Preparation of superhydrophobic paper mulch and study on its anti-UV performance

In order to improve the shortcomings of paper mulch, such as the low water resistance and weather fastness in practical application, the paper mulch with a superhydrophobic structure was prepared by depositing zinc oxide layer and silicon dioxide layer on the surface of paper mulch by the solution impregnation method, the paper mulch surface treatment method is simple and environmentally friendly. The surface chemical composition and surface morphology of paper mulch before and after UV aging were characterized, respectively. The wetting property, bouncing property, and mechanical stability of paper-based film were studied. The results showed that the static contact angle of the superhydrophobic paper mulch was as high as 161.77°, and the average sliding angle was only 3.5°, which also showed excellent droplet bounce performance and mechanical stability. After UV aging experiment, the static contact angle of super-hydrophobic paper mulch was increased to 163.64°, and the sliding angle was reduced to 2.5°. Its excellent performance could still be maintained, showing excellent UV resistance, which improved the weather fastness and water resistance of paper mulch to a certain extent, and laid a foundation for the next large-scale field test.     

Preparation of superhydrophobic composite paper mulching film

To study the influence of different concentrations of zinc oxide (ZnO)/silicon dioxide (SiO₂) composite coating on hydrophobic property and mechanical stability of paper mulch film, three kinds of ZnO/SiO₂ composite coating paper mulch films (2%, 4%, 6%) with different coating substance contents were prepared by brush coating method. Through particle size analysis, contact angle, rolling angle and mechanical stability test, combined with scanning electron microscope, three-dimensional morphology and roughness measuring instrument, the optimal concentration of ZnO/SiO₂ composite coated paper mulch film was screened out. Through acid-base salt corrosion test, silver mirror reaction and surface self-cleaning, the optimal concentration of composite coated paper mulch film was compared with the original paper mulch film to prove its excellent chemical stability and hydrophobicity. The results show that the paper mulch film with 4% coating material has excellent hydrophobicity and mechanical stability, can effectively reduce the surface roughness of paper mulch film, and has remarkable effects in resisting acid, alkali and salt and self-cleaning.     

Preparation of super-hydrophobic white carbon black from nano-rice husk ash

Nano-rice husk ashes were prepared by burning rice husk with a self-propagating method. The white carbon black with high purity was prepared by an alkali dissolving–acid reaction method from nano-husk ash. The super-hydrophobic SiO₂ films were prepared by the sol–gel method using hexamethyldisilazane as a modifier. The effects of the pH and reaction time in the acid reaction process on the purity of the white carbon black, and the effect of the modifier on the hydrophobic property of SiO₂ films were studied. The performances were characterized by XRD, BET, SEM, IR, and contact angle analyzer. The results showed that the purity of white carbon black reached 98.48 % when the NaOH solution with the rice husk ash was heated for 2 h at 90 °C, then the pH of the solution was adjusted by sulfuric acid to 3, and the acid reaction time was 2 h. The contact angle of SiO₂ films was more than 160° when volume ratio of the modifier to silica–sodium hydroxide mixed solution was 0.15. The mechanism of the modifier on SiO₂ surfaces is a graft copolymerization. The hydrophobic groups in the modifier replace the hydroxy groups on SiO₂ surfaces and make SiO₂ surfaces present super-hydrophobicity.     

疏水多孔硅制备及其对水中有机污染物的吸附

以硅酸钠为硅源,盐酸为催化剂,三甲基氯硅烷(TMCS)为表面改性剂,经溶胶-凝胶和表面改性过程制备出一种疏水性多孔硅材料.采用傅里叶变换红外(FTIR)光谱仪、接触角分析仪、氮气物理吸附仪和扫描电子显微镜(SEM)对其结构和性质进行表征.结果表明:所制备的多孔硅具有分等级孔道结构(中孔-大孔),比表面积为566m2·g-1,孔体积高达2.28cm3·g-1,多孔硅与水的接触角为156°,显示出超疏水特征.对甲苯、汽油、柴油和润滑油的吸附量均可高达自身质量的14倍,丰富的孔道使其在几分钟内即可达到饱和吸附.这种多孔硅在汽油/水混合体系中对汽油具有较高的选择性,同时具有良好的再生能力.经正己烷萃取再生后,多孔硅仍能基本保持初始吸附容量.此方法制备的多孔硅材料在吸附分离污水中的有机物和溢油处理方面具有很好的应用前景.     

