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The association of hydroxypropylcellulose (HPC) chains above their lower critical solution temperature (LCST, ∼41 °C) leads to metastable nanosphere aggregates instead of precipitation. Laser light scattering (LLS) measurements revealed that the size of the aggregates is dependent not only on temperature and HPC concentration but also on heating history. There existed a narrow temperature range from ∼41 to ∼44 °C in which narrowly distributed metastable nanospheres formed in a few minutes and lasted for a few days without changing their sizes and molar masses. Increasing temperature in this range and increasing HPC concentration resulted in larger and denser nanosphere aggregates. In situ cross-linking of self-associated HPC chains was performed in a LLS sample cuvette at 42 °C using divinyl sulfone as a cross-linker. Formation of HPC gel microspheres was monitored by LLS and demonstrated by allowing the gel microspheres to swell and shrink at temperatures below and above the LCST, respectively.

Optical properties of N-isopropylacrylamide (NIPA) microgel spheres in water have been investigated using light-scattering and turbidity methods. Two batches of NIPA microgel spheres with hydrodynamic radii of 132 and 216 nm were synthesized in water at 25 °C. Concentrations ranging from ∼0.01 to ∼14 wt % were obtained by dilution-condensation of the dispersions. The hydrodynamic radius distribution, the radius of gyration, and the molar mass of the microgel spheres were determined by combining dynamic and static light scattering. As the polymer concentration increases, the microgel spheres in dispersions exist in the liquid, crystalline, and glass states, while the optical appearance of the dispersions changes progressively from transparent to cloudy to colored (pink, green, blue, and purple gradually) and to transparent. The formation of large colloidal crystals in a very narrow concentration range (ca. 3∼5 wt %) at room temperature (∼18-22 °C) yields iridescent patterns from typical Bragg diffraction. For a colored dispersion, the turbidity exhibits a sharp shoulder-shaped increase at a certain wavelength λc that decreases linearly with decreasing interparticle distance. It is found that for a dilute dispersion light scattering is the main cause of the turbidity, while for a concentrated dispersion in which microgel spheres are close-packed, interparticle interference becomes dominant. Heating a concentrated NIPA microgel dispersion from room temperature to 35 °C leads to a continuous increase of turbidity. The ordered structure of microgel spheres was melted and transformed into a disordered liquid state at about 30 °C, which was lower than the volume phase-transition temperature of ∼34 °C. Phase inversion can be obtained either by condensation of the sample at room temperature or by heating a concentrated sample.

We report systematic investigations of the reaction conditions necessary for the production of selfcross-linked poly(N-isopropylacrylamide) (PNIPAM) microgel particles. Reaction temperatures (Tsyn) ranging from 40 to 90 °C and various monomer (CNIPAM) and initiator (CKPS) concentrations were investigated. Laser light scattering was used to characterize the resultant gel particles at 25 and 40 °C, below and above the phase transition temperature of PNIPAM. By comparing the molar masses measured at these two temperatures, well-defined ranges of T syn, CNIPAM, and CKPS were found in which the polymer chains were well self-cross-linked and formed gel networks. Variations in the size and solid density as a function of these parameters are also discussed.

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Poly(N-isopropylacrylamide) (PNIPAM) adsorbed on surfactant-free polystyrene (PS) nanoparticles has been studied by a combination of static and dynamic laser light scattering (LLS). In static LLS, the amount of PNIPAM adsorbed on the nanoparticles was determined from the absolute excess scattered intensity; and in dynamic LLS, the temperature dependence of the hydrodynamic radius of the nanoparticles adsorbed with PNIPAM was monitored to reveal the "coil-to-globule" transition of PNIPAM on the particle surface. We found that the amount of PNIPAM adsorbed on the nanoparticles depends not only on the PNIPAM concentration but also on the highest temperature to which the nanoparticles/ PNIPAM mixture was heated. Near the lower critical solution temperature (LCST) of PNIPAM in water, the collapse of the adsorbed chains leads to an additional adsorption of PNIPAM on the surface. For a given temperature below the LCST, as the amount of the adsorbed PNIPAM increases, the thickness of the adsorbed PNIPAM layer increases, but the average density of the adsorbed PNIPAM layer decreases, suggesting an extension of the adsorbed chains. Moreover, our results indicate that the adsorbed chains have a lower LCST than the PNIPAM chains free in water.

Vinyl ethylene sulfite (VES) is studied as a new additive in propylene carbonate (PC)-based electrolyte for lithium ion batteries. The electrochemical results show that the artificial graphite material exhibits excellent electrochemical performance in a PC-based electrolyte with the addition of the proper amount of VES. According to our spectroscopic results, VES is reduced to ROSO2Li (R=C4H6), Li2SO3 and butadiene (C4H6) through an electrochemical process which precedes the decomposition of PC. Furthermore, some of the Li2SO3 could be further reduced to Li2S and Li2O. All of these products are proven to be components of the solid electrolyte interface (SEI ) layer.National Natural Science Foundation of China (NNSFC) [29925310, 20433060, 20473068]; Ministry of Science and Technology, China [2007CB209702

The thermally responsive hydroxypropyl cellulose (HPC) microgels have been synthesized and characterized. The microgel particles were obtained by chemically cross-linking collapsed HPC polymer chains in water−surfactant (dodecyltrimethylammonium bromide) dispersion above the lower critical solution temperature of the HPC. The size distributions of microgel particles, measured by dynamic light scattering, have been correlated with synthesis conditions including surfactant concentration, polymer concentration, and reaction temperature. The final microgel size is determined by the balance between the hydrophobic interaction among HPC polymer chains and intermicelle electrostatic repulsion. The swelling and phase transition properties of resultant HPC microgels have been analyzed using both static and dynamic light scattering techniques as a function of temperature and cross-linker concentration. It is found that the increase in the cross-linker concentration reduces the shrinkage extent. The dilute HPC microgel particles (C < 1.0 × 10-5 g/mL) form a stable colloidal dispersion at room temperature and at 44 °C (above the volume phase transition temperature), probably due to steric effects. Adding salt to water leads to a decrease of the volume phase transition temperature of HPC microgels.