Transparent Organogel Films Showing Extremely Efficient and Durable Anti-Icing Performance.

Accumulation of ice and snow on solid surfaces causes destructive problems in our daily life. Therefore, the development of functional coatings/surfaces that can effectively prevent ice/snow adhesion by natural forces, such as airflow, vibration, solar radiation, or gravity, is in high demand. In this study, transparent organogel films possessing negligible ice adhesion strength were successfully designed by a simple cross-linking of poly(dimethylsiloxane) (PDMS) in the presence of commercially available oils.

Antiadhesive Properties of Oil-Infused Gels against the Universal Adhesiveness of Polydopamine.

Polydopamine (PDA) is well-known as the first material-independent adhesive, which firmly attaches to various substances, even hydrophobic materials, through strong coordinative interactions between the phenolic hydroxyl groups of PDA and the substances. In contrast, oil-infused materials such as self-lubricating gels (SLUGs) exhibit excellent antiadhesive properties against viscous liquids, ice/snow, (bio)fouling, and so on. In this study, we simply questioned: "What will happen when these two materials with contrary nature meet"? To answer this, we formed a PDA layer on a SLUG surface that exhibits thermoresponsive syneretic properties (release of liquid from the gel matrix to the outer surface) and investigated its interfacial behavior.

Spatially-Regulated Deposition of Quantum Dots on the Patterned Polymer Brush.

We have demonstrated direct patterning of surface initiator layer (SIL) for Atom Transfer Radical Polymerization (ATRP) using a sol-gel based "ink" containing (-chloromethyl)phenyltrimethoxysilane and tetraethoxysilane for an inkjet printer. Mechanically/chemically robust and smooth micropatterns of SIL several tens of micrometer in width and 15 nm thickness were directly printed on silicon substrates under mild conditions (open to the atmosphere, at ~28 °C under >60% relative humidity). Subsequent surface-initiated ATRP of glycidyl methacrylate (GMA) under the air atmosphere gave area-selective/stepwise growth of homogeneous polyGMA brushes (GMA) from the micropatterns of SIL.

Smooth and Transparent Films Showing Paradoxical Surface Properties: The Lower the Static Contact Angle, the Better the Water Sliding Performance.

Smooth and transparent hydrophilic films showing excellent water sliding properties were prepared by using a sol-gel solution of 2-[methoxy (ethyleneoxy) propyl]trimethoxysilane and tetraethoxysilane. The resulting hybrid films were statically hydrophilic (static water contact angles (CAs) were in the range of 30-45°), but water droplets (50 μL) could move smoothly on an inclined surface (minimum sliding angle was 6°) without pinning or tailing because of low CA hysteresis (5 ± 1°). Thanks to this hybrid film formation on aluminum (Al) substrate, drainage performance during condensation and frosting/defrosting markedly improved compared to that on hydrophilic, bare Al, or hydrophobic monolayer-covered Al substrates.

Omniphobic Metal Surfaces with Low Contact Angle Hysteresis and Tilt Angles.

Various metal (Al, Ti, Fe, Ni, and Cu) surfaces with native oxide layers were rendered "omniphobic" by a simple thermal treatment of neat liquid trimethylsiloxy-terminated polymethylhydrosiloxanes (PMHSs) with a range of different molecular weights (MWs). Because of this treatment, the PMHS chains were covalently attached to the oxidized metal surfaces, giving 2-10 nm thick PMHS layers. The resulting surfaces were fairly smooth, liquid-like, and showed excellent dynamic omniphobicity with both low contact angle hysteresis (≲5°) and substrate tilt angles (≲8°) toward small-volume liquid drops (5 μL) with surface tensions ranging from 20.

Polyurethane-Based Ionogels Exhibiting Durable Thermoresponsive Optical Behavior Under High-Temperature Conditions.

Polyurethane (PU)-based transparent and flexible ionogels, showing unusual thermo-responsive optical properties, were successfully prepared by mixing PU-precursor and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI). Although the initial ionogels were transparent at room temperature, significant increases in opacity were observed with increasing temperature up to 120°C, because of macroscopic phase separation of the PU-matrix and hydrophobic EMIM-TFSI. In addition, the optical transition temperature could be arbitrarily controlled simply by varying the mixing ratio of EMIM-TFSI within the PU-matrix.

