Wilhelmy Plate Method Research Articles

Chemical modification and wetting of medium density fibreboard produced from heat-treated fibres

The objectives of this study were to investigate the effect of heat treatment of fibres on the advancing and receding contact angles and wicking of panels by the Wilhelmy plate method; to verify the possible relationships between wetting properties and water absorption of the panels; and to determine the surface composition of heat-treated fibres by X-ray photoelectron spectroscopy (XPS). Fibres were treated at 150 and 180 °C for 15, 30 and 60 min. Our results showed that the treatment increased contact angles and decreased water absorption. Wicking was reduced by about 70% for the 150 °C group and 80% for the 180 °C group. XPS analysis demonstrated a slight decrease of the O/C ratio and changes of the C1/C2 ratio following treatment.

Characterization of the In Situ Structural and Interfacial Properties of the Cationic Hydrophobic Heteropolypeptide, KL4, in Lung Surfactant Bilayer and Monolayer Models at the Air−Water Interface: Implications for Pulmonary Surfactant Delivery

This study examines the various equilibrium in situ secondary structures of the pharmaceutical heteropolypeptide, KL 4, in the solid state, in solution, and in the monolayer state alone and mixed with dipalmitoylphosphatidylcholine (DPPC) and palmitoyloleoylphosphatidylglycerol (POPG). In situ surface circular dichroism spectroscopy, using a method first reported by Damodaran (Damodaran, S. Anal. Bioanal. Chem. 2003, 376, 182-188), of equilibrated KL 4, DPPC/KL 4, POPG/KL 4, and DPPC/POPG/KL 4 monolayers at the air-water interface was used to examine the in situ two-dimensional conformation of KL 4. Gravimetric vapor sorption by solid KL 4 was used to analyze the effects of water molecules on the conformation of KL 4 when confined as a monolayer at the surface of water. Solid-state KL 4 conformation was determined by X-ray powder diffraction (XRPD). The equilibrium interfacial and spreading properties were measured at 25 degrees C, 37 degrees C, and 45 degrees C using the Wilhelmy plate method and Langmuir film balance. Equilibrium phase transition temperatures were measured using differential scanning calorimetry (DSC). It was found that solid-state KL 4, which takes up very little water, exhibits beta-sheet and alpha-helix secondary structures, whereas KL 4 in solution appears to exist only as an alpha-helix. KL 4 forms a stable, insoluble monolayer, exhibiting beta-sheet and aperiodic structures. These structures provide KL 4, when confined in two-dimensions, the structural flexibility to maximize favorable cationic lysine-water interactions and favorable leucine-leucine hydrophobic and van der Waals interactions; while effectively "shielding" the leucine residues away from water. In DPPC/KL 4 monolayers, KL 4 retains its native beta-sheet and aperiodic structures, consistent with phase separation of DPPC and KL 4 in bilayers and monolayers. In POPG/KL 4 monolayers, KL 4 exhibits an increase in aperiodic secondary structures (loss of beta-sheet) to maximize favorable electrostatic interactions, consistent with the observed negative deviations from ideal monolayer mixing.

The influence of viscoelastic thermal compression on the chemistry and surface energetics of wood

The influence of the viscoelastic thermal compression (VTC) of wood on its surface chemistry, wettability, and surface free energy was evaluated. The changes in surface chemistry were studied by means of Fourier transform infrared spectroscopy (FTIR). Wettability was determined on the basis of the contact angle of water, using the Wilhelmy plate method. Surface free energy was determined according to the Owens Wendt Rabel and Kaelble (OWRK) theory, using the contact angle data of diiodomethane and formamide. The studied material was wood of the low-density hybrid poplar ( Populus deltoides × Populus trichocarpa), which was densified to three different degrees of densification (63%, 98%, and 132%) using the VTC process. The results, based on the FTIR spectra, revealed that the VTC process caused minor chemical changes on the wood surface. However, wettability changed significantly. The VTC wood surface exhibits rather hydrophobic behaviour. Evaluation of the surface energetics using the OWRK approach showed that total surface free energy dropped significantly due to the VTC process.

