Charged grafted polymer layers: Interactions, particle adsorption, and phase behavior
Abstract
Three different model systems involving grafted charged polymer layers have been studied. In the first chapter, the interactions between charged surfaces and surfaces with grafted polymers with a functional charged group have been studied using a molecular theory. We have studied the ability to control the range and strength of the interactions by changing the polymer chain length, surface coverage, surface charge density, solution ionic strength and position of the functional group along the chain. There are two relevant length scales in the problem: the grafted polymer layer thickness and the Debye length. These two length scales can be varied independently of each other enabling the manipulation of the range and strength of the effective interactions between the surfaces. Furthermore, changing the solutions ionic strength enables the manipulation of the interactions in a responsive way. In the second chapter, adsorption of nanoparticles on tethered weak polyelectrolyte layers driven by electrostatic attractions is studied, while the theory appropriately couples the inhomogeneous acid-base equilibrium with the thermodynamics. We study the amount, structure, and position of nanoparticle adsorption as a function of surface coverage, bulk salt concentration, solvent quality, and bulk pH. The adsorption is determined by the acid-base equilibirium and polymer layer structure. By tuning parameters generally easy to modify, such as temperature and bulk pH, dramatically different adsorptions can be obtained and the transition between those different adsorption behaviors is reversible. This serves as a theoretical guideline for design tool. The phase behavior of tethered weak polyelectrolytes and the charge regulation effect is discussed in the third chapter. A reverse salt effect is found regarding the stability of the polymer layers. The salt stabilizes the graft weak polyelectrolyte layer, while this effect is completely the opposite for strongly charged polymers. The results presented here provide guidelines for the conditions necessary to form stable layers.
Degree
Ph.D.
Advisors
Szleifer, Purdue University.
Subject Area
Polymers|Chemistry
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