Title page for ETD etd-07232004-141823


Type of Document Dissertation
Author Lokar, William Joseph
Author's Email Address wlokar@yahoo.com
URN etd-07232004-141823
Title Surfactant Adsorption during Collisions of Colloidal Particles: A Study with Atomic Force Microscopy (AFM)
Degree PhD
Department Chemistry
Advisory Committee
Advisor Name Title
Ducker, William A. Committee Chair
Anderson, Mark R. Committee Member
Esker, Alan R. Committee Member
Morris, John R. Committee Member
Yoon, Roe-Hoan Committee Member
Keywords
  • AFM
  • self-consistent field theory
  • Surfactant
  • proximal adsorption
  • adsorption
  • charge regulation
  • surface forces
Date of Defense 2004-07-19
Availability unrestricted
Abstract
The adsorption of cationic and zwitterionic surfactants is studied in aqueous electrolyte solutions. A Maxwell relation is applied to Atomic Force Microscopy (AFM) data to obtain changes in surfactant adsorption as a function of the separation between two glass surfaces. In addition, self-consistent field theory (SCF) is used to calculate the adsorption profiles and interaction energies when two solid surfaces are brought into close proximity. Addition of surfactant is shown to affect the surface forces when lateral surfactant chain interactions are significant. The surfactant adsorbs and desorbs in response to over-lapping electric double-layers, with the adsorption being affected at larger solid-solid separations when the double-layer force is longer ranged. Furthermore, elimination off the surface charge or net surfactant charge eliminates adsorption with decreased solid-solid separation. The magnitude of the changes in surfactant adsorption at decreased separations is shown to scale with the chain length of the surfactant. Surfactant adsorption exceeds that required to regulate the surface charge according to the constant potential boundary condition in Poisson-Boltzmann theory. An equation of state including short-ranged (contact) tail interactions is proposed to describe both the adsorption of surfactant and the surface forces at small separations, where the double-layers overlap. Furthermore, SCF calculations show confinement-induced phase transitions when the surfactant layers on opposite surfaces merge. These phase transitions lead to further surfactant adsorption and a corresponding attractive force.
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