Control over the synthesis of monodisperse silica particles up to mesoscopic scale is generally made difficult due to intrinsic limitation to submicrometric dimensions and secondary nucleation in seeded experiments. To investigate this issue and overcome these difficulties, we have implemented single step processing by quantifying the effects of the progressive addition of a diluted tetraethyl orthosilicate solution in ethanol on the size and monodispersity of silica particles. Contrary to particles grown in seeded polymerization, monodisperse particles with size up to 2 microm were synthesized. Moreover, the particles exhibit a final diameter (d(f)), which varies with V(-1/3) over more than 2 orders of magnitude in rate of addition (V). On the basis of a kinetic study in the presence of addition showing that particle growth is limited by the diffusion of monomer species, we developed a diffusion-limited growth model to theoretically explain the observed d(f)(V) behavior and quantitatively retrieve the measured amplitude and exponent. Using a single parameter procedure, we can therefore predict and generate in the room temperature range, monodisperse particles of a targeted size by simply adjusting the rate of addition.

The changes in microenvironments during a pH-induced volume transition of poly(acry1amide) (PAAm) gels with a dansyl group as a fluorescent probe in an acetone/water (9111) mixed solvent have been studied by the fluorescence spectrum, anisotropy, and lifetime measurements. Irrespective of the presence or absence of fluorescence probe groups labeled on the network of PAAm gels, the gels are in the collapsed state at pH = 1.0-5.0. They show a discontinuous volume phase transition (DVPT) at pH = 5.1 and remain swollen up to pH = 9.6. The fluorescence anisotropy ratio, r, also changes at pH = 5.1 for the dansyl group, but the peak shift of the fluorescence spectra of the dansyl group takes place at pH = 3.8, i.e., before the DVPT. The fluorescence decay measurements demonstrated two emitting states for the excited dansyl group depending on pH values. The microscopic changes in hydrophobicity and mobility around polymer segments are demonstrated at pH = 3.8 by the fluorescent dansyl probe, although the macroscopic DVPT occurs at pH = 5.1.

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