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

• Non-photochemicallaser-induced nucleation (NPLIN) hasemergedas a promising primary nucleation control technique offering spatiotemporalcontrol over crystallization with potential for polymorph control.So far, NPLIN was mostly investigated in milliliter vials, throughlaborious manual counting of the crystallized vials by visual inspection.Microfluidics represents an alternative to acquiring automated andstatistically reliable data. Thus we designed a droplet-based microfluidicplatform capable of identifying the droplets with crystals emergingupon Nd:YAG laser irradiation using the deep learning method. In ourexperiments, we used supersaturated solutions of KCl in water, andthe effect of laser intensity, wavelength (1064, 532, and 355 nm),solution supersaturation (S), solution filtration,and intentional doping with nanoparticles on the nucleation probabilityis quantified and compared to control cooling crystallization experiments.Ability of dielectric polarization and the nanoparticle heating mechanismsproposed for NPLIN to explain the acquired results is tested. Solutionswith lower supersaturation (S = 1.05) exhibit significantlyhigher NPLIN probabilities than those in the control experiments forall laser wavelengths above a threshold intensity (50 MW/cm(2)). At higher supersaturation studied (S = 1.10),irradiation was already effective at lower laser intensities (10 MW/cm(2)). No significant wavelength effect was observed besides irradiationwith 355 nm light at higher laser intensities (& GE;50 MW/cm(2)). Solution filtration and intentional doping experimentsshowed that nanoimpurities might play a significant role in explainingNPLIN phenomena. Thearticle describes a droplet-based microfluidic setupto study NPLIN with the droplets containing crystals identified usingthe deep-learning method. Experimental parameters such as solutionsupersaturation, laser wavelength, laser intensity, solution filtration,and intentional doping of nanoparticles are studied using supersaturatedaqueous KCl solutions to quantify its influence on nucleation kineticsand draw parallels to the proposed underlying NPLIN mechanisms inthe literature.

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NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

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