Droplet Transport in a polymer-coated nanochannel

KEVIN SPEYER; CLAUDIO PASTORINO

Buenos Aires

Workshop; Frontiers in Physical Sciences; 2016

Microfluidics is a relatively new technological platform for which the behavior of liquids and gases in confined regime must be investigated. Large surface area to volume ratios give rise to particular flowregimes (low Reynolds number), and enhances the role of the substrate-fluid interaction. Possible applications of lab-on-chip devices in engineering, chemistry, biochemistry and biotechnology has broughtattention to this field. Efforts are being made to control the flow inside the channel, by varying the physical and chemical properties of the confining medium. Polymer-brush coatings are promising systemsin microfluidics, because their properties can be fine-tuned to alter the surface-fluid interaction, by modifying macroscopic quantities, like temperature or pH. Polymer brushes are also known for reducingfriction, which reduces in turn the energy loss in mass transport.In this work, we investigate the flow of droplets in a nanochannel coated with semi-flexible hydrophobic polymers, via molecular-dynamics simulations. A simple liquid in coexistence with its vapor istransported across a slit channel by applying a constant external force to each fluid particle. The local rigidity of the polymers is varied from totally flexible to rigid rods, in order to study the effect onthe flow velocity profile. The distance between adjacent droplets is also varied, observing a strong influence on the limit velocity of the droplet. The effect of the gas phase on the fluid is examined andcompared to the friction force of the polymers. The slip of the liquid passing the soft substrate is estimated for various flow rates. We also analyze the polymer brush height and structure as a function ofthe droplet position.