Contact Angles Of Aqueous Solutions Research Articles

水晶結晶微量天秤とＬａｎｇｍｕｉｒ‐Ｂｌｏｄｇｅｔｔ法により評価した油汚れに対する洗浄力（原標題は英語）

The titled assessment was conducted using a quartz crystal microbalance (QCM) and the Langmuir-Blodgett (LB) method. The gold electrodes of QCM were coated with cellulose acetate, nylon 6 or polyethylene film by spin-coating. Spreading monolayers of long-chain fatty acid as oily contaminants on water were transferred onto spin-coated polymer film. LB films of arachidic acid were ultrasonically cleaned in aqueous solution. Detergency was determined based on the frequency change of the QCM due to cleaning. Detergency was greatest for cellulose acetate, followed by nylon 6 and polyethylene. For all films, detergency increased with the addition of ethanol, surfactant and alkali. Detergency is discussed in relation to contact angle of aqueous solution on polymer film. Liquid introduction between LB film and the polymer surface in the zone of contact appeared to be a significant factor in the removal of LB film from the polymer surface.

Unusual wetting dynamics of aqueous surfactant solutions on polymer surfaces

Static and dynamic contact angles of aqueous solutions of three surfactants—anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB), and nonionic pentaethylene glycol monododecyl ether (C 12E 5)—were measured in the pre- and micellar concentration ranges on polymer surfaces of different surface free energy. The influence of the degree of substrate hydrophobicity, concentration of the solution, and ionic/nonionic character of surfactant on the drop spreading was investigated. Evaporation losses due to relatively low humidity during measurements were taken into account as well. It was shown that, in contrast to the highly hydrophobic surfaces, contact angles for ionic surfactant solutions on the moderately hydrophobic surfaces strongly depend on time. As far as the nonionic surfactant is considered, it spreads well over all the hydrophobic polymer surfaces used. Moreover, the results obtained indicate that spreading (if it occurs) in the long-time regime is controlled not only by the diffusive transport of surfactant to the expanding liquid–vapor interface. Obviously, another process involving adsorption at the expanding solid–liquid interface (near the three-phase contact line), which goes more slowly than diffusion, has to be active.

Capillary Flow of Cationic Polyelectrolyte Solutions

The flow rates and the dynamic contact angles of aqueous solutions of cationic polyelectrolyte (CPE) in quartz capillaries with radius of 3–4 μm are measured. It is shown that the surface tension and viscosity of CPE solutions with concentrations from 10–1 to 10–5 g/l are the same as for water. Surface inactivity of CPE leads to the substantial difference between the capillary properties of their solutions and those of surfactant solutions. It is established that, as the solution concentration increases, the advancing contact angles are reduced from 83° to 75°; the receding contact angles lie between 10° and 20°. Large hysteresis of contact angle can probably be related to the formation of metastable wetting film behind the receding meniscus. Surface hydrophobization occurs as a result of the adsorption of CPE molecules on the negatively charged quartz surface. The specific features of the application of CPE solutions in the deposition technology of hydrophobic coatings, the capillary imbibition and displacement of oils from hydrophobic pores are discussed.

Surface properties of modified acrylates

Abstract Surface evaluation has been used to follow modification progress when acrylic copolymers were reacted with ethylenediamine. Among studied materials copolymer of trimethylolopropane triacrylates (TMPA), butyl acrylate (BA) and vinyl acetate (VA) was the most susceptible to aminolysis. Evaluation of surface polarity showed that modification was completed after 150 s. However, surface titration, e.g. registration of contact angle for aqueous solutions of HCl and NaOH with pH ranging from 2 to 12, indicated appearance of acidic and basic groups on modified surface. Moreover, surface basic groups were slowly replaced by carboxylic functionalities when the modification time was increased. The paper shows the usefulness of contact angle evaluation to monitor of polymer modification process.

Wetting Characteristics of Aqueous Surfactant-Laden Drops

Strategies to promote or control droplet spreading on solid surfaces is important to many industrial and biological processes. The manipulation of surface tension and contact angle by the addition of surface-active compounds to the bulk liquid of a drop offers one strategy for altering the adhesion tension maintaining drop integrity on a solid surface. Here, we present results of an experimental study of surfactant-laden drop behavior on solid surfaces. Wetting experiments were performed to determine how contact angles and contact angle hysteresis change with varying soluble surfactant concentration in the bulk liquid phase. Static, advancing, and receding contact angles of aqueous solutions of two different surfactants were measured over a wide range of surfactant concentrations on three different solids using an inclining surface. In general, adhesion tension increased and then plateaus as the surfactant concentration increased from very dilute values to higher concentrations. At surfactant concentrations above the critical micelle concentration, a continued decrease in contact angle was observed, leading to an increase in the adhesion tension. Subsequent experiments confirmed adsorption of surfactants to the solid substrate. Contact angle hysteresis was calculated from the experimental data. The behavior of the contact angle hysteresis was substrate and surfactant concentration dependent, but only at lower surfactant concentrations. Material combinations that led to partial wetting could be converted to complete wetting by the addition of sufficient surfactant in the bulk phase, but at the cost of increasing adsorption onto the solid, which restricts drop motion.

