Regioregular poly(3-hexylthiophene) (P3HT) produces thermoreversible gel in xylene. The gel is brownish-red in color. SEM and TEM studies indicate the presence of fibrillar network. WAXS and electron diffraction pattern indicate the presence of P3HT crystallites in the gel. The gels exhibit a first-order phase transition when heated in DSC. A time-dependent UV−vis study indicates that gelation in this system is probably accompanied by two different processes, e.g., (1) coil-to-rod transformation and (2) aggregation of rods to form the crystallites producing the gel. The gelation rate (t gel -1) measured from the test tube tilting method is analyzed using the equation t gel -1 = f(C) f(T), where f(c) = φ n , φ being the reduced overlapping concentration and n is an exponent. The average “n” value determined is 0.52, which indicates that three-dimensional percolation is a suitable model for this gelation. The gelation rate is analyzed according to the Flory−Weaver theory of coil-to-helix transition, and the free energy of activation (ΔF) for the coil-to-rod transformation is found to be 23.7 kcal/mol. It is also analyzed using the theory of fibrillar crystallization in solution, and the free energy of formation of critical size crystalline nucleus (ΔG*dil) is found to be 37.5 kcal/mol. The conductivity of the dried P3HT gel becomes enhanced by ∼10 times that of the cast film in the undoped state, but in the doped state there is an ∼50-fold increase.

Poly(vinylidene fluoride) (PVF2) produces thermoreversible gels in diesters. By variation of the number of intermittent carbon atoms (n = 0−7) of the diesters, the physical properties of the gels are studied. The morphology of the PVF2/diethyl oxalate (DEO) gel is spheroidal, but the morphology of PVF2−diethyl malonate (DEM) gel is a mixture of both spheroidal and fibrillar. The PVF2/diethyl succinate (DES), PVF2/diethyl gluterate (DEG), PVF2/diethyl pimelate (DEP), and PVF2/diethyl azelate (DEAZ) gels are “fibrillar-like” as evidenced from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The X-ray and solvent subtracted FT-IR spectra indicate the presence of α-polymorph PVF2 in all the gels. The enthalpy of gel formation and the enthalpy of gel fusion, measured from differential scanning calorimetry (DSC), show linear plot with PVF2 concentration for PVF2−DEO gels but others exhibit positive deviation from linearity. From the deviation vs PVF2 weight fraction (W PVF 2 ) plot, the compositions of the polymer solvent complexes are found to be 1:3, 1:2, 1:4, 1:4, and 1:3 in the molar ratio of the diester and PVF2 repeating unit, for gels in DEM, DES, DEG, DEP, and DEAZ, respectively. The phase diagrams of PVF2−DEM, PVF2−DES, and PVF2−DEP gels indicate polymer−solvent compound formation with a singular point while those of the PVF2−DEG and PVF2−DEAZ gels indicate compound formation with an incongruent melting point. The polymer solvent compound formation is also studied by molecular mechanics calculations using MMX program. The pairs of α-PVF2 and diester molecules with appropriate conformation to match the composition of the complex are energetically minimized. The distances between the >CF2 group and the carbonyl oxygen are lower than the summation of their van der Waals radii for all the diesters. The discrepancy between molecular modeling and morphology of the PVF2−DEO gels and the borderline morphology of PVF2−DEM gels have been explained from molecular mobility of the solvent and enthalpy of complexation (ΔH c). The gel melting temperature and gelation temperature increases with increase in intermittent length (n) for a particular PVF2 concentration. Also, ΔH c increases with “n”, and this indicates that the intermittent length of diesters has both enthalpic and entropic contribution on gel behavior of PVF2.

Here we report the grafting of N,N-dimethylaminoethyl methacrylate (DMAEMA) directly from poly(vinylidene fluoride) (PVDF) backbone in solution phase by atom transfer radical polymerization (ATRP). The graft length is same for different times of polymerization but graft density increases with increasing polymerization time. Four graft copolymers are prepared and depending on the time of conversion they are designated as PD-6, PD-12, PD-18, and PD-24, the number indicates time (h) of polymerization. A maximum of 36% (w/w) conversion with respect to monomer is achieved in the PD-24 sample. Gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), and polymerization kinetics study conclude the ATRP nature of the polymerization. The graft copolymer shows induced solubility in water and the effective particle diameter in aqueous medium decreases from PD-6 to PD-24 samples. The enthalpy of fusion values are same in graft copolymers with more than 50% reduction and the melting points reduce by 5−6 °C than that of pure PVDF. WAXS patterns of graft copolymers indicate the formation of mixture of α and β phases in dimethyl formamide cast films and also suggest the existence of self-organized short-range ordering from supramolecular interaction between the >CO group and the nitrogen atom of the substituted amino group of the grafting component as is evident from the FTIR study. The absence of any lamellar peak than that of pure PVDF in the SAXS data suggests the formation of fringed micelle crystals in the graft copolymers. Storage modulus of graft copolymers decreases more than that of PVDF due to a decrease in crystallinity. The tensile stress−strain experiment of the PD samples indicates 700−750% elongation, which is 45 times higher than that of PVDF. The toughness increases by 1970% in the graft copolymers over that of pure PVDF, and the gluing property is significantly larger. The graft copolymers produce and stabilize gold nanoparticles in aqueous medium; produce amphiphilic membranes and on its modification to trimethyl ammonium ion it shows 2.2 × 10−6 S/cm dc-conductivity. Because of its water solubility, the polymer promises great use in biotechnology, nanotechnology, energy research, and separation processes.

