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Amorphous Domains (amorphous + domain)
Selected AbstractsNovel amphiphilic polymer gel electrolytes based on (PEG- b -GMA)- co -MMAJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Dan Luo Abstract Amphiphilic conetwork,structured copolymers containing different lengths of ethylene oxide (EO) chains as ionophilic units and methyl methacrylate (MMA) chains as ionophobic units were prepared by free radical copolymerization and characterized by FTIR and thermal analysis. Polymer gel electrolytes based on the copolymers complexed with liquid lithium electrolytes (dimethyl carbonate (DMC) : diethyl carbonate (DEC) : ethylene carbonate (EC) = 1 : 1 : 1 (W/W/W), LiPF6 1.0M) were characterized by differential scanning calorimetry and impedance spectroscopy. A maximum ion conductivity of 4.27 × 10,4 S/cm at 25oC was found for the polymer electrolyte based on (PEG2000- b -GMA)- co -MMA with long EO groups. Moreover, the effect of temperature on conductivity of the amphiphilic polymer electrolytes obeys the Arrhenius equation. The good room temperature conductivity of the polymer electrolytes is proposed to relate to the enhancement in the amorphous domain of the copolymers due to their amphiphilic conetwork structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Miscibility in Blends of Isotactic/Syndiotactic Polystyrenes at Melt or Quenched Amorphous Solid StateMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2006Shu Hsien Li Abstract Summary: Miscibility in amorphous phase and behavior in a crystalline phase of blends of two semicrystalline and isomeric polymers, isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), was probed. Optical and scanning electron microscopy results indicate no discernible heterogeneity in iPS/sPS blends in either melt state or rapidly quenched amorphous super-cooled state, while the Tg behavior of the quenched amorphous blends shows an intimately mixed state of two polymer chains. The crystal forms of the blends were further analyzed to provide additional evidence of miscibility in the amorphous domain. The sPS in the iPS/sPS blends upon melt crystallization was found to predominantly exist as the more stable , -form (rather than mixed , -form and , -form in neat sPS), which also suggests evidence of miscibility in the iPS/sPS blends. The melting behavior of semicrystalline sPS in the iPS/sPS mixtures was analyzed using the Flory-Huggins approach for estimation of interactions. By measuring the equilibrium melting point of the higher-melting sPS species in the sPS/iPS blends, a small negative value, for the interaction parameter (,,,,,0.11) was found. Further, by introducing a third polymer, poly(2,6-dimethyl- p -phenylene oxide) (PPO), a ternary iPS/sPS/PPO blend system was also proven miscible, which constituted a further test for stable phase miscibility in the iPS/sPS blend. General nature of miscibility in blends composed of two crystalline isomeric polymers is discussed. Issues in dealing with blends of polymers of the same chemical repeat unit but different tacticities were addressed. X-ray diffractograms for neat sPS and iPS/sPS blends, each having been isothermally crystallized at 245,°C for 4 h. [source] Conformation analysis and molecular mobility of ethylene and tetrafluoroethylene copolymer using solid-state 19F MAS and 1H , 19F CP/MAS NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2004Keitaro Aimi Abstract The changes in the conformation and molecular mobility accompanied by a phase transition in the crystalline domain were analyzed for ethylene (E) and tetrafluoroethylene (TFE) copolymer, ETFE, using variable-temperature (VT) solid-state 19F magic angle spinning (MAS) and 1H , 19F cross-polarization (CP)/MAS NMR spectroscopy. The shifts of the signals for fluorines in TFE units to higher frequency and the continuing decrease and increase in the T1,F values suggest that conformational exchange motions exist in the crystalline domain between 42 and 145 °C. Quantum chemical calculations of magnetic shielding constants showed that the high-frequency shift of TFE units should be induced by trans to gauche conformational changes at the CH2CF2 linkage in the E,TFE unit. Although the 19F signals of the crystalline domain are substantially overlapped with those of the amorphous domain at ambient probe temperature (68 °C), they were successfully distinguished by using the dipolar filter and spin-lock pulse sequences at 145 °C. The dipolar coupling constants for the crystalline domain, which can be estimated by fitting the dipolar oscillation behaviors in the 1H , 19F CP curve, showed a significant decrease with increasing temperature from 42 to 145 °C. This is due to the averaging of 1H19F dipolar interactions originating from the molecular motion in the crystalline domain. The increase in molecular mobility in the crystalline domain was clearly shown by VT T1,F and 1H , 19F CP measurements in the phase transition temperature range. Copyright © 2004 John Wiley & Sons, Ltd. [source] Characterization of amorphous API:Polymer mixtures using X-ray powder diffractionJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2008Ann Newman Abstract Recognizing limitations with the