Living supramolecular polymerization realized through a biomimetic approach.

Various conventional reactions in polymer chemistry have been translated to the supramolecular domain, yet it has remained challenging to devise living supramolecular polymerization. To achieve this, self-organization occurring far from thermodynamic equilibrium--ubiquitously observed in nature--must take place. Prion infection is one example that can be observed in biological systems. Here, we present an 'artificial infection' process in which porphyrin-based monomers assemble into nanoparticles, and are then converted into nanofibres in the presence of an aliquot of the nanofibre, which acts as a 'pathogen'. We have investigated the assembly phenomenon using isodesmic and cooperative models and found that it occurs through a delicate interplay of these two aggregation pathways. Using this understanding of the mechanism taking place, we have designed a living supramolecular polymerization of the porphyrin-based monomers. Despite the fact that the polymerization is non-covalent, the reaction kinetics are analogous to that of conventional chain growth polymerization, and the supramolecular polymers were synthesized with controlled length and narrow polydispersity.

Fabrication of nanostructured poly(3-thiophene methyl acetate) within poly(vinylidene fluoride) matrix: new physical and conducting properties.

Nanostructured poly(3-thiophene methyl acetate) (PTMA) within the poly(vinylidene fluoride) (PVDF) matrix is achieved by reactive blending technique under melt-cooled condition. The nanoparticles are almost spherical showing a minimum size with 5% (w/w) PTMA concentration (PTMA5), and they become agglomerated at > or = 25% (w/w) PTMA concentration. Different phase separation mechanisms are used to explain the above variation of nanoparticle size. The lower size nanophase in the PTMA5 blend is attributed to spinodal decomposition, while the larger size nanophases are produced from binodal decomposition. The TGA study indicates increasing thermal stability of PVDF in the nanoblends. DSC study shows increasing melting and crystallization temperature of the nanoblends; the former is due to the attractive forces of PTMA nanostructure, and the latter is for the nucleating effect of nanophase PTMA. The long distance, lamellar distance, and amorphous overlayer distance decrease to different extents. The pi-pi* transition band of UV-vis spectra shows a red shift with increasing PTMA concentration, but the photoluminescence spectra of the nanoblends show a blue shift. The former is attributed to intrachain aggregation of PTMA, while the latter is caused from "static excimer" formation at the ground state. PTMA1 and PTMA3 show approximately 8 times increase in PL intensity except PTMA5 where interconnectivity between the nanodomains makes the nonradiative decay similar to bulk PTMA. The temperature variation of conductivity indicates a conformational transition of PTMA chain with increasing temperature facilitating better charge transport. The I-V characteristic curves are really interesting; the nanoblends show a negative hysterisis, but PTMA5 shows a memory effect attributed to the electrical bistability originated from the interconnected nanophases arising from spinodal decomposition.

Hierarchical tuning of 1-D macro morphology by changing the composition of a binary hydrogel and its influence on the photoluminescence property.

1-D morphological tuning in the riboflavine(R)-melamine(M) hydrogel system (from helical fiber to rod-like to tubular morphology) with an interesting photoluminescence property by changing the composition of the RM components.

A mechanistic approach on the self-organization of the two-component thermoreversible hydrogel of riboflavin and melamine.

The riboflavin (R) and melamine (M) supramolecular complex in the mole ratio of 3:1 (RM31) produces a thermoreversible gel in aqueous medium. The gelation mechanism has been elucidated from morphological investigations using optical, electron, and atomic force microscopy together with time-dependent circular dichroism (CD) and photoluminescence (PL) spectroscopy. Optical microscopy indicates spherulitic morphology at lower gelation temperature (

A two component thermoreversible hydrogel of riboflavin and melamine: Enhancement of photoluminescence in the gel form.

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

Preparation and characterization of silver-poly(vinylidene fluoride) nanocomposites: formation of piezoelectric polymorph of poly(vinylidene fluoride).

In situ Ag nanoparticles are produced on reduction of Ag+ with N,N-dimethylformamide in the presence of poly(vinylidene fluoride) (PVF2). The plasmon band transition is monitored with time in the reaction mixture for three sets of experiments by UV-vis spectroscopy. The plasmon band absorbance increases sigmoidally with log(time). Analysis of the data with the Avrami equation yields an exponent n value between 1.5 and 2.0, indicating two-dimensional nucleation with linear or diffusion controlled growth. The TEM study of the polymer nanocomposites (PNC) indicates both spherical and rodlike morphology for PNC0.5 and PNC2.5 samples, whereas the PNC11 sample has spherical and agglomerated structures (the numerical number associated with PNC indicates percentage (w/w) of Ag in the nanocomposite). The WAXS and FTIR studies indicate the formation of piezoelectric beta-polymorphic PVF2 in the nanocomposites. The DSC study indicates some increase of the melting point and enthalpy of fusion of PVF2 in the nanocomposite, although with increase in Ag nanoparticle concentration the increase is smaller. The crystallization temperatures of PNCs also increased, indicating nucleating effect of Ag nanoparticles in the composite. In the TGA curves, the PNCs exhibit a three-step degradation process. The degradation temperatures of PNCs are lower than that of PVF2. The storage modulus data indicate a significant reinforcement of the mechanical property in the PNCs where also the reinforcement effect decreases with increasing nanoparticle concentration. Both the loss modulus and tan delta plots indicate two peaks; the lower temperature peak has been attributed for glass transition temperature, whereas the higher one has been attributed to a similar type relaxation process for the crystalline-amorphous interface. The increase in the glass transition is marginal for the PNCs, but the increase of later transition temperature is somewhat higher. The FTIR study shows that the dipolar interaction of the >CF2 dipole with the surface charges of Ag nanoparticle stabilizes the nanoparticle in the nanocomposite.