Polyelectrolytes layer-by-layer surface modification of PDMS microchips for the production of simple O/W and double W/O/W emulsions: From global to localized treatment

Abstract

Abstract The fabrication of stable double emulsions remains a challenge in many industrial applications and appears as a hot topic in the microfluidics field. We apply a novel approach to selectively modify the wetting properties of the walls of the micro-emulsifier by deposing successive layers of polyelectrolytes on the targeted sections of the microsystems. The PDMS surface of a microfluidic droplet generator is locally modified by a layer-by-layer polyelectrolytes assembly of poly(allylaminehydrochloride) and poly(acrylicacid). This surface functionalization is successfully performed on flat surfaces, the complete microchip constituted of two steps flow-focusing, or on localized sections of the microsystem, which led to the hydrophilization of hydrophobic PDMS surfaces. The long lasting treatment, over a month, is confirmed. Direct O/W emulsions are enabled, and more interestingly, double W/O/W emulsions of controlled size and shell thickness are formed in PDMS microchip. This work presents an interesting alternative to the other systems commonly used such as imbricated glass capillary microsystems and also other approaches of surface modifications of PDMS microchips. This layer-by-layer surface functionalization on a microsystem displays the advantage of the versatility and ease of use of the PDMS. Polycarbonate and poly(methyl methacrylate) based microfluidic devices are successfully functionalized by simply transposing the process.