Adsorption and Diffusion of Highly Charged Cationic Polyelectrolyte into Silica Gel Particles

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Title: Adsorption and Diffusion of Highly Charged Cationic Polyelectrolyte into Silica Gel Particles
Author: Wu, Ning
Advisors: Martin A. Hubbe , Committee Chair
Orlando J. Rojas, Committee Co-Chair
Sunkyu Park, Committee Member
Abstract: An understanding and ability to predict permeation behavior is important when applying polyelectrolyte treatments in enhanced oil recovery, papermaking, biomass hydrolysis, catalytic process, chromatographic separation, water treatment etc. In this research, polydiallyldimethylammonium chloride (poly-DADMAC) was used as a probe molecule to investigate major factors affecting penetration of polyelectrolyte into small pores, including time, polyelectrolyte concentration, substrate consistency, molecular mass, pH, conductivity, etc. Streaming potential tests were used innovatively to understand polyelectrolyte diffusion and adsorption on external surface and in nanopore networks. The magnitude change in streaming potential, which was taken as evidence of permeation, increased increasing polyelectrolyte dosage, with decreasing molecular mass. Increasing ionic strength tended to enhance adsorption of high-mass cationic polymers on the outer surfaces, but only a relatively small effect on permeation of high-mass cationic polymer into silica gel (nominal pore sizes of 6 nm or 30 nm) was observed. Adsorption of very-low-mass cationic polymer onto the outer surfaces and inside the 6 nm pore size silica gel was maximized at an intermediate salt level (1000 μS/cm conductivity). Electrokinetic tests also were used to provide evidence of polyelectrolyte desorption from mesoporous material. Another technique, a streaming current titration with a particle charge detector (PCD) was used to quantitatively determine polyelectrolyte adsorption on the external and internal surfaces of silica gel particles at levels of the above factors. The diffusion slowed down as the extension of the time for adsorption experiment. The adsorbed amount of poly-DADMAC was controlled by both the pore size and the surface area. The highest adsorption amount, based on mass of the substrate, was achieved when using silica gel having an intermediate pore size (15 nm) at a relatively high solution concentration of very-low-mass poly-DADMAC. The results were fit well to an assumed Langmuir model of the adsorption process. Streaming potential tests and streaming current tests may produce different result due to the difference in measurement principles. Further investigation may be needed for confirmation. Several techniques, such as BET tests and gel permeation chromatography were used to characterize the substrates and poly-DADMAC.
Date: 2009-12-07
Degree: MS
Discipline: Wood and Paper Science

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