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.

No abstract

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.

No abstract

No abstract

Crystal growth speeds, crystal sizes and the morphology of sodium acetate (CH3COONa) crystals in the presence of polymaleic acid and polyacrylic acid with different concentrations were investigated in supersaturated solutions of sodium acetate. The technique of non-photochemical laser-induced nucleation (NPLIN) was used to produce initial crystallites of anhydrous CH3COONa. The anhydrous CH3COONa crystal growth in solution after laser irradiation resembled the formation of dandelion seed heads. Even though NPLIN could offer temporal–spatial control of crystal nucleation without the addition of acidic polymers, the crystal growth rates were heterogeneous for crystallites along the laser pathway, which led to irregular crystalline sizes and morphologies. Here, a controllable approach from crystal nucleation to crystal growth has been designed through the addition of acidic polymers in the laser-induced growth of anhydrous CH3COONa crystals. In the presence of an acidic polymer, both the crystal growth and the morphological modification were controlled from tuft-shaped crystals to dandelion-like crystals. As bulk solid thicknesses and crystal growth speeds can be modified by different mass fractions of acidic polymer, a mathematical model was established to analyse the dynamics of crystal growth under the effect of acidic polymers. The model reproduces remarkably well the experimental trend and predicts experimental results. The changes in supersaturation and the number of nuclei through the addition of acidic polymers were analysed to investigate the underlying mechanism of morphological difference.

A Z-scheme system In2S3/WO3 heterojunction was fabricated via a mild hydrothermal method and further applied for photocatalytic degradation of tetracycline (TCH) and Rhodamine B (Rh B) under visible light irradiation.