Understanding and controlling primary nucleation remains one of the central challenges in crystallization. Nucleation governs the physicochemical, optical, and mechanical properties of the resulting crystals. In this thesis, we investigate a novel pathway for inducing nucleation in supersaturated solutions using the hydrodynamic interaction of laser-induced tandem thermocavitation bubbles confined inside a microcapillary. When two cavitation bubbles are generated in antiphase, their asymmetric pressure fields give rise to micron-scale liquid microjets with velocities far exceeding those produced by single-bubble events. These jets penetrate the primary bubble interface, causing localized evaporation, strong solute redistribution, and transient supersaturation spikes. Using supersaturated aqueous potassium permanganate (KMnO₄) as a model system, we demonstrate that crystallization occurs exclusively under tandem-bubble conditions that produce a high-velocity piercing jet, whereas single-bubble cavitation—even at twice the laser energy—fails to nucleate crystals. The results reveal a clear correlation between jet velocity and nucleation probability, highlighting shear-driven solute transport and microjet-induced evaporation as the dominant mechanisms triggering nucleation. This work establishes microjet-mediated crystallization as a physically grounded and a relatively more energy-efficient alternative to conventional non-photochemical laser-induced nucleation mechanisms, with potential applications in controlled crystallization, microfluidic processing and pharmaceutical manufacturing. ... Read more

Crystallization is one of the most sought after separation and purification technique in the process industries. However, the fundamental understanding on the formation of crystals poses quite a challenge due to the inherent complexity and stochasticity associated with the process. In the past, several attempts put forth to control crystal nucleation have been anything but successful. But, more recently, the use of lasers to control primary nucleation have led to promising prospects.

In the current study, efforts were made to explore the phenomena behind Non-Photochemical Laser Induced Nucleation (NPLIN). Experiments were carried out starting with a confined microfluidic system for both supersaturated aqueous potassium permanganate and potassium chloride solutions and later extended to unconfined geometry with potassium chloride solutions. A single nanosecond laser pulse of 532 nm wavelength was employed to create vapour bubbles and the resulting crystal formation was quantified.

To begin with, a quadratic relationship between the laser energy supplied and the maximum radius of the bubble formed was observed. By systematically varying both the supplied laser energy and the solution supersaturation, the probability of crystal formation for various energy–supersaturation combinations were studied. A minimum laser energy threshold for crystal formation was observed to be a function of solution supersaturation. The results obtained in this study will aid in developing a numerical model that can apriori predict the minimum necessary laser and supersaturation conditions required for any given salt to undergo NPLIN. ... Read more

This thesis describes a study into pairwise particle interactions within a Hele-Shaw geometry, using stop-flow lithography. By exposing a photoreactive mixture to a strong UV-pulse, a hydrogel is formed. The shape of this hydrogel is controlled by masking part of the light beam. This process takes place while the Hele-Shaw channel is placed on the stage of a microscope, which allows these hydrogel particles to be viewed and tracked. Improvements were made to increase the accuracy and precision of the experimental set-up. No- tably, the initially present mismatch of intra-pair particle thickness was greatly reduced by changing the method of particle pair production. By tracking these pairs of particles, information is obtained regarding their motions and velocity relative to one another. Experiments were performed for a selection of particle shapes and compared to numerical simulations of identical geometries. Simulations predicted that attractive and repulsive velocities should be noticed depending on the separation distance and shape of the particles. Qualitatively, the experiments agree to a certain extent with the simulations. It was demonstrated that the pairwise interactions are indeed dependent on their shape. Furthermore, the magnitude of these interactions qualitatively matched with the experimental data. Quantitatively, the experimental data did not agree with the simulations, but strong evidence was presented to indicate that the UV-light hitting the sample was not uniformly distributed. This results in a discrepancy in particle thickness between the pair, which skews the experimental data. Novel insights were gained on the applicability of the current literature model on hydrogel particle propagation. In contrast to the current model, it was experimentally demonstrated that the shape and (in-plane) size of the particle affects its thickness. ... Read more