Surface tension parameters of ice obtained from contact angle data and from positive and negative particle adhesion to advancing freezing fronts

From contact angle data obtained on flat ice surfaces with a number of liquids, combined with data on particle and macromolecule adhesion or non-adhesion to advancing freezing fronts, the apolar (Lifshitz-van der Waals or LW) and polar (Lewis acid-base or AB) surface tension (γ) components and parameters have been determined. At 0°C these are γ^LW _iee = 26.9 and γ^AB _ice = 39.6 mJ/m². The latter consists of an electron-acceptor (γ^⊕) and an electron-donor (γ^?) parameter: γ^⊕ = 14 and γ^? = 28 mJ/m².     

Interaction mechanisms associated with organic colloid fouling of ultrafiltration membrane in a drinking water treatment system

The Extended Derjaguin Landau Verwey Overbeek (XDLVO) approach was introduced to predict organic colloid fouling of membranes in an initial ultrafiltration (UF) phase. Two polymeric UF membranes, made of polyvinylchloride (PVC) and polyvinylidene fluoride (PVDF) respectively, were selected to investigate membrane fouling by filtering water samples with different organic colloid compositions. The experiment was performed to determine the fouling contributions of van der Waals (LW) interactions, electrostatic (EL) interactions, as well as double layer and short-range acid–base (AB) interactions, to the total interaction energy caused by organic colloids attaching to UF membrane surfaces. The results showed that LW interaction energy predominated when the distance between the membrane surface and organic colloid was > 5 nm, while AB accounted for a key contribution to total interaction energy over short distances (< 2.5 nm). The influence of EL interaction energy was ignored in the total interaction energy composition. The surface energy, among all characteristics of membrane material, was a dominant factor affecting membrane fouling. The experimental results of initial ultrafiltration of raw water from the actual water source were in accordance with the predictions based on XDLVO theory, indicating that it was a feasible option for predicting membrane fouling during the initial ultrafiltration phase.     

A study on the adhesion of calcium carbonate to glass. Energy balance in the deposition process

This work describes an experimental investigation on the adhesion of in situ synthesized calcite colloidal particles to rotating glass slides. The relative importance of the hydrodynamic processes involved was analyzed by measuring the amount adhered as a function of both the temperature and the rotation velocity. The adhesion was found to be temperature-dependent. At a given rotation speed of the slide, there exists a value of the temperature for which the adhesion is maximum. This value is lower, the higher the rotation speed. Comparison between experimentally determined particle fluxes (number of particles adhered per unit time and unit surface area of collector) and those calculated from Levich's theory (where laminar flow and absence of particle-collector repulsion are assumed) suggests that the hydrodynamic regime in the vicinity of the slide changes from laminar to turbulent when either the velocity or the temperature is increased above a certain critical value, corresponding to maximum adhesion. The effect of the electrolytes CaCl₂ and MgCl₂ on the adhesion was also studied in the range of concentrations between 0.7 and 70 mM. For fixed hydrodynamic conditions and temperature, the adhesion between the particle and the collector was found to be controlled by the interfacial interactions, including Lifshitz-van der Waals (LW), electrostatic double layer (EL), and acid-base (AB). The calcite-solution and glass-solution interfaces were completely characterized by using electrophoresis, contact angle, and thin-layer wicking techniques, together with van Oss et al.'s model of interfacial thermodynamics. From these data, the total energy of interaction between the particle and the substrate was computed using either the classical DLVO model (EL + LW) or the extended theory (EL + LW + AB) for different electrolyte concentrations, and reasonably good agreement was found between the experimentally observed particle attachment and the predictions of the extended DLVO theory.     