Influences of freeze-drying and UV-irradiation on the microstructured morphology and on the wetting properties of PS 41–PAA 271 coating

Influences of freeze-drying process and of UV-irradiation are studied on morphology, surface composition and wetting properties of polystyrene– b-poly(acrylic acid) (PS 41–PAA 271) diblock copolymers (dip-coated on the substrate made of stainless steel). Observations by scanning electron microscopy (SEM) and measurements of static water contact angles highlight that morphology of non-UV-irradiated PS 41–PAA 271 is re-organised after steps of immersion/emersion in water and freeze-drying. These both processes modify PS 41–PAA 271 surface in a microstructured layer of polymer that covers a part of the stainless-steel substrate. Moreover, analyses by X-ray photoelectron spectroscopy (XPS) and measurements of dynamic wetting angles with the Wilhelmy plate method demonstrate that stimuli-responsive properties of PS 41–PAA 271, whose wetting properties depend on the environment, are enhanced after using a step of UV-irradiation for 20 min. This process influences the composition of the coating in order to stabilise the smart material. Consequently, repeated cycles of immersion/emersion in water showed that a maximum gap of 20–25° is obtained between the hydrophobic state (after drying at air for 90 min) and the hydrophilic state (after immersion in water).

Densities, Viscosities, Refractive Indices, and Surface Tensions for the Ternary Mixtures of 2-Propanol + Benzyl Alcohol + 2-Phenylethanol at T = 308.15 K

Densities, viscosities, refractive indices, and surface tensions for the ternary system of 2-propanol + benzyl alcohol + 2-phenylethanol were measured at T = 308.15 K and atmospheric pressure. Densities were determined using a vibrating-tube density meter. Viscosities were measured with an automatic Ubbelholde capillary viscometer. Refractive indices were measured using a digital Abbe-type refractometer. Surface tensions were determined by the Wilhelmy-plate method. The experimental data are used to calculate excess molar volumes VE, deviations in the viscosity Δη, deviations in the refractive index ΔnD, and deviations in the surface tension Δσ. The calculated quantities VE, Δη, ΔnD, and Δσ were fitted to the variable-degree polynomials.

Amphiphilic cellulose: Surface activity and aqueous self-assembly into nano-sized polymeric micelles

The aim of the present study was to design amphiphilic cellulose that can self-assemble into polymeric vesicle or as nontoxic surfactants. Sulfate was firstly introduced as hydrophilic groups, then the hydrophobic groups for three cellulose derivatives. Effects of the hydrophobic length on the surface tension and critical aggregate concentration (cac) were investigated by the conventional Wilhelmy plate method. Results showed that the cac value decreased from 0.28 to 0.08 wt% and the corresponding surface tension increased from 44 to 55 mN/m when the hydrophobic chain length changed from C 8 to C 18. The aqueous self-assembly of the modified polymer was investigated using transmission electron microscopy (TEM) and dynamic laser scattering (DLS). Results showed that three cellulose derivatives were capable of forming polymeric micelles in water with an average particle diameter ranging from 20 to 67 nm. And the diameter of the nano-micelles was proportional to the length of hydrophobic chain under the experimental conditions. These amphiphilic polymers showed more remarkable shear shinning rheological behavior as expected since higher shear rates lead to disruptions of hydrophobic associations. These data suggest that the amphiphilic cellulose derivative may form nano-micelles and might find use as surfactant or a potential drug carrier.