Modification of the wettability of a polymeric substrate by pH effect. Determination of the surface acid dissociation constant by contact angle measurements

The wetting properties of a substrate can be changed by chemical reaction. Here, we studied simple materials with acid-base properties, by preparing poly(vinyl chloride) films containing lauric acid. These substrates constitute simple polymeric surfaces the wettability of which can be easily controlled by the acid-base equilibrium. The roughness of the material was then varied by adding Aerosil (hydrophobic fumed silica). We then studied the wettability of these materials toward aqueous buffer solutions between pH 2 and 12 from contact angle measurements. The variation of the contact angle of a droplet of buffer solution with the pH of the solution was described by a simple thermodynamic model requiring only two parameters. Thus, we could characterize the acid polymer by an effective surface acid dissociation constant the value of which was consistent with those obtained with a similar surface. We showed that the behavior of any substrate could be described even if the surface geometry was not well-known.     

Formation of Hydrophobic Silica Coatings on Stones for Conservation of Historic Sculptures

The conservation of historic sculptures is receiving growing attention because of the increasing air pollution. A hydrophobic silica coating was synthesized to protect historic sculptures from weathering by starting from a solution of tetraethoxyorthosilicate (TEOS) precursor using hexadecyltrimethoxysilane (HDTMS) as hydrophobic modifier in the presence of ammonia as a catalyst. The molar ratio of ethanol, TEOS, H₂O and NH₄OH was kept constant at 8:0.045:3:2.8 and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 0.458. The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the coating was tested by the contact angle measurements. The stone surface morphology of sample treated with silica coating was characterized. The results showed that the nanocomposites were composed of spherical particles with grain size of about 190 nm in diameter. After the limestone's surface was modified, the contact angle of limestone increased from 20° to 100° for M0.458. The protective performance evaluated with its ability to resist acid rain reveals that the protective effects are satisfying.     

Recent Studies on Super-Hydrophobic Films

Summary.  Films whose water contact angle is higher than 150° have been the subject of great interest and enthusiastic study in recent years. These films, which are called super-hydrophobic, are fabricated by combining appropriate surface roughness with surfaces of low surface energy. Here we briefly review the fundamental theories on the wettability of a hydrophobic rough solid surface, together with recent works on the processing and properties of super-hydrophobic films. Though the practical application of these films is still limited, the obstacles to application are gradually being surmounted, providing a great opportunity for the development of various industrial products. Received June 23, 2000. Accepted (revised) September 4, 2000     

用含氟丙烯酸酯无规共聚物制备超疏水膜

用微乳液聚合法制备了丙烯酸全氟烷基乙酯和甲基丙烯酸甲酯的无规共聚物,并对其进行了表征.采用溶剂挥发成膜法一步制备了具有超疏水性的该聚合物膜,水滴在该聚合物膜上的静态接触角可达151°~160°,滚动角小于3°.通过扫描电子显微镜观察发现该聚合物膜表面分布了许多乳突状突起和微孔洞,并具有微米和纳米尺度相结合的复合杂化结构.该类超疏水表面的形成是由适度粗糙的表面和低表面能相互结合引起的.探讨了该类超疏水膜的形成机理.     