Contact Angles of Aqueous Solutions on Copper Surfaces Bearing Self-Assembled Monolayers

A laboratory exercise suitable for physical chemistry students at university level is described for the evaluation of contact angles. Students are required to modify copper surfaces by the adsorption of a self-assembled monolayer. The monolayers are formed from ethanolic solutions of long-chain alkanethiols that are terminated with either a methyl or a carboxylic acid group. Mixed monolayers are easily formed by immersion of the copper plates in solutions of mixed composition. The surface charge of monolayers bearing carboxylic acid groups can be modified by controlling the pH of the test solution. By these means the composition and degree of dissociation of the monolayer is manipulated, bringing about changes in interfacial energy. This results in a change in the wetting behavior, observed as a change in the measured contact angle. The results are interpreted in relation to the Young equation. The short range of the surface forces influencing the contact angle is highlighted. The experiment requires litt...

Influence of epiphytic micro-organisms on leaf wettability: wetting of the upper leaf surface of Juglans regia and of model surfaces in relation to colonization by micro-organisms.

Wetting of the upper leaf surface of Juglans regia L. and of model surfaces colonized by epiphytic micro-organisms was investigated by measuring contact angles of aqueous solutions buffered at different pH values. During June to October 1995, contact angles of aqueous solutions on the leaf surface of J. regia decreased by angles ranging from 12° (low pH values) to 25° at high pH values. At the end of this vegetation period, wetting was strongly dependent on pH showing significantly lower contact angles with alkaline solutions (pH 9·0) than with acidic solutions (pH 3·0). Contact angle titration measured angles on the leaf surface as a function of the pH of buffered aqueous solutions, covering a pH range from 3·0 to 11·0. Titration curves revealed inflection points around 7·5, indicating the existence of ionizable carboxylic groups at the interface of the phylloplane. Altered leaf-surface wetting properties observed on the intact leaf surface could be simulated in model experiments by measuring contact angles on artificial surfaces colonized by Pseudomonas fluorescens and by epiphytic micro-organisms isolated from the phylloplane of J. regia. Strong evidence is provided that interfacial carboxylic groups derive from epiphytic micro-organisms present on the phylloplane. Results suggest that the age-dependent increase in, and pH dependence of, wetting as leaves mature are related to the presence of epiphytic micro-organisms on the phylloplane. Ecological consequences of increased leaf-surface wetting, concerning the structure of the leaf surface as a microhabitat for epiphytic micro-organisms, are discussed.

Active Control of Wetting Using Applied Electrical Potentials and Self- Assembled Monolayers

We have used applied electrical potentials, in combination with self-assembled monolayers (SAMs) of alkanethiolates supported on gold films, to control the wettability of a surface over wide ranges. A surface can be transformed from nonwetting to wetting, or the reverse, with time constants of seconds. The method is based on a competition between reductive electrochemical desorption of a hydrophobic SAM and its re-formation from alkanethiol in solution. Self-assembled monolayers formed from either CH 3 (CH 2 ) 15 SH or CH 3 (CH 2 ) 2 SH were hydrophobic (80 o <θ<110 o , θ=contact angle) toward aqueous solutions of electrolyte at neutral potentials but became hydrophilic (θ∼10 o ) at reducing potentials (E<-1.3 V vs Ag wire): Contact angles of aqueous solutions containing CH 3 (CH 2 ) 2 SH returned to their initial values (θ∼80 o ) after the reducing potentials were removed. Because the change in wettability was dependent on the structure of the organic molecule in the monolayer, it was possible to prepare patterned SAMs in which certain regions were transformed from hydrophobic to hydrophilic by changing potential, while other regions were inert

Potential-Dependent Wetting of Aqueous Solutions on Self-Assembled Monolayers Formed from 15-(Ferrocenylcarbonyl)pentadecanethiol on Gold

