Characterizing Polymer Hydration Shell Compressibilities with the Small-System Method

The small-system method (SSM) exploits the unique feature of finite-sized open systems, whose thermodynamic quantities scale with the inverse system size. This scaling enables the calculation of properties in the thermodynamic limit of macroscopic systems based on computer simulations of finite-sized systems. We herein extend the SSM to characterize the hydration shell compressibility of a generic hydrophobic polymer in water. By systematically increasing the strength of polymer-water repulsion, we find that the excess inverse thermodynamic correction factor (Δ1/Γs∞) and compressibility (Δχs) of the first hydration shell change sign from negative to positive. This occurs with a concurrent decrease in water hydrogen bonding and local tetrahedral order of the hydration shell water. The crossover lengthscale corresponds to an effective polymer bead diameter of 0.7 nm and is consistent with previous works on hydration of small and large hydrophobic solutes. The crossover lengthscale in polymer hydration shell compressibility, herein identified with the SSM approach, relates to hydrophobic interactions and macromolecular conformational equilibria in aqueous solution. The SSM approach may further be applied to study thermodynamic properties of polymer solvation shells in mixed solvents.

DEPENDENCE OF DISSOLUTION ENTHALPY OF POLYVINYLPYRROLIDONE IN WATER ON ITS INITIAL MOISTURE CONTENT

Changes in integral and differential enthalpies of dissolution of polyvinylpyrrolidone (PVP) of different molecular weight in water were determined as a function of initial moisture content of the polymer. Hydration numbers were calculated.

Uso De Un Polímero Hidrófilo A Base De Poliacrilamida Para Mejorar La Eficiencia En El Uso Del Agua

As an alternative in search of new options to reduce overexploitation of groundwater that allow us to increase agricultural profitability in water scarce areas, the behavior of a commercial hydrophilic polymer based in polyacrylamide (PAM) Lluvia solida®, was analyzed by evaluating the polymer hydration capacity. The tests that we used showed that this polymer is capable of absorbing its own weight in 268 times when using distilled water. When salts are dissolved in the water, the polymer reduces its water absorbing capacity, the hydration capacity being lower as the salt content increases, with a water absorption reduction up to 116 times its weight. The polymer hydration capacity also decreases significantly when a complete nutritive solution is used, reducing water absorption up to 55 times its weight; in the presence of divalent (Ca2+ and Mg2+) and monovalent (K+ and NH4 +) cations the polymer hydration capacity reduces proportionally to the cation concentration as an exponential function. Urea did not have any effect in the polymer hydration, thus this fertilizer may be used along with the polymer. The use of this hydrophilic polymer is a tool that improves the water use efficiency but the effect depends on water quality, being reduced by the presence of salts in water.

The Effect of Redox Potential and Metal Solubility on Oxidative Polymer Degradation

Summary Oxidative degradation of polymers is a serious concern in their field application for enhanced oil recovery (EOR). This study is an attempt to resolve some of the discrepancies in the literature regarding the occurrence and extent of this degradation, as well as to present a coherent framework for discussing the multitude of possible radical reactions. Sodium carbonate and bicarbonate are demonstrated to play a key role in stabilizing polymer against multiple reported sources of degradation, and it seems likely that this is caused by their effect on iron solubility. Brines containing iron in the reduced state are often obtained from aquifers for use in polymer hydration. These brines are shown to be prone to causing immediate degradation if exposed to air during or after polymer hydration because of the oxidation of soluble iron. If this cannot be avoided, preaeration may be a feasible strategy to minimize degradation during hydration. However, care must be taken to ensure subsequent degradation is not caused by the injection of a polymer solution containing oxygen into a formation containing iron. For instance, sodium dithionite can be added downstream of the last exposure to oxygen. The use of sodium carbonate may also mitigate degradation caused by the oxidation of iron (II) during polymer hydration.