Showing papers in "Journal of Adhesion Science and Technology in 1999"
TL;DR: In this paper, the ageing process of polytetrafluoroethylene (PTFE) surfaces was investigated and it was shown that a hydrophobic environment and high temperatures promote faster recovery of the original properties of PTFE than low temperatures.
Abstract: Highly hydrophobic poly(tetrafluoroethylene) (PTFE) surfaces were modified with an air glow discharge plasma to improve their wettability. However, the hydrophilic character obtained diminishes with time, due to molecular movement in the polymer. We have determined that the ageing process is strongly affected by the environment and temperature in which the surfaces are stored. A hydrophobic environment and high temperatures promote faster recovery of the original properties of PTFE than low temperatures. Nonetheless, a hydrophilic environment, even at high temperatures, prevents the surface from losing the polar character obtained from the plasma treatment, stopping the ageing process. Moreover, this process is reversible since the character of the treated surface changes when the environment changes (i.e. from water to air). The hydrophilicity of the surfaces was evaluated by contact angle measurements of a droplet of water.
92 citations
TL;DR: In this article, a general analytical solution is presented for the equilibrium profile of the transition zone between a film and a droplet residing on a cylindrical fiber, and a new equation for apparent contact angles on fibers is derived.
Abstract: The modeling of liquid spreading and penetration into fibrous materials requires a better understanding of the interactions of thin liquid films and small droplets with single fibers. The wetting properties of fibers may differ significantly from those of plane solid surfaces. Convex surfaces of fibers imply a positive Laplace pressure acting on the liquid-gas interface. This effect causes liquid film instability and hinders droplet spreading. Liquid films on fibers arc stable when the destabilizing action of the Laplace pressure is balanced by liquid-solid adhesion. Equilibrium configurations of liquid droplets and films are determined by the competition between capillary and adhesion forces. A general analytical solution is presented for the equilibrium profile of the transition zone between a film and a droplet residing on a cylindrical fiber. A new equation for apparent contact angles on fibers is derived. Adhesion forces. including van der Waalls and polar interactions, are expressed in terms of disj...
88 citations
TL;DR: In this paper, a partial alternative to the traditional adhesion measurement approaches for organic coatings, the evaluation of adhesion by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) is discussed for different examples.
Abstract: Adhesion is considered in many situations to be a very important property of organic coatings for corrosion protection and much scientific work is devoted both to the study of the mechanism involved in polymer-metal adhesion and to the ways of measuring this property. The large number of experimental methods in existence to obtain information on coating adhesion is an indication of both the scientific and the technological interests in this material science and engineering area, but it is also a consequence of the difficulty in measuring adhesion in a general sense. As a partial alternative to the traditional adhesion measurement approaches for organic coatings, the evaluation of adhesion by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) is discussed for different examples. The influences on adhesion of different pretreatments or organic coatings are discussed, considering aluminium, galvanized steel, and stainless steel substrates, and we have shown that the information o...
66 citations
TL;DR: The adhesion of Alcaligenes denitrificans to several polymeric materials was investigated in this paper, where characteristics such as the electrokinetic potential and hydrophobicity were also determined and correlated with the capacity of bacterial cells to adhere to solid surfaces.
Abstract: The adhesion of Alcaligenes denitrificans to several polymeric materials was investigated. As the nature of the surfaces of the micro-organisms and the substrate materials is an important factor in the adhesion process, characteristics such as the electrokinetic potential and hydrophobicity were also determined and correlated with the capacity of bacterial cells to adhere to solid surfaces. The substrates used were high-density polyethylene (HDPE), polypropylene (PP), poly(vinyl chloride) (PVC), and poly(methyl methacrylate) (PMMA). The electrokinetic potential of the cells and the substrates was determined by measurements of electrophoretic mobility and the hydrophobicity was determined by contact angle measurements. All the substrates studied as well as the bacterial strain have a negative zeta potential, which means that adhesion is not mediated by electrostatic interactions. As far as hydrophobicity is concerned, PP is the most hydrophobic material, PMMA is the least hydrophobic, whereas HDPE and PVC ...