Adipic and Malonic Acid Aqueous Solutions: Surface Tensions and Saturation Vapor Pressures

The surface tension of adipic aqueous solutions was measured as a function of temperature (T=278-313 K) and adipic acid mole fraction (X=0.000-0.003) using the Wilhelmy plate method. A parametrization fitted to these data is presented. The evaporation rates of binary water-malonic and water-adipic acid droplets were measured with a TDMA technique at different temperatures (T=293-300 K) and relative humidities (58-80%), and the saturation vapor pressures of subcooled liquid malonic and adipic acids were derived from the data using a binary evaporation model. The temperature dependence of the vapor pressures was obtained as least-squares fits to the derived vapor pressures: ln(Psat,l) (Pa)=220.2389-22634.96/T (K)-26.66767 ln T (K) for malonic acid and ln(Psat,l) (Pa)=140.6704-18230.97/T (K)-15.48011 ln T (K) for adipic acid.

Effect of drying method on the surface wettability of wood strands

An experiment was conducted to investigate the effects of drying methods, namely rotary drum, lab oven, microwave and air-drying, on the surface wettability of wood strands by the Wilhelmy plate method. The measurements included the surface contact angle, free energy, and liquid sorption capacity. Thirty industrial strands including southern yellow pine (Pinus spp.) and poplar (Populus spp.) were randomly collected for each drying method. The results from this study showed that the surface contact angle of a strand depends on the liquid used as well as the drying method and wood species. Liquid sorption capacity of the pine strands increased with decreasing surface contact angle, but this trend was not observed with the poplar strands. The total surface energy was almost the same for strands within species, regardless of the drying method, but it was higher on poplar strands than on pines. The polar and disperse components of surface free energy varied with both drying method and wood species. The surface polar energies of oven-dried pine strands and rotating drum-dried poplar strands were higher than on strands dried by other methods. For lower temperature drying methods (air and microwave), the lowest polar component was observed on the radial face of the pine strands. For the higher-temperature drying methods (oven and rotary-drum), the lowest polar component was found to on the tangential face of the pine strands.

Densities, Viscosities, Refractive Indexes, and Surface Tensions for Binary Mixtures of 2-Propanol + Benzyl Alcohol, + 2-Phenylethanol and Benzyl Alcohol + 2-Phenylethanol at T = (298.15, 308.15, and 318.15) K

Densities, viscosities, refractive indexes, and surface tensions for three binary systems (2-propanol + benzyl alcohol, 2-propanol + 2-phenylethanol, and benzyl alcohol + 2-phenylethanol) were measured at T = (298.15, 308.15, and 318.15) K over the whole composition range at atmospheric pressure. Densities were determined using a vibrating-tube density meter. Viscosities were measured with an automatic Ubbelholde capillary viscometer. Refractive indexes were measured using a digital Abbe-type refractometer. Surface tensions were determined by the Wilhelmy-plate method. These results are used to calculate excess molar volumes, , deviations in the viscosity, Δη, deviations in the refractive index, ΔnD, and the deviations in the surface tension, Δσ, at these three temperatures. The calculated quantities of , Δη, ΔnD, and Δσ were fitted to the Redlich−Kister equation to estimate the binary interaction parameters.

Interfacial Properties of Aqueous Nonionic Fluorocarbon Surfactant Solutions

The equilibrium, dynamic surface tensions, and surface dilatational elasticity of aqueous solutions of nonionic fluorocarbon surfactant are reported. The critical micellar concentration, CMC (0.023 mM) and equilibrium surface tension (24.6 m N . m−1) at CMC were measured by Wilhelmy plate method for aqueous solution of C8F17SO2N(C3H7)(C2H4O)nH (n=20), abbreviated as EF122A. The surface tension decay is slower for C8F17SO2N(C3H7)(C2H4O)nH (n=10) system, abbreviated as EF122B compared to the EF122A system over short time region, which indicates the slow transport of the surfactant molecules to the surface. The relaxation time for surface tension decay is estimated by fitting a series of exponentials to the dynamic surface tension data and it decreases with temperature for EF122A. Slow exchange of monomers between bulk and interface is reflected in the high elasticity value of the air‐liquid interface for EF122B compared with EF122A within measured frequency window (0.125–1.25 Hz).

