A generalized Young’s equation for contact angles of droplets on homogeneous and rough substrates

Using Gibbs’ method of dividing surfaces, the contact angle of a drop on a flat homogeneous rough non-deformable solid substrate is investigated. For this system, a new generalized Young’s equation for the contact angle, including the influences of line tension and which valid for any dividing surface between liquid phase and vapor phase is derived. Under some assumptions, this generalized Young’s equation reduces to the Wenzel’s equation or Rosanov’s equation valid for the surface of tension.     

Measurement and modelling of the interfacial tension of triglyceride mixtures in contact with dense gases

The interfacial tension of various triglyceride mixtures in contact with carbon dioxide is compared. The interfacial tension of these triglyceride mixtures is similar. The interfacial tension in contact with carbon dioxide and nitrogen decreases with increasing pressure. Concerning the interfacial tension in contact with carbon dioxide, the interfacial tension increases at higher pressure with rising temperature. The interfacial tension of triglyceride mixtures and of many other liquids in contact with carbon dioxide can be described as a function of the carbon dioxide density.The modelling of the interfacial tension of triglycerides in contact with carbon dioxide or nitrogen using the density gradient theory (Macromolecules 14 (1981) 361) and the Sanchez-Lacombe equation of state (J. Phys. Chem. 80 (1976a/b) 2352 and 2568) is successful if one parameter for nitrogen and two parameters for carbon dioxide are employed. Nevertheless, an appropriate equation of state must be utilized for modelling the interfacial tension of a system. For complex systems, e.g. for triglyceride mixtures, it is indispensable to check the equation of state by means of experimental equilibrium data (e.g. density, volume, or mole fraction).     

Contact angle measurements and interpretation: wetting behavior and solid surface tensions for poly(alkyl methacrylate) polymers

Low-rate dynamic contact angles of a large number of liquids were measured on a poly(ethyl methacrylate) (PEMA) polymer using an automated axisymmetric drop shape analysis profile (ADSA-P). The results suggested that not all experimental contact angles can be used for the interpretation in terms of solid surface tensions: eight liquids yielded non-constant contact angles and/or dissolved the polymer on contact. From the experimental contact angles of the remaining four liquids, we found that the liquid-vapor surface tension times the cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γlv cos ζ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is again in harmony with those from other methacrylate polymer surfaces of different compositions and side-chains. The solid-vapor surface tension of PEMA calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 33.6 ± 0.5 mJ/m2 from the experimental contact angles of the four liquids. The experimental results also suggested that surface tension component approaches do not reflect physical reality. In particular, experimental contact angles of polar and nonpolar liquids on polar methacrylate polymers were employed to determine solid surface tension and solid surface tension components. Contrary to the results obtained from the equation-of-state approach, we obtained inconsistent values from the Lifshitz-van der Waals/acid-base (van Oss and Good) approach using the same sets of experimental contact angles.     

Correlation between surface tension and physical paint properties

Surface tension is a parameter of decisive importance for characterizing painted and unpainted surfaces related to wetting and adhesion phenomena. Measurements of the surface tension of solids by means of an automatic contact angle measurement device are presented. The theoretical evaluations provide for a separation of the surface tension into polar and disperse components. In addition, this paper briefly touches on other more far-reaching approaches (acid/base) and discusses a method for the determination of the dynamic surface tension of liquids.     

Surface tension and contact angle of herbicide solutions affected by surfactants

Contact angle and surface tension were measured for distilled and hard water solutions of adjuvants, Ortho X-77, Span-20, Sterox-NJ. Surfactant-WK, Triton B-1956, Triton X-114, Tween-20, and Sun Oil 11E. The same parameters were measured for suspensions of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine] with and without each adjuvant. All adjuvants reduced surface tension and contact angle of distilled water; Surfactant-WK was most effective and Tween-20 was least effective. Increasing concentration of surfactants from 0 to 0.1% (v/v) gave progressive reduction in surface tension and contact angle while higher concentrations, 0.1 to 2.0% (v/v), had no further effect. Surfactant-WK at 0.1% (v/v) in distilled water reduced the surfact tension from 72.8 dynes/cm to 27 dynes/cm and contact angle from 110° to 41°. An additional increase in Surfactant-WK concentration from 0.1% (v/v) to 2% (v/v) did not further reduce surface tension and contact angle. Sun Oil 11E was identical in behavior except that it was less effective than the surfactants. Water hardness up to 1,000 ppm as Ca ions did not affect surface tension and contact angle in surfactant solutions. An aqueous solution of atrazine had a higher surface tension and contact angle than ametryne in the absence of surfactants. However, these differences were not observed when surfactants were added to either herbicide.     