64 citations
TL;DR: In this article, a method to measure the advancing and receding contact angles on individual colloidal spheres is described, and the distance to which the microsphere jumps into its equilibrium position at the air-liquid interface of a drop or an air bubble is measured.
Abstract: In this paper, a method to measure the advancing and receding contact angles on individual colloidal spheres is described. For this purpose, the microspheres were attached to atomic force microscope cantilevers. Then the distance to which the microsphere jumps into its equilibrium position at the air-liquid interface of a drop or an air bubble was measured. From these distances the contact angles were calculated. To test the method, experiments were done with silanized silica spheres (4.1 μm in diameter). From the experiments with drops, an advancing contact angle of 101 ± 4° was determined. A receding contact angle of 101 ± 2° was calculated from the jump-in distance into a bubble. Both experimental techniques gave the same contact angle. In contrast, on similarly prepared planar silica surfaces, a clear hysteresis was measured with the sessile drop method; contact angles of 104.5 ± 1° and 93.8 ± 1° were determined for the advancing and receding contact angles, respectively.
61 citations
TL;DR: In this article, a conjecture is made that at a prescribed capillary pressure the criterion for the liquid phase to invade an empty pore is defined by the Young-Laplace equation, but with the expected dynamic contact angle used instead of the static one.
Abstract: The common assumption when modeling transient liquid flow in an unsaturated porous medium is that the capillary pressure-saturation degree relationship is independent of the macroscopic liquid flux. This assumption is not always applicable, and one reason for this is the dependence of the solid-liquid-gas contact angle at the moving liquid-gaseous interface on the flow velocities, as found in systems such as long cylindrical capillaries. In the present theoretical study, a conjecture is made that at a prescribed capillary pressure the criterion for the liquid phase to invade an empty pore is defined by the Young-Laplace equation, but with the expected dynamic contact angle used instead of the static one. An iterative procedure, based on a simplified description of the pore system, enables a quantitative estimation of the extent of the liquid flux dependence of the capillary pressure-saturation degree relationship. For a given capillary pressure, the degree of liquid saturation decreases with increasing li...
61 citations
TL;DR: In this paper, column wicking was used for determining contact angles on wood particles. Butler et al. measured the liquid front rise versus time for different probe liquids and observed a distinct temperature increase within the columns during the wicking of water, formamide, and methanol.
Abstract: 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-linearit...
55 citations
TL;DR: In this paper, the effects of external pressure on the filler resistance were measured by the four-point probe method using different conductive fillers, including Ni powder, Ni flake, Ag powder and Ni filament.
Abstract: Abstraet-The efficiency of electrical conduction in particle-filled conductive adhesives largely depends on the interparticle conduction. In order to gain insight into the pressure-dependent conduction behavior with particles of different sizes, shapes, and types, the effects of external pressure on the filler resistance were measured by the four-point probe method using different conductive fillers. The following types of particles were used: Ni powder, Ni flake, Ag powder, Ni filament, magnetite spindles, and Cu particles. Non-filament particle size was in the range 0.7-44 μm. The filaments were 20 μm in diameter and 160 or 260 μm in length. The particle treatment procedures investigated included silver coating using different methods, and the use of acid solutions including H3PO4, HF, and HCl to etch and remove the surface oxide layer. Resistivity levels were measured using a nonconductive hollow cylinder plunger device developed in our laboratories. The results of our work showed that when the pressur...
47 citations
TL;DR: In this article, the failure mechanism of bioadhesive bonding between a marine macrofouler, the Balanus improvisus barnacle, and room-temperature vulcanized poly(dimethylsiloxane) (PDMS)-based elastomers was investigated and compared with poly(methylmethacrylate) (PMMA) panels.
Abstract: The failure mechanism of bioadhesive bonding between a marine macrofouler, the Balanus improvisus barnacle, and room-temperature vulcanized poly(dimethylsiloxane) (PDMS)-based elastomers was investigated and compared with poly(methylmethacrylate) (PMMA) panels. The strength of barnacle bioadhesive bonds measured in the shear mode when barnacles were detached from PDMS coatings was much lower than on PMMA and was comparable to the adhesion strength obtained in a 'pseudobarnacle test' in which an epoxy adhesive was used. The failure surfaces were analyzed by scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA), contact angle measurements, and atomic force microscopy (AFM). Analysis of the fracture surfaces indicated that the failure mode was a cohesive failure within the PDMS coatings. It is suggested that the fouling-release properties of the silicone elastomers are facilitated by disentanglement and displacement of surface-enriched uncross-linked PDMS chains. The failure ...