Wetting of β-casein layers adsorbed at the solid–aqueous interface

The wetting by water of the adsorbed layer of β-casein on hydrophobised silica and pure (hydrophilic) silica surface was investigated by dynamic contact angle measurements based on the Wilhelmy plate principle. The results are discussed in relation to adsorption data obtained for the protein on similar surfaces by in situ ellipsometry. β-casein adsorption on a hydrophobic surface leads to a significant decrease of the contact angle, in particular in terms of the receding contact angle, which decreased by about 70°. This indicates a strong shielding of the hydrophobic surface by the hydrophilic domain of β-casein. Adding a specific enzyme, endoproteinase Asp-N, which previously has been proposed to remove a large fraction of the hydrophilic segments, results in a significantly decreased wettability of the solid surface. The layer is now more hydrophobic and the hysterises is much smaller. The receding contact angle after the proteolysis is roughly 70°. The results are consistent with the hypothesis that β-casein adsorbs at the hydrophobic surface to form a monolayer with the hydrophobic part of the protein anchored at the surface, leaving the hydrophilic segments dangling into the solution. Less dramatic effects are observed in terms of changes of the wettability on the hydrophilic surface. The surface is still quite hydrophilic both after adsorbing β-casein and exposing the layer to endoproteinase Asp-N. These results confirm the differences in the structure of β-casein layers on the hydrophobic and hydrophilic surface.     

铝合金表面原位自组装超疏水膜层的制备及耐蚀性能

采用阳极氧化法在铝合金表面原位构造粗糙结构, 经表面自组装硅氧烷后得到超疏水自清洁表面, 与水滴的接触角最大可达157.5°±2.0°, 接触角滞后小于3°. 通过傅立叶变换红外(FT-IR)光谱分析仪、场发射扫描电子显微镜(FE-SEM)、能谱仪(EDS)、原子力显微镜(AFM)和接触角测试对阳极氧化电流密度、硅氧烷溶液中水的含量和自组装时间等参数进行了分析, 并得到制备超疏水自清洁表面的最优工艺参数. FE-SEM及AFM的测试结果表明, 由自组装硅氧烷膜层的无序性形成的纳米结构和阳极氧化构造的微米级粗糙结构与硅氧烷膜层的低表面能的协同作用构成了稳定的超疏水表面. 电化学测试(动电位极化)的结果表明, 原位自组装超疏水膜层极大地提高了铝合金的耐蚀性.     

Hydrophobicity and drag reduction properties of surfaces coated with silica aerogels and xerogels

Superhydrophobic surfaces have application in self-cleaning, anti-fouling and drag reduction. Most superhydrophobic surfaces are constructed using complex fabrication methods. An alternative method is to use sol–gel methods to make hydrophobic aerogel and xerogel surfaces. In this work, hydrophobic silica aerogels and xerogels were made from the silica precursors tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMS) in volume ratios MTMS/TMOS of 0–75 % using a base-catalyzed recipe. Overall hydrophobicity was assessed using contact angle measurements on surfaces prepared from crushed aerogel and xerogel powders. The surfaces made from aerogels were super-hydrophobic (with contact angles of 167°–170°) for all levels of MTMS (10–75 %). Of the xerogel-coated surfaces, those made with 50 % MTMS were hydrophobic and with 75 % MTMS were superhydrophobic. Chemical hydrophobicity was assessed using Fourier transform infrared spectroscopy, which showed evidence of Si–CH₃ and Si–C bonds in the aerogels and xerogels made with MTMS. Morphological hydrophobicity was assessed using SEM imaging and gas adsorption. The drag characteristics of the aerogel- and xerogel-coated surfaces were measured using a rotational viscometer. Under laminar flow conditions all of the hydrophobic aerogel-coated surfaces (10–75 % MTMS) were capable of capturing an air bubble, thereby reducing the drag on a horizontal rotating surface by 20–30 %. Of the xerogel-coated surfaces, only the one made from 75 % MTMS could capture a bubble, which led to 27 % drag reduction. These results imply that morphological differences between silica aerogels and xerogels, rather than any differences in their chemical hydrophobicity, give rise to the observed differences in hydrophobicity and drag reduction for the sol–gel-coated surfaces.     