Surface properties and synthesis of the cellulose-based amphoteric polymeric surfactant

A new family of amphoteric surfactant – 2-hydroxy-3-( N, N-dimethyl- N-dodecyl-ammonium)-propyloxy cellulose sulfate (GDCS) was synthesized by etherification of cellulose sulfate with glycidyl dodecyl dimethylammonium chloride (GDDMAC) in this paper. GDCS was characterized by FT-IR spectroscopy, 13C NMR, elemental analysis and TG. The surface-active properties such as surface tension, critical aggregation concentration were determined by the Wilhelmy plate method. The micellar conformation of GDCS in aqueous solution at different concentration was investigated by environmental scanning electro microscopy (ESEM). Rheological measurements of GDCS indicated that the solution first behaved like a pseudoplastic property, the apparent viscosity decreased sharply, and then exhibited a Newtonian property, the apparent viscosity did not change obviously anymore.

Visualization of the curved liquid surface by means of the optical method

A simple technique for visualizing the curved liquid surface was developed, which is based on analyzing the reflection patterns from the curved liquid surface. Due to the wetting effect, a symmetric meniscus appeared around the needle which was inserted into the liquid. A round dark area reflection pattern was observed, when a collimated, expanded laser beam illuminates upon the curved liquid surface in a vertical direction. Particularly, the size of the dark area will change with the diameter of the laser beam. The relationships between them were theoretically analyzed, and the corresponding analytic expression of the curved liquid surface profile was derived. Based on the analytic expression, the surface tension of the liquid was obtained. Compared with the results of other methods, such as the Wilhelmy plate method and the rising method, they are in good agreement. It shows that an effective and practical technique for visualizing the curved liquid surface was found.

Universality of a surface tension—contact‐angle relation for hydrophobic soils of different texture

AbstractWettability of soil affects a wide variety of processes in soils like infiltration, percolation, preferential flow, and surface runoff. Even though efforts have been made to determine contact angles and surface tension or energy of smooth surfaces, the determination on granular materials like soil particles remains unsolved. One objective of this study was to test the consistency of contact angles (CA) measured with the newly modified and easy‐to‐apply Wilhelmy plate method by using solid particles and liquids with defined variations of surface tension. A second objective was to derive basic physical surface properties for the irregularly shaped and chemically heterogeneous soil particles. Advancing contact angles were determined by using model soils varying in texture from clay to coarse sand to check the impact of grain size on the CA measurements. Varying the solid‐surface tension with dichlorodimethlylsilane treatments provided for pure‐water wetting stages ranging from wettable to extremely hydrophobic. The surface tensions of the liquids were varied from 72 mN m–1 to 25 mN m–1 by using water or water‐ethanol mixtures. The surface tensions of the model soils were determined with the zero degree–contact angle method following Zisman's critical–surface tension concept. Results show that the measured CA varied continuously with the variations of the surface tension of the liquid and the solid phase, respectively. A general interpretation of the results is possible by using the concept of the Equation of State Approach.

Synthesis of biocompatible hydrophobic silica–gelatin nano-hybrid by sol–gel process

Silica–biopolymer hybrid has been synthesised using colloidal silica as the precursor for silica and gelatin as the biopolymer counterpart. The surface modification of the hybrid material has been done with methyltrimethoxysilane leading to the formation of biocompatible hydrophobic silica–gelatin hybrid. Here we are reporting hydrophobic silica–gelatin hybrid and coating precursor for the first time. The hybrid gel has been evaluated for chemical modification, thermal degradation, hydrophobicity, particle size, transparency under the UV–visible region and morphology. FTIR spectroscopy has been used to verify the presence of CH 3 groups which introduce hydrophobicity to the SiO 2–MTMS–gelatin hybrids. The hydrophobic property has also been tailored by varying the concentration of methyltrimethoxysilane. Contact angle by Wilhelmy plate method of transparent hydrophobic silica–gelatin coatings has been found to be as high as ∼95°. Oxidation of the organic group which induces the hydrophobic character occurs at 530 °C which indicates that the surface hydrophobicity is retained up to that temperature. Optical transmittance of SiO 2–MTMS–gelatin hybrid coatings on glass substrates has been found to be close to 100% which will enable the hybrid for possible optical applications and also for preparation of transparent biocompatible hydrophobic coatings on biological substrates such as leather.

