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Reverse osmosis (RO) membranes are becoming popular as energy saving and environmentally friendly materials for the desalination of water. Toward the rational design of RO membranes, we performed contrast-variation neutron scattering measurements and atomistic molecular dynamics (MD) simulations on polyamide/water systems with various water contents and deuteration ratios. The experimental and computational structure factors showed good agreement for all the systems examined. The structure of the water-rich polyamide/water system obtained from MD calculation showed that the water clusters are well connected to each other, and a relatively large number of water molecules are present at a distance over 3 A from the polyamide. The partial radial distribution functions were calculated, and strong interactions were observed between water and the carboxyl group in polyamide. Thus, the water permeability of the RO membrane can be expected to improve when more carboxyl groups are introduced. In addition, the polyamide–polyamide interaction was found to be equal to or smaller than the polyamide–water interactions and relatively weak in the water-rich system. Reverse osmosis membranes have been playing a main role for the desalination of water in the world. Hydration structure of polyamide functional layer of the membrane was studied via neutron scattering and atomistic molecular dynamics simulations. Experimental and computational structure factors, S(Q), of the polyamide/water system showed good agreement. Water clusters in water-rich system were well connected to each other and formed channel-like structure. Polyamide–water interactions and polyamide-polyamide interactions, which are thought to be important to enhance the performance of the membranes, were examined in detail.

Polyvinyl pyrrolidone (PVP) is well known as a biocompatible polymer used in the fields of medical devices and pharmaceuticals, and is associated with intermediate water, which is said to play an important role in developing the biocompatibility of medical materials. The states of water molecules interacting with PVP, i.e., the non-freezing water, slow and fast intermediate water are classified using 2H NMR. The non-freezing water is directly hydrogen-bonded to ca. 1.5 amide groups of PVP. The slow intermediate water interacts with PVP indirectly through non-freezing water. It then shows slow diffusion dynamics and forms cubic-form ice during cold crystallisation, while the fast intermediate water can diffuse as fast as free water, and can freeze to form normal hexagonal-form ice. Statement of significance For many of the medical materials, including artificial organs such as dialysis membranes and artificial blood vessels, polymers are used. Biocompatibility of polymer is an important property for materials used in medical devices and medicine. Although there are lots of studies about surface design of materials in terms of hydrophilicity, charge, or morphology, the unified expression factor of biocompatibility have not been clear. Recently, it is suggested that water molecules, especially intermediate water, on materials surface play important roles in the development of biocompatibility. However, the characteristics of the intermediate water have not been understood. It is important issues to be solved in the development of new and high-performance biocompatible polymer materials based on the concept of intermediate water. In present study, we have investigated the intermediate water on polyvinyl pyrrolidone (PVP), which is biocompatible polymer widely used in medical device and medicine. Differential scanning calorimeter (DSC), X-ray diffraction (XRD), and various nuclear magnetic resonance (NMR) methods for PVP aqueous solutions were performed in order to clarify the physical properties of the intermediate water. We found that the intermediate water has structural order and diffusive mobility just between free water and non-freezing water. These features of intermediate water are induced by structural interaction with polymer. The knowledge from present study expected to provide guidance for the design of biocompatible materials.

Simultaneous differential scanning calorimetry (DSC) and luminescence (LUM) measurements of polyacrylonitrile revealed that a precursory reaction progresses below the well-known endothermic cyclization reaction (i.e., peak temperature ca. 280 °C). The intensity of LUM increased above 90 °C, which is around the glass transition temperature. After the peak at 180–190 °C, the LUM intensity decreased with temperature up to 250 °C, i.e., below the onset temperature of cyclization reaction. Thermal signals cannot be seen on the DSC curve in the temperature range of the LUM peak. The activation energy (Ea) estimated from the heating rate dependence of the LUM peak temperatures was 122 kJ mol−1. However, the Ea obtained from the well-known exothermic peak temperatures of DSC measurements was 190 kJ mol−1. Electron spin resonance and nuclear magnetic resonance also support the chemical structure of the luminescence species. FT-IR and X-ray diffraction were also performed to confirm the change in chemical and physical structural. Finally, ab initio calculations suggest that thermally stable heterocyclic radical species with two to four fused six-membered rings are the main products of the precursory reaction.

Differential scanning calorimetry and fast scanning chip calorimetry heating experiments were carried out in a wide range of rates of temperature change from 0.2 to 60,000 K s−1 for isothermally crystallized polyamide 6. Multiple melting peaks were observed. With increasing heating rate, the highest-temperature endotherm shifts toward lower temperatures and finally disappears due to suppression of the reorganization. The critical heating rate to suppress reorganization was 15–50 times higher than the critical cooling rate to cause complete vitrification. On heating at rates higher than the critical heating rate to suppress reorganization, there were observed two melting processes of different kinetics. Four possible assignments were considered regarding the two crystal populations. These are (i) crystals grown during primary and secondary crystallization, (ii) crystals grown in the bulk and nucleated at the surface/substrate, (iii) crystals, which are subjected to different local stress originating from heterogeneities in interlamellar regions, and (iv) the crystal/mesophase polymorphism. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2126–2138