University of Illinois Urbana-Champaign

Relaxations in molecularly thin simple liquid films: Linear viscoelasticity and non-linear response to shear

Demirel, Adem Levent

This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.

Permalink

https://hdl.handle.net/2142/20059

Description

Title
Relaxations in molecularly thin simple liquid films: Linear viscoelasticity and non-linear response to shear
Author(s)
Demirel, Adem Levent
Issue Date
1996
Doctoral Committee Chair(s)
Weissman, Michael B.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • Engineering, Mechanical
  • Physics, Fluid and Plasma
  • Engineering, Materials Science
Language
eng
Abstract
  • To understand the relaxations of molecules under confinement, the linear and non-linear response of molecularly thin simple liquid films confined between two solid surfaces were studied. The method was to measure the resistance to applied oscillatory shear deformation as a function of frequency and amplitude of deformation, film thickness and normal pressure using the modified surface forces apparatus technique.
  • The investigation of the frequency spectra of linear viscoelastic response as a function of the film thickness with octamethylcyclotetrasiloxane (OMCTS) films confined between mica surfaces showed more than two orders of magnitude increase in the relaxation times from 7 to 1 molecular layers. The frequency spectra taken at different film thicknesses were found to superpose onto a master curve when shifted horizontally and vertically. The successful superposition of the frequency spectra of both predominantly viscous and elastic response was concluded to show that a discontinuous phase transition was not involved in the transition to the confinement induced elastic state, also ruling out the possibility of a phase transition from linear to non-linear response.
  • The transition from linear to non-linear response of elastic squalane films was associated with the yield of structure in the thin film. The transition as a function of applied force was reversible and repeatable, but with a significant hysteresis. Within the hysteresis loop, the time evolution of the viscoelastic parameters showed significant fluctuations in the form of triangular spikes on a constant baseline. The durations of the spikes were much larger than the oscillation period indicating a correlation of these changes over many periods. The dependence of the fluctuation amplitudes on the applied shear force was concluded to show the competition between the intermolecular forces and the externally applied shear.
Type of Resource
text
Permalink
http://hdl.handle.net/2142/20059
Copyright and License Information
Copyright 1996 Demirel, Adem Levent

Owning Collections

Graduate Dissertations and Theses at Illinois PRIMARY
Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Economics