Masters Theses

Date of Award

5-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Engineering Science

Major Professor

A.E.English

Committee Members

Mohamed Mahfouz, Mehran Kasra

Abstract

In recent years, the unique physical properties of synthetic hydrogels have been exploited in a number of interesting and novel applications. In particular polyampholytes have been the subject of many theoretical studies since they provide a model for studying the longrange interactions found in proteins and other forms of soft condensed matter. In balanced polyampholytes the net electrostatic forces are attractive so that in low ionic salt concentration, the chains have a tendency to collapse into compact globules. Addition of salt, which screens these interactions, induces a swelling of the chain. However the electrostatic interactions between polymeric and mobile charges that determine the hydrogel swelling equilibrium at high ionic strengths are still not very well understood.

The purpose of this Master’s thesis is to analyze the characteristics of balanced polyampholytes with different charge offsets produced by systematically varying the relative proportions of 2-sulfoethyl methacrylate -2-methacryloxyethyltrimethyl ammonium chloride (SEMA-MAETAC) in copolymers of 2-hydroxyethyl methacrylate (HEMA). Hydrogel equilibrium swelling measurements were made in different bath solutions such as DI (de-ionized) water, PBS (phosphate buffer solution) and different Nacl concentration. A slight swelling in DI water and collapse transitions at intermediate salt concentrations observed experimentally provides the equivalent results, compared with the earlier studies done on balanced polyampholytes. However the deswelling of the hydrogels in high ionic salt concentration found to be abnormal. Hydrogel membrane potential has been measured using a novel method considering the Donnan potential and the Diffusion potential at a charged membrane/salt solution interface. For the balanced polyampholyte hydrogel charges ranging from 0mM to 160mM we observe a negative slope in the steady state potential whereas we observe a positive slope in the steady state potential for the highest charged balanced polyampholyte hydrogel, which is 200mM in this case. Finally digital image processing techniques have been applied to examine the bacteria Pseudomonas fluorescens 5RL and hydrogel interactions. And the higher proliferation rates of the bacteria Pseudomonas fluorescens 5RL over neutral HEMA hydrogels compared to copolymer HEMA hydrogels with balanced charge densities in the range of 40 mM to 160 mM were analyzed using these techniques. Comparative change in the micro motion of the bacteria over balanced polyampholyte hydrogels and the unbalanced polyelectrolyte hydrogels were also presented. The cumulative result of this thesis is that the selection of the acidic and basic monomers used in the preparation of these hydrogels and their micro structural arrangements should be given importance and also the emphasis of digital image processing techniques in the application of molecular imaging.

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