Search

Isotactic poly (N-isopropylacrylamides) (PNIPAMs) with a wide range of tacticity exhibit upper critical solution temperature (USCT) type phase transition in an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSI]). The phase transition temperature becomes higher with increasing isotacticity, since more amide groups are aligned along the same side of backbones to form stronger intramolecular hydrogen bonding. Phase diagrams of highly isotactic PNIPAMs show prominent UCST peaks at low concentrations, similar with the typical polymer solution, which implies the dissolution of isotactic PNIPAMs is dominated by the entropy-driven effect. The increase in phase transition temperature with molecular weight is also from the entropic reason. The phenomena above reveal that the phase transition behavior of PNIPAMs in ionic liquids is highly influenced by tacticity effect.

Atomic force microscopy (AFM) indentation is the most suitable way to characterize micromechanical properties of soft materials such as bio tissues. However, the mechanical data obtained from force-indentation measurement are still not well understood due to complex geometry of the bio tissue, nonlinearity of indentation contact, and constitutive relation of hyperelastic soft material. Poly-N-isopropyl acrylamide (PNIPAM) filled with 5 wt% polystyrene (PS) sphere particles material system can be utilized as a simplified model for mimicking a whole host of soft materials. Finite element model has been constructed to simulate indentation as in AFM experiments using colloidal probes for a parametric study, with the main purpose of understanding the effect of particles on overall behavior of mechanical data and local deformation field under indentation contact. Direct comparison between finite element simulation and indentation data from AFM experiments provides a powerful method to characterize soft materials properties quantitatively, addressing the lack of analytical solutions for hard-soft composites, both biological and synthetic ones. In this framework, quantitative relations are found between the depth, at which the particle was embedded, the particle size and the elastic modulus of the overall composite. Comprehensive characterizations were established to distinguish indentation on a particle residing on top of the hydrogel from a particle embedded inside the hydrogel matrix. Finally, different assumptions of interface friction at the boundary between the particle and the hydrogel have been tested and directly compared with experimental measurements.

Random copolymer gels of N -isopropylacrylamide (NIPAM) and N -ethylacrylamide (NEAM) were synthesized in using different monomer compositions in 1:1 methanol-water mixtures and in pure water. The samples were characterized by cononsolvency study in methanol-water mixtures at various temperatures by swelling ratio measurements. It is observed that with the variation of the temperature and monomer compositions in the synthesis reaction mixture, the cononsolvency properties varied significantly. But the variation in the solvents compositions by keeping monomer compositions fixed does not affect the cononsolvency much. All results can be explained on the basis of the differences in thermoresponsive character or difference in the hydrophilicity of PNIPAM and PNEAM in water, preferential adsorption of the solvents by polymer networks, solvent-solvent interactions, heterogeneity of the polymer networks synthesized at different solvent compositions and at different temperatures, difference in their morphological properties, etc.

In the present study, rapid and highly efficient solid-state synthesis strategy has been successfully employed for the synthesis of zinc oxide nanoparticles (ZnO NPs). Herein, prepared ZnO NPs are characterized and used for the fabrication of highly sensitive, selective, and accountable gas sensors. Structural elucidation, surface composition, and morphological investigations of as-synthesized ZnO NPs respectively, are carried out using X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction measurement techniques. The gas sensing properties of ZnO NPs studied at various operating temperatures and towards different oxidizing and reducing gases demonstrated the ability of ZnO to detect hazardous chlorine (Cl2) gas (optimum @ 200 °C) with rapid response and recovery times. In addition, ZnO sensor film has detected the low 5 ppm concentration of Cl2 with reasonable response of 199% with outstanding repeatability and stability in response. The variation of ZnO response with respect to different Cl2 concentrations has systematically been investigated and explored. Finally, the plausible sensing mechanism of ZnO with Cl2 gas molecules has been proposed using energy band model diagram.

The synthesis of amphiphilic block-copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-acryloyl- l -phenylalanine methyl ester) (PNALPA) by RAFT polymerization is reported. The polymers were characterized by proton NMR (1H NMR), gel permeation chromatography (GPC), powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) to understand their structure-property relationships. All synthesized polymers show pH triggered release at acidic (pH 5) and biological pH (pH 7.4). Critical micellar concentration also varied systematically depending on the amphiphilic nature of the polymers. Biocompatibilities of the polymers are also determined to check their suitability for biomedical applications.

Well-defined amphiphilic poly( d , l -lactide)- b -poly( N -vinylpyrrolidone) (PDLLA- b -PNVP) block copolymers were successfully prepared using ring-opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. Synthesized PDLLA- b -PNVP block copolymers were characterized by 1 H NMR spectroscopy and GPC. Spherical micelles of ∼30.2 nm diameter were formed from the aqueous solution of amphiphilic diblock copolymer PDLLA 42 - b -PNVP 63 as revealed by TEM and supported by 1 H NMR and light scattering. The critical micelle concentration value of the block copolymers, determined by fluorescence spectroscopy using pyrene as probe, increased with the increase in the chain length of PNVP block. The average hydrodynamic radius ( R h ) of the micelles remained almost constant above the cmc value over the angles of scattering measurement. Thermal properties of these block copolymers were studied by TGA, DTA and DSC. Crystalline properties of these block copolymers were studied by WXRD.