Adhesion properties of polyacrylic block copolymer pressure-sensitive adhesives and analysis by pulse NMR and AFM force curve

The adhesion strength of a pressure-sensitive adhesive (PSA) is influenced by two factors, the interfacial adhesion and the cohesive strength. A suitable method for the estimation of these two factors was investigated. Blends of triblock and diblock copolymers consisting of poly(methyl methacrylate) (hard) and poly(n-butyl acrylate) (soft) blocks (A) and blends of triblock copolymer and poly(n-butyl acrylate) oligomer (B), both with different blend ratios, were prepared as model PSAs. The peel strength decreased with an increase in the hard block content for B, whereas it was independent for A. The tack increased with a decrease in the hard block content for A, whereas it was independent for B. The influence of the hard block content on the peel strength and tack was thus different. The ¹H pulse nuclear magnetic resonance analysis and force curve analysis showed that the molecular mobility was higher for B than for A. The Young's modulus and adhesive energy calculated by the Johnson–Kendall–Roberts two-point method using the atomic force microscopy (AFM) force curve qualitatively reflected the cohesive strength and the interfacial adhesion, respectively. The Young's modulus and adhesive energy are found to be useful parameters to investigate the adhesion mechanism. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47791.     

Use of a microcomputer with a gas permeation apparatus

Hardware and software for collecting and storing the data of gas permeation in polymer membranes from the vacuum detector and various sensors have been developed for the GP-IB microcomputer online system. The system uses BASIC language programs. In comparison to manual inputs and calculations, the programs allow reductions in the time required for data treatment and in the standard deviation for a determination and, moreover, an improvement in the reproducibility of the results.     

Compositional Engineering for Thermally Stable,Highly Efficient Perovskite Solar Cells Exceeding 20% Power Conversion Efficiency with 85 °C/85% 1000 h Stability

Perovskite solar cells have received great attention because of their rapid progress in efficiency, with a present certified highest efficiency of 23.3%. Achieving both high efficiency and high thermal stability is one of the biggest challenges currently limiting perovskite solar cells because devices displaying stability at high temperature frequently suffer from a marked decrease of efficiency. In this report, the relationship between perovskite composition and device thermal stability is examined. It is revealed that Rb can suppress the growth of PbI₂ even under PbI₂‐rich conditions and decreasing the Br ratio in the perovskite absorber layer can prevent the generation of unwanted RbBr‐based aggregations. The optimized device achieved by engineering perovskite composition exhibits 92% power conversion efficiency retention in a stress test conducted at 85 °C/85% relative humidity (RH) according to an international standard (IEC 61215) while exceeding 20% power conversion efficiency (certified efficiency of 20.8% at 1 cm²). These results reveal the great potential for the practical use of perovskite solar cells in the near future.     

Tack properties and adhesion mechanism of two different crosslinked polyacrylic pressure-sensitive adhesives

Tack properties of cross-linked random poly(n-butyl acrylate-acrylic acid) (A) and poly(2-ethylhexyl acrylate-acrylic acid) (B) copolymers as pressure-sensitive adhesives (PSAs) were compared by a probe tack test to know the optimal application in the industrial field. Tack increased remarkably with temperature, reached a peak, then decreased. The peak of tack appeared at higher temperature for B. Tack increased with increasing contact time and decreasing crosslinking agent level. The fracture energy at higher temperature was higher for B than A. From the observation of debonding behavior, the fibrillation occurred at the edge of probe. The wettability and deformability of PSA were larger for B than A. From a dynamic mechanical analysis, the shear storage modulus (G') in the rubbery plateau region was lower for B than for A. The good wettability and deformability were improved as a result of its lower G'. The relaxation behaviors of PSAs and vulcanized isoprene rubber were measured by ¹H pulsed nuclear magnetic resonance. This technique is found to be useful for estimating the degree of intermolecular interactions. The crosslinking degree hardly influenced. The intermolecular interaction was weaker for B. This was the reason of the lower G' for B.     

Effects of silane coupling agent hydrophobicity and loading method on water absorption and mechanical strength of silica particle-filled epoxy resin

A suitable silane coupling agent (SCA) structure to improve the water absorption and mechanical strength of silica particle-filled epoxy resin was investigated. Bonding, hydrocarbon, and fluorocarbon type SCAs were employed. The bonding type has glycidoxy or amino groups that react with epoxy resin, whereas the other types have only hydrophobic chains. The spherical silica particles were added to epoxy resin at amounts from 10 to 50 wt %. The effect of water absorption was consequently lowered in the order of hydrocarbon > bonding types. The fluorocarbon type SCA was also effective at zero and low silica content. Modification of the epoxy phase by SCA addition was clarified to have a more dominant effect than the adhesion of silica/epoxy interface for the lowering of water absorption, whereas it had been conventionally considered that interfacial adhesion had a more dominant effect. The mechanical strength was higher for the bonding type than the other type. Two addition methods were compared, a pretreatment method and an integral blend method in which all components were mixed simultaneously. The integral blend method was determined to be superior to the pretreatment method for both water absorption and mechanical strength, which was also contrary to the conventional view. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48615.     

