Adsorption of silane onto cellulose fibers. II. The effect of pH on silane hydrolysis,condensation, and adsorption behavior

The hydrolysis of four alkoxysilane agents, γ‐methacryloxypropyl trimethoxysilane (MPS), γ‐mercaptopropyl trimetoxysilane (MRPS), octyl trimethoxysilane OS), and N‐phenyl‐γ‐aminopropyl trimethoxysilane (PAPS), was carried out in an ethanol/water (80/20) solution under both acid and basic conditions. ¹H, ¹³C, and ²⁹Si NMR spectroscopy were used to provide quantitative analyses of the structural components during hydrolysis and condensation reaction. The analysis revealed that the acid‐catalyzed hydrolysis of silane allows the formation of high amount of silanol groups, reduced the selfcondensation reaction among silanol groups and stabilized the proportion of intermediary hydrolyzed species for several days. However, under basic condition, condensation reactions proceed as soon as the hydrolysis reaction started leading to the rapid consumption of silanol groups through selfcondensation and to the growth of three‐dimensional high molecular structures. The interaction of MPS and MRPS with cellulose fibers and the evolution of their surface properties were then investigated using adsorption isotherms and contact angle measurement. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

氨基磺酸型两性表面活性剂在石英砂上的吸附

通过静态吸附实验,研究了6种氨基磺酸型两性表面活性剂在石英砂上的吸附,讨论了溶液浓度、表面活性剂疏水基链长、温度和pH对吸附量的影响.结果表明:氨基磺酸盐在石英砂上的吸附具有Langmuir吸附等温式的特点;温度升高使吸附量降低;等温下,溶液浓度低于临界胶束浓度(cmc)时,表面活性剂疏水基链长对吸附量的影响符合Traube规则,溶液浓度高于cmc,疏水基链长增加,吸附平台下降,且疏水基碳数和饱和吸附量Tmax间呈线性关系;溶液pH的变化会导致氨基磺酸型两性表面活性剂和石英砂表面电荷不同,静电作用使吸附量随体系的pH不同而发生变化.     

Factors influencing contact angle measurements on wood particles by column wicking

The present work focuses on a capillary rise technique, referred to here as column wicking, for determining contact angles on wood particles. The liquid front rise versus time for different probe liquids has been measured for extracted and non-extracted spruce wood particles packed into glass columns. Wood is a porous, heterogeneous, and hygroscopic material. The sorption process of certain polar liquids in the wood substance, i.e. bulk sorption, is exothermic and causes swelling. This bulk sorption process and the resulting release of heat are observed as a distinct temperature increase within the columns during the wicking of water, formamide, and methanol. No temperature increase is observed for ethylene glycol, diiodomethane, and hexane. In some cases, the increase in temperature is observed in advance of the moving visible liquid front line. This may indicate that vapor is moving in advance of the liquid front, resulting in bulk sorption and the corresponding release of heat. An apparent non-linearity is observed when the square of the capillary rise is plotted versus time, mainly for water, formamide, and methanol. This non-linearity is strongly dependent on the probe liquid used and the variation in wood particle size. For the wicking of water, the bulk sorption, and hence the swelling of the wood particles, seems to appear instantaneously at the wetting front line, but for formamide and methanol a time delay is observed. The bulk sorption and resulting swelling of the wood particles strongly influence the determination of the effective interstitial pore radius between the particles, and thus the determination of contact angles by use of the Washburn equation.     

Mechanistic study of adsorption of cetyltrimethyl ammonium bromide on high purity iron using contact angle, polarization resistance and XPS

The mechanism of inhibition of carbon dioxide (CO₂) corrosion of high purity iron by cetyl trimethyl ammonium bromide (CTAB) was investigated by contact angle, polarization resistance and X-ray photoelectron spectroscopy (XPS). The wetting properties, corrosion inhibitor performance and the adsorption of the inhibitor on a high purity iron surface were investigated. Test conditions during corrosion testing were 25 °C, 3 wt% NaCl brine, initial pH 3.9 and 1 bar CO₂ partial pressure. The samples were precorroded for 5 h before inhibitor was added.The inhibitor performance data showed that addition of CTAB significantly reduced the corrosion rate of high purity iron. The decreased corrosion rate seems to be caused by a blocking effect, where the CTAB forms a surface structure on the iron surface. Chemisorption of the CTAB molecules, which could lead to gradually increasing inhibitor efficiency, might be the reason for the slowly decreasing corrosion rate. The XPS data confirmed a gradual accumulation of inhibitor on the surface but did not show any distinct change between different mechanisms at different exposure times. The contact angle measurements showed that the iron was water wet, with a contact angle higher than 160°, at all CTAB concentrations.     