45 citations
TL;DR: In this paper, the authors discuss the difficulties that can arise when the drop size changes, but the absolute resolution of the systasis is not changed. But they do not discuss how to quantify confidence in a deduction of elliptical deviations from optically recorded droplet profiles.
Abstract: The evaporation of small droplets of volatile liquids from solid surfaces depends on whether the initial contact angle is larger or less than 90°. In the latter case, for much of the evaporation time the contact radius remains constant and the contact angle decreases. At equilibrium, the smaller the drop, the more it is possible to neglect gravity and the more the profile is expected to conform to a spherical cap shape. Recently published work suggests that a singular flow progressively develops within the drop during evaporation. This flow might create a pressure gradient and so result in more flattening of the profile as the drop size reduces, in contradiction to expectations based on equilibrium ideas. In either case, it is important to develop methods to quantify confidence in a deduction of elliptical deviations from optically recorded droplet profiles. This paper discusses such methods and illustrates the difficulties that can arise when the drop size changes, but the absolute resolution of the syst...
42 citations
TL;DR: In this paper, a method was developed to determine the initial peripheral contact angle of sessile drops on solid surfaces from the rate of drop evaporation for the case where 1 < 90°.
Abstract: A method was developed to determine the initial peripheral contact angle of sessile drops on solid surfaces from the rate of drop evaporation for the case where 1 < 90°. The constant drop contact radius, the initial weight, and the weight decrease with time should be measured at the ambient temperature for this purpose. When water drops are considered, the relative humidity should also be known. The peripheral contact angle so obtained is regarded as the average of all the various contact angles existing along the circumference of the drop. Thus, each determination yields an average result not unduly influenced by irregularities at a given point on the surface. In addition, the error in personal judgment involved in drawing the tangent to the curved drop profile at the point of contact can be eliminated. The application of this method requires the use of the product of the vapor diffusion coefficient with the vapor pressure at the drop surface temperature. This product can be found experimentally by follo...
TL;DR: In this article, the viscoelastic properties of PU-fumed silica composites were improved by adding fumed silicas and only a solid-like behavior was obtained.
Abstract: Fumed silicas of different specific surface area (90-380 m2/g) were added to a thermoplastic polyurethane (PU) solution. After solvent removal, solid fumed silica-PU composites were obtained. The viscoelastic properties of PU were improved by adding fumed silica and only a solid-like behavior in PU-fumed silica composites was obtained. The increase in the specific surface area of the fumed silica up to 200 m2 / g increased the moduli of the composites. Fumed silica-PU interactions were responsible for the improved rheological properties of the composites. The activation energies for viscous flow of the composites were 14-16 kcal/mol and increased as the specific surface area of fumed silica increased. The glass transition temperature (obtained from DMTA and DSC experiments) and the crystallization rate of fumed silica-PU composites decreased compared with PU and also decreased with increasing surface area of the fumed silica. The contact angle values were similar in all the composites and the strength of ...
TL;DR: In this paper, the authors compared two approaches to determine the surface energy of solids, and its acid-base components in particular: inverse gas chromatography (IGC) and analysis of contact angle data using the Good-van Oss theory.
Abstract: This study compares two approaches to determine the surface energy of solids, and its acid-base components in particular: inverse gas chromatography (IGC) and analysis of contact angle data using the Good-van Oss theory. The comparison is made in the context of wood fibers from Eucalyptus globulus and Eucalyptus regnans pulped by the kraft and neutral sulfite semi-chemical (NSSC) processes, and of selected polymers. Contact angles on wood fibers were measured using the Wilhelmy method and on polymer samples using the sessile drop technique. For the dispersive component of the surface energy, the level of agreement between the two approaches was reasonable, using alkanes for the IGC measurements and diiodomethane for the Wilhelmy and sessile drop techniques. However, agreement was poor for the acid and base characteristics when monopolar probes were used for IGC and water, formamide, and diiodomethane for contact angle measurements. The Good-van Oss approach suggested that all fibers and polymers are monop...