Relationship between thermal properties and diffusion coefficients of gases for polyimide films

The relationships between the chemical structure, packing density (1/V_F), and cohesive energy density (CED) and the thermal properties of polyimides were investigated. Particularly, the correlation of tan δ measured by stress–strain/thermal mechanical analysis with 1/V_F and CED was found for eight polyimides. We measured the relationship between the apparent diffusion coefficient (D_a) and 1/V_F and CED, respectively, as described in previous articles. From these experiments, we found that the thermal properties, especially tan δ, were correlated with the apparent diffusion coefficient of gas. These results are well explained by use of micro-Brownian motion. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 389–397, 1997     

Sorption and diffusion of water vapor in poly(ethylene terephthalate) film

The sorption and diffusion of water vapor in poly(ethylene terephthalate) (PET) film were measured by applying a thermogravimetric analyzer (TG‐DTA), which customarily has been used to detect the weight loss of a sample with the increase of temperature under a given atmosphere. In this case, we detected the weight gain of PET film by sorption of water vapor under a given humidity at a constant temperature. Sorption‐rate curves were successfully obtained in spite of the low solubility of PET film and the presence of Fickian‐type curves. The solubility was better described according to the dual‐mode sorption model. The diffusion coefficients were determined in their initial slopes by the short‐time method. We found that the diffusion coefficient depended on vapor pressure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 67–74, 2000     

Synthesis of dioctyl sulfosuccinate-doped polypyrrole grains by aqueous chemical oxidative polymerization and their use as light-responsive liquid marble stabilizer

Polypyrrole grains are synthesized by aqueous chemical oxidative polymerization using ferric chloride as an oxidant in the presence of bis(2-ethylhexyl) sulfosuccinate sodium salt as both a dopant and a hydrophobizing agent. The resulting grain products are characterized in terms of their size, morphology, surface and bulk chemical compositions, hydrophilicity-hydrophobicity balance, (photo) thermal property, and electrical conductivity. Scanning electron microscopy studies indicate that the grains are aggregates of atypical primary grains with submicrometer size. Elemental microanalysis and thermogravimetric analysis confirm that the polypyrrole is preferably doped with dioctyl sulfosuccinate compared with chloride ion, and dioctyl sulfosuccinate/chloride ion dopant ratio increases with an increase of bis(2-ethylhexyl) sulfosuccinate sodium salt concentration in the polymerization systems. The grains show near-infrared light-to-heat photothermal property, which is confirmed by thermography. The data obtained through X-ray photoelectron spectroscopy indicate the presence of dioctyl sulfosuccinate dopants on the surface of the grains, and therefore the dried polypyrrole grains show hydrophobic character. The dried grains can work as a light-responsive liquid marble (LM) stabilizer. Motions of the LM can be driven by near-infrared laser irradiation-induced Marangoni flow on planar air-water surface. The release of internal liquid can be achieved by controlled disruption of the LM via external stimulus application.     

Heat shock regulation in the ftsH null mutant of Escherichia coli: dissection of stability and activity control mechanisms of sigma32 in vivo

The heat shock response of Escherichia coli is regulated by the cellular level and the activity of sigma32, an alternative sigma factor for heat shock promoters. FtsH, a membrane-bound AAA-type metalloprotease, degrades sigma32 and has a central role in the control of the sigma32 level. The ftsH null mutant was isolated, and establishment of the DeltaftsH mutant allowed us to investigate control mechanisms of the stability and the activity of sigma32 separately in vivo. Loss of the FtsH function caused marked stabilization and consequent accumulation of sigma32 ( approximately 20-fold of the wild type), leading to the impaired downregulation of the level of sigma32. Surprisingly, however, DeltaftsH cells express heat shock proteins only two- to threefold higher than wild-type cells, and they also show almost normal heat shock response upon temperature upshift. These results indicate the presence of a control mechanism that downregulates the activity of sigma32 when it is accumulated. Overproduction of DnaK/J reduces the activity of sigma32 in DeltaftsH cells without any detectable changes in the level of sigma32, indicating that the DnaK chaperone system is responsible for the activity control of sigma32 in vivo. In addition, CbpA, an analogue of DnaJ, was demonstrated to have overlapping functions with DnaJ in both the activity and the stability control of sigma32.     

Thermal decomposition of cellulose/synthetic polymer blends containing grafted products. II. Cellulose/polyacrylonitrile blends

The homogeneous grafting of acrylonitrile onto cellulose was carried out in a dimethyl sulfoxide/paraformaldehyde solvent system. The grafted products were added to cellulose/polyacrylonitrile (PAN) blends as compatibilizers. The thermal decomposition behavior of the blends was investigated by thermogravimetry. The thermal stability of the blends with higher grafted product content was lower by more than 100°C than that of the blends without grafted product. The accessibility values of the former blends were larger than those of the latter. The microphase-separated structures of the grafted product blends were finer than those without the product. Dynamic mechanical measurements and differential scanning calorimetry were performed to estimate the glass transition temperatures, T_g, of the blends. The variation in T_g was smaller than that in characteristic temperatures determined by thermogravimetry. The difference in thermal decomposition behavior was correlated to that in compatibility. Thermogravimetry was found to be effective for estimating the compatibility in cellulose/PAN blends containing grafted products. © 1996 John Wiley & Sons, Inc.