Wetting properties of homopolymers and copolymers of pentafluorostyrene and methylacrylate and homopolymer blends

Polypentafluorostyrene (PPFS), polymethylacrylate (PMA), and poly(pentafluorostyrene-co-methylacrylate), poly(PFS-co-MA) were prepared and the wetting characteristics of polymer blends of PPFS and PMA were compared with that of poly(PFS-co-MA) via contact angle measurements. The critical surface tension of polypentafluorostyrene was found to be 22.6 dyne/cm, which is comparable to the value reported for polytrifluoroethylene (22 dyne/cm). The critical surface tension of poly(PFS-co-MA) is not linearly related to its composition. The polymer blends of PPFS and PMA exhibit significant surface enrichment of the fluoropolymer. The harmonic-mean method¹ was employed to determine surface tensions of these polymers and many known polymers. It is found that the method produces useful surface tension data provided the contact angle values are derived from testing liquids of dissimilar polarity.     

Low-rate Dynamic Contact Angles on Poly(methyl methacrylate/n-butyl methacrylate) and the Determination of Solid Surface Tensions

Low-rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/n-butyl methacrylate) P(MMA/nBMA) copolymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that 6 liquids yield non-constant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining 6 liquids, it is found that the liquid- vapour surface tension times the cosine of the contact angle changes smoothly with the liquid-vapour surface tension, i.e., γ_iv cos θ depends only on γ_iv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and noninert (polar and non-polar) surfaces [34-42, 51 -53]. The solid-vapour surface tension calculated from the equation-of-state approach for solid -liquid interfacial tensions [14] is found to be 34.4 mJ/m², with a 95% confidence limit of \pm 0.8mJ/m², from the experimental contact angles of the 6 liquids.     

Low-rate dynamic contact angles on polystyrene and the determination of solid surface tensions

Low-rate dynamic contact angles of 13 liquids on a polystyrene polymer are measured by an automated axisymmetric drop shape analysis – profile (ADSA-P). It is found that 7 liquids yielded non-constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the other 6 liquids, it is found that the liquid-vapor surface tension times cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γ_lvcosθ depends only on γ_lv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non-inert (polar and non-polar) surfaces (7–13, 24–26). The solid-vapor surface tension calculated from the equation-of-state approach for solid-liquid interfacial tensions (33) is found to be 29.8 mJ/m², with a 95% confidence limit of ±0.5 mJ/m² from the experimental contact angles of 6 liquids.     

Alteration of the Surface Energy of Wood Using Lignin-(1-Phenylethene) Graft Copolymers

Graft copolymers of lignin, made by free radical graft copolymerization of 1-phenylethene on lignin, increased the contact angle of water on birch wood (Betula papyrifera) and decreased the critical surface tension of the wood when coated onto the wood surface from an N, N-dimethylformamide solution. The coating of copolymer changed the wood from hydrophilic (～50°) to hydrophobic (110°).

The most pronounced change in contact angle was produced by benzene-soluble extracts of the reaction product. These extracts contained lignin with long poly(1-phenylethylene) sidechains and pure poly(1-phenylethylene). They produced surfaces with the numerically highest contact angles with water and changed the wetting behavior of the surface more than physical mixtures of lignin and poly(1-phenylethylene) or either of the pure polymers.

Despite coating weights of less than 100 mg/cm, the critical surface tension of the birch wood coated with the various lignin-(1-phenylethylene) graft copolymers ranged from 26.9 to 44.9 dynes/cm while the uncoated birch had a critical surface tension of 49.6 dynes/cm.     

Adsorption of Binary Mixtures of Anionic Surfactants at Water–Air and Poly(Tetrafluoroethylene)–Water Interfaces

Measurements of the surface tension (γ _LV ) and the advancing contact angle (θ) on poly(tetrafluoroethylene) (PTFE) were carried out for aqueous solutions of sodium decyl sulfate (SDS) and sodium dodecyl sulfate (SDDS) and their mixtures. The results obtained indicate that the values of the surface tension and the contact angle of solutions of surfactants on PTFE surface depend on the concentration and composition of the surfactants mixture. On the curves presenting the relationship between the surface tension, contact angle and monomer mole fraction of SDDS (α) in the mixture of SDDS and SDS, there is a minimum at α equal to 0.8 which together with the negative values of the interaction parameters indicate that synergism occurs in surface tension and contact angle reduction almost in the range of concentration corresponding to the saturated monolayer of surfactants at the water–air interface. The results and calculations obtained also indicate that for single surfactants and their mixtures at a given concentration in the bulk phase, the values of surface excess concentration of the surfactants at water–air and PTFE–water interfaces are nearly the same, which suggests that the orientation of SDDS and SDS molecules at both interfaces in saturated monolayer should be vertical to the interfaces. Taking into account the values of the monomer mole fractions of the surfactants in a mixed monolayer at the water–air interface and values of the contact angle of a single surfactant on the PTFE surface, it is possible in a simple way to predict the values of the contact angle of a mixture at a given concentration and composition.     

