Temperature-invertible gel for manipulation of colloidal particles*

We develop an actuatable, responsive gel surface with a set of periodically spaced, temperature-invertible ridges and demonstrate that this surface enables us to create large, dynamic arrays of a range of colloidal particles through multiple physical mechanisms. The surface is constructed from a responsive gel that is spatially patterned on a topographically ridged surface to form gel ridges that collapse to form valleys. Using both experiments and numerical simulations, we show that we can obtain fine-grained control over the amplitude of surface topography, where the exact trajectory of the surface change depends on the rate and direction of temperature change. We then sediment particles on the surface and quantitatively demonstrate how the dynamic features of this gel enable us to pattern colloidal assembly and release under low Reynolds number shear flow. Finally, we introduce biological particles on the surface and show how such a multifunctional surface provides opportunities in creating antifouling surfaces whose properties can be tuned on demand.