Self-Healing Superhydrophobic Materials Showing Quick Damage Recovery and Long-Term Durability.

Superhydrophobic coatings/materials are important for a wide variety of applications, but the majority of these man-made coatings/materials still suffer from poor durability because of their lack of self-healing ability. Here, we report novel superhydrophobic materials which can quickly self-heal from various severe types of damage. In this study, we used poly(dimethylsiloxane) (PDMS) infused with two liquids: trichloropropylsilane, which reacts with ambient moisture to self-assemble into grass-like microfibers (named silicone micro/nanograss) on the surfaces and low-viscosity silicone oil (SO), which remains within the PDMS matrices and acts as a self-healing agent.

Transparent gel composite films with multiple functionalities: Long-lasting anti-fogging, underwater superoleophobicity and anti-bacterial activity.

Transparent gel-based composite films with multiple functionalities, showing long-lasting anti-fogging properties, underwater superoleophobicity, and anti-bacterial activity were successfully prepared from polyvinylpyrrolidone (PVP) and aminopropyl-functionalized clay (AMP-clay). Due to the addition of glutaraldehyde (GA, cross-linker) into the PVP matrices, and AMP-functionalities to the substrate surfaces, both the adhesion properties in water and durability of the anti-fogging properties were significantly improved. In addition, this durability was also found to be markedly improved by increasing the film thickness via deposition of several PVP/AMP/GA layers, while still retaining excellent transparency.

Anti-Fogging/Self-Healing Properties of Clay-Containing Transparent Nanocomposite Thin Films.

Highly transparent antifogging films were successfully prepared on various substrates, including glass slides, silicon, copper and PMMA, by spin-coating a mixture of polyvinylpyrrolidone and aminopropyl-functionalized, nanoscale clay platelets. The resulting films were superhydrophilic and showed more than 90% transmission of visible light, as well as excellent antifogging and self-healing properties.

A multifunctional role of trialkylbenzenes for the preparation of aqueous colloidal mesostructured/mesoporous silica nanoparticles with controlled pore size, particle diameter, and morphology.

Both the pore size and particle diameter of aqueous colloidal mesostructured/mesoporous silica nanoparticles (CMSS/CMPS) derived from tetrapropoxysilane were effectively and easily controlled by the addition of trialkylbenzenes (TAB). Aqueous highly dispersed CMPS with large pores were successfully obtained through removal of surfactants and TAB by a dialysis process. The pore size (from 4 nm to 8 nm) and particle diameter (from 50 nm to 380 nm) were more effectively enlarged by the addition of 1,3,5-triisopropylbenzene (TIPB) than 1,3,5-trimethylbenzene (TMB), and the enlargement did not cause the variation of the mesostructure and particle morphology.

Continuous, High-Speed, and Efficient Oil/Water Separation using Meshes with Antagonistic Wetting Properties.

We report a novel oil/water separation device, allowing continuous, high-speed, and highly efficient purification of large volumes of oily water. This device uses a pair of hydrophilic/hydrophobic polymer-brush-functionalized stainless steel meshes, which have antagonistic wetting properties, i.e.

Polymer Brush Surfaces Showing Superhydrophobicity and Air-Bubble Repellency in a Variety of Organic Liquids.

Silicon (Si) substrates were modified with polyalkyl methacrylate brushes having different alkyl chain lengths (C(n), where n = 1, 4, 8, and 18) using ARGET-ATRP at ambient temperature without purging the reaction solution of oxygen. The dynamic hydrophobicity of these polymer brush-covered Si surfaces when submerged in a variety of organic solvents (1-butanol, dichloromethane, toluene, n-hexane) depended markedly on the alkyl chain length and to a lesser extent polymer solubility. Long-chain poly(stearyl methacrylate) brushes (C(n) = 18) submerged in toluene showed excellent water-repellant properties, having large advancing/receding contact angles (CAs) of 169°/168° with negligible CA hysteresis (1°).

An underwater superoleophobic surface that can be activated/deactivated via external triggers.

