7 September 2018 Control over phase separation and nucleation using a optical-tweezing potential
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Control over the nucleation of new phases is highly desirable but elusive. Even though there is a long history of crystallization engineering by varying physicochemical parameters, controlling which polymorph crystallizes or whether a molecule crystallizes or forms an amorphous precipitate is still a black art. Although there are now numerous examples of control using laser-induced nucleation, a physical understanding is absent and preventing progress. We will show that concentration fluctuations in the neighborhood of a liquid-liquid critical point can be harnessed by an optical-tweezing potential to induce concentration gradients. A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in liquid mixtures using a low-power laser diode confirm the effect. Phase separation and nucleation through an optical-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter.
Conference Presentation
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Klaas Wynne and Finlay Walton "Control over phase separation and nucleation using a optical-tweezing potential", Proc. SPIE 10723, Optical Trapping and Optical Micromanipulation XV, 107230O (7 September 2018); doi: 10.1117/12.2324119; https://doi.org/10.1117/12.2324119

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