Adsorption-Equilibrium Surface Tension of Surfactant Solutions; Examination by the Drop Volume Method

Abstract The surface tension of aqueous solutions of cationic, nonionic, and anionic surfactants was measured as a function of the size of drop formed under the tip of a glass capillary and the time for which the drop is allowed to stand by a previously developed apparatus based on the drop volume method. The surface tension of cationic and nonionic surfactant solutions was slightly dependent on the drop size and the adsorption time at low concentrations, and we could easily obtain the adsorption-equilibrium surface tension values by use of an intact capillary. However, the surface tension of anionic surfactant solutions showed a strong dependence on these factors, and the equilibrium surface tension values could not be obtained by use of the intact capillary at all. This situation was drastically improved by use of the water-repellent capillary coated with a silane-coupling reagent. We proposed that the equilibrium surface tension value of surfactant solutions can be determined by adopting the adsorption time at which the surface tension value becomes constant on the surface tension vs the drop size curves. Further, the conditions under which the equilibrium surface tension value of surfactant solutions could be acquired by means of the drop volume method were quite different than those of the Wilhelmy plate method.

Surface activity of a non-micelle forming compound containing a surface-active impurity

Purpose. The purpose of this study is to characterize the surface activity of a water-soluble compound and its ability to form aggregates/micelles. Methods. Aqueous solutions of the compound were prepared at various concentrations. Surface tension was determined using drop volume and Wilhelmy plate methods. Moreover, conductivity and osmolality measurements of aqueous solutions were also determined at various concentrations. Results. Even though the compound appeared to be surface active, no change in the slope was found of either molar conductivity (S cm 2/mol) versus square root of concentration ( R 2 = 0.994) or osmolality (mOsm/kg) versus concentration ( R 2 = 0.999). Moreover, no clear critical micelle concentration was observed when surface tension was plotted versus log concentration. These results indicated no micelle formation in these solutions. In order to investigate this behavior further, the main impurity in the compound was also tested. Surface tension measurements of solutions containing different concentrations of the impurity indicated that the impurity was more surface active than the compound. Conclusions. This study shows the importance of characterizing the behavior of surface-active compounds using multiple techniques. This work also emphasizes the importance of determining whether surface activity in aqueous solutions is due to the main compound, its impurities or both.

Synthesis and aggregates of cellulose-based hydrophobically associating polymer

A novel cellulose-based hydrophobically associating water-soluble polymer-cellulose octaonate sulfate (COS) was synthesized in this paper. The basic physico-chemical properties such as surface tension and the critical aggregation concentration ( cac) were measured by the conventional Wilhelmy plate method. The obtained cac value was compared with environmental scanning electron microscopy (ESEM) and Rheology data. All these results indicated that cac of this amphiphilic polymer was between the range 0.04 and 0.2 wt% and the corresponding surface tension was around 55 mN/m. The conformation of aggregates and size of particles in aqueous solution were carefully investigated by ESEM and dynamic laser scattering (DLS) measurements. When the concentration is around 0.04 wt%, loose aggregates are formed; around 0.5 wt%, network structure formed. DLS results indicated that average size of particle was increased from 54.7 nm to 73 nm and finally to 168.1 nm with the increase of concentration from 0.04% to 0.1% and even to 0.2%. These results suggested that almost all of micelles in aqueous solution aggregated at the experimental concentration range 0.04–0.5 wt%. Rheological properties of this polymer were similar to hydrophobically associating polymers’ (HMP). As the shear rate increased, the solution passed through a shear-thickening region before exhibiting a sharp decrease in viscosity, eventually exhibited Newtonian behavior.