Poly[(2-dimethylamino)ethyl methacrylate] (pDMAEMA) brush surfaces were prepared using a facile aqueous Activators ReGenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET-ATRP) protocol at ambient temperature without any need to purge reaction solutions of oxygen. This produced underwater superoleophobic surfaces, which exhibited high advancing (θA, 164-166°) and receding (θR, 153-165°) contact angles (CAs) and low CA hysteresis (1-11°) with a variety of oils. Both in situ spectroscopic ellipsometry and dynamic CA measurements confirmed that pDMAEMA brush surfaces responded to three different external stimuli (pH, ionic strength, and temperature) by changing their thicknesses, degree of hydration, or their chemical composition.

Large-scale and environmentally friendly synthesis of pH-responsive oil-repellent polymer brush surfaces under ambient conditions.

Contrary to conventional ATRP, aqueous A(R)GET-ATRP at ambient temperature without deoxygenating reaction solutions is an extremely facile method to create polymer brushes. Using these techniques, extremely thick poly[2-(dimethylamino)ethyl methacrylate] polymer brushes can be prepared (∼700 nm), or reaction solutions can be low chemical-content, consisting of 99% v/v water. Based on these techniques, we have also developed an easy and inexpensive method, referred to as "paint on"-ATRP, that directly pastes reaction solutions onto various large-scale real-life substrates open to the air.

Why can organic liquids move easily on smooth alkyl-terminated surfaces?

The dynamic dewettability of a smooth alkyl-terminated sol-gel hybrid film surface against 17 probe liquids (polar and nonpolar, with high and low surface tensions) was systematically investigated using contact angle (CA) hysteresis and substrate tilt angle (TA) measurements, in terms of their physicochemical properties such as surface tension, molecular weight/volume, dielectric constant, density, and viscosity. We found that the dynamic dewettability of the hybrid film markedly depended not on the surface tensions but on the dielectric constants of the probe liquids, displaying lower resistance to liquid drop movement with decreasing dielectric constant (ε < 30). Interfacial analysis using the sum-frequency generation (SFG) technique confirmed that the conformation of surface-tethered alkyl chains was markedly altered before and after contact with the different types of probe liquids.

Critical roles of cationic surfactants in the preparation of colloidal mesostructured silica nanoparticles: control of mesostructure, particle size, and dispersion.

Mesoporous silica nanoparticles are promising materials for various applications, such as drug delivery and catalysis, but the functional roles of surfactants in the formation and preparation of mesostructured silica nanoparticles (MSN-as) remain to be seen. It was confirmed that the molar ratio of cationic surfactants to Si of alkoxysilanes (Surf/Si) can affect the degree of mesostructure formation (i.e.

Unusual dynamic dewetting behavior of smooth perfluorinated hybrid films: potential advantages over conventional textured and liquid-infused perfluorinated surfaces.

From a viewpoint of reducing the burden on the environment and human health, an alternative method for preparing liquid-repellent surfaces without relying on the long perfluorocarbons (C((X-1)/2)F(X), X ≥ 17) has been strongly demanded lately. In this study, we have successfully demonstrated that dynamic dewettability toward various probe liquids (polar and nonpolar liquids with high or low surface tension) can be tuned by not only controlling surface chemistries (surface energies) but also the physical (solid-like or liquid-like) nature of the surface. We prepared smooth and transparent organic-inorganic hybrid films exhibiting unusual dynamic dewetting behavior toward various probe liquids using a simple sol-gel reaction based on the co-hydrolysis and co-condensation of a mixture including a range of perfluoroalkylsilanes (FASX, C((X-1)/2)F(X)CH2CH2Si(OR)3, where X = 3, 9, 13, and 17) and tetramethoxysilane (Si(OCH3)4, TMOS).

Smooth perfluorinated surfaces with different chemical and physical natures: their unusual dynamic dewetting behavior toward polar and nonpolar liquids.

The effects of surface chemistry and the mobility of surface-tethered functional groups of various perfluorinated surfaces on their dewetting behavior toward polar (water) and nonpolar (n-hexadecane, n-dodecane, and n-decane) liquids were investigated. In this study, three types of common smooth perfluorinated surfaces, that is, a perfluoroalkylsilane (heptadecafluoro-1,1,2,2-tetrahydrooctyl-dimethylchlorosilane, FAS17) monomeric layer, an amorphous fluoropolymer film (Teflon AF 1600), and a perfluorinated polyether (PFPE)-terminated polymer brush film (Optool DSX), were prepared and their static/dynamic dewetting characteristics were compared. Although the apparent static contact angles (CAs) of these surfaces with all probe liquids were almost identical to each other, the ease of movement of liquid drops critically depended on the physical (solidlike or liquidlike) natures of the substrate surface.

