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The effect of pH, temperature, and ionic strength on the molecular conformation of five industrial polyacrylamide-based flocculants was investigated by determining intrinsic viscosities on dilute flocculant solutions. The Fedors equation was found to be most suitable for all flocculants for determining the intrinsic viscosity. The results indicated that the flocculants are fully extended in distilled water at natural pH and at 25°C as evidenced by the high intrinsic viscosities. The data pointed to the strong dependence of the intrinsic viscosity on the presence of salts as a result of the shielding of negatively charged carboxylate groups by the counterions. At a constant ionic strength of 0.01M NaCl, the flocculants assumed a coiled conformation, and further coiling was observed in the presence of small quantities of calcium chloride. CaC1₂ (0.001 mo1/L) There was a decrease in intrinsic viscosities at high pH (~8.5 and 10.5) that was merely attributed to an increase in ionic strength with the increase in concentration of Na⁺ at high pH. Intrinsic viscosity measurements at higher temperatures (35°C and 50°C) showed a small effect of temperature on the conformation of the flocculants. Higher temperature, however, seemed to accelerate the aging of the flocculant solutions. The degrees of anionicity of the flocculants were found to be in the range 1.5% to 50%, as determined through chemical analysis. It was established that determination of total organic carbon content and sodium assays is an accurate way of obtaining the degrees of anionicity of industrial flocculants. The solution stability of the flocculants in distilled water and in 0.01M NaCl was investigated over a period of three days. The reduced viscosities of the anionic flocculant in distilled water steadily decreased. The decrease was more dramatic at high temperature (50°C) than at room temperature, but no viscosity loss was observed in the presence of NaCl. The viscosity of the nonionic flocculant was stable in both distilled water and NaCl. The viscosity loss with time in the case of the anionic flocculant can be correlated with the hydrolysis of the weakly acidic carboxylate (C00⁻) groups to release OH⁻ ions and simultaneous association into uncharged carboxylic (C00H) groups that promote coiling of polyacrylamide. This effect is therefore very similar to the earlier-mentioned effect of sodium chloride.

The effects of a simulated in vitro digestion model on the viscosity of solutions of locust bean gum, guar gum, fenugreek gum, xanthan gum, gum Arabic, psyllium, flaxseed gum and soy soluble polysaccharides (SSPS) were examined in this study. All hydrocolloid solutions were formulated for low viscosity (LV), medium viscosity (MV) and high viscosity (HV), which were subsequently subjected to 3 treatments of equal volumes each. The treatments consisted of 1) H2O-dilutions, 2) acid and alkali in the absence of enzymes/bile and 3) an in vitro digestion model simulating the gastric and duodenal phases with pH changes in the presence of hydrolytic enzymes and bile salts. All hydrocolloids showed substantial reductions in viscosity, with dilutions exerting the greatest effect. Depending on the concentration, xanthan gum retained 20-50% of its initial viscosity while the other solutions were in a lower range of 1-16%, thereby showing considerable resilience to the 3 simulated conditions. / NSERC

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Molecular simulations performed on modern computers provide a powerful tool for the investigation of both static and dynamic properties of liquid crystals. In this thesis several properties of liquid crystal mesogens have been investigated using state-of-the-art Monte Carlo (MC) and molecular dynamics (MD) simulation techniques. The helical twisting power, βm, determines the pitch of the chiral nematic phase produced when a nematic liquid crystal is doped with a low concentration of chiral solute molecules. A new simulation technique that allows the prediction of both the sign and the magnitude of βm is described. The method employs fully atomistic MC simulations of a chiral dopant molecule in the presence of a twisted nematic solvent composed of Gay-Berne particles. Eighteen different chiral dopant molecules were examined and in all cases the results were in good agreement with existing experimental data. The Kirkwood correlation factor, g(_1), has been evaluated for the molecules PCH5, PCH5-C1, me5NF and GGP5C1 using MD simulations in the pre-transitional region of the isotropic phase. The calculations employed an all-atom force field, which was developed specifically for liquid crystal molecules. PCH5 and meSNF were seen to favour anti-parallel dipole alignment whereas, PCH5-C1 and GGP5C1 preferred a parallel arrangement of the molecular dipoles. With the exception of GGP5C1, the simulations gave g(_1) values that were in accordance with existing experimental dielectric measurements. Detailed analysis of the MD trajectories showed that certain molecular pair configurations were preferred in the bulk and indicated which molecular groups were responsible for the stabilization of these configurations. Equilibrium molecular dynamics simulations were carried out in order to evaluate the rotational viscosity coefficient, γ(_1), for a Gay-Berne mesogen using two independent analysis techniques. The methods gave consistent results, which were comparable to experimental data for real mesogens of similar shape and size.

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Optimal trade execution aims at balancing price impact and timing risk. With respect to the mathematical formulation of the optimization problem, we primarily focus on Mean Variance (MV) optimization, in which the two conflicting objectives are maximizing expected revenue (the flip side of trading impact) and minimizing variance of revenue (a measure of timing risk). We also consider the use of expected quadratic variation of the portfolio value process as an alternative measure of timing risk, which leads to Mean Quadratic Variation (MQV) optimization. We demonstrate that MV-optimal strategies are quite different from MQV-optimal strategies in many aspects. These differences are in stark contrast to the common belief that MQV-optimal strategies are similar to, or even the same as, MV-optimal strategies. These differences should be of interest to practitioners since we prove that the classic Almgren-Chriss strategies (industry standard) are MQV-optimal, in contrary to the common belief that they are MV-optimal. From a computational point of view, we extend theoretical results in the literature to prove that the mean variance efficient frontier computed using our method is indeed the complete Pareto-efficient frontier. First, we generalize the result in Li (2000) on the embedding technique and develop a post-processing algorithm that guarantees Pareto-optimality of numerically computed efficient frontier. Second, we extend the convergence result in Barles (1990) to viscosity solution of a system of nonlinear Hamilton Jacobi Bellman partial differential equations (HJB PDEs). On the numerical aspect, we combine the techniques of similarity reduction, non-standard interpolation, and careful grid construction to significantly improve the efficiency of our numerical methods for solving nonlinear HJB PDEs.