Stimuli-response of chlorosilane-functionalized starch suspension under applied electric fields

Chlorosilane-functionalized starch particles were prepared and adopted as a dry-based potential stimuli-responsive electrorheological (ER) material under an applied electric field. This ER fluid, prepared by dispersing the chlorosilane-functionalized starch particles in silicone oil, is considered to be a smart and intelligent material because the state of fluid changes from liquid-like to solid-like very quickly and reversibly under applied external electric fields. The ER behavior of the chain formation was examined using optical microscopy, while flow curves and dynamic moduli were investigated using a rotational rheometer with a Couette geometry under applied electric field strengths. The fluid exhibited typical ER characteristics of shear-dependent yield stress as a function of electric filed strength with a slope of 2.0, following a polarization model. It was also found that its ER performance was well correlated with the fluid’s dielectric characteristics through Cole–Cole plot.     

Chitosan gel formation via the chitosan-epichlorohydrin adduct and its subsequent mineralization with hydroxyapatite

A novel hybrid material of chitosan-hydroxyapatite (HAp) composite gel is proposed. The introduction of epoxy ring onto chitosan via phthaloylchitosan to obtain a precursor from homogeneous DMF solution is demonstrated. The reaction of the precursor with hydrazine in water gives the recovery of amino groups as well as the ring opening reaction of oxirane for gelation. An alternate soaking with calcium and phosphate solution develops HAp mineralization and initiates the gel strength. Cell culture studies reveal 50% cell adhesion, whereas the mineralization with HAp reduces the cell adhesion.     

Silver nanoparticle-loaded chitosan–starch based films: Fabrication and evaluation of tensile,barrier and antimicrobial properties

The fabrication of silver nanoparticles was accomplished by γ-ray irradiation reduction of silver nitrate in a chitosan solution. The obtained nanoparticles were stable in the solution for more than six months, and showed the characteristic surface plasmon band at 411 nm as well as a positively charged surface with 40.4 ± 2.0 mV. The silver nanoparticles presented a spherical shape with an average size of 20–25 nm, as observed by TEM. Minimum inhibitory concentration (MIC) against E. coli, S. aureus and B. cereus of the silver nanoparticles dispersed in the γ-ray irradiated chitosan solution was 5.64 µg/mL. The silver nanoparticle-loaded chitosan–starch based films were prepared by a solution casting method. The incorporation of silver nanoparticles led to a slight improvement of the tensile and oxygen gas barrier properties of the polysaccharide-based films, with diminished water vapor/moisture barrier properties. In addition, silver nanoparticle-loaded films exhibited enhanced antimicrobial activity against E. coli, S. aureus and B. cereus. The results suggest that silver nanoparticle-loaded chitosan–starch based films can be feasibly used as antimicrobial materials for food packaging and/or biomedical applications.     

Size-controllable nanospheres prepared by blending a thermoset monomer in confined morphology with thermoplastic elastomer

Bisphenol-A based benzoxazine monomer (BZ) forms a polybenzoxazine (polyBZ) thermoset after thermal curing. However, when BZ is blended with polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene triblock copolymer (SEBS) matrices and is allowed to polymerize, phase separation at the nanometer level confines BZ in a way that can be controlled by the blending process, resulting in nanospherical polyBZ (polyBZ-NS) in the SEBS matrix. By simply changing the morphology of BZ and SEBS, through blending protocols ranging from sheet to electrospun micro-fibers and to electrospun core-sheath nanofibers, the sizes of polyBZ-NS so obtained vary from～150–500 nm, to ～80 nm, and to as low as ～12 nm, respectively. This shows a new method to obtain well-defined mono-disperse nanospherical thermoset resins with a controllable size by controlling blend conditions.     

Existence of microdomain orientation in thermoplastic elastomer through a case study of SEBS electrospun fibers

Although the microdomains of polymeric systems including the thermoplastic elastomers in the as-spun electrospun fiber were reported, the orientation of microdomains has not yet been well clarified. The present work shows an existence of microdomain orientation through a case study of a well-aligned electrospun fibers of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene triblock copolymer (SEBS) obtained from an electrospinning unit equipped with a rotational disk fiber-collector. Two-dimensional small-angle X-ray scattering (2D-SAXS) patterns of the as-spun electrospining SEBS fibers show elliptical and four-point patterns suggesting an orientation of distorted and fragmented lamellar microdomains. The electrospun fibers obtained from a low rotational disk collector speed (31.5 m/min) exhibits a significant microdomain distortion whereas the fibers obtained from high take-up velocities (310 m/min, 620 m/min, and 1240 m/min) show higher fragmented-microdomain stretching. By annealing the electrospun fibers, the fibers develop an isotropic SAXS pattern with traces of the remained anisotropic orientation. Based on the above mentioned evidences in SEBS, the present work, for the first time, clarifies that the as-spun thermoplastic elastomers fibers show not just a simple microdomain as used to be observed by transmission electron microscope (TEM) but rather with orientation which can be confirmed by SAXS.     

Microstructural Analyses of Biaxially Oriented Polylactide/Modified Thermoplastic Starch Film with Drastic Improvement in Toughness

This study presents microstructural regularization of biaxially oriented polylactide blended with a silane‐modified thermoplastic starch (BO‐PLA/mTPS) film, traced by X‐ray diffraction and scattering, and differential scanning calorimetry techniques. Interfacial adhesion improvement of mTPS favors PLA crystallization, and produces a large δ‐crystal (100–150 nm) with isotropic orientation when combining with BO stretching. High draw ratio (5 × 5), and BO stretching rate (75 mm s^?1) lead to tight packing of PLA lamellae in both BO‐PLA/TPS and BO‐PLA/mTPS films, resulting in drastic toughness improvement (i.e., fivefold increases of Young's modulus and tensile strength, and threefold increase of elongation, as compared to those of the films without the BO process) with significantly decreased water absorption. However, the effect of reactive compatibility by mTPS on mechanical and water barrier properties is hindered by the BO process in which the V_H‐type patterns of TPS and mTPS are unclearly present, overlapped with (203) diffraction plane of PLA crystal, especially applying fast stretching.     

Balancing crystalline and amorphous domains in PLA through star-structured polylactides with dual plasticizer/nucleating agent functionality

The development of the first star-structured poly(l-lactides) (s-PLLAs) with dual functionality as both nucleating agent and plasticizer in polylactide (PLA) blends is described. Mechanisms controlling this functionality are deduced. Blends of PLA containing s-PLLAs show significant improvements in thermal and mechanical properties. The s-PLLAs are made by using appropriate saccharides, e.g., methyl-α-d-glucopyranoside and β-cyclodextrin, as star-shaped core macroinitiators for l-lactide polymerization. Varying the l-lactide mole ratio gives control of the degree of polymerization (DP_n) of PLLA branches from 5 to 30. Blending ≈1 wt% of the new s-PLLAs with PLA resins produces a drastic decrease in the glass transition temperature (T_g) (from 57 °C to 22 °C), and an increase in the elongation at break (30–40%) confirms significant increases in chain mobility and plasticity. A concomitant reduction of crystallization temperature (from 127 °C to 81 °C) as well as a higher crystallization rate (a factor of four increase) implies rapid nucleation of crystalline domains. With only 1 wt% of s-PLLA in the blend of PLA film, the elongation at break of PLA increases eightfold. In addition to the dual functionality, the PLLA branches also provide miscibility with PLA in the blend (as confirmed by a single T_g, combined with estimates from the Fox equation and solubility parameters).     

Stable and effective proton exchange membrane formation via cross-linking the polymeric proton donor and proton acceptor in a layer-by-layer structure

Systematic arrangement of the proton donor and acceptor as a layer-by-layer (LbL) structure is one of the simplest surface modification methods to improve the proton conductivity of a proton exchange membrane. In general, LbL assembly occurs via physical or chemical interaction between each deposited layer. Here, the stabilization of the proton donor and acceptor polymers by cross-linking those two layers together was applied as a concept. The challenge was the molecular design of the proton donor and accepter polymer species to each have compatible cross-linkable functional groups as well as proton transfer species in the molecules. Poly(acrylic acid) decorated with different amounts of thiol groups (PAA-M) was synthesized, while benzimidazole decorated branching polyethyleneimine was functionalized with maleimide groups (BIm-PEI-MI). The cross-linkable proton donor and acceptor were alternately LbL deposited on a sulfonated poly(ether ether ketone) (SPEEK) surface. The LbL membrane with an optimum crosslink level showed a proton conductivity of up to 2 orders of magnitude higher than that of the pure SPEEK membrane even at a temperature as high as 170 °C.     

Thermo and electrochemical characterization of sulfonated PEEK–WC membranes and Krytox-Si-Nafion® composite membranes

Two types of membranes, the sulfonated PEEK-WC (poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxyphenylene)(SPWC) and Krytox-Si-Nafion® (KSiN) composite membranes are proposed for DMFC applications.The properties based on water uptake, ion exchange capacity, proton conductivity, gas permeability, thermal stabilityand methanol crossover are summarized. The comparative studies on SPWC and Nafion® 117 membranes clarify us that the amorphous sulfonated PEEK-WC polymer shows thermal and mechanical stability with less methanol flux and gas permeability. The membrane also exhibits the increase in water uptake, ion exchange capacity and proton conductivity as sulfuric acid doping agent concentration was increased. The KSiN is unique in term of its miscible hybrid structure of silica particles modified with Nafion® structured Krytox 157 FSL chain (KSi) andNafion®. Based on the KSiN membranes with different KSi content, it was found that when KSi content increased, the reduction of gas permeability, methanol crossover and thermal stability are improved. The composite membrane performs the proton conductivity in the wide range of high temperature (60–130°C).     

Systematic studies on benzimidazole derivatives: Molecular structures and their hydrogen bond networks formation toward proton transfer efficiency

A series of benzimidazole derivatives with varied benzimidazole groups, i.e., mono- (B-1), di- (B-2 and B-3), and trifunctional (B-4), are focused as model compounds for a systematic study to understand the relationship between the hydrogen bond network including its consequent packing structure and the proton conductivity in an anhydrous system. The different number of benzimidazole units in a molecule initiates a different packing structure under the hydrogen bond network of which B-1 provides a perpendicular hydrogen bond network, B-2 and B-3 provide a parallel hydrogen bond network under a lamellar structure, and B-4 forms a helical hydrogen bond network under a columnar structure. The study reveals that the proton conductivity of heterocycles in anhydrous system and doped with polyphosphoric acid is significant when (i) more benzimidazole groups is exist in a single molecule to form hydrogen bond networks, (ii) each benzimidazole is closely packed to allow an effective proton transfer from an NH in one benzimidazole unit to another, and (iii) the packing structure forms a specific channel to favour efficient proton transfer such as columnar packing structure. The present work is a guideline to develop high efficient benzimidazole-based membrane for a high temperature polymer electrolyte membrane fuel cell (PEMFC).