Icephobicity of Hierarchically Rough Aluminum Surfaces Sequentially Coated with Fluoroalkyl and PDMS Alkoxysilanes.

Superhydrophobic surfaces fabricated by grafting 1H,1H,2H,2H-heptadecafluorodecyl trimethoxysilane (FD-TMS) and polydimethylsiloxane triethoxysilane (PDMS-TES) onto a nano-micro hierarchical aluminum (Al) surface are considered to possess substantial anti-icing functionality, with delayed freezing and low ice-adhesion strength (IAS). Verifying the impacts of PDMS and the synergism of PDMS and FD on the anti-icing performance is the goal of this study. Roughness, one of the prerequisites for superhydrophobicity, was obtained by etching Al substrates in aqueous HCl, followed by immersion in boiling water. FD-TMS and PDMS-TES were then coated on the rough Al substrates layer by layer; a congener coated with a single layer was also prepared for comparison. The FD-PDMS1.92 (1.92 wt.%) coating, in which FD-TMS and PDMS-TES were used as primary and secondary coating materials, respectively, exhibited superior icephobicity, with the lowest IAS of 28 kPa under extremely condensing weather conditions (-20 °C and 70% relative humidity, RH) and the longest freezing delay time of 230 min (at -18 °C). These features are attributed to the incorporation of a dense coating layer with a low-surface-tension FD and the high mobility of PDMS, which lowered the contact area and interaction between the ice and substrate. The substrate coated with FD-PDMS1.92 exhibited improved durability with an IAS of 63 kPa after 40 icing/melting cycles, which is far less than that achieved with the FD single-layer coating.

Facile Synthesis of Fluorinated Polysilazanes and Their Durable Icephobicity on Rough Al Surfaces.

Superhydrophobic Al surfaces with excellent durability and anti-icing properties were fabricated by coating dual-scale rough Al substrates with fluorinated polysilazane (FPSZ). Flat Al plates were etched using an acidic solution, followed by immersion in boiling water to generate hierarchical micro-nano structures on their surfaces. The FPSZ coatings were synthesized by grafting 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS-17), a fluoroalkyl silane), onto methylpolysilazane, an organopolysilazane (OPSZ) backbone. The high water contact angle (175°) and low sliding angle (1.6°) of the FPSZ-coated sample with an FAS-17 content of 17.3 wt% promoted the efficient removal of a frozen ice column with a low ice adhesion strength of 78 kPa at -20.0 °C (70% relative humidity), which was 4.3 times smaller than that of an OPSZ-coated surface. The FPSZ-coated Al surface suppressed ice nucleation, leading to a decrease in ice nucleation temperature from -19.5 to -21.9 °C and a delay in freezing time from 334 to 4914 s at -19.0 °C compared with the OPSZ-coated Al surface. Moreover, after 40 icing-melting cycles the freezing temperature of a water droplet on the FPSZ-coated Al surface remained unchanged, whereas that on the FAS-17-coated Al surface increased from -22.3 to -20.7 °C. Therefore, the durability of the polymeric FPSZ coating was superior to that of the FAS-17 monolayer coating.

Changes in Mechanical Properties of Polyhydroxyalkanoate with Double Silanized Cellulose Nanocrystals Using Different Organosiloxanes.

Polyhydroxyalkanoate (PHA) is a biodegradable plastic with great potential for tackling plastic waste and marine pollution issues, but its commercial applications have been limited due to its poor processability. In this study, surface-modified cellulose nanocrystals were used to improve the mechanical properties of PHA composites produced via a melt-extrusion process. Double silanization was conducted to obtain hydrophobically treated CNC-based fillers, using tetraethyl orthosilicate (TEOS) and methyltrimethoxysilane (MTMS). The morphology, particle size distributions, and surface characteristics of the silanized CNCs and their compatibility with a PHA polymer matrix differed by the organosiloxane treatment and drying method. It was confirmed that the double silanized CNCs had hydrophobic surface characteristics and narrow particle size distributions, and thereby showed excellent dispersibility in a PHA matrix. Adding hydrophobically treated CNCs to form a PHA composite, the elongation at break of the PHA composites was improved up to 301%, with little reduction of Young's modulus, compared to pure PHA. Seemingly, the double silanized CNCs added played a similar role to a nucleation agent in the PHA composite. It is expected that such high ductility can improve the mechanical properties of PHA composites, making them more suitable for commercial applications.