On the Predominant Electron-Donicity of Polar Solid Surfaces

The reasons for the predominant electron-donicity of almost all solid polar surfaces and its implications are discussed in this paper. By contact angle or interfacial tension measurements, the electron-accepting as well as the electron-donating properties of polar liquids can be ascertained, through the interplay between their energies of adhesion and cohesion. For the solid-liquid interface, direct interfacial tension measurements are not possible, but indirectly, solid/liquid interfacial tensions of polar systems can be obtained by contact angle measurement. However, as the energy of cohesion of a solid does not influence the contact angle formed by a liquid drop placed upon its surface, one can only measure the solid surface'ks residual polar property, manifested by the energy of adhesion between solid and liquid. This residual polar property is of necessity the dominant component; in most cases this turns out to be its electron donicity. When, by means of contact angle measurements with polar liquids, both electron-accepting and electron-donating potentials are found on a polar solid, it is most likely still partly covered with a polar liquid: usually water. The amount of residual water of hydration of a polar solid follows from its polar (Lewis acid-base) surface tension component (γ^AB). The degree of orientation of the residual water of hydration on a polar solid can be expressed by the ratio of the electron-donating to electron-accepting potentials (γ^?/γ^⊕), measured on the hydrated surface.     

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.     

Solid‐Liquid Adhesion Energies of Composite Propellant Components Determined by Solution Calorimetry

The energetic or adhesive interaction between binder matrix and solid fillers as well as plasticizers and fillers is a property determining mechanical properties as strain capacity and stress at maximum or stress at break. To know such interaction energies is therefore of interest. An isoperibolic solution calorimeter is used to measure such interaction energies or heats of immersion of the solid propellant components ammonium perchlorate (AP) and aluminium (AL) with the liquid plasticizers bis‐(2‐ethylhexyl) adipate (DEHA) and azido‐terminated oligomeric glycidylazide (GAP−A). The determined heats indicate wettability and interaction energy in units of energy per surface area of the solid component. For AP, three different grain sizes with mean diameter about 200, 90, 42 μm were used. Results indicate dependence of AP wetting on mean particle diameter: Successful wetting occurs for AP at diameters from above 90 μm. The polar interactions between the ionic AP and GAP−A greatly enhance wetting as compared to DEHA.     

Deconvolution of the structural and chemical surface properties of carbon nanotubes by inverse gas chromatography

The thermodynamic surface characteristics of carbonaceous nanomaterials (here carbon nanotubes) can be studied by inverse gas chromatography. One potential difficulty is that the effects of surface chemistry and surface topography may become convoluted. To solve this problem, measurements were performed with two distinct sets of probe molecules, each selected to isolate the contribution of either structural or chemical surface features to the vapour retention observed, allowing an unambiguous assessment of solid surface characteristics. The differences in net retention times showed that as-received, high-temperature annealed and thermally oxidised carbon nanotubes are relatively similar in their surface structure but exhibited considerably different concentrations of polar surface groups. The symmetry and tailing of the chromatographic signals was interpreted in terms of structural and chemical surface heterogeneity. The dispersive surface energies, γ^d, of the as-received and modified carbon nanotubes were found to be very similar while the specific surface energies differed significantly, contributing between 10% and 30% to the total surface energy, depending on the modification treatment. The effect of energetic surface heterogeneity on the IGC results is briefly discussed and assessed quantitatively in terms of γ^d heterogeneity profiles as a function of surface coverage.     

Surface interaction of quaternary amines with hair

Surface analysis by X-ray photoelectron spectroscopy (XPS) has shown specific 1∶1 (ionic) interaction between cationic alkyl quaternary surfactant molecules and the anionic sulfonate groups present on the hair surface. The primary driving force for the adsorption of alkyl quaternary amine molecules to the surface of the hair from aqueous solution is the ionic interaction between quaternary groups and the surface SO₃ ⁻ on the hair. Cationic quaternary molecules incorporating ester and alcohol functionalities (ester quats) demonstrate a lower number of surface quaternary nitrogens per sulfonate group, indicating an altered surface interaction mechanism. For the ester quats, a combination of electrostatic interaction modes exists in addition to the ionic N⁺/SO₃ ⁻ interaction, specifically, H-bonding interactions of the −C−O, −C−OH, and −C(O)O− polar groups with SO₃ ⁻ and other polar groups on the hair. Surface coverage of the ester quat is not reduced despite the decrease in ionic interaction at the surface. Both types of molecules orient their alkyl tails toward the surface. Molecular dynamics modeling of the surfactant/hair surface interaction indicates higher adsorption energies due to increased dipolar interactions for ester quat molecules.     

