(425j) Nonphotochemical Laser-Induced Nucleation of Glycine Aqueous Solution in Microfluidics

The phenomenon of non-photochemical laser induced nucleation was observed and reported for the first time in 1996 by Garetz et al. that nanosecond pulses of intense laser induced homogeneous nucleation in supersaturated urea solution¹. Since then, the same phenomenon has been observed in numerous systems, namely alkali halide^2–4, glycine⁵, and proteins⁶. In the present work, we integrated a microfluidic device with real-time microscopy for the continuous characterization of laser-induced nucleation of glycine solutions. With a thermoelectric cooling module installed, our apparatus can create supersaturation conditions on the chip. We examined the influences of “aging” time, flow rate, laser power density, laser exposure, and supersaturation. Dynamic light scattering data suggested that submicron-sized liquid-like structures exist in aged supersaturation solutions. The existence of these nanodroplets was then proved crucial to laser-induced nucleation. The liability and threshold laser intensity measured were consistent with literature values in static cells⁷. An increase of crystal size was observed with increasing supersaturation. Moreover, crystal morphology shifted from alpha- to gamma-form with increasing supersaturation. Dielectric polarization model from Alexander et al.⁸ was modified with two-step nucleation theory to account for the existence of the secondary liquid structures.

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