Hydrophobic Silica Aerogels Strengthened with Nonwoven Fibers

Hydrophobic silica aerogels were prepared via a sol‐gel process by surface modification at ambient pressure. Nonwoven fibers were distributed inside the silica aerogels as a composite to act as a supporting skeleton which increased the mechanical property of the silica aerogels. The morphology and pore structure of the composites were characterized by scanning electron microscopy (SEM) and N₂ adsorption analyzer. The contact angle and the adsorption capacities of the composites were also determined. The results show that silica aerogels dispersed uniformly and maintained high porosity in the aerogel‐fiber composites. They have excellent hydrophobic properties and are excellent adsorptive materials.     

Encapsulation of aluminum flakes with hybrid silica/poly(acrylic acid) nanolayers by combination of sol–gel and in situ polymerization methods: a corrosion behavior study

A combination of sol–gel method and in situ polymerization was used to form a hybrid silica/poly(acrylic acid) nanolayer for the corrosion protection of aluminum pigments. To this end, the pigment particles were first coated with a silica layer by sol–gel method. Tetraethylorthosilicate was used as a precursor and during a condensation reaction, an inorganic silica layer was formed. Then, 3-methacryloxypropyltrimethoxysilane was attached on the surface and in situ polymerization of acrylic acid (AA), as a hydrophile monomer, was performed. The obtained Al/Si/PAA flakes were characterized by different methods such as Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The attached PAA chains on the surface were deattached by HF aqueous solution and analyzed by gel permeation chromatography. Also, the surface energy of samples was measured using Owens and Wendt equation by means of contact angle data. As results, the characterizing tests approved the successful encapsulation of Al pigments and TEM image showed a 10–15 nm silica layer and a 20–25 nm PAA layer. Although the Al/Si pigments showed a quantity of evolved hydrogen, the hybrid coated pigments had excellent anticorrosive properties in acidic and alkaline solutions. Also, the surface free energy of Al/Si/PAA showed an increase compared to that of Al.     

Polymer-in-a-silica-crust membranes: macroporous materials with tunable surface functionality

We report on alkaline hydrolysis of tetraethoxysilane (St?ber synthesis) inside a macroporous polymer matrix resulting in a homogeneous coverage of silica onto the polymer surface. The encapsulation of the polymer struts by a continuous silica crust allows further functionalization with hydrophilic and hydrophobic silylating agents. The porous silica polymeric hybrid material combines the morphological control and mechanical flexibility of the polymeric matrix with the convenient surface modifications developed for glass and amorphous silica. This concept is applied to macroporous membranes where alteration in surface functionality allows tuning of hydrophobicity (contact angle and liquid entry pressure), streaming potential, and adsorption capacity of double-stranded DNA.     

含氟环氧树脂杂化纳米二氧化硅超疏水材料的制备与性能

目前超疏水材料的制备方法大都存在着制备工艺复杂的缺点。 本文采用传统自由基聚合方法,以甲基丙烯酸缩水甘油酯(GMA)和苯乙烯(St)为单体,合成具有交联性的前驱聚合物P(GMA-r-St)。 再用三氟乙酸(TFA)对其进行接枝改性,制备含氟环氧聚合物P(GMA-r-St)-g-TFA。 利用γ-氨丙基三乙氧基硅烷(KH-550)改性纳米二氧化硅(SiO₂),对其进行傅里叶变换红外光谱(FTIR)、热重(TG)表征。 氨基改性的纳米二氧化硅与含氟环氧聚合物混合制备的超疏水改性材料,棉织物表面经其浸泡,可快速构建超疏水结构。 通过改变改性纳米颗粒的含量,探究其构筑的棉织物的疏水性能和耐溶剂性能。 研究结果表明,经浸泡改性的棉织物,水接触角为160°,耐溶剂性时间为130 min,具备很好的耐溶剂性。 该方法可广泛应用于多种基底材料表面的疏水改性。     

Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel

Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N₂ adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH₃)₃ to result in a hydrophobic SiO₂ powder as confirmed by contact angle measurements with H₂O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m²/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m²/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process.     

