Multiple interesting systems like anti-fogging and lab-on a chip devices as well as DNA microarrays and microfluidic chips have liquid dynamics as the most important working component. Surface wettability has a main influence on liquid dynamics at solid-liquid interfaces. Surface gradients in wettability are known to be able to drive liquid motion without the need of an external force. These gradients need to be precisely designed, which is labor-intensive and expensive. Therefore, a new cheap and easy way to create a surface gradient in wettability is presented in this project. Where moving droplets, since they were first discovered by Whitesides et. al.,[1] were limited by side effects like spreading, here a new approach for functional autonomous liquid motion is shown. Using Polydimethylsiloxane (PDMS) in combination with air plasma shielded with a metal mask (Fig. 1b), leads to surface wettability gradients ranging from 25° up to 110° in static water contact angle (Fig. 1a). This droplet movement was utilized to create directed and controlled water movement on different PDMS-surfaces and channels (Fig.1c-f). This controlled movement was used to create a chemical fluidic motility chip, enabling silver nanoparticle synthesis as a model reaction in a chip solely based on autonomous movement of two droplets. The size distribution of the resulting nanoparticles could be controlled by the channel length of the mixing chip, which can be linked to the mixing time of the solutions (Fig.2).[2] [1] M. Chaudhury, G. Whitesides, Science 1992, 256, 1539 [2] P. T. Kühn, B. S. de Miranda, P. van Rijn, Adv. Mater. 2015, DOI 10.1002/adma.201503000.

Directed autonomic flow: Functional motility fluidics

251st National Meeting (2016)

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