Low Surface Free Energy Research Articles

Polysilazane‐Based Coatings with Anti‐Adherent Properties for Easy Release of Plastics and Composites from Metal Molds

AbstractPolysilazanes are excellent coating materials, because of their self‐crosslinking in air at low temperatures, high chemical and thermal stability, elevated hardness, and excellent adhesion to many different substrates. Therefore, coatings of two chemically different polysilazanes (crosslinked Durazane 1800 (HTTS)/perhydropolysilazane (PHPS)) are deposited by either dip or spray coating and crosslinked at 200 or 300 °C in air to investigate the chemical composition, surface energy, and coating adhesion in dependency on the precursor type and crosslinking temperature. The silazane HTTS possesses a higher amount of nonpolar organic groups resulting in a lower surface free energy. The anti‐adherence properties are investigated by using a phenolic resin via pull‐off adhesion, which is slightly reduced from 13 MPa for uncoated aluminum to less than 10 MPa for HTTS coated substrates. The addition of different amounts of poly(tetrafluoroethylene) (PTFE) particles causes a remarkable reduction of the surface free energy leading to a strongly reduced pull‐off adhesion of less than 4 MPa of the phenolic resin from the HTTS/PTFE coated substrates. The anti‐adherent properties remain even after repeated pull‐off tests. Because of the excellent properties, the HTTS/PTFE coatings are a very suitable system for easy mold release of plastic parts from metal molds and to replace commercial nonstick PTFE coatings.

Preparation of Fluorine-Free Superhydrophobic Cotton Fabric with Polyacrylate/SiO₂ Nanocomposite.

Fluorine-free superhydrophobic cotton fabric was fabricated by coating polyacrylate (PA)/SiO₂ nanocomposite. PA/SiO₂ nanocomposite was prepared based on the modified SiO₂ nanoparticles with double bonds and hexadecyl groups by solution polymerization of butyl acrylate (BA), methyl methacrylate (MMA) and octadecylmethacrylate (OMA). The obtained cotton fabric showed excellent superhydrophobicity with a water contact angle of 152.2±0.4° and a water shedding angle of 8.0±0.2°, due to the simultaneous introduction of surface topography constructed by modified SiO₂ nanoparticles and low surface free energy PA adhesive layer and hexadecyl groups onto cotton fibers. The as-obtained products were characterized by Fourier-transform infrared spectrometry (FT-IR), thermal gravimetric analysis (TG), scanning electron microscopy (SEM) and size distribution analysis. The obtained superhydrophobic fabric coated by PA/SiO₂ demonstrated good mechanical stability and self-cleaning. The PA/SiO₂ coating treatment caused little loss in the tensile strength, breathability, and whiteness of the treated fabric. This approach with improved human/environmental friendliness can pave the potential way for the preparation of superhydrophobic surfaces.

Liquid-Repellent Films Comprising Octamethylsilsesquioxane Selected Based on Three-Dimensional Solubility Parameters.

On the basis of Hansen solubility parameters (HSP), we investigated octamethylsilsesquioxane (OMS), a siloxane compound with a cage-like structure and methyl side chains, as an omniphobic substance. The HSP of OMS were determined through dissolution tests to be similar to those of polytetrafluoroethylene (PTFE), leading to the prediction that films comprising OMS should possess liquid-repellency comparable to films comprising PTFE. Indeed, an electroless-plated Ni-P film composite with OMS particles (Ni-P/OMS film) exhibited liquid-repellency comparable to or higher than that of the Ni-P film composite with PTFE particles, except toward 1-bromonaphthalene, which has a low surface free energy. Moreover, the hydrophilic influence of the Ni-P matrix was eliminated by the use of polydimethylsiloxane (PDMS) as the matrix instead of Ni-P, resulting in enhanced liquid-repellency and water-sliding behavior of the solution-sprayed PDMS film composite with the OMS particles (PDMS/OMS film). These films comprising OMS particles are promising candidates for nonfluorinated liquid-repellent films.

