Ha Soo Hwang

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-PDMS_1.92 (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-PDMS_1.92 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.

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.

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.

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.

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.

Ferroaluminophosphate (FAPO₄‐5)/MgSO₄ composites were prepared as a series of new materials with low charging temperatures and improved volumetric heat storage capacities. A microporous zeolithic compound FAPO₄‐5 was used as an adsorbent of water vapor and a matrix of MgSO₄ salt particles. Composites with various MgSO₄ contents (5‐40 wt%) were then prepared using a wet impregnation method. The MgSO₄ salt particles were impregnated into the micropores and textural pores of FAPO₄‐5 without the crystal structure of the host material, confirmed by XRD patterns. Although nitrogen adsorption isotherms of the composites showed approximately a half of FAPO₄‐5 pore was blocked by MgSO₄, the water uptake of the composites reached the sum of those from FAPO₄‐5 and MgSO₄. The dehydration temperature of MgSO₄ in the FAPO₄‐5 matrix decreased with its decreasing content due to the easier dehydration of FAPO₄‐5. The heat storage recovery of the 25 wt% loaded sample at 80°C was 85.5% while that of MgSO₄ was 52.2%. The swelling and agglomeration of the composites containing 25 wt% and less salt were suppressed by the micro and textural pores of FAPO₄‐5. The composite at 25 wt% of MgSO₄ loading exhibited a total volumetric heat storage capacity of 174 kW h m⁻³ based on the volume in the hydrated state.

Poly(oxyethylene methacrylate) (POEM) anchored TiO₂ nanoparticles were synthesized via the surface thiol-lactam initiated radical polymerization of POEM in the presence of thiol functionalized TiO₂ nanoparticles. The grafting of POEM onto the surface of TiO₂ nanoparticles was investigated by FT-IR, XPS, EDX, TGA, XRD, and TEM analyses. The experimental findings suggested that a strong interaction prevailed between grafted POEM and TiO₂ nanoparticles. The TEM image of POEM-g-TiO₂ showed that the agglomeration propensity of TiO₂ nanoparticles was reduced significantly upon the functionalization of POEM. Moreover, an improved thermal property of the POEM in the POEM-g-TiO₂ nanocomposites was observed by TGA.