Kohei Sanui

Ionic conductivity and mobility in network polymers from poly(propylene oxide) containing lithium perchlorate

Ionic conductivity σ and mobility μ in the amorphous network polymers from poly(propylene oxide) (PPO) containing lithium perchlorate (LiClO4) at the concentration of [LiClO4]/[PO unit]=0.042 and 0.076 were investigated by means of complex impedance and time‐of‐flight methods. The σ values of the PPO–LiClO4 complexes reached 10−5 S cm−1 at 70 °C. The temperature dependence of σ deviated from a single Arrhenius behavior above a critical temperature (−1 °C and 11 °C) which approximately corresponded to the glass transition temperature Tg. The μ values were relatively high and changed from 10−6 to 10−5 cm2 V−1 s−1 in the temperature range of 40–100 °C. The Nernst–Einstein equation correlated μ with the ionic diffusion coefficient D. The Williams–Landel–Ferry equation with C1≂5 and C2≂30–50 held with a temperature dependence of D in the order of 10−8–10−7 cm2 s−1. The change in the number of ionic carriers n with temperature obeyed the Arrhenius equation with the activation energy of 0.26 and 0.34 eV. The deg...

Synthesis and proton conductivity of thermally stable polymer electrolyte: poly(benzimidazole) complexes with strong acid molecules

Abstract We synthesized thermally stable proton-conducting polymers composed of poly(benzimidazole) (PBI) and strong acids. PBI films were doped with strong acids such as phosphoric, sulfuric, and hydrochloric acid by immersing them into a mixed solution of strong acid and methanol. We found that the PBI films and strong acids formed polymer complexes because they showed the acid–base or the hydrogen bonding interactions between imidazole groups of PBI and acid molecules. The PBI/H 3 PO 4 complexes were thermally stable up to 500°C, and the proton conductivity of anhydrous complexes reached 10 −5 S cm −1 at 160°C.

THERMO-RESPONSIVE SWELLING AND DRUG RELEASE SWITCHING OF INTERPENETRATING POLYMER NETWORKS COMPOSED OF POLY(ACRYLAMIDE-CO-BUTYL METHACRYLATE) AND POLY(ACRYLIC ACID)

Abstract The swelling behaviour of interpenetrating polymer networks (IPN) composed of poly (acrylic acid) (PAAc) and poly (acrylamide(AAm)-co-butyl methacrylate (BMA)) in water was studied and compared to crosslinked poly(AAm-co-BMA) and crosslinked poly(AAm-co-AAc-co-BMA). The IPNs were prepared by a sequential IPN method in which crosslinked PAAc chains were formed inside of three-dimensional networks ofpoly(AAm-co-BMA) as initial gels. Crosslinked poly(AAcco-AAm-co-BMA) gels (random gels) were also synthesized with the same monomer compositions as the IPNs to elucidate the effect of gel first-order structure on swelling behaviour. Positive swelling changes, i.e. lower swelling ratio at lower temperature and higher swelling ratio at higher temperature, were observed with temperature changes for both the IPNs and the random gels, while no change in swelling was observed for crosslinked poly(AAm-co-BMA) without AAc. In particular, IPN swelling showed a transition point at a certain temperature as a function of temperature change, while random gels showed simple and dull swelling changes with temperature change. The transition temperature of the IPNs shifts to higher temperature with increasing BMA content in IPNs. The positive temperature dependence is suggested to be linked to the formation and dissociation of hydrogen-bond complexes between AAc and AAm with temperature changes in IPNs and random gels. The observed transition in swelling changes in the IPN series is hypothesized to result from concurrent dissociation of continuous ladder-like polymer complexes between PAAc and PAAm matrices in the IPN. The shift of transition temperature induced by incorporation of BMA was due to the stabilization of the complex at higher temperature by increasing hydrophobic interactions. Reversible swelling changes, i.e. higher swelling ratio at high temperature (20°C, 30 °C, 40 °C) and lower swelling ratio at 10°C, in response to step-wise temperature changes between low and high temperature, were observed only for BMA-incorporated IPNs, while irreversible swelling was observed for IPNs without BMA. This result suggests that the presence of hydrophobic BMA had an important role in reversible swelling change of IPNs in response to temperature change. To evaluate the feasibility of IPNs for drug delivery systems, the release of ketoprofen from IPNs was performed with fluctuation of temperature between 10°C and 30 °C. The release rate of drug was reduced at 10°C, while it was increased at 30 °C. The difference of release rate between 10°C and 30 °C was considered to be due to different drug diffusivities between the temperatures induced by swelling changes of IPNs.

Estimation of Li+ transport number in polymer electrolytes by the combination of complex impedance and potentiostatic polarization measurements

Abstract The Li + transport numbers of two types of polymer electrolytes have been estimated by means of the combination of the complex impedance and potentiostatic polarization measurements. Type I electrolytes were the network polymers with dissolved LiClO 4 obtained from poly (ethylene oxide) (PEO) and from PEO-grafted-polydimethylsiloxane. Type II electrolyte was the network polymer obtained from PEO where -COO − Li + groups were linked to the polymer backbone by covalent bonds. The ionic conductivity and Li + transport number well reflected the differences in the polymer structures. The type I electrolytes had higher conductivities than the type II electrolyte, whereas the Li + transport numbers were considerably lower than unity. In contrast, the type II electrolyte had the Li + transport number of unity.

