To understand, at a molecular scale, the effect of water on the structure of the amorphous region of polyamide 6,6 (PA6,6), atomistic molecular dynamics simulations have been carried out. Our results concerning the very local water organization relative to PA moieties agree qualitatively with a two-step sorption model. The first sorption mode seems to be saturated well below the lowest water concentration studied (5% relative to the amorphous phase). Moreover, above this saturation, the overall water organization displays at 300 K larger clusters than the 2−3 molecules usually assumed in the literature. The temperature dependence of free volume, hole size, and hydrogen bonding has also been investigated. It shows a transition between plasticized and antiplasticized behavior.

We have investigated with computational chemistry techniques the visible spectra of substituted anthraquinones. A wide panel of theoretical methods has been used, with various basis sets and density functional theory (DFT) functionals, in order to assess a level of theory that would lead to converged excitation energies. It turns out that the hybrid Becke-Lee-Yang-Parr and Perdew-Burke-Erzenrhof functionals with the 6-31G (d,p) atomic basis set provide reliable lambda(max) when the solvent effects are included in the model. Combining the results of both DFT schemes allows the prediction of lambda(max) with a standard deviation limited to 13 nm.

Understanding the chemistry and physics of polyelectrolyte systems challenges scientists from a wide spectrum of research areas, ranging from colloidal science to biology. However, despite significant progress in the past decades, the calculation of large open polyelectrolyte systems on a detailed level remains computationally expensive, due to the highly polymeric nature of the macromolecules and/or long-range character of the intermonomer interactions. To cope with these difficulties, field-theoretic methodologies based on the mean-field approximation have emerged recently and have proven to provide useful results in the regime of high polyelectrolyte concentration. In this paper we present applications of a low-cost field-theoretic calculation approach based on the method of Gaussian equivalent representation, which has recently been proven useful for delivering accurate results in case of polymer solutions beyond the mean field level of approximation. Here we demonstrate its effectiveness on the example of a Gaussian effective potential, mimicking the effective interactions between weakly charged polyelectrolyte coils, and a screened Coulomb model, describing the effective intermonomer interactions of Debye-Hückel chains. Moreover, we show that the approach opens perspectives to extend the range of applicability of the grand canonical ensemble to dense liquid and solid phases of more sophisticated polyelectrolyte models. Finally, we demonstrate that our approach is also much more reliable for determining the phase boundaries of these models than conventional mean field and grand canonical Monte Carlo approaches.