A new experimental setup for high-throughput controlled non-photochemical laser-induced nucleation: application to glycine crystallization

High-speed imaging of non-photochemical laser-induced nucleation in aqueous cesium chloride

A study of non-photochemical laser-induced nucleation (NPLIN) of cesium chloride in aqueous supersaturated solutions is presented. Single, unfocused laser pulses (duration 5 ns, peak power density 180 MW cm-2) of 532 nm laser light were used to induce crystal nucleation, and the resulting dynamics were studied using imaging at frame rates up to 250 000 frames per second (4 μs per frame). Thermocavitation events were observed in a surrounding index-matching fluid, both in the bulk and at the exterior walls of vials. These events were attributed to heating of solid particles by the laser light. The cavities were observed to oscillate in size, with the initial expansion and collapse lasting approximately 50 μs. In some cases, a small persistent gas bubble (lifetime >1 s) was observed after the cavitation event. Within the supersaturated salt solutions, new objects were observed in the image frame of the laser pulse, which faded within 20 μs. These objects were attributed to cavitation: this is the first time that thermocavitation has been observed during NPLIN using an unfocused laser pulse. Crystals were observed to grow at the locations of cavitation events, and the growth was faster at higher supersaturations. Crystals were sometimes observed to form in the location of particles that were observed before the laser pulse, which we consider to be impurity particles that trigger NPLIN. The results provide direct evidence for the nanoparticle-heating mechanism for NPLIN, which begins with thermocavitation. The possible role of stable gas bubbles in NPLIN of crystals is discussed.

Microfluidic Laser-Induced Nucleation of Iron (II,III) Oxide Nanoparticle-Doped Supersaturated Aqueous KCl Solutions

A capillary-based microfluidic system designed for nonphotochemical laser-induced nucleation (NPLIN) studies coupled with real-time microscopy was used to study NPLIN of iron (II,III) oxide doped aqueous KCl solutions. Supersaturation was achieved by lowering the solution temperature using thermoelectric cooling, and heating was used for the dissolution of crystals downstream to prevent clogging during the flow. The effect of nanoparticle concentration, supersaturation, laser intensity, and filtration was studied. We report laser-induced nucleation using laser intensities as low as 1 MW/cm2 with nanoparticle number densities of ∼109 particles per mL of solution at KCl supersaturations from 1.06 to 1.08. The number of crystals increased with increasing laser intensity, supersaturation, and nanoparticle concentration. We discuss our results with respect to the colloidal impurity-heating mechanism hypothesis and propose a semiempirical model based on the nanoparticle heating and bubble formation due to the absorption of laser energy.

Effect of Laser-Exposed Volume and Irradiation Position on Nonphotochemical Laser-Induced Nucleation of Potassium Chloride Solutions

Herein, we study the influences of the laser-exposed volume and the irradiation position on the nonphotochemical laser-induced nucleation (NPLIN) of supersaturated potassium chloride solutions in water. The effect of the exposed volume on the NPLIN probability was studied by exposing distinct milliliter-scale volumes of aqueous potassium chloride solutions stored in vials at two different supersaturations (1.034 and 1.050) and laser intensities (10 and 23 MW/cm2). Higher NPLIN probabilities were observed with increasing laser-exposed volume as well as with increasing supersaturation and laser intensity. The measured NPLIN probabilities at different exposed volumes are questioned in the context of the dielectric polarization mechanism and classical nucleation theory. No significant change in the NPLIN probability was observed when samples were irradiated at the bottom, top, or middle of the vial. However, a significant increase in the nucleation probability was observed upon irradiation through the solution meniscus. We discuss these results in terms of mechanisms proposed for NPLIN.

