Micromolding Surface-Initiated Polymerization: A Versatile Route for Fabrication of Coatings with Microscale Surface Features of Tunable Height

and the inability to tune the size of the features independent of the mold. Here, we seek to employ soft lithography to develop robust chemically bound coatings with microscale surface features of tunable heights. This paper describes the combination of soft lithographic molding and a surfaceinitiated polymerization (SIP) to produce a versatile process termed micromolding surface-initiated polymerization (μMSIP) for the fabrication of microscale-textured, surface-bound polymer coatings. Specifi cally, μMSIP involves the molding of a microscale-textured master with a polymeric composite comprising hard-PDMS (h-PDMS) and Sylgard 184 PDMS to produce a negative replica exhibiting the corresponding inverted structures of the master. This mold is then fi lled with pure monomer and subsequently pressed against an activated surface, i.e., a surface containing anchored initiator species to promote a polymerization. As the polymerization progresses, the surface-tethered growing polymer chains form a uniform fi lm at the base and begin fi lling the inverted structures in the mold, thereby producing a coating where the surface topography reproduces the corresponding surface features of the master. Furthermore, we show that we are able to modulate the height of the surface features by tuning the conversion of the monomer through control of the initiator amount by means of a surface-bound monolayer or macroinitiator or by systematically varying process variables such as temperature and polymerization time. If achievement of the full height of the master features is desired, either the monolayer or the macroinitiation approaches can be combined with the addition of initiator species into the mold. Here, as the SIP, we use the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of 5-(perfl uorooctyl)norbornene (NBF8) onto gold-coated solid supports to yield partially fl uorinated coatings with surface microfeatures and ultralow critical surface tensions (9 mN/m). [ 11 ] Representative examples of surface microstructures obtained through μMSIP include arrays of pyramids and inverted pyramids. Extensive research efforts have established SI-ROMP as a robust, versatile polymerization technique. [ 12 ] SI-ROMP has become a useful technique for synthesizing polymers that exhibit attractive biological, electronic, and mechanical DOI: 10.1002/admi.201400055 C. A. Escobar, T. J. Cooksey, M. P. Spellings, Prof. G. K. Jennings Department of Chemical and Biomolecular Engineering Vanderbilt University Nashville , TN 37325 , USA E-mail: [email protected] This article introduces a process termed micromolding surface-initiated polymerization (μMSIP) as a versatile route to provide surface-bound, partially fl uorinated polymer coatings with a homogeneous array of microscale surface features. The process employs hard-polydimethylsiloxane (h-PDMS) to mold the surface structure of master substrates exhibiting patterned microscale features. Upon fi lling the mold with the monomer 5-(perfl uorooctyl)norbornene (NBF8) and placing against a surface that is pre-activated for surface-initiated ring-opening metathesis polymerization (SI-ROMP), a partially fl uorinated polymer fi lm propagates from the surface with features that grow into the recesses of the mold to produce the fi nal microtextured coating. The heights of these features can be tuned from 20–100% of the full height of the mold features based on the amount of initiator employed as well as the polymerization time and temperature. Reproduced topographies include pyramidal and inverted pyramidal structures. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that the fi nal polymer fi lm exhibits a homogeneously microstructured surface that resembles that of its corresponding master.