Microstructure and Dynamics of Concentrated Hydrocolloid Polymer Networks

Concentrated polymer networks are encountered in various industrial processes, for example, polymer filtration and purification, hydraulic fracturing in oil and gas production, pharmaceutical gel formulation. This thesis work focuses on two types of concentrated polymer networks: dense uncrosslinked networks of guar gum and associatively crosslinked networks of hydrophobically modified polyacrylic acid. For the concentrated guar filter cakes, we present two physical models of concentration polarization that predicts the guar concentration profile and pressure drop developed in the filter cake formation process. The Osmotic Pressure-Permeability model is based on the force balance between the osmotic pressure and the hydrodynamic drag on the polymer networks by the solvent flow at the steady state. The dynamic Elastic Network model is based on the poro-elastic theory. The two models are developed based on parameters determined from independent measurements: osmotic pressure and permeability as a function of polymer concentration. A nonuniform polymer concentration in the filter cake is predicted. The steady state pressure as a function of flow rate calculated from the two models compares well with experimental results for the hydroxylpropyl guar filter cakes on a membrane surface. Enzymatic degradation kinetics of concentrated guar filter cakes is diffusion-controlled. The transport of ovalbumin protein that mimics the enzymes used for degradation of concentrated hydroxylpropyl guar polymer solutions has been studied by NMR. The NMR measurements include both translational diffusion and rotational diffusion. CF3 groups are chemically tagged to protein to differentiate the protein from polymer matrix. 19F pulsed field gradient NMR is used to measure translational diffusion coefficient, while T1 and T2 relaxation of the 19F signal is measured to obtain rotational diffusion coefficient. Both translational and rotational diffusions are compared with micro-mechanical hydrodynamic theories. It is found that the protein diffusion in the mesoscopic regime is closely related to the thermal fluctuation of the polymer network. In the highly concentrated polymer networks, the translational diffusion of proteins is greatly hindered but the rotational mobility is much less hindered. The two correlation times are correlated in a stretched exponential form. A novel associative polymer network with tunable rheological properties is developed based on cyclodextrin-hydrophobe inclusion. The network is formed from mixtures of two polyacrylic acid (PAA) backbone polymers, one with pendant cyclodextrin groups and one with pendant hydrophobic alkyl groups. The binary nature of cyclodextrin-hydrophobe inclusion prevents hydrophobes from forming non-stoichiometric multiple associations. Only intermolecular association is allowed. This system serves as a model associative polymer network to test associative polymers theories. Dynamic rheological properties of this mixture solution can be tuned by adding free cyclodextrins or sodium dodecylsulfate (SDS) to displace polymer-to-polymer associations. Dynamic moduli change three orders of magnitude from a gel state to a sol state. The phase behavior of this mixture solution is experimentally studied by light scattering measurements and rheology and further compared with the theoretical phase diagram. The thermodynamics and kinetics of the cyclodextrin-hydrophobe interaction is independently studied using isothermal titration calorimetry, surface plasmon resonance and adsorption study. With the binding energy and activation energy independently measured, a very good prediction for the zero shear viscosity of the...