Risei Wada

Crystallization and gelation of poly(vinylidene fluoride) in organic solvents

Poly(vinylidene fluoride) (PVdF) converts easily to thermally reversible gel at room temperature in aliphatic ketones or cyclic ketones such as 3-pentanone, 3-hexanone, cyclohexanone, and -butyrolactone, etc. Gelation of PVdF in these ketones took place through crystallization of polymers from solution. The crystallization process was investigated in detail by Fourier transform infrared (FTIR) measurements. The FTIR spectra were recorded continuously at room temperature until the solution converted to gel. It was suggested from spectral data that polymer chains packed together (i.e., crystallization took place) into the TTTGTTTG¯ conformation in the case of PVdF/γ-butyrolactone solution, followed immediately by gelation. On the other hand, crystallization occurred into the TGTG¯ conformation in the case of other ketones and gelation immediately took place. Melting temperatures of PVdF gels thus prepared from these solvents were measured. showed a solvent dependence.

Antibacterial Properties of Silicone Membranes after a Simple Two-Step Immersion Process in Iodine and Silver Nitrate Solutions

　Silicone is widely used in packing materials, medical equipment, and separation membranes. Since microbial cells easily adhere to the surface of silicone materials and form biofilms, techniques for incorporating antimicrobial activity into silicone materials are in high demand. This study describes the preparation of silver (Ag)/silicone composite membranes through a simple two-step immersion process, utilizing an iodine solution followed by a silver nitrate solution at room temperature. Scanning electron microscopy (SEM) observations revealed that particles with sizes of several nanometers to several tens of nanometers were present on the silicone membrane surface; these particles were identified as silver iodide using energy-dispersive X-ray spectroscopy (EDS) . The Ag/silicone membrane possessed excellent antibacterial efficacy against Escherichia coli and Staphylococcus aureus, and the antibacterial efficacy (R) against both types of bacteria was R > 4, even after stomacher treatment or acidic treatment of pH 2-6 for 24 h. The mechanical strength of the silicone membrane was also maintained after antibacterial treatment, with Youngs modulus values of 7.9±1.2 MPa and 8.3±1.5 MPa for the untreated membrane and Ag/silicone membrane, respectively (p > 0.05) . In addition, the reduction in permeation performance of the Ag/silicone membrane was only 20%, despite the antibacterial treatment on the membrane surface. This antibacterial treatment method of silicone membranes can be conducted at room temperature (25℃) without special equipment, and may be applied to other types of silicone materials.