Comparison of bacterial adhesion and biofilm formation on zirconia fabricated by two different approaches: an in vitro and in vivo study

ABSTRACT Prepared by dry and wet approaches, respectively, the surface properties and bacterial adhesion of conventional zirconia (CZ) and self-glazed zirconia (SGZ) were investigated. Each zirconia was divided into unpolished and polished groups. Our results revealed that SGZ showed significantly lower surface roughness than CZ (P < 0.05) and lower surface-free energy (P < 0.05) in both polished and unpolished groups. The number of bacteria attached to SGZ was less than CZ in vitro (P < 0.05), but no significant difference was found between two kinds of zirconia in vivo (P > 0.05). Our findings suggest that SGZ, due to its excellent surface characteristics, is superior to CZ in bacterial adhesion and zirconia polishing serves as an indispensable procedure in clinics.

Silicone-Based Fouling-Release Coatings for Marine Antifouling

Marine biofouling profoundly influences marine industries and activities. It slows the speed and increases the fuel consumption of ships, corrodes offshore platforms, and blocks seawater pipelines. The most effective and economical antifouling approach uses coatings. Fouling-release coatings (FRCs) with low surface free energy and high elasticity weakly adhere to marine organisms, so they can be readily removed by the water shear force. FRCs have attracted increasing interest because they are biocide-free and hence ecofriendly. However, traditional silicone-based FRCs have weak adhesion to substrates, low mechanical strength, and low fouling resistance, limiting their applications. In recent years, many attempts have been made to improve their mechanical properties and fouling resistance. This review deals with the progress in the construction of high-performance silicone-based fouling-release surfaces.

Naturally pre-designed biomaterials: Spider molting cuticle as a functional crude oil sorbent

Diverse fields of modern environmental technology are nowadays focused on the discovery and development of new sources for oil spill removal. An especially interesting type of sorbents is those of natural origin—biosorbents—as ready-to-use constructs with biodegradable, nontoxic, renewable and cost-efficient properties. Moreover, the growing problem of microplastic-related contamination in the oceans further encourages the use of biosorbents. Here, for the first time, naturally pre-designed molting cuticles of the Theraphosidae spider Avicularia sp. “Peru purple”, as part of constituting a large-scale spider origin waste material, were used for efficient sorption of crude oil. Compared with currently used materials, the proposed biosorbent of spider cuticular origin demonstrates excellent ability to remain on the water surface for a long time. In this study the morphology and hydrophobic features of Theraphosidae cuticle are investigated for the first time. The unique surface morphology and very low surface free energy (4.47 ± 0.08 mN/m) give the cuticle-based, tube-like, porous biosorbent excellent oleophilic–hydrophobic properties. The crude oil sorption capacities of A. sp. “Peru purple” molt structures in sea water, distilled water and fresh water were measured at 12.6 g/g, 15.8 g/g and 16.6 g/g respectively. These results indicate that this biomaterial is more efficient than such currently used fibrous sorbents as human hairs or chicken feathers. Four cycles of desorption were performed and confirmed the reusability of the proposed biosorbent. We suggest that the oil adsorption mechanism is related to the brush-like and microporous structure of the tubular spider molting cuticles and may also involve interaction between the cuticular wax layers and crude oil.

Mechanically durable biomimetic fibrous membrane with superhydrophobicity and superoleophilicity for aqueous oil separation

Developing an effective and mechanically durable biomimetic membrane for the separation of highly emulsified aqueous oil is significant but challenging owing to its low water flux and serious membrane fouling. In this work, a biomimetic membrane with superhydrophobicity and superoleophilicity was rationally developed via co-electrospinning of polysulfonamide/polyacrylonitrile (PSA/PAN) emulsion solution, followed by decorating of α-Fe2O3 nanowire onto the membrane surface to create membrane roughness, and grafting of 1H,1H,2H,2H-perfluorododecyltrichlorosilane (FTCS) to lower membrane surface free energy. Benefiting from the nanowire-wrapped rough membrane structure and the low surface free energy FTCS, the resultant membrane showed superhydrophobicity with a high water contact angle (WCA) of 156°, superoleophilicity with a low oil contact angle (OCA) of 0°, which can separate the highly emulsified aqueous oil with an ultrahigh permeation flux over 7000 L m−2 h-1 and high separation efficiency of about 99%. Significantly, the biomimetic membrane also displayed robust stability for long-term separation owing to its advantage of antifouling property, showing great potential applications in large-scale aqueous oil treatment.