Azelaic Acid/Expanded Graphite Composites with High Latent Heat Storage Capacity and Thermal Conductivity at Medium Temperature.

A novel azelaic acid/expanded graphite (AA/EG) phase change composite (PCC) was fabricated as a shape-stabilized phase change material (PCM) for latent heat storage at medium temperatures. The composite exhibited a low supercooling degree and high heat storage capacity. Despite the impregnation of a high quantity of AA (85 wt %) in the porous network of EG, there was no leakage of liquid AA. This was attributed to the capillary forces and surface tension forces. The pure AA exhibited a melting temperature of 108.0 °C, with an intrinsically low supercooling degree of 5.8 °C. The melting temperature of AA in the PCC decreased slightly to 105.8 °C, and there was a significant decrease in the supercooling degree to 1.0 °C. The AA/EG PCC exhibited a high latent heat storage capacity of 162.5 J/g, and there was a significant gap between the decomposition temperature and the phase change temperature range. Therefore, the composite exhibited high thermal stability during operations. The results of an accelerated thermal cycling test (200 cycles) indicated the high cycling durability and chemical stability of the PCC. The thermal conductivity of AA increased by 15.7 times after impregnation in EG, as compared to that of the pure AA, and thus, thermal kinetics of the PCC was improved. The results of a heat storage/release test with 15 g of the PCM revealed that the melting and solidification of the AA/EG PCC were 5.0-fold and 7.4-fold faster, respectively, than those of the pure AA. This was attributed to the high thermal conductivity of the PCC.

n-Octadecane/Fumed Silica Phase Change Composite as Building Envelope for High Energy Efficiency.

A novel n-octadecane/fumed silica phase change composite has been prepared as a building envelope with a high content of phase change material and improved energy efficiency. With a high porosity (88 vol%), the fumed silica provided sufficient space to impregnate a high quantity of n-octadecane (70 wt%). The composite exhibited high latent heat storage capacity (155.8 J/g), high crystallization fraction (96.5%), and a melting temperature of 26.76 °C close to that of pure n-octadecane. A 200 accelerated thermal cycle test confirmed good thermal reliability and chemical stability of the phase change composite. The thermal conductivity of n-octadecane was reduced by 34% after impregnation in fumed silica. A phase change composite panel was fabricated and compared to a commercial polystyrene foam panel. When used as the roof of a test room, the phase change composite panel more efficiently retarded heat transfer from a halogen lamp to the room and delayed the increase in the indoor temperature than that by the polystyrene panel. The indoor temperatures of the room with the phase change composite panel roof were 19.8 and 22.9 °C, while those with the polystyrene panel roof were 29.9 and 31.9 °C at 2200 and 9000 s after lamp illumination.

Effect of Silica Size and Content on Superamphiphobic Properties of Silica-Fluoropolymer Core-Shell Coatings.