Transparent and hard zirconia-based hybrid coatings with excellent dynamic/thermoresponsive oleophobicity, thermal durability, and hydrolytic stability.

Smooth, transparent, and extremely hard zirconia (ZrO2)-based inorganic-organic hybrid films showing excellent dynamic oleophobicity, thermal durability, and hydrolytic stability were successfully prepared through a simple combination of zirconium tetrapropoxide (Zr(O(CH2)2CH3)4) with stearic acids. In this study, we have particularly focused on the effects of stearic acid molecular architecture (linear-stearic acid (LSA) and branched-stearic acid (BSA)) on surface physical/chemical properties. Although, in each case, the resulting hybrid (Zr:LSA and Zr:BSA) films achieved by a simple spin-coating method were highly smooth and transparent, the final surface properties were markedly dependent on their molecular architectures.

Preparation of aqueous colloidal mesostructured and mesoporous silica nanoparticles with controlled particle size in a very wide range from 20 nm to 700 nm.

Particle size control of colloidal mesoporous silica nanoparticles (CMPS) in a very wide range is quite significant for the design of CMPS toward various applications, such as catalysis and drug delivery. Various types of CMPS and their precursors (colloidal mesostructured silica nanoparticles (CMSS)) with different particle sizes (ca. 20-700 nm) were newly prepared from tetraalkoxysilanes with different alkoxy groups (Si(OR)4, R = Me, Et, Pr, and Bu) in the presence of alcohols (R'OH, R' = Me, Et, Pr, and Bu) as additives.

A thermally stable, durable and temperature-dependent oleophobic surface of a polymethylsilsesquioxane film.

Polymethylsilsesquioxane (PMSQ) films prepared by a simple sol-gel reaction of methyltriethoxysilane were found to possess thermally stable, durable, and temperature-dependent oleophobic properties under high temperature (~350 °C) conditions.

Novel transparent zirconium-based hybrid material with multilayered nanostructures: studies of surface dewettability toward alkane liquids.

We have successfully prepared unique inorganic-organic hybrid materials that demonstrate excellent transparency and dewettability toward various alkane liquids (n-hexadecane, n-dodecane and n-decane) without relying on conventional surface roughening and perfluorination. Such coatings were made using a novel family of hybrid materials generated by substituting carboxylic acids, with a range of alkyl chain lengths (CH(3)(CH(2))(x-2)COOH where x = total carbon number, i.e.

How to reduce resistance to movement of alkane liquid drops across tilted surfaces without relying on surface roughening and perfluorination.

Alkylsilane-derived monolayer-covered surfaces generally display a reasonably good level of hydrophobicity but poor oleophobicity. Here, we demonstrate that the physical attributes of alkylsilane-derived surfaces (liquid-like or solid-like) are dependent on the alkyl chain length and density, and these factors subsequently have significant influence upon the dynamic dewetting behavior toward alkanes (C(n)H(2n+2), where n = 7-16). In this study, we prepared and characterized hybrid films through a simple sol-gel process based on the cohydrolysis and co-condensation of a mixture of a range of alkyltriethoxysilanes (C(n)H(2n+1)Si(OEt)(3), where n = 3, 6, 8, 10, 12, 14, 16, and 18) and tetramethoxysilane (TMOS).

A physical approach to specifically improve the mobility of alkane liquid drops.

Seamless control of resistance to liquid drop movement for polar (water) and nonpolar alkane (n-hexadecane, n-dodecane, and n-decane) probe liquids on substrate surfaces was successfully demonstrated using molten linear poly(dimethylsiloxane) (PDMS) brush films with a range of different molecular weights (MWs). The ease of movement of liquid drops critically depended on polymer chain mobility as it relates to both polymer MW and solvent swelling on these chemically- and topographically identical surfaces. Our brush films therefore displayed lower resistances to liquid drop movement with decreasing polymer MW and surface tension of probe liquid as measured by contact angle (CA) hysteresis and tilt angle measurements.