Analysis and surface energy estimation of various model polymeric surfaces using contact angle hysteresis

Wetting of hydrophobic polymer surfaces commonly employed in electronic coatings and their interaction with surfactant-laden liquids and aqueous polymer solutions are analyzed using a contact angle hysteresis (CAH) approach developed by Chibowski and co-workers. In addition, a number of low surface tension acrylic monomer liquids, as well as common probe liquids are used to estimate solid surface energy of the coatings in order to facilitate a thorough analysis of surfactant effects in adhesion. Extensive literature data on contact angle hysteresis of surfactant-laden liquids on polymeric surfaces are available and are used here to estimate solid surface energy for further understanding and comparisons with the present experimental data. In certain cases, adhesion tension plots are utilized to interpret wetting of surfaces by surfactant and polymer solutions. Wetting of an ultra-hydrophobic surface with surfactant-laden liquids is also analyzed using the contact angle hysteresis method. Finally, a detailed analysis of the effect of probe liquid molecular structure on contact angle hysteresis is given using the detailed experiments of Timmons and Zisman on a hydrophobic self-assembled monolayer (SAM) surface. Hydrophobic surfaces used in the present experiments include an acetal resin [poly(oxymethylene), POM] surface, and silane, siloxane and fluoro-acrylic coatings. Model surfaces relevant to the literature data include paraffin wax, poly(methyl methacrylate) and a nano-textured surface. Based on the results, it is suggested that for practical coating applications in which surfactant-laden and acrylic formulations are considered, a preliminary evaluation and analysis of solid surface energy can be made using surfactant-laden probe liquids to tailor and ascertain the quality of the final coating.     

Effect of uniaxial drawing on surface chain structure and surface tension of poly(trimethylene terephthalate) film

Changes in the surface chain structure and the critical surface tension of poly(trimethylene terephthalate) (PTT) film under uniaxial drawing were examined by polarized attenuated total reflection infrared (ATR-IR) spectroscopy and contact angle measurement. It was observed from the stress-draw ratio curve and density measurement that the strain-induced crystallization occurs at the draw ratio of 2.5. From the ATR-IR spectra, it was also realized that the surface chain structure changes with the draw ratio, showing a remarkable increase in the surface crystallinity at the draw ratio between two and three. The critical surface tension of uniaxially drawn films increases with the draw ratio due to an increase in the surface crystallinity developed by the strain-induced crystallization. It is concluded that the surface properties of PTT film such as the chain structure at the surface and the critical surface tension are very closely related to the condition of uniaxial drawing.     

Refinement of solid layers via wetting on homogeneous lyophilic surfaces

Surface control additives (SCAs), or surfactants, can obstruct the wetting of liquid films on lyophilic surfaces even though they lower surface tension. In this work, this unusual behavior was used to decrease the widths of printed organic and nanoparticle lines on different homogeneous surfaces. A decrease in line width accompanied a change in its cross section. The ability of a SCA to decrease the line width was correlated with contact angle but not the surface tension of the solution. Line refinement was consequently attributed to an increase in contact angle. Because there were no reports that surfactants increased contact angles, the mechanisms to increase contact angle were discussed in static and dynamic terms. First, Owens and Wendt’s theory revealed that contact angle changes depended on SCA-induced modification of polar and dispersive interfacial components. However, a definitive increase in contact angle could not be deduced from this theory alone. Second, the effect of solutal Marangoni forces induced by the SCAs on contact angle was discussed by considering the wetting behaviors of binary solvents. SCA concentration dependence of surface tension at higher than the initial SCA concentration correlated well with the ability of the SCA to decrease line width.     