We present a facile approach to fabricate superamphiphobic surfaces by spray coating silica-fluoropolymer core-shell particles without substrate pretreatment with an additional binder resin. A series of SiO2@poly(1H,1H,2H,2H-heptadecafluorodecyl methacrylate) (SiO2@PFMA) core-shell particles with core particles of different sizes were prepared via thiol-lactam initiated radical polymerization (TLIRP). The surface of each SiO2 particle with an average particle size of 12, 80, 150, and 350 nm was modified with (3-mercaptopropyl) trimethoxysilane and used as a seed for TLIRP. The SiO2@PFMA particles with various SiO2 sizes and contents were coated on aluminum substrates by a spray gun and then thermally treated to form a stable, rough composite layer. During the spray coating, the core-shell particles were aggregated by rapid evaporation of the solvent and then irregularly adhered to the substrate resulting in hierarchical structures. In the case of SiO2@PFMAs with low SiO2 contents, the roughness created mainly by the polymer shell disappeared during heat treatment. However, the substrates coated with SiO2@PFMAs with high SiO2 contents maintained the roughness even after heat treatment. The core-shell particles prepared with 12 nm SiO2 formed a stable superamphiphobic surface. The water/hexadecane contact and sliding angles on an aluminum plate coated with SiO2@PFMA, prepared using 12 nm silica at 46 wt% silica content (12 nm-SiO2(46)@PFMA), were 178.5°/159.2° and 1°/7°, respectively. The cross-cut tape test showed that adhesion between the 12nm-SiO2(46)@PFMA and the aluminum substrate was classified as 5B. A glass surface spray-coated with the core-shell composite particles exhibited transparent superhydrophobicity and translucent superamphiphobicity by controlling the concentration of the coating solution.

Facile fabrication of transparent superhydrophobic surfaces by spray deposition.

Herein, we present a one-step facile spray-deposition process for fabricating a new superhydrophobic surface with a novel statistical copolymer. The polymeric material is relatively inexpensive, easily prepared, transparent, solvent-processable, very simple, and applicable to rugged substrates. The materials presented herein also feature a near-perfect superhydrophobic surface with a static water contact angle of 178° and a transmittance of higher than 75% at 550 nm wavelength.

Fabrication of polymer-silica core-shell particles using copolymeric spheres prepared via precipitation polymerization.

Silica-coated polymeric particles were synthesized based on cationic colloidal particles which were prepared by precipitation polymerization of divinylbenzene in the presence of a cationic monomer, N-[3-(dimethylamino)propyl]methacrylamide. Negatively charged silica precursors were interacted with the cationic charged dimethylamine groups in colloidal particles. The resulting polymer/silica core/shell particles were characterized by scanning electron microscopy (SEM). Moreover, omniphobic particles were achieved by coupling reaction of the core/shell particles with nonafluorohexyl-triethoxysilane. Their water/oil static contact angles were investigated.

Synthesis of poly(methyl methacrylate)/ montmorillonite nanocomposites using a 3-D surfactant as an organic modifier.

Poly(methyl methacrylate)/Montmorillonite clay nanocomposites were synthesized via the free radical polymerization of methyl methacrylate in the presence of alkyl ammonium substituted polysilsesquioxane surfactant-modified clay and AIBN initiator in ethanol and aqueous ethanol solvent. MMT clay was initially cation exchanged with the surfactant to enhance its hydrophobicity and to expand the interlamellar spaces of silicate platelets. The 3-D structured surfactant and water molecules reduce the surface energy of the clay dramatically, which promotes miscibility of polymer/ clay nanocomposites. The intercalation and dispersion of clay were quantified by both X-ray diffraction and transmission electron microscopy, and the morphologies of the nanocomposites were observed by scanning electron microscopy. Both the alkyl ammonium polysilsesquioxane surfactant and filler clay enhanced thermal and mechanical properties of the nanocomposites as investigated with thermo gravimetric analysis and differential scanning calorimetry.

Role of water on PMMA/clay nanocomposites synthesized by in situ polymerization in ethanol and supercritical carbon dioxide.

Poly(methylmethacrylate) (PMMA)/montmorillonite clay nanocomposites were synthesized via the free radical polymerization of MMA in the presence of alkyl ammonium substituted polysilsesquioxane surfactant-modified clay and AIBN initiator in supercritical CO(2) and ethanol. The reactions were also conducted by adding a small amount of water to observe the intercalation and exfoliation behavior of the clay and the properties of the nanocomposites. Initially, clay was cation exchanged with the surfactant to enhance its hydrophobicity and to expand the interlamellar spaces of silicate platelets. Organophilization with the three dimensional surfactant and a small amount of water molecules in the solvent reduced the surface energy of clay dramatically, which promoted the miscibility of polymer/clay nanocomposites. The morphology of the nanocomposites was characterized by scanning electron microscopy. The intercalation and dispersion of the clay were quantified by both X-ray diffraction and transmission electron microscopy. Due to the three dimensional structure, alkyl ammonium substituted polysilsesquioxane surfactant gives stable clay separation and dimension stability of the nanocomposites. Different distribution of the clay also plays an important role in physical properties. Thermogravimetric analysis and differential scanning calorimetry were employed to investigate the thermal properties and glass transition temperature of the nanocomposites.

