Studies of Labile polyelectrolyte at solid-liquid interfaces

Abstract

<p>p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Times}</p> <p>Guar is naturally occurring polysaccharide. This thesis presents studies on hydroxypropyl guar (HPG) - borate, a Labile polyelectrolyte, interacting with a number of model tear film (eye) components including sulfate-stabilized polystyrene latex, anionic lipid-stabilized emulsions and cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) liposomes. The presence of borate ions converts nonionic HPG into an anionic polyelectrolyte. However, the borate ions on HPG chains do not inhibit HPG-borate adsorption onto anionic polystyrene latex. Both HPG and HPG-borate show the same adsorption isotherms. As a comparison, HPG slightly oxidized to give C6 carboxyl groups, with a degree of substitution close to HPG-borate, does not adsorb onto anionic polystyrene latex when the polymer is fully ionized.</p> <p>p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Times} span.s1 {font: 11.0px Helvetica}</p> <p>Although HPG and HPG-borate do not adsorb onto anionic lipid-stabilized emulsions, the emulsions aggregate at high polymer concentration (> 0.1 g/L) because of depletion flocculation. Borate ions do not influence the depletion threshold polymer concentration. However, HPG provides gravitational stability for flocculated emulsions to against phase separation.</p> <p>p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Times}</p> <p>Our work has shown that cationic colloids in the presence of HPG-borate display bridging flocculation, depletion flocculation, steric stabilization, salt induced</p> <p>coagulation, or no change at all, depending upon the HPG and salt concentrations. Developed were novel stability maps showing these phenomena mapped onto a log salt concentration versus log HPG concentration plane. The maps were generated by a combination of published models and experimental results. This portrayal of complex behaviors will be valuable to formulators because it clearly shows the effects of changing HPG molecular weight, colloids size and colloid volume fraction.</p>