Droplet manipulation and application

Abstract

Droplet is ubiquitous in natural environment, our daily life and industrial process. Droplet manipulations, droplet-based fabrications and applications have attracted more and more attentions due to their tremendous potential in various areas like industry/agriculture productions, bio-detections, chemical reactions and mass transport. For example, droplet would bounce off from non-wetting surfaces like a spring, which is undesired in technical applications like ink-jet printing, spraying, painting and coating. The methods controlling droplet deposition and manipulation need to be developed for improvement of production efficiency. Moreover, loss-free, reliable and fast droplet manipulation has been anticipated for a long time for manufacturing based on droplets, like biological diagnosis and chemical reactions. However, the durability of droplet manipulation platform cannot be satisfactory for practical applications. Besides, it is crucial to fabricate the controllable and monodisperse droplets as the request from the applications like diagnostics and advanced material fabrication involving particles synthesis from droplets. The present work first focuses on the droplet arresting and manipulating on non-wetting surface, which needs to be addressed for industrial applications. Mediated by air pockets and vapour film, impacting droplets spontaneously rebound off those surfaces. A method enabling enhanced liquid deposition on different super-repellent surfaces being adaptable for a wide spectrum of fluids remains out of reach. By overlaying droplets with an ultrathin preferential-wetting liquid layer, droplets can be effectively arrested on diverse super-repellent surfaces. Moreover, post-deposition states of droplets can be well-controlled, enabling well-directed self-collection of liquids. A durable droplet manipulation platform was further developed for applications like diagnostics and micro-reactions. A citrus-peel-like micro-cavity structure for the design of durable slippery liquid-infused porous surfaces (SLIPS) was presented. Micro-cavity SLIPS displays two orders of magnitude enhancement in durability. Precise droplet manipulation by harnessing Marangoni effect using photo-thermal control was demonstrated. Patterned cavity-smooth SLIPS can initiate multiple-droplet coalescence. Then, droplet application for the fabrication of monodispersed microencapsulated phase change materials with high thermal performance was investigated, which possesses core-shell structure templated from double-emulsion droplet. Microencapsulation of phase change materials (PCMs) can prevent shape change and the leakage of PCMs and enhance heat transfer with increased surface area to volume ratio, and thus benefit pragmatic applications. In a word, the simple, durable and effective strategies and techniques for droplet manipulation and application are developed. The strategies and techniques would open new avenues for the industrial/agricultural productions, biological detections and chemical reactions.