Masaki Kakiage

Size-Selective Diffusion in Nanoporous but Flexible Membranes for Glucose Sensors

A series of nanoporous membranes prepared from polyethylene-block-polystyrene were applied for size-selective diffusion of glucose and albumin molecules. Millimeter-sized test cells for characterization of such molecular diffusions were designed assuming an implantable glucose sensor. The prepared nanoporous membrane exhibits excellent flexibility and toughness compared to conventional nanoporous membranes of brittle alumina. Pore size of the membranes could be controlled from 5 to 30 nm by varying preparation conditions. All of these nanoporous membranes prepared in this study let glucose pass through, indicating a continuous pore connection through the entire thickness of the membrane in a few tens of micrometers. In contrast, membranes prepared under optimum conditions could perfectly block albumin permeation. This means that these vital molecules having different sizes can be selectively diffused through the nanoporous membranes. Such a successful combination of size selectivity of molecular diffusion in nanoscale and superior mechanical properties in macroscale is also beneficial for other devices requesting down-sized manufacture.

Phase transitions during heating of melt-drawn ultrahigh molecular weight polyethylenes having different molecular characteristics.

Changes in the crystalline structure during heating of melt-drawn ultrahigh molecular weight polyethylenes (UHMW-PEs) having different molecular characteristics were analyzed by in situ wide-angle X-ray diffraction measurements. A phase transition from the orthorhombic into the hexagonal phase was observed for all samples, but the perfection was enhanced and the possible temperature window for the hexagonal phase was greater for the sample containing only a higher molecular weight component. In contrast, an increase in retractive stress during heating was confirmed for the sample containing a lower molecular weight component, reflecting melting of the folded-chain crystal (FCC). Differential scanning calorimetry and transmission electron microscopy revealed the dependency of the molecular characteristics of the sample on the resultant morphologies. These results demonstrate that the existence of FCC determines both the quality and the width of the temperature window for the hexagonal phase during heating of melt-drawn UHMW-PEs.

Structure and property gradation from surface to bulk of Poly(l-lactic acid)/Poly(d-lactic acid) blended films as estimated from nanoscratch tests using scanning probe microscopy.

Structure and property gradation from surface to bulk of poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) blended films was estimated from nanoscratch tests using scanning probe microscopy (SPM). The PLLA/PDLA blended film was prepared by melting, following isothermal crystallization at 150 °C due to the formation of stereocomplex crystal (sc-crystal). Grazing-incidence X-ray diffraction measurements revealed that the fraction of sc-crystal on the surface was higher than that of bulk. Two types of morphologies were observed in an SPM nanoscratch test conducted under a higher applied load: a less-deformed morphology and a plowed-up morphology. These results demonstrate that a hierarchical structure with an sc-microcrystallite networked surface could be developed by optimizing the processing conditions.

Remnant Features in Melt Crystallized Samples of Polyethylenes Originated from Reactor Powders

A series of reactor powders of ultrahigh molecular weight (UHMW) polyethylenes with different morphology was melted at 160°C for 5 min and cooled in ice water. Low‐frequency Raman spectroscopy was used to characterize the straight‐chain‐segment (SCS) length distribution of both initial and melt‐crystallized materials. A bimodal SCS length distribution was found in the melt‐crystallized sample originated from the reactor powder with a very tenuous amorphous phase. In other samples recrystallized from powders with more ordered structure, the SCS length distribution was unimodal and approximately identical. The result is explained in terms of perfection of lamellar crystals formed under limited time and thermal conditions from differently organized initial structure.

Effect of Molecular Structure of Polyols with Different Molecular Characteristics on Synthesis of Boron Carbide Powder

Crystalline boron carbide (B4C) powder was synthesized by the carbothermal reduction of condensed products formed from boric acid (H3BO3) and polyols with different molecular characteristics, i.e., glycerin, mannitol, and poly (vinyl alcohol) (PVA). The effect of the molecular structure of the polyol on the thermal decomposition conditions and the obtained morphology of the B4C powder was discussed in this study. The thermal decomposition in air of each condensed product was performed before the carbothermal reduction in order to eliminate the excess carbon, where the decomposition conditions varied with the type of polyol. Crystalline B4C powder with less residual free carbon was synthesized from the thermally decomposed products by heating at 1250 °C for 5 h in an Ar flow. The thermal decomposition conditions and the particle size of the obtained B4C powder reflected the molecular characteristics of the polyols.

Practical NMR Analysis of Morphology and Structure of Polymers

Abstract Practical analytical methods to investigate the relationship between polymer morphology and properties by a combination of 1 H pulse NMR and/or high-resolution NMR in the solid state with other techniques, such as electron microscopy, X-ray diffraction and so on, are reviewed. The complete free induction decay (FID) fitting method by exponential, Weibullian and Weibullian/sine function is introduced. Applications of this method to polyethylenes prepared by various conditions successfully explain the morphology and physical properties. Crystallisation mechanism of nylon 46 by high-resolution NMR in the solid state is also introduced.

Property development for biaxial drawing of ethylene-tetrafluoroehtylene copolymer films and resultant fractural behavior analyzed by in situ X-ray measurements.

The property development of the ethylene-tetrafluoroethylene copolymer (ETFE) membrane induced by simultaneous biaxial drawing was investigated. Commonly, tensile strength can be increased by drawing; conversely, tear resistance decreases. In this study, the balance between tensile strength and tear resistance for the resultant ETFE membrane was optimized achieved by a combination of lamination of low molecular weight (LMW) and high molecular weight (HMW) layers and subsequent biaxial drawing. The structural factor determining tear resistance of these biaxially drawn membranes was determined based on in situ small-angle X-ray scattering (SAXS) measurement during tensile deformation simulating tearing tests. Lozenge shaped scattering, which indicated inclined lamellae, was observed during such tensile deformation of the resultant membranes. Remarkably, this inclined lamellar structure was observed for the pure LMW membrane; however, it also appeared at the interface between LMW and HMW layers within biaxially drawn membranes. For the membrane exhibiting the highest tearing strength, the fraction of such inclined lamella increased up to the critical strain corresponding to the actual sample breaking. These results confirm that the inclined lamellar structure absorbed strain during membrane tearing.

Robust and transparent membrane of crystalline silicone via a melt-drawing technique

A melt-drawing technique was applied to crystalline silicone, poly(tetramethyl-p-silphenylenesiloxane) (PTMPS) containing a rigid phenylene ring in the main chain. The resultant melt-drawn membrane had double-melting endotherms located at the usual 130 °C and the higher temperature of 160 °C. The higher melting temperature for PTMPS is expected, but has not been experimentally observed. A series of in situ structural analyses during heating also reveal that it is attributed to the melting of the extended chain crystals within the melt-drawn PTMPS membrane. Due to the highly oriented crystalline structure, the obtained melt-drawn PTMPS membrane is transparent but exhibits an excellent tensile modulus and strength of 2 GPa and 20 MPa, which are a few hundred times greater than those of commercial silicone elastomers.

Straight-Chain Segment Length Distributions in UHMWPE Reactor Powders of Different Morphological Types

Abstract A series of reactor powders of ultrahigh molecular weight polyethylene obtained using supported and unsupported Ziegler catalysts were studied with the help of low-frequency Raman spectroscopy. This experimental technique allows one to calculate the length distribution of straight-chain segments (SCS) in a polymer sample without differing between the SCS localized in either crystalline or amorphous regions of the sample. A comparison of the scanning electron microscopy images of powders with their SCS distributions showed that the samples with pronounced fibrous morphology exhibit bimodal distribution functions, while the granular morphological pattern yields unimodal SCS length distributions.

In Situ SAXS Analysis during Uniaxial Drawing of Polyethylene-block-Polystyrene Copolymer Film

Structural deformation during uniaxial drawing of polyethylene-block-polystyrene (PE-b-PS) copolymer film was analyzed by in-situ small angle X-ray scattering (SAXS) measurement. The PE-b-PS film was prepared by solution casting, followed by isothermally crystallizing from melt. The obtained film exhibits the characteristic bicontinuous crystalline/amorphous morphology. Initial stage of uniaxial drawing induces the orientation of such crystalline/amorphous phases, but these phase separation is destroyed in the latter stage. In contrast, solvent swelling treatment successfully induces the orientation of crystalline/amorphous phases with keeping the phase continuity.