Polyaniline (PANI) forms thermoreversible gels in four different sulfonic acids, e.g., dinonylnaphthalene sulfonic acid (DNNSA), dinonylnapthalene disulfonic acid (DNNDSA), (camphor-10-sulfonic acid (CSA), and dodecyl sulfonic acid (DSA), when made from the formic acid medium. The gelation behavior of 15% PANI-sulfonic acid (weight to weight) gels are reported here. The morphology, studied from the scanning electron microscopy (SEM) and transmission electron microscopy (TEM), indicates the presence of fibrillar network structure in all of the systems. The thermal study of the gels indicates reversible first-order phase transition during both cooling and heating processes in a differential scanning calorimeter (DSC-7). The WAXS patterns of the gels are different from that of the PANI (EB) from and from each other. Sulfonic acid-subtracted FT-IR spectra of the gels indicate presence of new peaks due to gelation. From the WAXS, electron diffraction, and thermal investigations of the gels, it has been inferred that crystallization is the cause of gelation. The conductance of the gels have an order of 10 -2 to 10 -1 S/cm at 27 °C. A lamellar model for the gel structure, consisting of PANI layer and sulfonic acid layers, is used to explain the gel, and the thermoreversibility is believed to be due to the crystallization of the extended tails of the sulfonic acids under the doped condition.

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A new thermoreversible hydrogel of riboflavin and melamine supramolecular complex (> or =0.02%, w/v) shows enhanced photoluminescence properties through H-bonding.

The cocrystallization behavior of poly(3-alkylthiophene)s (P3ATs) of varying regioregularity and alkyl chain length was explored via differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) studies. For the regioregular samples both DSC and WAXS studies revealed that cocrystallization was limited to the difference of the alkyl chain length by two carbon atoms. On the other hand, P3AT samples with the same alkyl chain length but different regioregularities cocrystallized with a difference of 17 mol % head to tail (H-T) regularity studied here. P3AT samples with varying regioregularity and alkyl chain length by two carbon atoms showed cocrystallization for a regioregularity difference of 7 mol %. The WAXS study indicated that cocrystals had crystallized within the same interchain lamella and noncocrystals had crystallized within the independent interchain lamella of the components. It also indicated the formation of type 1 P3AT crystals with a noninterdigited side chain during the cocrystallization by melt-quenched conditions for all the samples. The phase diagrams clearly revealed that in some systems at the lower melting component rich region there exist two phase regions. The conductivity of the cocrystals, in both the doped and undoped states, is either intermediate or lower than the line joining their component conductivity values.

Thermoreversible gelation behavior of polyaniline (PANI) in the presence of varying concentrations of sulfonic acids are studied. Four different sulfonic acids are used, e.g., dinonylnaphthalene sulfonic acid (DNNSA), dinonylnaphthalene disulfonic acid (DNNDSA), (()-camphor-10-sulfonic acid (CSA), and n-dodecyloxo sulfonic acid (DOSA). The composition range studied here is WPANI ) 0.05-0.80 (WPANI is the weight fraction of PANI in the gel). It has been found from the SEM study that for all the sulfonic acids in the composition range WPANI ) 0.05-0.40, fibrillar network is present. The TEM study also supports the above viewpoint. The thermodynamic study of the gels has been done by DSC-7, and for all the systems broad peaks consisting of two fused gel melting/gel formation peaks are observed. After proper deconvolution of the two peaks the gel melting/gel formation temperatures are measured. When they are plotted with WSO3H (weight fraction of sulfonic acid), typical phase diagrams consisting of two almost parallel curves are found. They are explained by considering the lamellar model where the bilayer and monolayer portions of the surfactant form different crystalline domains. The higher melting point curve is due to the former and the lower one is due to the later in each phase diagram. The lowering of gel melting/gel formation points with increase in PANI concentration of each curve has been attributed to the dilution effect of PANI in the gel. The corresponding enthalpy values (∆H) also show similar decrease with increasing PANI concentration and are explained also from the dilution effect of PANI. The conductance of these gels varies with weight fraction of PANI (WPANI), showing a maximum, and it has been explained by considering that conductivity in the gel is due to both intrachain and interchain contributions. Attempt is made to discuss the above results by using a molecular model of the PANI-DOSA system with the help of MMX program.