Adsorption of lithium onto zirconium alloys. The role of acid-base interactions

The surface properties of oxides of two kinds of zirconium alloy (namely Zircaloy-4 and ZrNb, which are commonly used as the cladding for nuclear fuel rods) are investigated. XPS analyses were carried out on both samples after a standard thermal treatment in a pressurized autoclave. An oxide essentially composed of ZrO₂ characterizes the surface of Zircaloy-4, with some tin detected in the oxide layer, whereas the surface of the ZrNb alloy presents an oxide layer composed of both zirconium and niobium oxides. Angle-resolved analysis shows the surface to be enriched in niobium oxide (presumably Nb₂O₅). Wettability experiments were then performed on both alloys, which had been air-aged or aged in an aqueous solution simulating the coolant solution of pressurized water reactors (PWRs). The dispersive and acid-base components of the work of adhesion were determined. In addition, the points of zero charge of both samples were determined by measuring the contact angle versus the pH of the aqueous solution. Under the conditions studied, the wetting measurements seem to indicate that lithium adsorption, which is present in the coolant PWR solution, is easier at the ZrNb surface than at the Zircaloy-4 surface. This observation was confirmed by AES investigations of the interfaces between the PWR coolant solution and zirconium alloy oxides. In addition, the wetting measurements with respect to the pH of the PWR coolant solution indicate a more complex evolution of the surface charges on the ZrNb surface than on the Zircaloy-4 surface.     

Combined XPS and contact angle studies of flat and rough ethylene‐vinyl acetate copolymer films

Flat and rough thin films were prepared by dip coating using LDPE, PVAc, and EVA polymers containing 12–40% VA contents. Surface free energy of flat films was determined by measuring contact angles. Surface atomic composition was investigated by XPS at 0° and 60° take‐off angles. XPS results show that hydrophobic PE component was found to enrich at the near‐surface region for all EVA samples for a depth of ～ 5 nm for both flat and rough surfaces, whereas hydrophilic VA component was enriched on the surface when VA < 18% for only at 10 nm depth. The difference between the XPS results of the flat and rough surfaces was not significant for EVA samples except EVA‐33 surface where the atomic oxygen content decreased 15–20% for rough surfaces. Contact angle hysteresis values for the rough samples were much larger than that of the flat samples for LDPE and EVA‐12 surfaces due to the presence of partial trapping of air pockets on these rough surfaces. A good agreement was obtained between surface concentration of atomic oxygen in the 5 nm outermost layer and γ surface free energy component especially for the samples having high VA contents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Study of humic acid adsorption on nanofiltration membranes by contact angle measurements

Membrane fouling is a major problem, which extent depends on the respective natures of the solute and membrane material. Membrane surface characterization under different fouling conditions may help in understanding the fouling mechanism. Such characterization was performed for the case of humic substances filtered on two nanofiltration membranes, using special contact angles measurements. The measured contact angles allowed the calculation of polar and non-polar contributions to the surface energy of dry, hydrated and fouled membranes. The results reveal significant differences in the two membrane behaviours and information about the way that fouling material may be adsorbed on membrane surface.     

Adsorption of iso-/n-butane on an anatase thin film: a molecular beam scattering and TDS study

Binding energies and adsorption probabilities have been determined for n/iso-butane adsorption on an anatase thin film grown on SrTiO₃(001) by means of thermal desorption spectroscopy (TDS) and molecular beam scattering. The sample has been characterized by X-ray diffraction (XRD) and Auger electrons spectroscopy (AES).     

Roles of molecular interactions in adhesion,adsorption, contact angle and wettability

This study is aimed at understanding the controversy between the surface tension component (STC) theory and the equation of state (EQS) approach for interfacial tensions. We attempt to relate molecular interactions to various components of surface tension. Molecular interactions consist of electrostatic (ES), charge transfer (CT), polarization (PL), exchange-repulsion (EX), dispersion (DIS), and coupling (MIX) components. These interactions can be the basis for the STC theory involving Lifshitz-van der Waals (LW) and the short range acid-base (AB) or donor-acceptor interaction. Each of these components is shown to contain two major parameters. New equations for the interaction energy and surface tension for polar molecules are proposed to include the ES and EX parameters, which happen in some cases to balance each other or nearly cancel out without being detected. The roles of molecular interactions on adhesion, adsorption, contact angle, and wettability are illustrated through the spreading coefficient S, the Hamaker coefficient A, and Derjaguin's disjoining pressure . We have found that the STC theory is applicable to the systems involving either physisorption or chemisorption, whlie the EQS applies to those involving ony physisorption.     

基于核磁-能谱实验的中变质烟煤煤尘低润湿性分析

为从微观角度分析中变质烟煤的低润湿特性,以巨野煤田赵楼气肥煤为例,选用核磁共振（NMR）与X射线光电子能谱（XPS）手段对其微观分子结构进行实验,并分析了分子结构参数对其润湿性的影响规律。结果表明,赵楼气肥煤煤尘的芳香度为0.77,芳香结构含量较高,且主要以质子化芳环为主;脂肪链结构中以链状烷烃和环烷烃侧链为主,且存在一定的甲基侧链;煤尘表面含氧官能团主要为醚基（C-O-C）,其次为羰基（C=O）与羟基（C-OH）,含量最少的是羧基（COOH）,上述4种含氧官能团含量之比约为4∶2∶2∶1.5。赵楼气肥煤煤尘不仅芳香度较高,芳香簇尺寸较大,缩合度偏高,而且烷基侧链少而短,导致煤尘分子结构单元表现出较强的疏水性;而对表面亲水性贡献较大的羧基（COOH）和羟基（C-OH）含量却只占表面含氧官能团总量的13.53%、21.45%。因此,受微观分子结构的影响,赵楼气肥煤煤尘总体表现出疏水性的特点,润湿性较差。     

Investigation of surface molecular orientation of poly(dimethylsiloxane-co-diphenylsiloxane)-modified poly(amic acid) films using dynamic contact angle measurements,NEXAFS and XPS

Since poly(dimethylsiloxane)-modified poly(amic acid) was not wetted by the photoresist, poly(dimethylsiloxane-co-diphenylsiloxane)-modified poly(amic acid) was synthesized to improve the wettability of photoresist. From a study on dynamic contact angles of water, the initial advancing contact angles on poly(dimethylsiloxane)-modified poly(amic acid) and those on poly(dimethylsiloxane-co-diphenyl-siloxane)-modified poly(amic acid) are almost the same, but the equilibrium advancing contact angles on poly(dimethylsiloxane-co-diphenylsiloxane)-modified poly(amic acid) are much smaller than those on poly(dimethylsiloxane)-modified poly(amic acid). The decrease in equilibrium advancing contact angles on poly(dimethylsiloxane-co-diphenylsiloxane) appears to indicate migration of phenyl groups to the surface in the polar environment. Thus, photoresist could be wetted on the poly(dimethylsiloxane-co-diphenylsiloxane)-modified poly(amic acid) film. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy (XPS) were used to investigate the orientation and surface migration of molecules in poly(dimethylsiloxane-co-diphenylsiloxane).     

Adsorption of BSA on passivated chromium studied by a flow-cell EQCM and XPS

The adsorption of bovine serum albumin (BSA) on a passivated chromium surface in deaerated pH 4 sulphate solution was studied in situ using a switch-flow cell in combination with an electrochemical quartz crystal microbalance (EQCM) and ex situ by X-ray photoelectron spectroscopy (XPS). EQCM measurements showed that the kinetics of BSA adsorption was fast, and that a steady-state was reached about 10 min after introducing the protein. They also showed that BSA adsorption was an irreversible process, or that the kinetics of desorption was very slow. The equivalent thicknesses of the adsorbed BSA layer estimated in situ by EQCM and ex situ by XPS are in excellent agreement, and are equal to 3.5 ± 0.7 nm, which corresponds to one horizontally orientated monolayer.     

Influence of post-etch cleaning and silane heat treatment on resin bond strength to silica-based leucite: an in vitro study

Adhesive cementation of bonded all-ceramic restorations is critical for their long-term clinical performance. The objective of this study was to evaluate the role of post-etch cleaning (PEC) and silane heat treatment on the micro-tensile bond strength of silica-based leucite (SBLE) ceramic when bonded to composite resin. Twenty-four blocks of SBLE ceramic (HeraCeram Press®, Heraeus Kulzer GmbH Grüner Weg 11 63450 Hanau) were fabricated and bonding surfaces were etched using 9.5% hydrofluoric acid. Six experimental groups were made from the various surface treatment combinations including: PEC (37.5% phosphoric acid for 1 min, rinsed with water for 20 s and ultrasonic bath immersion), silane application and silane heat treatment (100 °C for 5 min). An adhesive resin and a light-cured restorative composite were used to bond the ceramic and composite resin blocks under standard conditions. Three hundred and sixty specimen sticks (8 × 1 mm²) were subjected to micro-tensile testing. The means of the micro-tensile bond strength (μ-TBS) were analysed with ANOVA and Tukey–Kramer multiple comparison test. The specimens tested were assessed for mode of failure using scanning electron microscopy. The highest μ-TBS value (38.25 ± 3.40 MPa) of the specimen was achieved by PEC and heated silane. PEC and silane application showed statistically significant improvements in the μ-TBS (p < 0.01). The mean maximum difference was due to PEC (18.91 ± 3.70 MPa). In the surface treatment of SBLE ceramics, PEC had the most significant factor which affected the μ-TBS of resin composite.     

XPS法研究表面活性剂、碱和聚合物在固体颗粒表面吸附的协同效应

利用光电子能谱法(XPS)研究了表面活性剂、碱和聚合物在固体颗粒表面上的吸附量及相互之间的协同效应。表面活性剂和碱在S iO2固体颗粒上的最大吸附量随着浓度的增大而增加,分别在1 200,5 000 mg/L达到最大吸附量1.15 mg/g和1.65 mg/g,吸附量达到最大值后趋于稳定;聚合物的平衡吸附曲线随着浓度的增大吸附量先增加后减少,600 mg/L达到最大吸附量1.30 mg/g,后减小至0.40 mg/g基本不变;在表面活性剂、碱和聚合物复合吸附体系中,碱的存在大大降低了表面活性剂在固体表面上的吸附量,在一定程度上增加了聚合物在固体表面上的吸附量,聚合物和表面活性剂在共存竞争吸附影响下S iO2表面上的吸附量都有了较大的减少;在表面活性剂、碱和聚合物复合体系中,聚合物与碱协同吸附的固体表面吸附层比其它情况下厚。     

Characterization of air plasma‐treated polymer surfaces by ESCA and contact angle measurements for optimization of surface stability and cell growth

A radiofrequency air plasma has been used to incorporate new functionalities at the surface of cycloolefin polymers (Zeonex® and Topas®), polymethyl methacrylate (PMMA), styrene–acrylonitrile copolymer (SAN), and polystyrene (PS). The main goals with the plasma treatment of the different plastics were to hydrophilize the surfaces and to provide good cell culture properties. Surfaces treated at high RF power/gas flow ratios (50 to 100 W/sccm) became highly hydrophilic (water contact angles of about 5 degrees) and stable towards washing in 70% (v/v) ethanol. Those treated at lower power/gas flow ratios (3 to 10 W/sccm) were less hydrophilic and not wash‐stable. Cell growth properties of HeLa cervix carcinoma cells as good as on commercial tissue‐culture polystyrene could be obtained for Zeonex, SAN, and PS, treated at relatively low RF power/gas flow ratios. However, no untreated plastics were suitable for culturing these cells. XPS spectra features show that ester, ether/alcohol, and ester/carboxyl groups are formed during the plasma treatments of the different plastics. Measurable amounts of carboxylic acid carbon after plasma treatment were only observed for PS and Topas. Furthermore, at high RF power/gas flow ratios fluorine, aluminium and silicon were incorporated in all investigated plastics surfaces due to ablation–deposition processes in the reaction chamber. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2618–2625, 2002     

几种偶联剂改性粉石英的改性效果比较研究

本文采用单一铝酸酯DL-411偶联剂、单一硅烷KH-570偶联剂,以及铝酸酯DL-411偶联剂和硅烷KH-570偶联剂的复合物对粉石英进行改性,利用粘度、浸润性、活化指数、填充高聚物基复合材料的力学性能等方法表征评价了不同偶联剂改性粉石英的改性效果.     

鸟嘌呤和腺嘌呤吸附和电氧化行为的电化学石英晶体微天平研究

基于压电电化学石英晶体微天平(EQCM)技术,研究了腺嘌呤(A)和鸟嘌呤(G)在裸金电极和多壁碳纳米管(MWCNTs)修饰金电极上的吸附和电氧化行为。结果表明,在金电极上,A的吸附量和氧化电流均比G大,而在MWCNTs/Au电极上,A和G可类似地吸附,但其氧化峰电位负移且氧化峰电流增大,表明MWCNTs对A和G的氧化具有催化作用。实验发现,A和G在裸金电极上氧化的电子转移数分别为5.4(RSD=±2.3%)和1.9(RSD=±1.3%),而在MWCNTs/Au电极上的氧化电子转移数分别为5.1(RSD=±1.8%)和1.5(RSD=±1.6%)。     

XPS and flow-cell EQCM study of albumin adsorption on passivated chromium surfaces: Influence of potential and pH

The adsorption of albumin (BSA: bovine serum albumin) on passivated chromium surfaces was studied in deaerated sulphate solutions as a function of potential (in the passive state) and pH (from 4 to 10). In situ switch-flow cell EQCM measurements were coupled to ex situ XPS analyses. EQCM results showed that (i) the initial adsorption rate is about 3.3 ng cm⁻² s⁻¹ which corresponds to 3 × 10¹⁰ molecules cm⁻² s⁻¹, irrespective of the passive potential and pH, and (ii) the passive potential as well as the pH have no influence on the amount of adsorbed BSA (Δm = 440 ± 70 ng cm⁻² on the adsorption plateau). From the XPS N 1s and C 1s signals, which provide a fingerprint for the protein, it can be concluded that BSA is adsorbed on the Cr surface and is chemically intact. The XPS results show that (i) when increasing the passive potential, the oxide layer thickness increases (mean value: d_ox = 2.2 ± 0.2 nm), and (ii) the passive film is not modified by the adsorption of protein. From combined EQCM and XPS data, a full coverage of the Cr surface by the adsorbed proteins (γ = 1) is demonstrated at pH 4 (whatever the passive potential). The thickness of the continuous BSA layer (h_BSA) is 3.3 ± 0.3 nm, which corresponds to one monolayer “side-on”, i.e. oriented parallel to the surface. At pH 5.5 and 10, the adsorbed proteins form islands. The surface coverage is much lower (γ ∼ 0.5), and the height of the protein islands is significantly higher (h_BSA ∼ 6.5 nm). The results suggest a strong interaction (partially covalent) between the protein and the passivated chromium surface.     

Surface characterization of poly(styrene‐co‐ fluoroalkylfumarate): XPS and contact angle measurement study

We studied styrene and fluoroalkylfumarate (FAF) copolymers and their surfaces by means of contact angle measurement and X‐ray photoelectron spectroscopy (XPS). The surfaces of the copolymers were very hydrophobic (even with a small amount of FAF) because of the concentration of FAF segments at the surface. The hydrolyzed surfaces of the copolymers became slightly hydrophilic compared to the as cast. The XPS data suggested that the fluoroalkyl groups seemed to be primarily hydrolyzed. The surfaces with a large amount of FAF changed their characteristics to hydrophobic again under atmospheric conditions. This phenomenon was due to the inversion of the carboxyl and the fluoroalkyl groups. These hydrolyzed surfaces seemed to be useful for modifying polymer surfaces by attaching to other functional molecules. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1049–1054, 1999