Masters Theses

Date of Award

5-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

Donald C. Bogue

Abstract

An atomic force microscope has been used to measure the interaction and adhesion forces between a polystyrene particle and a mica surface in aqueous solutions. The interaction and adhesive pull-off forces, as well as particle deformation, have been measured as a function of contact force and contact time for particles with glass transition temperatures of 29°C (PS29) and 57°C (PS57). These particles (2 μm) are commercial products produced by Mitsubishi Rayon Company, Ltd., Hiroshima, Japan. These particles are copolymers made from n-butyl acrylate monomer and st3a'ene monomer, and are currently being used as intermediates for other processes. The company’s objective is to gain a better understanding of the coagulation characteristics for particles of varying softness by direct measurements via atomic force microscope. The results from this research indicated that a noticeable particle deformation occurs during approach of the mica surface to the polystyrene particle and after contact. Various relationships were established, obtaining a more complete understanding of the interaction forces of soft particles at the microscopic level including repulsive interactions before contact and attraction forces, and particle deformation at contact. For the particle with a transition temperature of 29°C (PS29), a study was completed that varied the approaching velocity of the mica surface to the particle in order to assess this effect on the resulting interaction forces during approach. It was found that due to particle deformation the maximum repulsive forces (at 20 nm from the mica surface) and corresponding pull-on forces were dependent on the speed at which the surface and particle were brought together. This interpretation is supported by the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory. At contact, the relationship of adhesive pull-off force and particle deformation with contact force and contact time was studied. The PS29 particle displayed roughly three times the attractive force of the PS57 particle at zero contact load. A linear relationship between the particle deformation and contact force was observed. This linearity is supported by the Maugis and Pollock (MP) theory, and was used to predict the yield strength and work of adhesion. The studies of adhesive pull-off force with contact time were completed by holding the contact force constant, while the approaching speed was varied. Both particles showed a marked increase in adhesive pull-off force and deformation with contact time resulting from the increase in contact area of the polystyrene particle and mica surface.

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