无粉检查手套用氟化聚氨酯润滑涂饰剂的制备和应用

采用氟醇改性热反应型水性聚氨酯,制备氟化聚氨酯(PU)乳液,实验表明最佳合成工艺为:氟醇与聚氨酯预聚体的反应温度控制在60~70℃,反应时间2.5~3.5 h,合成的乳液在3个月内稳定。测定了氟化PU乳液的粒径和表面张力,对乳液粒子的形态进行观察,并对乳液和无粉检查手套进行了红外光谱表征。结果发现:乳液粒径随氟含量的增加而增加,而胶粒结构未发生明显的改变,仍能保持球形结构;乳液的表面张力在引入氟醇后由46.0 mN/m降至22 mN/m,具有良好的润湿性能。氟化PU乳液应用于无粉检查手套的润滑涂饰,整理中无需添加润湿剂,整理后手套与水的接触角最大可增至105°,滑爽性达到5级。     

Estimation of the surface free energy of polymers

A method for measuring the surface energy of solids and for resolving the surface energy into contributions from dispersion and dipole-hydrogen bonding forces has been developed. It is based on the measurement of contact angles with water and methylene iodide. Good agreement has been obtained with the more laborious γ_c method. Evidence for a finite value of liquid-solid interfacial tension at zero contact angle is presented. The method is especially applicable to the surface characterization of polymers.     

PAA、PLiAA和PNaAA涂膜结晶度对其表面性能的影响

采用辊涂的方式将聚丙烯酸（PAA）、聚丙烯酸锂（PLiAA）和聚丙烯酸钠（PNaAA）溶液涂覆在铝箔上，通过控制不同的烘干时间和温度以获得不同结晶度的涂膜。用x-射线衍射测定聚丙烯酸、聚丙烯酸锂和聚丙烯酸钠涂膜的表面结晶度，实验测定了涂膜的表面张力和水在涂膜表面的铺展速度常数。讨论了表面结晶度、表面张力、水铺展速度常数与涂膜表面亲水性之间的关系，结果表明具有高表面张力和结晶度的涂膜有利于亲水性的提高。     

Effect of Activated Gas Plasma on Surface Characteristics and Bondability of RTV Silicone and Polyethylene

An RTV silicone and high density polyethylene are exposed in an activated gas plasma for varying times and varying conditions. Both oxygen and argon are used. Changes in critical surface tension of wetting as determined by contact angle measurements are reported. Bondability of the treated surfaces is evaluated with both the aged bonds and aged surfaces prior to bonding being evaluated. In contradiction to some of the recent work reported in the literature on the effect of activated inert gas on surface characteristics, contact angles always decreased on the materials studied indicating an increase in surface energy. The significance of the results on present adhesion theories is discussed.     

Interfacial tension and density measurement of the system corn germ oil – carbon dioxide at low temperatures

In this article, the physical properties of corn germ oil at high pressures of up to 30 MPa and at low temperatures from ?10 °C to 22 °C are presented. We measured the interfacial tension of the commercially available corn germ oil Mazola® and of unrefined corn germ oil in contact with carbon dioxide, as well as the density of carbon dioxide‐saturated corn germ oil. The interfacial tension of refined and unrefined corn germ oil in contact with gaseous carbon dioxide at temperatures above ?10 °C depends on time, while at higher pressures the equilibrium value of the interfacial tension is reached immediately after the formation of the drops or bubbles. The interfacial tension of unrefined corn germ oil in contact with carbon dioxide is higher than the interfacial tension of refined corn germ oil. This fact is explained in this article. The interfacial tension of refined and of unrefined corn germ oil in contact with carbon dioxide decrease with rising pressure and can be described as a function of the carbon dioxide density for the examined temperature range. The density of carbon dioxide‐saturated corn germ oil is linearly dependent on pressure, with a high slope if carbon dioxide is gaseous and with a low slope if carbon dioxide is liquid.     

Experimental study of frosting on different wettability surfaces under magnetic field

The frosting laws of three kinds of wettable surfaces under different magnetic field strengths were studied under cold surface temperature T_w=-10℃ and -30℃, environmental relative humidity RH=60% and 80%. Through visual observation method,image binarization is processed and calculated,the effect of frost morphology,water droplets diameter,water droplets crystallization time,water droplets coverage,frost crystal coverage,frost layer thickness and frost density under the different magnetic field intensity and surface contact angle are well explained. The results showed that adding magnetic field in combination with hydrophobic surface,the diameter of water droplets decreases by about 40%, and the crystallization time is prolonged by more than 500 s,the distribution of condensate droplets is more sparse. Frost thickness and frost density decrease as the increase of magnetic field strength and surface contact angle,providing possibility of restrain the frosting effectively. As the temperature of the cold surface decreases and the relative humidity increases, the influence of the surface properties and the external magnetic field on the frosting process decreases.