Interaction forces measured between mica-adsorbed quaternarized poly(2-vinylpyridine) layers: Effects of pH and compression

The surface forces apparatus was used to measure directly the interaction forces between mica-adsorbed quaternarized poly(2-vinylpyridine) (QP2VP) layers as a function of solution pH. The interaction is repulsive at large-surface separations and is dominated by a double layer interaction. At shorter range, electrosteric forces dominate until, at small-surface separations, attractive bridging forces lead to intersurface adhesion. The bridging attractive forces are attributed to both intersurface bridging and polyelectrolyte chain entanglement. These are extremely sensitive to the conformation of the adsorbed polyelectrolyte, which changes significantly with solution pH. Surface forces measured on compression of the adsorbed QP2VP layers do not clearly reflect changes in the adsorbed conformation and surface excess of this polyelectrolyte. Rather, the polyelectrolyte conformation is manifest more dramatically on measurement of adhesion, upon retraction/decompression of the surfaces from contact. There is a strong dependence of the adhesion between the polyelectrolyte layers on the compressive load, time in contact, and compression history since the molecular rearrangements required for chain entanglement and intersurface bridging occur on a long time scale, i.e., of the order of minutes. Under a small compressive load, the surfaces are closer together, facilitating segment-surface andsegment-segment interactions across the two interacting layers.     

The Use of AFM and Surface Energy Measurements to Investigate Drug-Canister Material Interactions in a Model Pressurized Metered Dose Inhaler Formulation

The aim of the project was to investigate the interactions between micronized salbutamol sulphate, budesonide, and formoterol fumarate dihydrate and different canister surfaces materials (Aluminium, anodized aluminium, perfluoroalkoxy, fluorinated ethylene propylene—polyether sulphone, and polytetrafluoroethylene) used in pressurized metered dose inhalers (pMDIs).

The surface component approach for polar and apolar interfacial interactions was used to predict the adhesion behavior of micronized drugs with the inner surfaces of pMDI canisters. This was achieved using a combination of in situ colloid probe atomic force microscopy (AFM) measurements and theoretical treatment of the surface free energy measurements, via a contact angle–based technique of the interacting surfaces.

All three drugs exhibited similar dispersive surface energy free values. A greater variation was, however, found in the polar component of the surface free energy measurements. These results were also reflected in the dispersive and polar components of the canister materials. Moreover, the linear relationship between the work of adhesion and AFM measured adhesion was shown to be correlated on the polar contributions of the surface free energies of the interacting materials. AFM measurements indicated that salbutamol sulphate was found to have the strongest adhesive forces with respect to the canister surface materials while budesonide and formoterol fumarate dihydrate appeared to have similar adhesive characteristics. The present study suggests that investigations into the design and characterization of pMDI formulations would benefit from considerations of the polar contribution of the surface free energy and relative work of adhesion of the drug and various components of a pMDI system.     

Experiments on contact of a loop with a substrate to measure work of adhesion

A technique for characterizing surface energies of solid materials is investigated experimentally and numerically. A narrow strip is bent into a loop, pushed into contact with a flat substrate, and then pulled off the substrate. Provided the loop is sufficiently flexible, the size of the contact zone during this process was expected to depend on the interfacial interactions. Larger adhesion forces should tend to increase the contact size, in a manner analogous to the JKR technique. The experiments involve a poly (dimethyl siloxane) (PDMS) loop and glass substrates with various coatings. Anticlastic bending of the loop affects the contact zone. Hysteresis is observed between the loading and unloading data. A three-dimensional finite element analysis is conducted in which adhesion forces are not included, and results from a two-dimensional elastica model of the loop are utilized for comparison purposes. The contact zone appears to be insensitive to the adhesive interactions between the loop and the substrate for the systems studied.     

EXPERIMENTS ON CONTACT OF A LOOP WITH A SUBSTRATE TO MEASURE WORK OF ADHESION

A technique for characterizing surface energies of solid materials is investigated experimentally and numerically. A narrow strip is bent into a loop, pushed into contact with a flat substrate, and then pulled off the substrate. Provided the loop is sufficiently flexible, the size of the contact zone during this process was expected to depend on the interfacial interactions. Larger adhesion forces should tend to increase the contact size, in a manner analogous to the JKR technique. The experiments involve a poly (dimethyl siloxane) (PDMS) loop and glass substrates with various coatings. Anticlastic bending of the loop affects the contact zone. Hysteresis is observed between the loading and unloading data. A three-dimensional finite element analysis is conducted in which adhesion forces are not included, and results from a two-dimensional elastica model of the loop are utilized for comparison purposes. The contact zone appears to be insensitive to the adhesive interactions between the loop and the substrate for the systems studied.     