Surface free energy analysis for stable supercooling of sodium thiosulfate pentahydrate with microcosmic-visualized methods

A novel method of microcosmic-visualizing was employed in investigating the supercooling stability of a phase change material (PCM). The supercooling behavior of the PCM under circumstances of different surface free energy was studied both dynamically and statically, and a theory analysis of how the surface free energy of the substrate affects the stable supercooling of PCM was carried out. The results showed that, the PCM droplets phase changed after a 20-cm free fall on substrate with larger surface free energy, while remained supercooled on substrate with lower surface free energy. The PCM in PTFE container initiated crystallization at −8.99 °C, withstood over 400% on hours at liquid state compared with the sample in glass container, while a large supercooling degree of over 57 °C was achieved. It indicated that containers made of materials with lower surface free energy could be considerably beneficial in stabilizing supercooling of PCMs, which could give a guide to the practical application on long-term energy storage of PCMs. What is more, the surface free energy theory also works on the air-liquid interface. The oil-covered PCM sample withstood a temperature of 5 °C for 10 months without crystalized in a refrigerator, showing great potential on supercooling stabilization.

Engineering construction of robust superhydrophobic two-tier composite membrane with interlocked structure for membrane distillation

The major challenge in membrane distillation for seawater desalination and/or wastewater purification is the development of high-efficiency membrane distillation (MD) membranes with high porosity, hydrophobicity, and adequate mechanical strength for long-term operation. Herein, a superhydrophobic two-tier interlocked composite membrane based on a hierarchically structured isotactic polypropylene (iPP) coating and an electrospun poly(vinylidene fluoride) (PVDF) nanofibrous support was engineering constructed. The obtained coating layer possessed a deformed micro/nanostructured microsphere surface with robust superhydrophobicity and further glorious anti-fouling property, which was owed to the synergistic effect of the low surface free energy material and hierarchical roughness. Specially, the middle transitional interlocking zone between the crystalline iPP microsphere coating and PVDF nanofibers endowed the resultant composite membrane with excellent structural integrity including the remarkable enhancement in mechanical performance compared with PVDF flat sheet or nanofibrous membranes, and also resulted in the iPP/PVDF composite membranes with robust durability against ultrasonication in isopropanol and strong acid/base attacks. Moreover, for the simulated high salinity sunset yellow (SY) wastewater, the optimized superhydrophobic composite membrane exhibited a competitive permeate flux of 53.9 kg/(m2·h) and complete rejection over 50 h operation (ΔT = 40 °C) because of its highly porous nanofibrous support and firmly sustainable liquid repellency.

Polyfluoroalkyl-silica porous coatings with high antireflection properties and low surface free energy for glass in solar energy application

Polyfluoroalkyl-silica porous coating stacks with durable antireflection (AR) properties have been obtained for photovoltaic (PV) application. An acid-catalyzed sol-gel process combined with evaporation induced self-assembly and the presence of a non-hydrolyzable polyfluoroalkyl group linked to the central atom of the silicon alkoxide was conducted. The aim was to obtain a low surface energy coating, devised to mitigate soiling adherence, without losing the AR properties of a baseline coating. In particular, the influence of polyfluoroalkyl chain length on the thickness, the water contact angle and optical transmission properties was first analyzed. The optimized polyfluoroalkyl-silica porous coating presented low surface energy < 20 mJ/m2, even with the desired low roughness values required for obtaining a negligible scattering of the incoming solar radiation. This coating was studied as an AR mono-layer and as an external coating in an AR bi-layer stack, with the presence of an inner dense-structured silica layer, that contributed to both the optical performance and durability, acting as an alkali diffusion preventing layer. The AR bi-layer stack deposited on two sides of glass provided a transmittance gain of 7.1%. Those optical properties were inalterable after accelerated aging tests, which sustains the reliability of the materials for solar energy applications.

Correlation between physical bonding and mechanical properties of wood–plastic composites: part 2: effect of thermodynamic factors on interfacial bonding at wood–polymer interface

The main objective of this study was to find out if there is any significant correlation between physical properties and interfacial bonding of interphases in wood–plastic composites. To this end, high-density polyethylene (HDPE), mixture of 3% maleic anhydride grafted polyethylene (MAPE) and HDPE (coded as MHDPE) and polylactic acid (PLA) were separately interacted with veneers to identify factors underlying interfaces. Plastics were first melted at 180 °C and dispensed on wood surfaces so that the contact angle (CA) could be directly measured. Wood sanding moderately decreased the CAs of plastics in order of PLA, MHDPE, and HDPE. The treatment of veneers with MAPE comprehensively improved wetting, as the CA of HDPE was significantly reduced on the wood surface after the treatment. Thereafter, the interfacial shear strengths (IFSS) of the wood–polymer interface were determined using the automated bonding evaluation system. PLA had the highest IFSS both for unsanded and sanded veneers. Comparing both parts of this research finally revealed that applying sanding or/and MAPE treatments resulted in lower surface free energy and higher IFSS at the wood–polymer interface. However, our observations support the idea that, at higher temperatures, wetting of composites is mainly influenced by polymer properties rather than interfacial tension at the wood–polymer interface.

Effects of Finishing and Polishing Methods on the Surface Roughness and Surface Free Energy of Bulk-fill Resin Composites.

The purpose of this study was to determine the influence of finishing and polishing methods on surface properties of bulk-fill resin composites through surface roughness (Ra) and surface free energy (SFE) measurements, and scanning electron microscopy (SEM) observations. Three bulk-fill resin composites, Tetric EvoCeram Bulk Fill (TB), Filtek Bulk Fill (FB), and Filtek Bulk Fill Flowable Restorative (FF), and two conventional resin composites, Clearfil AP-X (AP) and Estelite ∑ Quick (EQ) were used. Seventy cured specimens of each resin composite were prepared and divided into seven groups of 10 specimens. Ra, SFE measurements, and SEM observations were conducted after finishing and polishing procedures. Three groups of specimens were finished with a fine grit diamond bur (FDB), and three with a tungsten carbide bur (CBB). After finishing, one group from each type of finishing was polished with aluminum oxide flexible disks (SSD) and one group from each type of finishing was polished with diamond particles embedded in a silicone point (CMP). A baseline group of samples that were neither finished nor polished after removing the translucent strips from the surface was examined. Although the baseline group showed significantly lower Ra values than the other groups, most resin composites showed lower Ra values with CBB+SSD than with the other finishing and polishing groups. Among the tested resin composites, EQ showed significantly lower Ra values than the other resin composites, regardless of the finishing and polishing methods. On the other hand, AP showed significantly higher Ra values than the other resin composites in all finishing and polishing groups, apart from FB with FDB. For the finished specimens, most resin composites showed higher SFE values with CBB than with FDB. For the polished specimens, all the tested resin composites with CMP showed lower γS values than those with SSD, regardless of the finishing method. The baseline groups of TB and FB showed significantly lower SFE values than the other finished and polished groups. In the SEM observations, all the examined resin composites showed rougher surfaces after finishing with FDB than with CBB. However, when comparing the different polishing methods (CMP and SSD), surface smoothness appeared to be material dependent.

The investigation of de-icing and uni-directional droplet driven on a soft liquid-metal chip controlled through electrical current

To realize the functions of de-icing and self-propelling of droplet, one soft and superhydrophobic microfluidic chip (SMC) equipped with the liquid metal was successfully fabricated in this work. After modification via nanostructures and lower surface free energy cover, the SMC surface shows self-cleaning performance. The surface not only could realize self-propelling of droplet at room temperature but also uni-directional de-icing even −30 °C after melting. The results indicate the driving force is induced by the thermal gradient, which is generated by resistance heating of liquid metal (GaIn24.5). This study is significant for extending the applications of microfluidic chip in low temperature condition.