聚酯织物表面耐用超疏水涂层的制备及在油水分离中的应用

使用在含有甲基MQ(M:单官能团Si-O单元R₃SiO_1/2, Q:四官能团Si-O单元SiO₂)硅树脂与疏水SiO₂的二甲苯溶液中浸渍的方法,在聚酯织物表面制备了耐用超疏水涂层。经过处理后,微米级聚酯纤维表面被紧密的疏水纳米颗粒包裹,通过这种方法降低了纤维的表面能。聚酯织物展现出良好的超疏水特性,与水滴的静态接触角为156°,滚动角为5°。得到的超疏水聚酯织物在机械磨损、酸碱环境及紫外线照射条件下,表现出了良好的稳定性。此外,用超疏水聚酯织物作为过滤材料得到的油水分离效率达99%以上。该方法为大面积工业制备超疏水织物提供了新的思路。     

Contact-angle hysteresis on super-hydrophobic surfaces

The relationship between perturbations to contact angles on a rough or textured surface and the super-hydrophobic enhancement of the equilibrium contact angle is discussed theoretically. Two models are considered. In the first (Wenzel) case, the super-hydrophobic surface has a very high contact angle and the droplet completely contacts the surface upon which it rests. In the second (Cassie-Baxter) case, the super-hydrophobic surface has a very high contact angle, but the droplet bridges across surface protrusions. The theoretical treatment emphasizes the concept of contact-angle amplification or attenuation and distinguishes between the increases in contact angles due to roughening or texturing surfaces and perturbations to the resulting contact angles. The theory is applied to predicting contact-angle hysteresis on rough surfaces from the hysteresis observable on smooth surfaces and is therefore relevant to predicting roll-off angles for droplets on tilted surfaces. The theory quantitatively predicts a "sticky" surface for Wenzel-type surfaces and a "slippy" surface for Cassie-Baxter-type surfaces.     

Study of hydrophilicity and stability of chemically modified PDMS surface using piranha and KOH solution

Successful realization of various BioMEMS devices demands effective surface modification techniques of PDMS elastomer. This paper presents a detailed report on a simple and cost effective approach for surface modification of PDMS films involving wet chemical treatment in two‐step processes: primarily involving piranha solution followed by KOH dip to improve hydrophilicity and stability of PDMS surface. Chemical composition of the solution and surface treatment condition have been varied and optimized to significantly increase the surface energy. The effect of surface modification of the elastomer after wet chemical treatment is analyzed using contact angle measurement and FTIR‐ATR study. PDMS surface treated in piranha solution with H₂O₂ and H₂SO₄ in the ratio of 2:3 followed by a dip in KOH solution for 15 min duration each, demonstrated a maximum reduction of contact angle to ～27° as compared to untreated sample having a contact angle of ～110°. The removal of hydrophobic methyl group from elastomer surface and subsequent hydrophilization of surface by wet chemical process was confirmed from FTIR‐ATR spectra. This result is also supported by improved adhesion and electrical continuity of deposited aluminum metal film over the modified PDMS surface. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface Modification of Silicone Rubber by CF<Subscript>4</Subscript> Radio Frequency Plasma Immersion

Silicone rubber samples were treated by CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF₄ flow rate of 20 sccm, respectively. Static contact angle, ATR-FTIR and XPS, and AFM were employed to characterize the changes of surface on hydrophobicity, functional groups, and topography. The results indicate the static contact angle is improved from 100.7 to 150.2°, and the super-hydrophobic surface, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of surface roughness created by the ablation reaction of CF₄ plasma and the formation of [–SiF _x (CH₃)_2−x –O–] _n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.