Phase separation and coacervate complex formation of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) were investigated as model pair of oppositely charged, weak polyelectrolytes in aqueous solution. Both fully or partially neutralized PAA (sodium polyacrylate) and PAH were employed. Important factors affecting the complexation were systematically varied including the polyacid/polybase mixing ratio (10−90 wt %), ionic strength as salt concentration (0−4700 mM), polymer concentration (0.02−2.0 wt %), pH (5 and 7), and temperature (30−75 °C). Sample turbidity was utilized as an indicator of polyelectrolyte complex formation. Phase separation in the solution was also observed by optical microscopy in the distinguishable forms of either precipitate or coacervate. In the absence of salt, polyelectrolyte complexation always resulted in the formation of a precipitate. In the presence of sodium chloride, complex formation does not take place (neither precipitate nor coacervate) when either polyelectrolyte is present in large excess. Increasing salt concentration causes a change from solid precipitate to fluid coacervate phase, and finally a one-phase polyelectrolyte solution is obtained. Temperature affected the precipitate-to-solution transition only in the case of samples with low concentrations of either PAA or PAH. The data generated led to the construction of phase diagrams that illustrate how the various parameters control the demixing and the precipitate−coacervate−solution phase transitions. We find such phase diagrams for simple, flexible synthetic macromolecular systems to be rare in the polymer science literature. Ternary phase diagrams were prepared, which showed the influence of relative polymer and salt concentration on the phase behavior of the aqueous PAA/PAH system. We believe data such as these will both improve both the reliable applications of polymer coacervates and the development of new macromolecular assemblies based on charge complexation.

This mini-review highlights the recent development of mussel-inspired hydrogels in biomedical and environmental fields.

Natural rubber foam (NRF) can be prepared from concentrated natural latex, providing specific characteristics such as density, compression strength, compression set, and so on, suitable for making shape-memory products. However, many customers require NRF products with a low compression set. This study aims to develop and prepare NRF to investigate its recoverability and other related characteristics by the addition of charcoal and silica fillers. The results showed that increasing filler loading increases physical and mechanical properties. The recoverability of NRF improves as silica increases, contrary to charcoal loading, due to the higher specific surface area of silica. Thermodynamic aspects showed that increasing filler loading increases the compression force (F) as well as the proportion of internal energy to the compression force (Fu/F). The entropy (S) also increases with increasing filler loading, which is favorable for thermodynamic systems. The activation enthalpy (∆Ha) of the NRF with silica is higher than the control NRF, which is due to rubber–filler interactions created within the NRF. A thermodynamic concept of crosslinked rubber foam with filler is proposed. From theory to application, in this study, the NRF has better recoverability with silica loading.

We detail a method originally described by Okahata et al. (Macromol. Rapid Commun. 2002, 23, 252-255) to prepare noncovalent self-assembling films by exchanging the counter-ions of the nucleic acid phosphate moieties with those of cationic lipid amphiphiles. We are able to control the strength and surface properties of these films by varying the composition between blends of DNA of high molecular weight and RNA of low molecular weight. X-ray and AFM results indicate that these films have a lamellar multilayered structure with layers of nucleic acid separated by layers of cationic amphiphile. The tensile strength of the blended films between DNA and RNA increases elastically with DNA content. The length as well as the molecular structure of nucleic acids can affect the topology and mechanical properties of these films. We suspect that the permeability properties of these films make them good candidates for further biological applications in vivo.