standard method of determining whether an amorphous API,polymer mixture is miscible based on the number of glass transition temperatures (Tg) using differential scanning calorimetry (DSC) measurements, we have developed an X-ray powder diffraction (XRPD) method coupled with computation of pair distribution functions (PDF), to more fully assess miscibility in such systems. The mixtures chosen were: dextran,poly(vinylpyrrolidone) (PVP) and trehalose,dextran, both prepared by lyophilization; and indomethacin,PVP, prepared by evaporation from organic solvent. Immiscibility is detected when the PDF profiles of each individual component taken in proportion to their compositions in the mixture agree with the PDF of the mixture, indicating phase separation into independent amorphous phases. A lack of agreement of the PDF profiles indicates that the mixture with a unique PDF is miscible. In agreement with DSC measurements that detected two independent Tg values for the dextran,PVP mixture, the PDF profiles of the mixture matched very well indicating a phase separated system. From the PDF analysis, indomethacin,PVP was shown to be completely miscible in agreement with the single Tg value measured for the mixture. In the case of the trehalose,dextran mixture, where only one Tg value was detected, however, PDF analysis clearly revealed phase separation. Since DSC can not detect two Tg values when phase separation produces amorphous domains with sizes less than approximately 30 nm, it is concluded that the trehalose,dextran system is a phase separated mixture with a structure equivalent to a solid nanosuspension having nanosize domains. Such systems would be expected to have properties intermediate to those observed for miscible and macroscopically phase separated amorphous dispersions. However, since phase separation has occurred, the solid nanosuspensions would be expected to exhibit a greater tendency for physical instability under a given stress, that is, crystallization, than would a miscible system. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4840,4856, 2008 [source] Molecular Dynamics Simulations of Amorphous Si,C,N Ceramics: Composition Dependence of the Atomic StructureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003Nicoletta Resta We have performed classical molecular dynamics simulations of amorphous Si,C,N materials. The dependence of the local order and of the microstructure on the chemical composition was investigated. Our simulations show that for a stoichiometric nitrogen/silicon ratio equal to or higher than 4/3, the amorphous ceramic separates into different amorphous domains, namely C-rich, SiN-rich, and SiC-rich phases. Below this ratio, the material is composed of mixed structures, homogeneously spread within the material. For a very particular composition range, we found that carbon atoms crystallize into monoatomic graphitic layers surrounding the SiN-rich domains. [source] Partially Sulfonated Polystyrene and Poly(2,6-dimethyl-1,4-phenylene oxide) Blend Membranes for Fuel CellsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2004Bokyung Kim Abstract Summary: Based on Flory,Huggins parameters (,), the miscibility and the effect of morphological change on proton conductivity and methanol permeability of partially sulfonated polystyrene (SPS) and partially sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO), having an identical ion exchange capacity, were investigated. When 50 wt.-% of SPPO was blended, both the proton conductivity and methanol permeability had the highest values, which resulted from the change of amorphous domains and the hydrogen bonding between the two ionomers. The proton conductivities, water uptake and methanol permeability for the SPPO/SPS blend membranes studied here. The membranes with 50 wt.-% SPPO clearly showed the greatest increase in these properties. [source] Solid-state 1H , 19F/19F , 1H CP/MAS NMR study of poly(vinylidene fluoride)MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2002Shinji Ando Abstract Solid-state 1H , 19F and 19F , 1H cross-polarization magic angle spinning (CP/MAS) NMR spectra have been investigated for a semicrystalline fluoropolymer, namely poly(vinylidene fluoride) (PVDF). The 1H , 19F CP/MAS spectra can be fitted by five Lorentzian functions, and the amorphous peaks were selectively observed by the DIVAM CP pulse sequences. Solid-state spin-lock experiments showed significant differences in T1,F and T1,H between the crystalline and amorphous domains, and the effective time constants, THF* and T1,*, which were estimated from the 1H , 19F CP curves, also clarify the difference in the strengths of dipolar interactions. Heteronuclear dipolar oscillation behaviour is observed in both standard CP and 1H , 19F inversion recovery CP (IRCP) experiments. The inverse 19F , 1H CP-MAS and 1H , 19F CP-drain MAS experiments gave complementary information to the standard 1H , 19F CP/MAS spectra in a manner reported in our previous papers for other fluoropolymers. The value of NF/NH (where N is a spin density) estimated from the CP-drain curve is within experimental error equal to unity, which is consistent with the chemical structure. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||