The nucleation of glycine from aqueous supersaturated solution has been studied using nonphotochemical laser-induced nucleation (NPLIN), ultrasound (sonocrystallization), and mechanical shock of sample vials. It was found that at higher supersaturation, samples were more susceptible to nucleation and produced more of the g-glycine polymorph. The results are described in terms of a mechanism common to all three nucleation methods, involving the induction of cavitation events and pressure shockwaves. The switch in preference from a-to g-glycine was observed to occur over a narrower range of supersaturation values for NPLIN. We attribute this to induction of cavitation events with higher energies, which result in higher localized pressures and supersaturations. Experiments on NPLIN using circularly versus linearly polarized light showed no evidence for binary polarization switching control of glycine polymorphism.
In a seminal report on laser-induced nucleation in aqueous supersaturated solutions (Phys. Rev. Lett., 1996, 77, 3475) it was noted that needle-shaped crystals of urea were aligned with the direction of the electric field of the linearly polarized laser pulse. The results gave rise to a new mechanism for control of crystal nucleation involving alignment of solute molecules (optical Kerr effect) now commonly known as non-photochemical laser-induced nucleation (NPLIN). Recent theoretical and experimental work has cast doubts on the optical Kerr effect mechanism. In the present letter we present results from digital imaging of urea-crystal growth immediately following laser-induced nucleation. Analysis of the data shows no statistically significant correlation between crystal angle and direction of linear polarization. The results overturn a long-held result that has shaped theoretical and experimental studies of NPLIN.
An approach to controlling
morphology and size is presented through
the combination of laser-induced nucleation and polymer additives.
Here, we apply the technique of non-photochemical laser-induced nucleation
to irradiate a supersaturated solution (S = 1.15)
of cesium chloride (CsCl). The solution immediately responds to laser
exposure, and spherical crystallites are produced along the laser
pathway. The crystals gradually grow into snowflake-like crystals
with different sizes. In this report, two types of acidic polymers
including polyepoxysuccinic acid (PESA) and polyaspartic acid (PASA)
were individually added in supersaturated CsCl solution to shape its
crystalline morphology; we found that a particular property of this
control from PESA is uniformity in modification of crystal sizes.
Additionally, we observed that both PESA and PASA were able to decrease
crystal growth velocity and the quantity of crystals after laser irradiation.
With the effect of more than 0.2 wt % PESA in solution, spherical
crystallites were initially induced by laser; after that, crystal
growth velocities and sizes became slower and smaller with increase
in mass fraction of PESA, which led to identical crystal sizes. With
the effect of more than 5 wt % PESA, the resulting crystalline morphology
obtained by laser was flower-like crystals, whilst cuboid-shaped crystals
could be obtained by spontaneous nucleation. Classical nucleation
theory, crystal growth rate, and additives as large-size impurities
were discussed to analyze the underlying mechanism of the change in
morphology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.