Control over phase separation and nucleation using a laser-tweezing potential

• Published in: Nature chemistry Vol. 10; no. 5; pp. 506 - 510
• Main Authors: Walton, Finlay, Wynne, Klaas
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2018; Nature Publishing Group
• Subjects: 639/638/440/94; 639/638/440/951; Analytical Chemistry; Biochemistry; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Concentration gradient; Critical point; Crystallization; Free energy; Inorganic Chemistry; Laser beams; Lasers; Nucleation; Organic Chemistry; Phase separation; Photochemicals; Physical Chemistry; Physicochemical properties; Semiconductor lasers
• ISSN: 1755-4330; 1755-4349; 1755-4349
• DOI: 10.1038/s41557-018-0009-8

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 poorly understood practice. Although there are now numerous examples of control using laser-induced nucleation, the absence of physical understanding is preventing progress. Here we show that the proximity of a liquid–liquid critical point or the corresponding binodal line can be used by a laser-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 a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation using a laser-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter. A low-power laser can cause phase separation or trigger the nucleation of a new phase in the proximity of a liquid–liquid critical point, or binodal, using a laser tweezing potential. This effect explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter.