Search

Passive daytime radiation refrigeration (PDRR) is a new type of refrigeration that requires no extra energy consumption and also cools objects by reflecting radiant heat from sunlight and mid-infrared wavelengths. However, the properties of ordinary radiative refrigerative (RR) materials are degraded by surface dust accumulation during use. In this work, superhydrophobic radiative refrigerative (SRR) polytetrafluoroethylene/polyvinylidene fluoride (PTFE/PVDF) coating was prepared by one-step spraying method with PTFE as white pigment, PVDF as binder, and N, N-dimethylacetamide (DMAC) as solvent. The PTFE/PVDF coating (containing 20 wt% of PTFE) exhibits synergistic effect with high water contact angle (CA, 153.7°), low water sliding angle (SA, 7.7°), high solar reflectivity (SR, 93.7%), and high infrared emissivity (IE, 93.3%). Under a clear sky and direct sunlight, the coating achieves a RR temperatures of 5.8 °C (shielding convection heat) and 5.3 °C (without shielding convection heat) respectively under two measurement conditions. In addition, the coating exhibits excellent self-cleaning properties that can automatically remove dust accumulated on the surface with the assistance of rainfall, thus maintaining its RR performance for a long time. More importantly, the mechanical robust self-cleaning function also provides excellent corrosion resistance and anti-UV aging ability. The PTFE/PVDF SRR coating developed in this work is simple to fabricate, can be applied over a large area, and has good durability, which is conducive to promoting the practicalization of RR coatings. [Display omitted] • Superhydrophobic radiative refrigerative PTFE/PVDF coating was prepared by a one-step spraying method. • The PTFE/PVDF coating exhibits a water CA of 153.7° and a water SA of 7.7°. • The PTFE/PVDF coating achieves a RR temperature of − 5.8 °C under direct sunlight. • The PTFE/PVDF coating possessed robust superhydrophobicity and sustainable RR performance. [ABSTRACT FROM AUTHOR]

In the present work, superhydrophobic silver surface was prepared by immersing a copper plate in an aqueous solution of AgNO 3 for 20 min. The sample exhibits superhydrophilicity after dried at 150 °C for 30 min in an oven. The as-prepared silver surfaces exhibit contact angle (CA) larger than 160° and sliding angle (SA) lower than 5°. Neither low surface free energy (SFE) materials nor organic compounds were used during the producing process. It was suggested that the spontaneously adsorbed carbon contaminant with low SFE was very critical for the superhydrophobicity of silver surface during heat treatment. Additionally, the silver surface could be switched between superhydrophobicity and superhydrophilicity by alternating UV irradiation and heat treatment for many times. Our findings in this work might provide a simple route to rational control the spontaneously adsorbed carbon contaminant on solid surface to endow the metal or other solid surfaces with superhydrophobicity or superhydrophilicity. [ABSTRACT FROM AUTHOR]

A novel bilayer superhydrophobic film was constructed on Cu substrate by a simple multi-step process. First, (3-mercaptopropyl) trimethoxysilane (MPTMS) molecules were self-assembled onto the pre-etched Cu surface via covalent bonding followed by hydrolysis and condensation, then 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (PFDTS) were grafted onto the resultant hydroxyl terminated surface via the Si-O-Si bonding. The so-prepared sample was defined as Cu-MPTMS-PFDTS. The structure and morphology of the samples were characterized by means of contact angle measurement, X-ray photoelectron spectroscopy and scanning electron microscopy. The corrosion behaviors of the films were evaluated by Tafel plot and electrochemical impedance spectroscopy on an electrochemical work station. The results indicated that the bilayer superhydrophobic film possessed better corrosion protection as compared with the control samples. The superiority of the corrosion protection was mainly ascribed to the following two aspects: the superhydrophobicity and polysiloxane micro-structures of the Cu-MPTMS-PFDTS. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Colorful superhydrophobic coatings were prepared by brushing. • The brushing method can be applied to various substrates with large-area and complex-shape. • The solar reflectance of the yellow brown coating is 0.65, and the near infrared reflectance is 0.81. • The yellowish brown superhydrophobic coating has remarkable cooling performance and self-cleaning function. • The colorful superhydrophobic coatings exhibits desirable weatherability and high mechanical robustness. In the present work, the colorful superhydrophobic coating with high solar reflectivity was prepared using WPC (White Portland cement), color pigments, Polymethylhydrosiloxane and water as raw materials. The superhydrophobicity of the coating surface comes from the combination of the micron/sub-micron rough structure formed by the accumulation of cement hydration products and pigment particles and the low surface energy provided by PMHS (Polymethylhydrosiloxane). The superhydrophobic coating exhibits excellent resistance to corrosion of aggressive solutions, pollution of liquid foods, and accumulation of dust. The SR (Solar reflectance) of superhydrophobic coatings was optimized by changing the type, content and collocation of pigments. The results show that the superhydrophobic coating filled WP (with white pigment) and YP (yellow pigment) has the best performance. The optimized coating is yellowish brown with IR reflectance of 0.8191 and SR of 0.6569, which meets the building energy saving standard. The results of solar radiation experiments show that the surface temperature of the yellow–brown superhydrophobic coating is reduced by 5.7 °C compared with the ordinary Portland cement coating, which has a significant cooling effect. The colorful superhydrophobic coatings also possessed excellent weatherability and high mechanical robustness. Therefore, the coating developed in this work can be used on the exterior wall and roof of the building to reduce the energy consumption of the building in summer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sodium laurate aqueous solution was used as surface superhydrophobic modifier for HCP. • The HCP surface exhibits superhydrophobicity after immersed in sodium laurate solution for 5 s. • Colored superhydrophobic HCP can be prepared by using pigments or dyes. • Sodium laurate surface modification can be extended to other non-cement substrates. • The superhydrophobic HCP surface exhibits excellent repairability. • The capillary water absorption coefficient and water absorption rate of the HCPs decreased remarkably. In the present work, a novel and fast fabrication method was proposed to modify the surface of hardened cement paste (HCP) imparting superhydrophobic properties. Sodium laurate was selected as the modifier among the 6 kinds of sodium carboxylates because of its good water solubility and remarkable hydrophobic modification effect. After immersing in the aqueous solution of sodium laurate at room temperature for only 5 s, the ordinary Portland cement-based HCP surface exhibits superhydrophobicity, with a water contact angle (CA) of 154.3° and a sliding angle of 8.7°. Colored superhydrophobic HCP can be prepared by using pigments or dyes to give the HCP surface a decorative effect. The aqueous solution of sodium laurate also imparts the superhydrophobic modification to the HCPs of aluminous cement and sulfoaluminous cement. Additionally, using the method of "cement coating + surface treatment", the non-cement-based substrates can also be modified into a superhydrophobic surface with sodium laurate, thereby expanding the application range of this method. Furthermore, due to the extremely fast preparation speed, when the surface of HCP is damaged, its superhydrophobicity can be quickly repaired. After superhydrophobic modification, the capillary water absorption coefficient and water absorption rate of the HCPs decreased by 63.81% and 97.77% respectively in comparison with the pristine HCPs. Such easy fabrication, low cost, environmentally friendly, and easy repairable superhydrophobic surfaces have potential applications in the field of building materials such as rendering mortars with self-cleaning functions and colorful decorative effects. [ABSTRACT FROM AUTHOR]

• The HCM exhibits integral hydrophobicity after using PDMS as cement admixture. • PDMS is much cheaper than silane. • The water absorption of the M-HCM is greatly reduced. • The corrosion resistance of the reinforcing steel bar in the M-HCM increased significantly. • The M-HCM exhibits excellent durability against efflorescence, sulfate attach and leaching. The currently used cement hydrophobic additives are either expensive or damageable during use, limiting their large-scale application on concrete. In this study, low-cost and commercially available polydimethylsiloxane (PDMS) is proposed as a cement admixture for the hydrophobic modification of cement mortar. The uniform distribution of PDMS in hardened cement mortar (HCM) attributes integral hydrophobicity to HCM. The PDMS modified HCM (M-HCM) surface exhibits superhydrophobicity, with a contact angle of 157.3° and a sliding angle of 8.7°. The superhydrophobic M-HCM is mechanically robust after being abraded for 110 m distance. In addition, the water absorption of the M-HCM reduced approximately 92.51%, and the corrosion resistance of the M-HCM obviously improved. The compressive strength and flexural strength of the M-HCM reduced by 30.9% and 18.1%, respectively, while the toughness of the M-HCM improved. Furthermore, the durability of the M-HCM against weathering, sulfate attack, and leaching significantly improved in comparison with the U-HCM. This type of mechanically robust superhydrophobic M-HCM material can be used in the waterproof concrete and anti-corrosive concrete. [ABSTRACT FROM AUTHOR]

[Display omitted] • The multifunctional coating is prepared by simple brushing method. • The coating exhibits self-cleaning property and thermochromic function. • The coating shows corrosion resistance, mechanical stability and anti-UV aging. • The thermochromic coating effectively reduces the total annual energy consumption. This work proposes to use a superhydrophobic coating with reversible thermochromic function as the surface coating of building envelope to reduce building energy consumption. The coating consists of Portland cement, thermochromic microcapsules (TCM) and other additives. The switching temperature (T s) of the thermochromic coating is 30 °C. When T < T s (in winter), the thermochromic coating is in the state of color development, with dark color and low solar reflectance; When T > T s (in summer), the thermochromic coating is in the state of decolorization, showing a light color and a high solar reflectance. The the thermochromic coating is beneficial to building heating in winter and cooling in summer. In additional, the thermochromic coating has bright color and can change with the change of temperature, which has a strong decorative effect. Furthermore the coating surface has self-cleaning performance, which can prevent the deterioration of spectral reflectance caused by the accumulation of dust on the coating surface. The superhydrophobic coating has excellent corrosion resistance, mechanical stability and UV aging resistance. EnergyPlus energy consumption simulation results show that the thermochromic coating can effectively reduce the total annual energy consumption in cold winter and hot summer areas. [ABSTRACT FROM AUTHOR]

Superhydrophobic surface (SHS) was fabricated on aluminum via surface roughening by NaClO and surface passivation by hexadecyltrimethoxysilane. The long-term durability for storing the sample in air and the chemical stability for contacting the sample with NaCl solution were investigated. The short-term corrosion resistance for immersing the sample in NaCl solution for 1 h was investigated by potentiodynamic polarization, and the long-term corrosion resistance for immersing the sample in NaCl solution for 7 days was investigated by variation analyses on surface wettability, surface morphology, and surface chemistry. All experimental results suggested that the so-obtained SHS possessed good stability and good corrosion resistance under the testing conditions. [ABSTRACT FROM AUTHOR]

In the presence of NaF, silver (Ag) was galvanically deposited onto aluminum (Al) substrate quickly (typically 10 s) from dilute aqueous AgNO 3 solution. Subsequent immersion into ethanolic solution of stearic acid (SA, for 30 s) rendered Al superhydrophobic. The deposition and morphological evolution of Ag were investigated in detail. It was found that NaF was indispensable to initiate the Ag galvanic deposition by dissolving the barrier oxide layer. Moreover, as reaction time prolonging, surface morphology and surface wettability varied synchronously. This strategy to fabricate superhydrophobic surface (coded as SHS) was also applicable to many other metals, such as Fe, Co and Mo with oxide passivation layer (NaF was needed) or Mg, Zn, Sn, Pb, and Cu with no apparent oxide passivation layer (NaF was not needed). In summary, the strategy to fabricate SHS based on Ag deposition and SA modification was quite impressive for its time-saving benefits and wide substrate applicability. [ABSTRACT FROM AUTHOR]

Abstract: Superhydrophobic surfaces (SHS) are successfully prepared by 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (coded as PFOTS) chemically and physically adsorbed onto the etched Ti alloy substrate. The film formation and its structures are characterized by the measurements of water contact angle (WCA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the SHS in the NaCl solutions is investigated using the potentiodynamic polarization. The results show that the corrosion resistance of the substrate is improved greatly due to the composite wetting states or interfaces with numerous air pockets between SHS and NaCl solutions. Moreover, it is found that the stability and corrosion resistance of SHS is influenced greatly by the interfacial bonding between PFOTS and the substrate. The strong chemical interfacial bonding (i.e., Tih name="sbnd" />Si) between PFOTS and the oxidized titanium substrate accounts for a higher stability and much lower corrosion current density as compared by SHS with physically adsorbed PFOTS outerlayer. [Copyright &y& Elsevier]