2020/10/03 by Kerstin Schirrmann, Schirrmann, Kerstin, Gabriel Cáceres-Aravena +3
Engineering · Materials Science · #Electrowetting and Microfluidic Technologies #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Innovative Microfluidic and Catalytic Techniques Innovation #Pickering emulsions and particle stabilization #Soft Condensed Matter (cond-mat.soft)
paper · pdf · doi:10.48550/arxiv.2010.08109
openalex publication_date 2020/10/03 · openalex created_date 2022/07/25 · openalex updated_date 2026/07/28
We report observations of the self-assembly of coated droplets into regular\nclusters at the sudden expansion of a microfluidic channel. A double emulsion\nconsisting of a regular train of coated microdroplets was created upstream of\nthe channel expansion, so that the inter-drop distance, droplet length,\nvelocity and coating thickness could be varied by imposing different inlet\npressures, albeit not independently. Provided that the enlarged channel remains\nsufficiently confined to prohibit propagation in double file, droplets can\nassemble sequentially into regular linear clusters at the expansion. Droplets\njoin a cluster via the coalescence of their coating film with that of the group\nahead. This coalescence occurs when the droplets approach each other to within\na critical distance at the expansion, enabled by hydrodynamic interactions\nwithin the train. Clusters comprising a finite number of droplets are obtained\nbecause reconfiguration of the droplet assembly during coalescence increases\nthe distance to the following droplet. Decreasing the inter-drop distance\nincreases the cluster size up to a maximum value beyond which continuous\nclusters form. Formalising these observations in a simple model reveals that\nclusters of any size are possible but that they occur for increasingly narrow\nranges of parameter values. Our experimental observations suggests that\nbackground experimental fluctuations limit the maximum discrete cluster size in\npractice. This method of self-assembly offers a robust alternative to flow\nfocusing for encapsulating multiple cores in a single coating film and the\npotential to build more complex colloidal building blocks by de-confining the\nclusters.\n