Correlation between physical bonding and mechanical properties of wood plastic composites: Part 1: interaction of chemical and mechanical treatments on physical properties

This study investigated the mode of action between wood and thermoplastic interphases. For this purpose, the effect of sanding and chemical treatments on the wood surface wettability has been simultaneously evaluated. Contact angle measurements were tested on wood veneers (spruce) using Van Oss-Chaudhury-Good (VOCG) method to determine the surface free energies (SFE). To better understand the mechanism of treatments on the physical interactions, veneers were either/both sanded or/and treated by maleic anhydride grafted with polyethylene (MAPE) so that the analysis of surface pre-coating and its influence on the polarity and the dispersive properties of the wood-polymer interface can be further studied. The results showed a significant increment of both surface roughness and interfacial area after sanding which improved pre-coating of plastic on the wood surface consequently. Analysis of wetting parameter showed compatibility between two types of surface modification, as the treatment of veneers by sanding and MAPE together resulted in higher contact angles and lower surface free energy (SFE) on the wood surfaces. MAPE could entirely cover the wood veneers and form a non-polar surface, which suggests the effectiveness of this chemical and its compatibility with the sanding operation on the wood surface.

Giant Rashba spin splitting induced by heavy element adsorption at germanene

Density functional theory calculations have been performed to investigate the structural and electronic properties of the Pb@germanene adsorption system. By employing equilibrium ab initio atomistic thermodynamics and phonon spectra analysis a dynamically stable configuration have been found. It is a (1 × 1) structure with coverage of 1 monolayer [(1×1)′@germanene]. The surface configuration shares some structural similarities with the sTable (1 × 1) phase of Pb@Ge(111), however, it favors a different adsorption site, and facilitates more Pb–Ge bonds per adsorbed atom. This results in (1×1)′@germanene having lower surface free energy than its Ge(111) counterpart. The electronics have been investigate using both GGA-type PBE and hybrid HSE functionals in order to ensure the accuracy. In both cases the system is a metal. Strong spin-orbit interaction of electrons in Pb facilitates a giant spin splitting of metallic bands up to 646 meV at the Fermi level, which makes the system an interesting platform for two-dimensional spintronics.

Transitions of component, physical, rheological and self-healing properties of petroleum bitumen from the loose bituminous mixture after UV irradiation

In the bituminous mixture, the petroleum bituminous film wrapped in the surface of aggregate is very thin, which is obviously different from the neat bitumen. In this research, the most commonly used dense bituminous mixture (AC-13) was designated for the ultraviolet (UV) irradiation simulation test. The loose bituminous mixture was exposed under the UV irradiation for 7, 14 and 28 days respectively, and the UV irradiation intensity was 21.0 w/m2. After aging, the bitumen was recovered with the centrifuge separation method, the SARA components of the recovered bitumen (RB) was studied by the Thin-layer chromatography with flame ionization detection (TLC-FID). Meanwhile, the physical and rheological performance of the RB was investigated by the three major conventional indices and dynamic shearing parameters. In addition, the self-healing performance of bitumen was characterized by complex viscosity frequency-sweep test, capillary test and surface energy test before and after UV irradiation. The results show that with the extension of UV irradiation time, the chemical components of RB change obviously, which results in the deterioration of its colloid stability. Meanwhile, the physical and rheological performance of RB transitioned significantly (the decreases of penetration, ductility and phase angle of RB, and the increase of the softening point and complex modulus), indicates the RB becomes more embrittlement and hardening. Also, the worse flow behavior, the worse capillary fluidity and the lower surface free energy of RB result in the degradation of the self-healing performance of bituminous concrete.

Enhancement of Polyvinyl Acetate (PVAc) Adhesion Performance by SiO2 and TiO2 Nanoparticles

Post press processes include various types of bonding and adhesives, depending upon the nature of adherends, the end use performance requirements and the adhesive bonding processes. Polyvinyl acetate (PVAc) adhesive is a widely used adhesive in the graphic industry for paper, board, leather and cloth. In this study, the enhancement of PVAc adhesion performance by adding different concentrations (1%, 2% and 3%) of silica (SiO2) and titanium dioxide (TiO2) nanoparticles was investigated. The morphology of investigated paper-adhesive samples was analyzed by SEM microscopy and FTIR spectroscopy. In addition, the optimal adhesion at the interface of paper and adhesive was found according to calculated adhesion parameters by contact angle measurements (work of adhesion, surface free energy of interphase, wetting coefficient). According to obtained surface free energy (SFE) results, optimum nanoparticles concentration was 1%. The wettability of the paper-adhesive surface and low SFE of interphase turned out as a key for a good adhesion performance. The end use T-peel resistance test of adhesive joints confirmed enhancement of adhesion performance. The highest strength improvement was achieved with 1% of SiO2 nanoparticles in PVAc adhesive.

