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Liquid Phase Transitions (liquid + phase_transition)
Selected AbstractsComparison of Physicochemical Properties of New Ionic Liquids Based on Imidazolium, Quaternary Ammonium, and Guanidinium CationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2007Prashant Abstract More than 50 ionic liquids were prepared by using imidazolium, quaternary ammonium, and guanidinium cations and various anions. In these series, different cationic structures such as 1-benzyl-3-methylimidazolium [Bzmim]+, 1,3-dibenzylimidazolium [BzmiBz]+, 1-octyl-3-methylimidazolium [C8mim]+, 1-decyl-3-methylimidazolium [C10mim]+, tricapryl-methylammonium [Aliquat]+, benzyltriethylammonium [BzTEA]+, phenyltrimethylammonium [PhTMA]+, and dimethyldihexylguanidinium [DMG]+ were combined with anions, p -toluenesulfonate [TSA],, dicyanoamide [DCA],, saccharine (2-sulfobenzoic acid imide sodium salt) [SAC],, trifluoroacetate [TFA],, bis(trifluoromethanesulfonyl)imide [Tf2N],, trifluoromethanesulfonate [TfO],, and thiocyanate [SCN],. Important physical data for these ionic liquids are collated, namely solubility in common solvents, viscosity, density, melting point and water content. Apart from the viscosity, the Newtonian and non-Newtonian behavior of these ionic liquids is also disclosed. Stability of these ionic liquids under thermal, basic, acidic, nucleophilic, and oxidative conditions was also studied. The features of the solid,liquid phase transition were analyzed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid. A degradation temperature of each ionic liquid was also determined. Comparisons of the properties of various ionic liquids were made. [source] Temperature-sensitive hydrogel microspheres formed by liquid,liquid phase transitions of aqueous solutions of poly(N,N -dimethylacrylamide- co -allyl methacrylate)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2005Xiangchun Yin Abstract Poly(N,N -dimethylacrylamide- co -allyl methacrylate) (DMA- co -AMA) copolymers were prepared by the copolymerization of N,N -dimethylacrylamide with allyl methacrylate (AMA). The methacryloyl group of AMA reacted preferentially, and this resulted in pendant allyl groups along the copolymer chains. Aqueous solutions of these DMA- co -AMA copolymers were thermoresponsive and showed liquid,liquid phase transitions at temperatures that depended on the AMA content. Hydrogel microspheres were prepared from these thermally phase-separated liquid microdroplets by the free-radical crosslinking of the pendant allyl groups. The morphologies of the resulting thermoresponsive microspheres as a function of the reaction temperature and the amount of the initiator were examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1641,1648, 2005 [source] Investigations of thermotropic phase behavior of newly developed synthetic PEGylated lipids using Raman spectro-microscopyBIOPOLYMERS, Issue 11 2008Rajan K. Bista Abstract In this article, a temperature-controlled Raman spectro-microscopic technique has been utilized to detect and analyze the phase behaviors of two newly developed synthetic PEGylated lipids trademarked as QuSomesÔ, which spontaneously form liposomes upon hydration in contrast to conventional lipids. The amphiphiles considered in this study differ in their hydrophobic hydrocarbon chain length and contain different units of polyethylene glycol (PEG) hydrophilic headgroups. Raman spectra of these new artificial lipids have been recorded in the spectral range of 500,3100 cm,1 by using a Raman microscope system in conjunction with a temperature-controlled sample holder. The gel to liquid phase transitions of the sample lipids composed of pure 1,2-dimyristoyl- rac -glycerol-3-dodecaethylene glycol (GDM-12) and 1,2-distearoyl- rac -glycerol-3-triicosaethylene glycol (GDS-23) have been revealed by plotting peak intensity ratios in the CH stretching region as a function of temperature. From this study, we have found that the main phase transitions occur at a temperature of ,5.2 and 21.2°C for pure GDM-12 and GDS-23, respectively. Furthermore, the lipid GDS-23 also shows a postphase transition temperature at 33.6°C. To verify our results, differential scanning calorimetry (DSC) experiments have been conducted and the results are found to be in an excellent agreement with Raman scattering data. This important information may find application in various studies including the development of lipid-based novel substances and drug delivery systems. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 1012,1020, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||