Adsorption and Aggregation Properties of Heterogemini Surfactants Containing a Quaternary Ammonium Salt and a Sugar Moiety

A novel heterogemini surfactant comprising two hydrocarbon chains and two different hydrophilic groups such as a quaternary ammonium cation and gluconamide nonion N,N-dimethyl-N-[2-(N'-alkyl-N'-gluconamide)ethyl]-1-alkylammonium bromides (2CnAmGlu, where n represents hydrocarbon chain lengths of 8, 10, 12, and 14) was synthesized by reacting N,N-dimethylethylenediamine with alkyl bromide, followed by a reaction with 1,5-D(+)-gluconolactone. The adsorption properties of 2CnAmGlu were characterized by surface tension measurements made using the Wilhelmy plate method, and their aggregation properties were investigated by dynamic light scattering and cryogenic transmission electron microscopy techniques. The relationship between the hydrocarbon chain length and the logarithm of the critical micelle concentration (cmc) for 2CnAmGlu exhibited a linear decrease when the chain length was increased up to 12 and then a departure from linearity at n=14. The surface tension reached 24-26 mN m-1 at each cmc, indicating high efficiency in lowering the surface tension of water. Furthermore, it was found that the structure of the aggregate formed for 2CnAmGlu in solution was influenced by the hydrocarbon chain length; that is, for n=10 and 12, micelles with a hydrodynamic radius of 2-5 nm were formed, whereas vesicles were also observed for n=14.

CLOUD POINT AND DYE SOLUBILIZATION STUDIES OF AMPHIPHILIC DRUG SOLUTIONS: THE EFFECT OF ELECTROLYTES AND NONELECTROLYTES

The effect of electrolytes and nonelectrolytes on the micellar behavior of amitriptyline (AMT), an amphiphilic drug, has been investigated using cloud point (CP) and dye solubilization techniques. The critical micelle concentration (cmc) of AMT determined by the Wilhelmy plate method was about 40 mM in the presence of 10 mM sodium phosphate, and it reduced to about 20 mM in the presence of 500 mM sodium phosphate. Interestingly, the CP phenomenon was observed even below the cmc in cationic AMT solutions. Increasing AMT concentration reduced the CP below the cmc, while it had the opposite effect above the cmc. An increase in the pH of the AMT solutions from 6.2 to 6.8 at a given AMT concentration decreased the CP and increased the AMT micellar size. Addition of an electrolyte such as sodium chloride to 100 mM AMT in water increased both the CP and the AMT micellar size. On the other hand, added nonelectrolytes such as dextrose, sucrose, and urea decreased both the CP and the micellar size. Experimental results have been interpreted in terms of electrostatic effect and interactions between additives and AMT head groups.

Applicability of Interfacial Theories of Surface Tension to Water‐Repellent Soils

Most methods used to characterize the magnitude of soil water repellency consist of direct or indirect measurements of the initial advancing contact angle (θ) at the solid–liquid–vapor interface. Aqueous ethanol solutions (AETS) are commonly used as testing liquids having different liquid–vapor surface tensions (γLV); however, θ measurements using AETS have rarely been performed on water‐repellent soils (WRS). Measurements of θ in this study were conducted using both the Wilhelmy plate method (WPM) and the CRM (weight‐gain capillary rise method) for three natural and four hydrophobized WRS (water‐repellent soils). The values of the Young equation (solid–vapor and solid–liquid surface tension) were calculated, and correlated with the Goods–Girifalco interaction parameter, Φ. The factor Φ was found to be a linear function of the solid–liquid surface tension: Φ = 1 − 0.011γSL, with no significant differences between soils. This relation was then used to formulate an ESIT (empirical equation of state of interfacial tension), suggesting that from one universal constant, θ can be predicted as function of γSV The applicability of the ESIT approach to WRS was found to be inferior, in contrast to its successful use for ideal solid polymers. Nevertheless, it was found that for a water–WRS system, Φ was ∼0.6 rather than 1.0 as previously assumed. Applying Φ = 0.6 was successfully used in predicting γSV as well as the hydrophilic domain of θ vs. γLV for water and AETS.