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Thermoreversible Gels (thermoreversible + gel)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Thermoreversible Poly(vinylidene fluoride) Gels: A Precursor to Multiporous Polymeric Materials

MACROMOLECULAR SYMPOSIA, Issue 1 2008
D. Dasgupta
Abstract Summary: The thermodynamics of gelation of poly(vinylidene fluoride)(PVF2) with camphor (CP) and ethylene carbonate (EC) suggest polymer-solvent compound formation. The presence of solvent molecules in the polymer crystalline phase of the gel is accordingly shown by wide angle X-ray diffraction studies. The dried gels exhibit porous network morphology. Thermoreversible gel of PVF2 in diethyl azelate is also exploited to create multiporous polymer foam. Porosity measurements with the dried PVF2 gels using Mercury intrusion porosimetry and nitrogen sorption ensure the presence of macro and mesopores in the same matrix although the mesoporosity in dried PVF2 -CP gels strongly depend on method of drying. [source]

Nanocomposites of silver nanoparticle and dinonylnaphthalene disulfonic acid-doped thermoreversible polyaniline gel

POLYMER ENGINEERING & SCIENCE, Issue 3 2010
Ashesh Garai
Silver/polyaniline-dinonylnaphthalene disulfonic acid (PANI-DNNDSA) gel nanocomposites are prepared from the reduction of silver salt by polyaniline in formic acid medium. Scanning electron micrographs (SEM) indicate the presence of three-dimensional fibrillar network structure and the silver nanoparticles remain dispersed within the PANI-DNNDSA fibrillar network. Differential scanning calorimetric (DSC) study shows reversible first-order phase transition characterizing the composite to behave as a thermoreversible gel. Transmission electron micrographs (TEM) show a decrease of nanoparticle size with increasing AgNO3 concentration. Wide angle X-ray scattering (WAXS) patterns show lamellar structure in the gel as well as in the gel metal nanocomposites (GMNCs) and the two melting peaks in the DSC patterns correspond to the melting of monolayer and bilayer crystals produced from the interdigitation of DNNDSA tails anchored from PANI chains within the PANI lamella. The above melting points are greater in the GMNCs than that of pure gel indicating the formation of complex melting thermogram with crystallites produced from the anchored surfactants tails at the surface of Ag nanoparticles. The GMNCs show a higher thermal stability than that of pure PANI-DNNDSA gel. PANI-DNNDSA gel has an emission peak at 354 nm but fluorescence quenching occurs in the GMNCs and the emission peak becomes red shifted. Also in the UV,vis spectra the , band-polaron band transition peak shows a red shift and the DC conductivity increases with increasing Ag nanoparticle concentration in the GMNCs. The current (I),voltage (V) characteristic curves indicate Ohmic nature of conductivity of the gel and the current at the same voltage increases appreciably with increasing Ag nanoparticle concentration. These GMNCs are easily processible due to its thermoreversible nature. So, an easily processible, thermally stable and highly conducting DNNDSA-doped PANI-Ag gel nanocomposite with interesting photoluminescent property has been successfully developed suitable for optoelectronic applications. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source]

Agarose Sols and Gels Revisited

MACROMOLECULAR SYMPOSIA, Issue 1 2006
Jean-Michel Guenet
Abstract Agarose sols have been seen for long as solutions of flexible chains that, on cooling, produce thermoreversible gels through double-helix formation. Investigations of the chain conformation in the sol state by small-angle neutron scattering reveals instead a rigid chain with a very large persistence length (lp,>,9 nm). The chain cross-section radius and mass per unit length correspond to characteristics of helices as those described by Foord and Atkins. These results lead one to a reappraisal of the occurrence of double helices in the gelation process, as they rather suggest a transition of the type loose-single helix,tight single helix. Studies of gels from agarose/water/cosolvent where the cosolvent is Dimethyl Sulfoxide (DMSO), Dimethyl Formamide (DMF), and Methyl Formamide (MF) have led one to conclude on the formation of agarose/water/ cosolvent ternary complexes. The contrast variation method by neutron scattering gives further support to this assumption. Finally, determination of the gel nanostructure allows one to account for the two regimes observed for the variation of the elastic modulus vs concentration. [source]

Encapsulation of magnetic self-assembled systems in thermoreversible gels

MACROMOLECULAR SYMPOSIA, Issue 1 2003
Jean-Michel Guenet
Abstract We describe two different ways of encapsulating within the fibrils of thermoreversible polymer gels the filaments of a supermolecular polymer formed by self-assembly of a bicopper complex. Heterogeneous nucleation is brought about with gels made from isotactic poly(styrene) while compound formation occurs with gels made from poly(hexyl isocyanate). These ways depend upon the interaction between the wings of the supermolecular polymer and the side groups of the polymer. In all cases, the filaments retain their 1-D structure. Preliminary results from magnetic susceptibility measurements show a striking difference between the pure and the encapsulated supermolecular polymer. [source]