Aqueous solutions of 0.1 M NaClOr (pH 1.5, 10 mM KHzPOn) show potential-dependent wetting on self-assembled monolayers (SAMs) formed from 15-(ferrocenylcarbonyl)pentadecanethiol (FcCO(CH2)lbSH; Fc = [45-CbHs]Fehl5-CsHsl) adsorbed on Au surfaces. Contact angles (d) decreased from 71o to 43o (A cos d = -0.40) when the electrical potential of the SAM was increased from 0.3 to 0.5 V (vs a Ag wire reference electrode) and then increased from 43o to 58o when the potential of the SAM was returned to 0.2 V. Repeated cycling between these values of the potential leads to a progressively decreasing response, as the Fc groups were destroyed by side reactions. Contact angles of aqueous solutions on SAMs formed from CH3(CHz)pSH decrease by only 2o (from -115o to 113o, A cos d = 0.05) over the same range of potentials (Sontag-Huethorst, J. A. M.; Fokkink, L. G. J. Langmuir 1992,8, 2560-2566). The contrast between the wettability of SAMs terminated with Fc and CH3 groups suggests that potential-dependent wetting of the former is caused primarily by the electrochemical oxidation of the electrically neutral, surface-confined Fc to the more polar and plausibly more wettable Fc+ cation. Linear sweep cyclic voltammetric measurements upport this hypothesis. Surfaces of gold patterned with SAMs formed from FcCO(CHz)rsSH and CHg(CH2)IsSH were used to construct a micrometer-scale gate that controls the flow of liquid down a surface.

Effect of disinfectant solutions on the wettability of elastomeric impression materials

The wettability of impression material affects the number or volume of air bubbles generated during the pouring of gypsum casts. This study was done to determine the effect of various commercial disinfectant solutions on the wettability of elastomeric impression materials. The technique of measuring advancing contact angles of aqueous solutions of calcium sulfate was used to determine changes in the wettability of four types of impression material before and after immersion in one of five disinfectants. All disinfectant solutions that were tested increased the wettability of polysulfide. Chlorine dioxide produced the greatest increase in the wettability of polysulfide by decreasing the contact angle on polysulfide at least 48 degrees. All disinfectants decreased the wettability of hydrophilic addition silicone by increasing the contact angle up to approximately 30 degrees. The differences were significant as determined by paired Student t-tests. Addition silicone was the material most resistant to change in contact angle. Chlorine dioxide had the greatest beneficial effect on wettability.

Oxynitride Glass Reinforced Cement Composites

AbstractGlass fiber reinforced composites made with an oxynitride analogue of alkali resistant glass were tested in tension after accelerated aging. The results were compared to composites made from oxide alkali resistant glass. The strength of the oxynitride glass reinforced composites was almost double that of the oxide glass based material. The results are related to the improved properties of oxynitride glass over oxide glass. In particular previous work has shown that surface chemistry of the oxynitride glass inhibits the formation of a strong bond between fiber and matrix. The difference in surface chemistry was examined by measuring the contact angle of aqueous solutions with respect to nitrogen content of the glass.

Contact angles of aqueous solutions on an organoclay

Values for the critical surface tension of octadecylammonium bentonite and dioctadecyldimethylammonium bentonite were derived from measurements of the contact angle with aqueous solutions of ethanol and acetone. Depending on the preparation of the dry organoclay surfaces, γ c for toluene cast surfaces were 22–25 mN m −1 and for mechanically pressed disks were 19 to 21 mN m −1 with ethanol solutions. Acetone solutions gave γ c in the range of 23 to 26 mN m −1. Comparisons to established values of γ c for polymers containing organic groups similar to those in the organoclays are made.

Adsorption of 1-butanol and 1-pentanoic acid from the aqueous solution on polymers. Analysis of the solid—liquid interfacial activity

In order to evaluate the solid—liquid interfacial activity of surfactant, contact angles of aqueous solutions of 1—butanol and 1—pentanoic acid on polypropylene (PP), polystyrene (PSt), polyvinyl chloride (PVC), and polymethyl methacrylate (PMMA) were measured. In many cases, discontinuities in slope of the contact angle θ vs concentration x (mole fraction) curves were observed, which was attributed to the change of the adsorption state from the horizontal to the vertical one. From these data, the decrease of the solid—liquid interfacial tension Δ γSL due to adsorption of surfactant was calculated. A parameter α, defined as lim ( ΔγSL x ), was introduced which was determined by extrapolation of Δγ- x plot. x → 0 The free energy of adsorption ΔG ads 0 was calculated from α value, and ΔG ads ∗ was calculated by: ΔG ads ∗ = ΔG ads 0 - NA 0γLV 0 cos θ 0 , where the last term represents the work of immersion of polymer into water per the area NA 0 of one mole of solute. The α values (and also − ΔG ads 0) are large for PP and small for PMMA. However, −ΔG ads ∗ values are small for PP and large for PMMA, which corresponds to the stronger interaction of PMMA with surfactant than of PP due to the larger polarity of PMMA.