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Multiple melting characteristics of a highly isotactic polypropylene (iPP) were studied by means of differential scanning calorimetry (DSC). Double melting characteristics were observed on melting iPP crystallized isothermally at temperatures ranging from 110 to 140 ° C. iPP crystallized below and above 125 ° C exhibited different double melting characteristics from each other. For iPP crystallized below 125 ° C, the single melting peak split into two peaks during slow DSC heating scans without changing the total crystallinity in the polymer. On the other hand, the double melting endotherm of iPP crystallized above 125 ° C seemed to come from two preexisting crystal fractions having different [T.sub.m]. There existed an optimum annealing temperature range where the five-minute annealing of iPP raised [T.sub.m] of the polymer significantly. The treatment also increased the crystallinity of iPP crystallized isothermally at 110 ° C by 12%., INTRODUCTION Melting of isotactic polypropylene (iPP) has been studied to correlate melting temperature ([T.sub.m]) with tacticity of the polymer (1, 2). Multiple melting peaks were generally observed on differential scanning [...]

A high-temperature radical scavenger, 2,2-diphenyl-l-picryl hydrazyl (DPPH), has been used to study the reaction mechanisms of polyacrylonitrile (PAN) on thermal treatment. The effect of DPPH on the cyclization reaction of PAN in both air and nitrogen, investigated by differential scanning calorimetry (DSC), helped to verify the proposed reaction mechanisms, i.e., the free radical and the ionic ones. For PAN homopolymer, the peak temperature of the reaction exotherm shifted to higher temperatures and the heat of reaction was decreased with increasing DPPH concentration. For PAN copolymer with methylacrylate and itaconic acid, however, the effects of DPPH on DSC thermograms were insignificant. The effects of DPPH suggest that the reaction of the nitrile groups proceeds by free radicals for the homopolymer while by ions for the copolymer. The activation energies for the thermal reactions of PAN in both air and nitrogen were also estimated by the dynamic DSC method, and they proved to be highly dependent on reaction mechanism, environment of thermal treatment, and DPPH concentration.

We observed the retention loss of dot domains (36 nm diameter) and square domains with sizes of 1 and 25 μm2 that were reversed by applying an electric field at an atomic force microscopy (AFM) conductive tip on a heteroepitaxial PbTiO3 thin film with + polarization in the virgin state, which was fabricated via hydrothermal epitaxy below Tc. Through theoretical calculations, it was discussed that the retention loss phenomena of a domain reversed by using an AFM tip were derived from the summation of the depolarization field energy and the strain-polarization coupling energy. Since the retention loss of the reversed domain with a straight c/c domain wall by applying a homogeneous electric field did not occur, we suggest that a cylindrical domain, which has a nearly straight c/c domain wall that extends to the bottom electrode on the given thin film, would be free from the retention loss. [ABSTRACT FROM AUTHOR]

We observed the retention loss of dot domains (36 nm diameter) and square domains with sizes of 1 and 25 μm2 that were reversed by applying an electric field at an atomic force microscopy (AFM) conductive tip on a heteroepitaxial PbTiO3 thin film with + polarization in the virgin state, which was fabricated via hydrothermal epitaxy below Tc. Through theoretical calculations, it was discussed that the retention loss phenomena of a domain reversed by using an AFM tip were derived from the summation of the depolarization field energy and the strain-polarization coupling energy. Since the retention loss of the reversed domain with a straight c/c domain wall by applying a homogeneous electric field did not occur, we suggest that a cylindrical domain, which has a nearly straight c/c domain wall that extends to the bottom electrode on the given thin film, would be free from the retention loss. [ABSTRACT FROM AUTHOR]

A heteroepitaxial PbZr1-xTixO3 (PZT) thin film was fabricated by means of hydrothermal epitaxy at 210 °C below Curie temperature without undergoing the paraelectric to ferroelectric phase transition. From transmission electron microscope and piezoresponse force microscope observations, it was confirmed that the fabricated PZT thin films had only a -c monodomain without an a domain in the as-synthesized state. The polarization-electric-field hysteresis curve and the fatigue behavior of the heteroepitaxial PZT capacitor with a Pt top and n-type semiconductor bottom electrode was observed. The remanent polarization 2Pr of the PZT capacitor was about 63 μC/cm2. This value was much lower compared to that of the PbTiO3 capacitor, which was also fabricated by means of hydrothermal epitaxy at 160 °C below Curie temperature. It was suggested that a lower polarization of the PZT capacitor was due to the nonswitchable interfacial layer grown in the initial growth stage. However, this layer did not exert an influence on the fatigue behavior of the PZT capacitor: the PZT capacitor with an ordinary Pt top electrode and a Nb-doped SrTiO3 semiconductor bottom electrode revealed fatigue-free behavior in up to 1011 switching cycles. [ABSTRACT FROM AUTHOR]