribution to journalArticlepeer-review

Abstract

Fluids of mesoscopic thickness can be sheared and their molecular orientation probed concurrently with the new instrument described in this paper. The fluid is confined between parallel optically flat windows whose spacing is controlled, using piezoelectric inchworms, from submicrometer thickness to ∼500 μm, with no essential lower limit apart from surface roughness. Capacitance sensors or optical interferometry is used to monitor spacing between the windows with submicrometer accuracy. Piezoelectric bimorphs are used to apply periodic shear displacements with amplitude 0.1-10 μm and frequency 0.1-700 Hz. Shear-induced molecular alignment during sinusoidal shear cycles is determined, with up to 5 μs time resolution, using step-scan time-resolved infrared spectroscopy. To demonstrate capabilities of this new instrument, we describe an experiment in which shear and electric fields were applied in orthogonal directions to 5-cyanobiphenyl (5CB), a simple nematic liquid crystal. Provided that the molecule lacked the time to relax during the period of oscillation, the molecule tilted back and forth around the equilibrium orientation under the action of small-amplitude oscillating shear. The shear alignment appeared to be proportional to the shear displacement, not to the effective shear rate.

Original languageEnglish (US)
Pages (from-to)1156-1161
Number of pages6
JournalLangmuir
Volume14
Issue number5
DOIs
StatePublished - Mar 3 1998
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

Fingerprint

Dive into the research topics of 'Optorheological studies of sheared confined fluids with mesoscopic thickness'. Together they form a unique fingerprint.

Cite this