Bradley J. Sparks

Superhydrophobic Hybrid Inorganic-Organic Thiol-ene Surfaces Fabricated via Spray-Deposition and Photopolymerization

We report a simple and versatile method for the fabrication of superhydrophobic inorganic-organic thiol-ene coatings via sequential spray-deposition and photopolymerization under ambient conditions. The coatings are obtained by spray-deposition of UV-curable hybrid inorganic-organic thiol-ene resins consisting of pentaerythritol tetra(3-mercaptopropionate) (PETMP), triallyl isocyanurate (TTT), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (TMTVSi), and hydrophobic fumed silica nanoparticles. The spray-deposition process and nanoparticle agglomeration/dispersion provide surfaces with hierarchical morphologies exhibiting both micro- and nanoscale roughness. The wetting behavior, dependent on the concentration of TMTVSi and hydrophobic silica nanoparticles, can be varied over a broad range to ultimately provide coatings with high static water contact angles (>150°), low contact angle hysteresis, and low roll off angles (<5°). The cross-linked thiol-ene coatings are solvent resistant, stable at low and high pH, and maintain superhydrophobic wetting behavior after extended exposure to elevated temperatures. We demonstrate the versatility of the spray-deposition and UV-cure process on a variety of substrate surfaces including glass, paper, stone, and cotton fabric.

Synthesis of multifunctional polymer brush surfaces via sequential and orthogonal thiol-click reactions

Fabrication of multifunctional surfaces with complexity approaching that found in nature requires the application of a modular approach to surface engineering. We describe a versatile post-polymerization modification strategy to synthesize multifunctional polymer brush surfaces via combination of surface-initiated photopolymerization (SIP) and orthogonal thiol-click reactions. Specifically, we demonstrate two routes to multifunctional brush surfaces: in the first approach, alkyne-functionalized homopolymer brushes are modified with multiple thiolsvia a statistical, radical-mediated thiol-yne co-click reaction; and in the second approach, statistical copolymer brushes carrying two distinctly-addressable reactive moieties are sequentially modified via orthogonal base-catalyzed thiol-X (where X represents an isocyanate, epoxy, or α-bromoester) and radical-mediated thiol-yne reactions. In both cases, we show that surface properties, in the form of wettability, can be easily tuned over a wide range by judicious choice of brush composition and thiol functionality.

Thiol–isocyanate “click” reactions: rapid development of functional polymeric surfaces

Functional, micropatterned and multicomponent polymer brush surfaces can be rapidly fabricated via base-catalyzed thiol–isocyanate “click” reactions.

Spray-deposition and photopolymerization of organic-inorganic thiol-ene resins for fabrication of superamphiphobic surfaces.

Superamphiphobic surfaces, exhibiting high contact angles and low contact angle hysteresis to both water and low surface tension liquids, have attracted a great deal attention in recent years because of the potential of these materials in practical applications such as liquid-resistant textiles, self-cleaning surfaces, and antifouling/anticorrosion coatings. In this work, we present a simple strategy for fabricating of superamphiphobic coatings based on photopolymerization of hybrid thiol-ene resins. Spray-deposition and UV photopolymerization of thiol-ene resins containing hydrophobic silica nanoparticles and perfluorinated thiols provide a multiscale topography and low-energy surface that endows the surface with superamphiphobicity. The wettability and chemical composition of the surfaces were characterized by contact-angle goniometry and X-ray photoelectron spectroscopy, respectively. The hierarchical roughness features of the thiol-ene surfaces were investigated with field-emission scanning electron microscopy. Droplet impact and sandpaper abrasion tests indicate the coatings respectively possess a robust antiwetting behavior and good mechanical durability.

Sequential thiol click reactions: formation of ternary thiourethane/thiol-ene networks with enhanced thermal and mechanical properties.

We report the physical properties of thiol-ene networks modified with thiourethane or urethane linkages, either along the main chain or as a branched component in the network, respectively. Because of the robust and orthogonal nature of thiol-isocyanate and thiol-ene reactions, these networks can be formed in a two-step, one-pot synthesis. Resultant networks were characterized using dynamic mechanical analysis, mechanical testing and other complementary techniques. It was found that incorporating (thio)urethanes into the networks increased Tg, but also increased strain at break and toughness while decreasing cross-link density. The changes in physical properties are discussed in terms of a proposed dual network morphology. These facile modifications to thiol-ene networks demonstrate how molecular-level, nanoscale changes can have a profound influence on the macroscale properties through hierarchical development of network morphology.

Cyclic Tetravinylsiloxanetetraols as Hybrid Inorganic-Organic Thiol-ene Networks

In this work, organic-inorganic hybrid materials containing stable silanol functionalities were designed by incorporating cyclic tetravinylsiloxanetetraols into photopolymerized polymer networks via the thiol-ene reaction, with the intent of tailoring the thermal and mechanical properties of the resulting materials. The effects of the cyclic tetravinylsiloxanetetraols concentration on the thermomechanical properties and thermal stability of pentaerythritol triallyl ether/pentaerythritol tetra(3-mercaptopropionate) (APE-PETMP) and allyl isocyanurate/pentaerythritol tetra(3-mercaptopropionate) (TTT-PETMP) ternary networks were evaluated using dynamic thermomechanical analysis and thermogravimetric analysis, respectively. Photopolymerization kinetics were monitored using real-time FTIR. Interestingly, an increase in glass transition temperature was observed with the APE-PETMP networks while a decrease in glass transition temperature was observed for the TTT-PETMP networks with increasing concentration of [Vi(OH)SiO]4. These observations are discussed in terms of cross-link density and monomer rigidity.