Interaction of Colloidal Particulates with Dynamic Microstructured Polymer Brushes: Computer Simulations

Microstructured surfaces composed of adherent domains and stimuli-responsive polymer domains (that undergo swelling-shrinking upon stimuli, e.g., temperature change around the low critical solution temperature, LCST) were proven to catch and release colloidal particulates (CP) effectively. Such structures have the advantage over just uniform stimuli-responsive surfaces because on the microstructured surface, sticky and pushing-off properties are decoupled so that the properties of each domain can be adjusted in a broad range. We consider the adsorption and desorption of particulates on the stimuli-responsive surface made of tethered poly(acrylic acid) (PAA) domains that contain the adherent functional motifs and thermoresponsive poly(<i>N</i>-isopropylacrylamide) (PNIPAM) domains, both arranged into regular micropatterns. At temperatures above the PNIPAM LCST, the PNIPAM domains collapse in water, allowing the adsorption of the particulates on the PAA regions. When cooled below the LCST, PNIPAM swells and pushes particles off the surface. We develop coarse-grained models for the CP on the microstructured surfaces and use computer simulations to analyze the optimal structure of such surfaces in terms of the PAA chain length, types of the micropatterns, the ratio between surface areas of the PAA and PNIPAM domains, and micropattern graininess in relation to particle dimensions. The study is relevant and motivated by the problems of harvesting and sorting prokaryotic and eukaryotic cells on microstructured surfaces.