Preparation and characterization of natural lower dimensional layered perovskite-type compounds

Abstract Thin films of layered perovskite compounds (CnH2n+1NH3)2(CH3NH3)m−1PbmBr3m+1 (m=1, 2 and 3) were prepared by the spin-coating method from their DMF (N,N-dimethylformamide) solutions. The control of the inorganic layer thickness in layered perovskites can be achieved by changing the ratio of the two amines (CnH2n+1NH3/CH3NH3). The layered perovskite films showed a strong, clear exciton absorption peak at room temperature due to their large exciton binding energy. With increasing numbers of inorganic layers, a red shift of the exciton absorption was observed due to the decrease in transfer energy. X-ray diffraction patterns clearly demonstrated that the spin-coated film was highly oriented normal to the surface, which is consistent with ‘mono’, ‘bi’, and ‘tri’ layer structures, respectively. The effect of the alkyl chain length of the organic part was also investigated.

Structure-conductivity relationsihp in polymer electrolytes formed by network polymers from poly[dimethylsiloxane-g- poly(ethylene oxide)] and litegum perchlorate

The combination of LiClO4 and network polymers from poly[dimethyl-siloxane-g-poly(ethylene oxide)] has been applied to polymer electrolytes as an Li+ ion conductor, and the structure/conductivity relationship has been investigated. The ionic conductivity is about 10−6 S cm−1 at room temperature. The polymer electrolytes form a micro-heterogeneous structure from the constituent segments, and the incorporated LiClO4 preferentially interacts with the poly(ethylene oxide) segments. The segmental motion of poly(ethylene oxide) appears to contribute to the ionic migration, while that of poly(dimethylsiloxane) does not. Not all of the incorporated LiClO4 functions as carrier ions.

Evaluation of ionic mobility and transference number in a polymeric solid electrolyte by isothermal transient ionic current method

We proposed a new method for evaluating mobilities of both Li+ and SCN− ions in a polymeric solid electrolyte formed by poly (ethylene succinate) and LiSCN. The method is based on the isothermal transient ionic current (ITIC) technique by using an ion‐blocking platinum electrode and an ion‐reversible lithium electrode. The differences of the ITIC profiles, depending on the kind of the electrodes, provided both mobilities of Li+ and SCN− ions, and their assignment. The mobilities of Li+ and SCN− ions at 90 °C were 1.3–4.2×10−6 cm2 V−1 s−1 and 5.3–10.7×10−8 cm2 V−1 s−1, respectively. The transference number of Li+ ions was 0.92–0.99.

Secretory function of adrenal chromaffin cells cultured on polypyrrole films

Polypyrrole (PPy) is a conducting polymer and is obtained electrochemically on an electrode such as indium-tin oxide (ITO). In this study, in order to develop a novel cell-culture system which makes it possible to communicate with cultured mammalian cells, bovine adrenal chromaffin cells were cultured on PPy-coated ITO plates for 7 days and the influence of PPy-coating on the cell functions was investigated. Since the chromaffin cells synthesize and secrete catecholamines such as adrenaline and noradrenaline, the amount of synthesized and released catecholamines from the chromaffin cells cultured on PPy-coating and ITO itself were measured. The cells on the PPy-coated ITO plate could be kept in culture, without any significant changes in morphology and in the secretory responsiveness to acetylcholine as compared with those of the cells cultured on collagen. On the contrary, the cells on the ITO plate lost the responsiveness, while the amount of catecholamines synthesized was affected little by both PPy and ITO surfaces. It is suggested that PPy supports the secretory function of the chromaffin cells when they are cultured on it. This paper describes that PPy films are applicable as a polymer-modified electrode which support the cell function without collagen.

Ion conduction mechanism in network polymers from poly(ethylene oxide) and poly(propylene oxide) containing lithium perchlorate

Abstract Ion conduction mechanism in network polymers from poly(ethylene oxide) and poly(propylene oxide) containing lithium perchlorate was investigated in their amorphous and rubbery state, based on the results of the temperature dependences of ionic conductivity and mobility. The temperature dependences of ionic diffusion coefficient and the number of carrier ions obeyed the WLF-type and the Arrhenius equations, respectively. The ionic conductivity was interpreted by the superposition of these processes. The difference in the ionic conductivity for these two polymer complexes was discussed.

Electrochemical control of drug release from redox-active micelles

Abstract Electrochemical control of drug release was demonstrated by redox-active micelles of non-ionic surfactants having a ferrocenyl moiety (FPEG). The surfactants formed micelles at the concentrations above the critical micelle concentration (CMC = 0.1 mM) in normal saline solutions when they existed as the reduced form (FPEG), whereas the micelles were disassembled into monomers when they existed as the oxidized form (FPEG + ). This change was reversible and electrochemically controlled. The electroactivity of FPEG determined by cyclic voltammetry was quite sensitive to the aggregation states. Perylene, which was used as a model of hydrophobic drugs, could be solubilized in a 2 mM FPEG + normal saline solution, however, it was hardly solubilized in a 2 mM FPEG + solution that was made by oxidation of the former solution. Quick and discrete response for releasing perylene from the redox active micelles was achieved by using controlled potential bulk electrolysis method.