Oxygen transport and surface active properties of silicone containing copolymers of methyl methacrylate II

New organofunctional siloxanes from γ-methacryloxypropyltrimethoxysilane (MPTMS) were synthesized by transesterification of methoxy groups with linear high alcohols, ether alcohols, and α-hydroxyacids. The factors affecting the substitution ratios were determined. These siloxanes were copolymerized with methyl methacrylate (MMA), crosslinked with ethylene glycol dimethacrylate (EGDM) in order to examine the effect of substituted groups to the oxygen permeability coefficient (P_d) and surface free energy properties of the resultant copolymers. The substitution of the oxygen containing polar groups decreased the oxygen permeability due to the interactions between polar groups decreasing the free volume. However, these groups increased the polar component of surface free energy (γ) and thus total surface free energy (γ_S). The hydrophilicity of the carbitol and 2-ethoxyethanol containing siloxane-MMA copolymers was found to be suitable for biomedical applications.     

Determination of the acid-base characteristics of clay mineral surfaces by contact angle measurements-implications for the adsorption of organic solutes from aqueous media

The apolar and the polar (electron-acceptor and electron-donor, or Lewis acid-base) surface tension components and parameters of solid surfaces can be determined by contact angle measurements using at least three different liquids, of which two must be polar. With swelling clay minerals (e.g. smectite clay minerals), smooth contiguous membranes can be fabricated, upon which contact angles can be measured directly. With non-swelling clay minerals (e.g. talc), contact angles can be determined by wicking, i.e. by the measurement of the rate of capillary rise of the liquids in question through thin layers of clay powder adhering to glass plates. The apolar and polar (acid-base) surface tension components and parameters thus found for various untreated and quaternary ammonium base-treated clays allowed the determination of the net interfacial free energy of adhesion of human serum albumin onto the various clay particle surfaces immersed in water. The free energies of adhesion, thus found, correlate well with the experimentally observed degree of adsorption of human serum albumin.     

Acid–base interactions and covalent bonding at a fiber–matrix interface: contribution to the work of adhesion and measured adhesion strength

The work of adhesion, W _A, and the practical adhesion in terms of the interfacial shear strength, τ, in some polymer-fiber systems were determined to establish a correlation between these quantities. An attempt was made to analyze the contributions of various interfacial interactions (van der Waals forces, acid-base interaction, covalent bonding) to the 'fundamental' and 'practical' adhesion. The surface free energies of the fibers were altered using different coupling agents. To characterize the strength of an adhesion contact, the ultimate adhesion strength, τ_ult, was determined for the onset of contact failure. The adhesion of non-polar polymers occurs through van der Waals interaction only; therefore, fiber sizing does not affect the adhesion strength. For polar polymers, such as poly(acrylonitrile butadiene styrene) and polystyrene, adhesion is sensitive to fiber treatments: suppression of the acid-base interaction by using an electron-donor sizing agent γ-aminopropyltriethoxysilane results in a decrease of both 'fundamental' and 'practical' adhesion. In the case of epoxy resins, the main contribution to the work of adhesion is made by covalent bonds. Since the process of their formation is irreversible, the work of adhesion determined from micromechanical tests seems to be more reliable than indirect estimations, such as from wetting and inverse gas chromatography techniques. Fiber treatment by sizing agents results in considerable changes in the intensity of adhesional interaction with the epoxy matrix. A correlation between the work of adhesion, the ultimate interfacial shear strength, and the strength of macro-composites has been found.     

