Superhydrophobic Microporous Substrates via Photocuring: Coupling Optical Pattern Formation to Phase Separation for Process- Tunable Pore Architectures Saeid Biria † and Ian D. Hosein* ,† † Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York 13244, United States *S Supporting Information ABSTRACT: We present a new approach to synthesize microporous surfaces through the combination of photo- polymerization-induced phase separation and light pattern formation in photopolymer−solvent mixtures. The mixtures are irradiated with a wide-area light pattern consisting of high and low intensity regions. This light pattern undergoes self- focusing and filamentation, thereby preserving its spatial profile through the mixture. Over the course of irradiation, the mixture undergoes phase separation, with the polymer and solvent located in the bright and dark regions of the light profile, respectively, to produce a binary phase morphology with a congruent arrangement as the optical pattern. A congruently arranged microporous structure is attained upon solvent removal. The microporous surface structure can be varied by changing the irradiating light profile via photomask design. The porous architecture can be further tuned through the relative weight fractions of photopolymer and solvent in the mixture, resulting in porosities ranging from those with discrete and uniform pore sizes to hierarchical pore distributions. All surfaces become superhydrophobic (water contact angles >150°) when spray- coated with a thin layer of polytetrafluoroethylene nanoparticles. The water contact angles can be enhanced by changing the surface porosity via the processing conditions. This is a scalable and tunable approach to precisely control microporous surface structure in thin films to create functional surfaces and antiwetting coatings. KEYWORDS: superhydrophobicity, microporous, phase separation, photopolymerization, PTFE nanoparticles ■ INTRODUCTION Living systems abound 1 with examples of surface anatomies that possess porous, textured, or roughened surface designs that confer special interfacial properties. Examples include the lotus leaf, 2−5 insect legs 6 and wings, 7 bird feathers, 8 mosquito eyes, 9 fish scales, 10 and even human bone. 11 These structures have inspired creation of their biomimetic counterparts 12 as a critical aspect of material surface design for numerous applications, including functional surfaces, water collection, antifouling, self- healing, tissue engineering, and regenerative medicine, among many others. 13−27 Extensive effort has focused on developing methods to fabricate surfaces, particularly with tailored porosity, and include electrospinning, 28 templating, 29 differ- ential etching, 30 photolithography, 31 replication, 32 treated fabrics, 33 meshes, 34,35 coatings, 19 filter paper, 36 and nano- particle layers. 37 Such porous structures provide the necessary microscopic surface porosity and roughness to induce hydro- phobicity, 38 which can be enhanced through additional coating or surface functionalization. 14,39 However, while significant progress has been achieved with such methods, all suffer from their inherent trade-off between precise control over structure and scalability. For example, lithography is the most precise but least scalable; deposition methods are quite scalable but least precise. Precise, scalable processing is important for applica- tions in which not simply porosity but specific pore geometries and arrangements are necessary. Hence, such a synthetic approach is highly desirable to tune the structure and functionality for large-scale applications. Photopolymerization is an attractive approach to materials synthesis owing to its low-energy input, scalability, and ease in controlling the reaction via irradiation intensity. It is widely used to develop materials for applications in thin films, coatings, printing, artwork, dental materials, contact lenses, and electronics. 40 To create microporous materials, several groups have employed photopolymer−solvent mixtures that upon irradiation undergo a polymerization-induced phase separation (PIPS), 41−44 where after removing the solvent produces a microporous surface structure. While characteristi- cally straightforward and scalable, presently only random porous structures are attained, and this inhibits their engineer- ing to a degree at which finely tuned structure−property relations may be established. In terms of surface design, Received: October 22, 2017 Accepted: December 26, 2017 Published: January 10, 2018 Research Article www.acsami.org Cite This: ACS Appl. Mater. Interfaces 2018, 10, 3094-3105 © 2018 American Chemical Society 3094 DOI: 10.1021/acsami.7b16003 ACS Appl. Mater. Interfaces 2018, 10, 3094−3105