Fabrication of a super hydrophobic polyvinylidene fluoride–hexadecyltrimethoxysilane hybrid membrane for carbon dioxide absorption in a membrane contactor

To obtain a super hydrophobic hollow fiber membrane for using in membrane contact absorption of carbon dioxide (CO2), hybrid polyvinylidene fluoride-hexadecyltrimethoxysilane (PVDF–HDTMS) membranes were fabricated via the non-solvent induced phase-inversion method with ammonia water as the non-solvent additive and dehydrofluorination reagent, and HDTMS as the hydrophobic modifier. The membranes exhibited super-hydrophobicity which was attributed to the formation of rough nanoscale microstructure and low surface free energy of the outer surface. The largest contact angle of water and diethanolamine (DEA) on the membrane outer surface attained 150°. Scanning electron microscopy images revealed that the membrane outer surfaces consisted of rough microscale hierarchical spherulitic particles with a nanoscale stereoscopic coralliform microstructure. Attenuated total reflectance–Fourier transform infrared spectroscopy of the membranes indicated that the HDTMS chains grafted in the PVDF were mainly located on the outer layer of the hollow fiber membranes. The membranes showed excellent CO2 mass transfer flux compared to our previously fabricated membrane with 8 wt % of phosphoric acid as the non-solvent additive in the dope (PVDF-PA-8). The membrane contactor with the membrane obtained by adding 1.5 wt% of HDTMS in the dope achieved the maximum CO2 mass transfer flux of 2.23 × 10−3 mol/m2s with the inlet gas (CO2/N2 = 19/81, v/v) at a flow rate of 20 mL/min and the absorbent liquid (1 mol/L DEA) at a flow rate of 50 mL/min. CO2 mass transfer flux of this membrane decreased by 17% after 17 days of operation and then remained stable.

M35 USING LONGITUDINAL DATA TO REFINE MAJOR DEPRESSIVE DISORDER CASE AND CONTROL STATUS INCREASES THE PRECISION OF POLYGENIC RISK SCORES

Density functional theory calculations have been performed to investigate the structural and electronic properties of the [email protected] adsorption system. By employing equilibrium ab initio atomistic thermodynamics and phonon spectra analysis a dynamically stable configuration have been found. It is a (1 × 1) structure with coverage of 1 monolayer [(1×1)′@germanene]. The surface configuration shares some structural similarities with the sTable (1 × 1) phase of [email protected](1 1 1), however, it favors a different adsorption site, and facilitates more Pb–Ge bonds per adsorbed atom. This results in (1×1)′@germanene having lower surface free energy than its Ge(1 1 1) counterpart. The electronics have been investigate using both GGA-type PBE and hybrid HSE functionals in order to ensure the accuracy. In both cases the system is a metal. Strong spin-orbit interaction of electrons in Pb facilitates a giant spin splitting of metallic bands up to 646 meV at the Fermi level, which makes the system an interesting platform for two-dimensional spintronics.

Regulating the performance of polybenzoxazine via the regiochemistry of amide substituents

A new strategy for the property regulation of polybenzoxazine via the regiochemistry of amide substituents was reported in this work. After the benzoxazine isomers, 2,6BAP-abz and 3,5BAP-abz, were synthesized, their chemical structures were confirmed by NMR, FT-IR and MS spectra. Then, how does the regiochemistry of amide substituent regulate the curing behaviors of benzoxazine monomers, as well as the thermal properties and flame retardancy of cured resins, poly(2,6BAP-abz) and poly(3,5BAP-abz), were investigated. Results showed that the intramolecular H-bonding involved with the ortho-CONH and O in oxazine ring in 3,5BAP-abz was much stronger than that in 2,6BAP-abz, which was responsible for its higher curing reactivity. As for the cured resin, poly(2,6BAP-abz) demonstrated higher glass transition temperature (Tg) and lower surface free energy (SFE) due to the formation of more intramolecular N–H⋯N interaction between pyridine and ortho-CONH. In addition, this H-bonding was also related with the oxazole ring formation temperature and fire retardancy of poly(2,6BAP-abz) and poly(3,5BAP-abz). Overall, a deeper insight into the effect of regiochemistry on properties of polybenzoxazine was achieved.