Spreading of liquid drops over solid substrates: 'like wets like'

The classic hydrodynamic wetting theory leads to a linear relationship between spreading speed and the capillary force, being determined only by the surface tension of the liquid and its viscosity. Both equilibrium and dynamic processes of wetting are important in adhesion phenomena. The theory appears to be in good agreement with the results generated from experiments conducted on the spreading of poly(dimethylsiloxane) (PDMS) on soda-lime glass substrate and fails to account for the behavior of other liquids. In this study, the spreading kinetics of four different liquids (hexadecane, undecane, glycerol and water) was determined on three different solids, namely, soda-lime glass, poly(methyl methacrylate) (PMMA) and polystyrene (PS). Droplets from the same liquid allowed to spread under identical conditions on three different substrates produce distinctly different behaviors. The results show that the equilibrium contact angles are qualitatively ranked in accordance with the critical surface tension of wetting (γ _c) of the respective solid, i.e., high-γ _c solids caused the low surface tension liquids to assume the least equilibrium spreading (largest contact angle). On the other end, low-γ _c solids with the lowest surface tension liquid produce the most wetting (smallest contact angle). The results suggest that equilibrium spreading could be explained on the basis of the axiom 'like wets like'; in other words, polar surfaces tend to be wetted by polar liquids and vice versa.     

Peel Adhesion: Influence of Surface Energies and Adhesive Rheology

The adhesion properties of polymers are known to be influenced by both intermolecular forces operative at the interface and the rheological history of both bonding and unbonding. Recent adsorption and viscoelastic theories of adhesion and cohesion are implemented in a comprehensive examination of these phenomena. Eight peel force “master curves” extending over 14 decades of reduced rate and representing glassy state to flow region rheology are superimposed to provide a composite response envelope. Each master curve represents rate-temperature reduced adhesion of an alkyl acrylate adhesive (γ_c = 26 dyne/cm) to substrates ranging from low adhesion fluorinated polymers (γ_c = 15 to 17 dyne/cm) to polar poly-amide surfaces (γ_c = 45 dyne/cm) and glass. The rate dependent transition from interfacial to cohesive failure, a subject not treated by adsorption theory, is shown to be coincident with the onset of entanglement slippage within the polymeric adhesive. Thermodynamic criteria of polymer adhesion are shown to be applicable only to the flow region of polymeric response. This study indicates that measured surface tensions or calculated surface energies of polymeric solids do not properly account for the contributions of three dimensional network structure of the polymeric bulk phase to its total work of cohesion. Evidence of true interfacial failure of a polymer-polymer bond is supported by critical surface tension measurements.     

Cell surface properties of the demulsifying strain Alcaligenes sp. S-XJ-1 governing its behavior in oil–water biphasic systems

Bacterial behavior in oil–water biphasic systems plays an essential role in hydrophobic contaminant degradation, oil recovery, and emulsion breaking. Less is known about the cell surface properties that govern their behaviors in oil–water biphasic systems. In this study, biphasic partitioning and aggregation of a demulsifying strain of Alcaligenes sp. S-XJ-1 were experimentally measured and evaluated based on the cell surface properties of surface charge, surface free energy, and cell surface hydrophobicity (CSH). The S-XJ-1 was cultivated with five different carbon sources, and the results showed a highly varied partitioning, aggregation behavior, and cell surface properties. The calculated interaction energies, based on the cell surface properties, were consistent with the results of their behavior. Among the cell surface properties, the electron-donor character (γ^?, range 8.8–57.0 mJ/m²), which correlated well with CSH (ΔG_bwb), was an essential indicator of cell behavior. A low γ^? value enhanced the cell–interface and cell–cell interaction energies, which promoted cell partitioning and aggregation eventually leading to demulsification. The results and analysis provide important information for researchers concerned with cell–cell and cell–interface interactions.     

Reversible and Irreversible Adhesion of Polymers: Possibilities for Measurement and Calculation

Comparative analysis of existing direct and indirect techniques for estimation of the work of adhesion (W_A ) between a polymer and a solid surface - inverse gas chromatography (IGC), wetting, direct adhesion forces measurement - has been carried out. The work of adhesion was calculated from experimental data obtained using different techniques for identical polymer/solid systems. The relationship between the work of adhesion and the bond strength was analyzed, including possible W_A estimations from destructive micromechanical tests. For non-polar polymers, whose adhesion is due to dispersion interaction only, all techniques are in good agreement with each other. However, the estimates of work of adhesion obtained by different techniques considerably differ for polar polymers. The reason for this obviously consists in deficiency of theoretical knowledge about non-dispersion interactions at interfaces. Each of the considered approaches has its own advantages and shortcomings. The problems concerning the estimation of non-dispersion component of the work of adhesion can be solved only by comprehensive use of several different techniques.