Design and Validation of a Droplet-based Microfluidic System To Study Non-Photochemical Laser-Induced Nucleation of Potassium Chloride Solutions

Non-photochemical laser-induced nucleation (NPLIN) has emerged as a promising primary nucleation control technique offering spatiotemporal control over crystallization with potential for polymorph control. So far, NPLIN was mostly investigated in milliliter vials, through laborious manual counting of the crystallized vials by visual inspection. Microfluidics represents an alternative to acquiring automated and statistically reliable data. Thus we designed a droplet-based microfluidic platform capable of identifying the droplets with crystals emerging upon Nd:YAG laser irradiation using the deep learning method. In our experiments, we used supersaturated solutions of KCl in water, and the effect of laser intensity, wavelength (1064, 532, and 355 nm), solution supersaturation (S), solution filtration, and intentional doping with nanoparticles on the nucleation probability is quantified and compared to control cooling crystallization experiments. Ability of dielectric polarization and the nanoparticle heating mechanisms proposed for NPLIN to explain the acquired results is tested. Solutions with lower supersaturation (S = 1.05) exhibit significantly higher NPLIN probabilities than those in the control experiments for all laser wavelengths above a threshold intensity (50 MW/cm2). At higher supersaturation studied (S = 1.10), irradiation was already effective at lower laser intensities (10 MW/cm2). No significant wavelength effect was observed besides irradiation with 355 nm light at higher laser intensities (≥50 MW/cm2). Solution filtration and intentional doping experiments showed that nanoimpurities might play a significant role in explaining NPLIN phenomena.

A Review of Laser-Induced Crystallization from Solution

Crystallization abounds in nature and industrial practice. A plethora of indispensable products ranging from agrochemicals and pharmaceuticals to battery materials are produced in crystalline form in industrial practice. Yet, our control over the crystallization process across scales, from molecular to macroscopic, is far from complete. This bottleneck not only hinders our ability to engineer the properties of crystalline products essential for maintaining our quality of life but also hampers progress toward a sustainable circular economy in resource recovery. In recent years, approaches leveraging light fields have emerged as promising alternatives to manipulate crystallization. In this review article, we classify laser-induced crystallization approaches where light-material interactions are utilized to influence crystallization phenomena according to proposed underlying mechanisms and experimental setups. We discuss nonphotochemical laser-induced nucleation, high-intensity laser-induced nucleation, laser trapping-induced crystallization, and indirect methods in detail. Throughout the review, we highlight connections among these separately evolving subfields to encourage the interdisciplinary exchange of ideas.

In situ optical spectroscopy of crystallization: One crystal nucleation at a time

While crystallization is a ubiquitous and an important process, the microscopic picture of crystal nucleation is yet to be established. Recent studies suggest that the nucleation process can be more complex than the view offered by the classical nucleation theory. Here, we implement single crystal nucleation spectroscopy (SCNS) by combining Raman microspectroscopy and optical trapping induced crystallization to spectroscopically investigate one crystal nucleation at a time. Raman spectral evolution during a single glycine crystal nucleation from water, measured by SCNS and analyzed by a nonsupervised spectral decomposition technique, uncovered the Raman spectrum of prenucleation aggregates and their critical role as an intermediate species in the dynamics. The agreement between the spectral feature of prenucleation aggregates and our simulation suggests that their structural order emerges through the dynamic formation of linear hydrogen-bonded networks. The present work provides a strong impetus for accelerating the investigation of crystal nucleation by optical spectroscopy.

Laser-induced nucleation promotes crystal growth of anhydrous sodium bromide

It is demonstrated that laser-induced nucleation enables preferential crystallization of metastable anhydrous solids from solution.

Supersaturation dependence of glycine polymorphism using laser-induced nucleation, sonocrystallization and nucleation by mechanical shock

Nucleation of glycine by laser, ultrasound and mechanical shock exhibits a transition from the alpha to the gamma polymorph with increasing supersaturation.

Polarization independence of laser-induced nucleation in supersaturated aqueous urea solutions

Imaging reveals no alignment of urea crystal axis with the electric field direction, contrary to current understanding of laser-induced nucleation.