Computer Simulation Studies on the Polymer-Induced Modification of Water Properties in Polyacrylamide Hydrogels

Abstract

The interactions between polyacrylamide and SPC/E water molecules in polymer gels and solutions were analyzed using computer simulations. Several polymer structures with different concentrations, connectivity characteristics, and pore sizes were used in order to investigate different polymer environments. It was shown that the structure of water was strongly modified in the presence of the polymer. This polymer-induced modification could be characterized in a very detailed way using the spatial distribution function, which considers both the distance as well as the orientation of the water molecules relative to the amide side groups. The dynamics of water, as manifested in the translational and rotational diffusion and residence probability of water is slowed down in the presence of the polymer. The strongest modifications are found in the shell of bound water, but also long-ranged effects were detected. The hydrogen bonds in the vicinity of amide side groups become stronger and longer lived. By setting the partial charges in the amide side groups to zero in some systems, artificial apolar polymer network model systems were defined, whose influence on the structure of water is remarkably different from the influence of the polar networks, although their influence on the transport properties of the surrounding water molecules was found to be quite similar.

Static and dynamic properties of stretched water

“…For example, negative pressures are observed, 21 and seem to play an important role in the mechanism of water transport in plants. Therefore is similar to the effect of stretching ͑as is the case in some hydrogels 19 ͒, also influence its dynamical behavior. Dynamic properties, such as the diffusion constant, have been studied in detail for water systems at atmospheric and at high positive pressures, both experimentally 22,23 as well as by computer simulations.…”

“…[1][2][3][4]19,20 The effect not only of applied pressure, but also of negative pressure ͑''stretching''͒, is remarkable. The study of the behavior of this fluid under negative pressures is relevant not only from the academic point of view, but also for realistic systems.…”

Effect of Cross-Linking on the Diffusion of Water, Ions, and Small Molecules in Hydrogels

“…In recent times, molecular dynamics simulation has been used to study physical gels [30], poly(vinyl alcohol) [31,10], poly(vinyl methyl ether) [32], poly(N-isopropylacrylamide) [32], polyacrylamide [33], epoxy-amine networks [34], etc. Structure and dynamics of the polymer-water interface in poly(vinyl alcohol) (PVA) for a mesh size of 1 nm was studied recently [10].…”

Supercooled Water in PVA Matrixes. II. A Molecular Dynamics Simulation Study and Comparison with QENS Results

“…7,8 The availability of new experimental approaches probing distances and times on the molecular level provided by modern facilities as high-flux neutron sources and X-ray synchrotrons [9][10][11] has allowed detailed insight into this subject. The parallel development of computational methods applied to protein and other macromolecular species 12 has also triggered interest in the gel state.…”

“…The authors focused on the hydrogen-bonded structure of the entangled chains and on their dynamics and on the diffusion behavior of water as well as of O 2 and N 2 , treated as penetrants. 30 Chemical polyacrylamide hydrogels have been simulated at high polymer concentrations (from 27 to 41 wt %) at temperatures ranging from 270.6 to 301.7 K. 8 A polymer-induced modification of solvent properties has been detected in the first hydration shell, resulting in an anisotropic spatial distribution of bound water around the matrix with a decreased diffusion coefficient and increased residence probability.…”