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Title: Conformation of cellulose-based polyelectrolytes and development of microflow scattering approaches
Author: Gonzalez Lopez, Carlos
ISNI:       0000 0004 7228 3249
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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The work reported on this thesis is primarily a small angle neutron scattering (SANS) and rheology study of cellulose derivative polyelectrolyte Sodium Carboxymethyl Cellulose (NaCMC) in aqueous solutions. We measure, for the first time using SANS, the relevant structural length scales as a function of polymer (cp) in aqueous salt free and NaCl solutions. The intrinsic persistence length is measured by SANS to be 55 A, characteristic of a semi-flexible polymer. In salt-free solutions, the correlation length is found to scale as cp^-1/2 across the entire semi-dilute and concentrated range. Both SANS and viscosity measurements are in general agreement with scaling theory predictions for flexible polyelectrolytes in salt free solution. The crossover between the semidilute and concentrated regimes cannot be explained as arising from the overlapping of correlation and electrostatic blobs, and appears to relate to the intrinsic persistence length of the polymer. As expected, the addition of salt leads to a decrease in viscosity and an increase in the correlation length. Flexible scaling theory cannot describe the variation of these two quantities accurately, as it neglects the intrinsic rigidity of the chains. The scaling picture put forward by Odijk appears to be correct in the high salt limit, although it suffers from several approximations, namely the use of a simplified expansion factor and an inaccurate expression from the excluded volume. Once these are corrected, theory and experiment show good agreement. We finally report the combination of SANS with microfluidics, which is a useful technique to probe the soft matter dynamics under flow, and illustrate it with well-known strongly scattering liquid crystal systems, quantifying alignment through a contraction-expansion flow field. Different microfabrication techniques and materials are discussed in terms of their compatibility with SANS. Finally, we outline a roadmap for microfluidic SANS, enabling the spatiotemporal investigation of conformational changes under flow, focusing on low scattering systems, including NaCMC in solution.
Supervisor: Cabral, Joao Sponsor: Engineering and Physical Sciences Research Council ; Unilever (Firm)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral