Papers by Keyword: Polarizing Microscopy

Abstract: Novel liquid crystalline oligomers were prepared using different compositions of kink-structured aromatic dicarboxylic acids, aromatic diols, and 4-hydroxybenzoic acid via high-temperature polycondensation. The reaction products were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and polarized optical microscopy. As a result, the samples containing kinked units with phenyl or naphthalene moiety had a broad processing window limited by the melting process and the isotropization, whereas one based on diphenic acid was almost entirely in an amorphous state. The surface properties of the oligomers were evaluated by wetting measurements using a static contact angle analysis.

Abstract: The copolyesters derived from dimethyl ester of terephthalic acid, ethylene glycol, and 4-hydroxybenzoic acid (HBA) have been synthesized via catalytically promoted polycondensation omitting the acetylation step. FTIR spectroscopy results have evidenced an insertion of HBA along a polymer backbone. Of note, thermal gravimetric analysis has shown that the HBA moieties substantially improved the thermal stability of polyesters. As found by differential scanning calorimetry and polarizing microscopy, the copolyesters are capable of forming an anisotropic phase in a temperature range of 150-170 °C. Additionally, the free surface energy of the samples was determined to evaluate the compatibility of thermotropic copolyesters with other high-molecular compounds.

Abstract: The initiation, propagation and broadening of crazes in polycarbonate were studied with the aid of polarizing microscopy. A loading instrument supplying uniaxial stretch is designed to match polarizing microscopy. With polarizing microscopy, online observations of crazes and stress field can be done simultaneously. Crazes appear in bilateral anteriority of the crack tip and direction of length is perpendicular to the maximum principal stress. Stress on the boarder of the crazing zone is taken as the initiating point of the crazes and length to time of crazes follows exponent law. The initiation, propagation and broadening of crazes is a time-dependent process.

Abstract: Amyloid fibrils have long been established as the well-known a-helix to b-sheet transition that characterizes the conversion of the cellular form of prion proteins into a scrapie form. A very short sequence of the Yeast prion-like protein GNNQQNY(SupN) is responsible for the aggregation that induces diseases. As such, in the current study, a GST-fused monomer SupN vector is used to express the SupN peptide in Escherichia coli(E. Coli). In addition, a method for the production, purification, and cleavage of the recombinant SupN in E. coli is also described, which yields as much as 2mg per liter of growth of natural abundance fusion proteins in LB media. To gain a better understanding of the aggregation-structure relationship of the 7 residues of the Yeast prion-like protein, the change in the conformational structure is studied by Transmission Electron Microscopy and will be further studied by 13C solid-state NMR. Accordingly, this is the first investigation of the fibril formation of a heptamer peptide expressed in E.coli.