Heather YarosGraduate Student, Ph.D. Programco-advised by John Newman
Northwestern University Research Interest: |
 hez@radke.cchem.berkeley.edu Personal Homepage Research |
Research Summary:
The overall objective of this project is to characterize and understand the forces present in dispersions and foams. Thin liquid films are used as a model system. The approach taken is three fold. Dilute bulk solution behavior and film conductance isotherms provide insight into the structure of the thin films. Disjoining pressure isotherms directly measure the intermolecular forces present in the film. Accordingly, an apparatus to measure film conductance, disjoining pressure, and thickness simultaneously has been designed. From film conductance isotherms, information is obtained about the concentrations and mobilities of ions present in the film, as compared to their bulk values. Disjoining pressure isotherms in conjunction with film conductance isotherms will test classic DLVO theory.
The first objective of this project is to build an apparatus that measures disjoining pressure, film conductance, and thickness simultaneously. A modified thin-film balance measures P, AC impedance determines c, and, thin film interferometry determines film thickness, h. Our design is based on a previous design by Swayne. It was necessary to redesign the film holder for two major reasons: the mechanical pressure seal proved unreliable and the thickness measurements were calibrated with another film. The latest design is shown in Figure 1.
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The outer ring consists of a porous glass frit fused to a glass capillary
tube. Fusing the two glass pieces together ensures a good seal. The electrical resistance
of the film holder must be negligible compared to the resistance of the film. Glass has a
very high resistance therefore the glass outer ring must be coated with a highly
conductive coating. The film holders are coated with chrome and then either gold or
platinum. The annulus design presents a number of difficulties to measuring the thickness by film interferometry. Most significantly, the annulus design produces stray reflections that are not uniform around the annulus. Currently, we are trouble shooting the apparatus. |
Reference:
Swayne, E. N., John Newman, C. J. Radke (1998). “Surface Conductivity and Disjoining Pressure of Common Black Films Stabilized with Sodium Dodecyl Sulfate.” Journal of Colloid and Interface Science 203: 69-82.