Surfactant-free hydroxypropyl cellulose (HPC) microgels have been synthesized in salt solution. The average size and size distributions of microgel particles have been correlated with polymer concentration, salt concentration, and reaction temperature using light scattering techniques. It is found that the low critical solution temperature of HPC polymer chains decreases upon the increase of sodium chloride concentration. In a narrow sodium chloride concentration range from 1.3 to 1.4 M, HPC chains can self-associate into colloidal particles at room temperature. These particles remained stable in solution for weeks without changing their sizes. The microgel particles were then obtained in situ by bonding self-associated HPC chains at 23 °C using divinyl sulfone as a cross-linker. The volume phase transition of the resultant HPC microgels has been studied as a function of temperature at various salt concentrations. A theoretical model based on Flory-Huggins free energy consideration has been used to explain the experimental results.

The kinetics of crystallization of poly-N-isopropylacrylamide (PNIPAM) particles has been investigated using the UV-visible transmission spectroscopy. Since the particle size decreases with the increase in temperature, microgel dispersions of different volume fractions have been obtained by varying the temperature of a single sample. It is found that the rates of the change in crystallinity, the average crystallite size, and the number density of crystallites at the most rapid stage over a certain time interval at various temperatures can be described by the power-law relations. At 19 degrees C, the PNIPAM system behaves as a hard sphere system under microgravity. The hard sphere theory based on Monte Carlo simulation has been used as a reference point to compare with conventional hard spheres, soft spheres, and PNIPAM spheres.

The melting kinetics of three-dimensional colloidal crystals consisting of poly(N-isopropylacrylamide) microgels was investigated by using UV-visible transmission spectroscopy. It was found that the melting was initiated with a decrease of the interplanar spacing of the crystals and that crystallites broke into smaller pieces at large overheating temperatures. The crystallites reach a minimum burst size before completely broken apart. The complete melting occurs as the average thermal fluctuation of the particles reach around 19%. The experimental results corroborate with recent computer simulations that conciliate the Lindemann criterion of melting with Born's mechanical instability.

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