Acid-sensitive semiperfluoroalkyl resorcinarene: an imaging material for organic electronics.

An acid-sensitive semiperfluoroalkyl resorcinarene was synthesized, and its lithographic properties were evaluated. Its solubility in segregated hydrofluoroether solvents enables the patterning of delicate organic electronic materials.

Critical flocculation density of dilute water-in-CO2 emulsions stabilized with block copolymers.

The critical flocculation density (CFD), that is, the CO(2) density below which flocculation occurs, was studied for dilute water-in-CO(2) (W/C) miniemulsions stabilized with poly(1,1-dihydroperfluorooctyl methacrylate)-b-poly(ethylene oxide) (PFOMA-b-PEO) surfactants. The CFD, which was measured by turbidimetry, decreased as the PFOMA molecular weight was increased, the average droplet size was decreased, the surfactant loading was increased, and the temperature was increased. A simple model, which addressed both the van der Waals attraction between droplets and osmotic solvent-tail interactions, was in good qualitative agreement with the experimentally observed trends for the CFD and predicted a decrease in emulsion stability as the CO(2) density was lowered toward the theta density for PFOMA in bulk CO(2).

Inverse Opal Nanocrystal Superlattice Films.

We describe the single-step self-organization of nanocrystal superlattice films infused with spatially ordered arrays of micrometer-size pores. In a humid atmosphere, water droplets condense on the surface of evaporating thin-film solutions of nanocrystals. Nanocrystals coated with the appropriate ligands stabilize the water droplets, allowing them to grow to uniform size and ultimately pack into very ordered arrays. The droplets provide a temporary template that casts an ordered macroporous nanocrystal film. This process could serve as a reliable bottom-up self-assembly approach for fabricating two-dimensional waveguides with tunable optical properties for single-chip integration of photonic and electronic technologies.

Synthesis of TiO2 nanoparticles utilizing hydrated reverse micelles in CO2.

Titanium dioxide nanoparticles were produced by the controlled hydrolysis of titanium tetraisopropoxide (TTIP) in the presence of reverse micelles formed in CO2 with the surfactants ammonium carboxylate perfluoropolyether (PFPECOO-+NH4) (Mw = 587) and poly(dimethyl amino ethyl methacrylate-block-1H,1H,2H,2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA). Based on dynamic light scattering measurements, the amorphous TiO2 particles formed by injection of TTIP are larger than the reverse micelles, indicating surfactant reorganization. The size of the particles and the stability of dispersions in CO2 were affected by the molar ratio of water to surfactant headgroup (w(o)), precursor concentration, and injection rate. The amorphous particle size did not change upon depressurization and redispersion in CO2. PDMAEMA-b-PFOMA provided greater stability against particle aggregation at higher reactant concentration compared with PFPECOO-+NH4. The crystallite size after calcination, which was examined by X-ray diffraction and transmission electron microscopy, increased with w(o).

Formation of TiO2 nanoparticles in water-in-CO2 microemulsions.

Titanium dioxide nanoparticles can be produced by the controlled hydrolysis of titanium tetraisopropoxide in water-in-CO2 (w/c) microemulsions stabilized with the surfactants ammonium carboxylate perfluoropolyether (PFPE-NH4) and poly(dimethyl amino ethyl methacrylate-block-1H,1H,2H,2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA); the greater control of hydrolysis and particle growth with PDMAEMA-b-PFOMA is consistent with the differences in the stabilities and interactions for these two microemulsions.