TL;DR: In this paper, the surface free energy of comb-like polymers with controlled grafting rates and macromolecular structures was derived from the contact angles of standard liquids on the solid surfaces.
Abstract: To analyze various approaches for the determination of surface free energies of solids from liquid-solid contact angles, comb-like polymers with controlled grafting rates and macromolecular structures have been synthesized. The surface free energy parameters were calculated from the contact angles of standard liquids on the solid surfaces. A mathematical approach of the so-called acid-base theory of adhesion was used to characterize the nucleophilic and/or electrophilic behavior of the polymeric solid surfaces. Thus, correlations were established between the macromolecular structures and the dispersive component of the surface free energy, on the one hand, and the acid and base components, on the other. The main conclusion is that the surface free energy components are relevant for the characterization of functional comb-like polymeric materials: the dispersive and base components increase with the number of grafted electron-donating groups, whereas the acid component decreases.
TL;DR: In this article, the detachment of particles with coarse and fine roughness from surfaces in a turbulent boundary layer flow including electrostatic effects is studied, where the real area of contact is determined by elastic deformation of asperities, and the effect of topographic properties of surfaces is included.
Abstract: The detachment of particles with coarse and fine roughnesses from surfaces in a turbulent boundary layer flow including electrostatic effects is studied. It is assumed that the real area of contact is determined by elastic deformation of asperities, and the effect of topographic properties of surfaces is included. The Johnson-Kendall-Roberts (JKR) adhesion model is used for analyzing the behavior of individual asperities. For an average Boltzmann charge distribution, the saturation charge condition as well as a fixed charge per unit mass, the Coulomb, the image, the dielectrophoretic, and the polarization forces acting on the particle in the presence of an imposed electric field are evaluated. The theories of rolling and sliding detachment are used to study the onset of removal of bumpy particles and those with fine roughness from plane surfaces. The hydrodynamic forces and torques acting on the particle attached to a wall, along with the adhesion force for the particle, are used in the model development....
TL;DR: In this article, a series of model adhesives were extended to the case of industrial formulations: one SIS triblock copolymer-based PSA formulation and one EVA copolymers-based hot-melt formulation.
Abstract: Three factors govern the adhesion properties of hot-melt and pressure-sensitive adhesives: (1) thermodynamic interfacial properties (Dupre adhesion energy); (2) interfacial losses due to specific interactions; and (3) viscoelastic losses in the bulk related to the rheological properties of the adhesive. In the present paper, we focus on the main factor in the adhesion properties, which is the viscoelastic factor. We extend in this paper the results obtained on a series of model adhesives to the case of industrial formulations: one SIS triblock copolymer-based PSA formulation and one EVA copolymer-based hot-melt formulation. After studying the rheological properties of these adhesives over a wide frequency range using time-temperature equivalence, we present data obtained on peel tests at various temperatures. As with model adhesives, the peel rate-temperature equivalence leads to the same shift factors as rheology. The experiments demonstrate that there is a one-to-one relationship between the cohesive fr...
TL;DR: In this article, the surface composition of Kevlar fibers was investigated by scanning electron microscopy (SEM) and electron spectroscopy for chemical analysis (ESCA), respectively.
Abstract: Kevlar 49 fibers were surface-modified by chlorosulfonation and subsequent reaction of -SO2Cl with some reagents (allylamine, ethylenediamine, and deionized water) to improve the adhesion to 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMPP) resin. The change in fiber surface morphology and the surface functional groups introduced to the surface of the fiber were investigated by scanning electron microscopy (SEM) and electron spectroscopy for chemical analysis (ESCA), respectively. From the results of ESCA analysis, it was confirmed that the surface composition of the Kevlar fibers was significantly different from that of the bulk composition. After chlorosulfonation, the surface concentration of carbon was markedly decreased. The subsequent reaction with ethylenediamine, allylamine, and deionized water also changed the surface composition of the fiber; e.g. treatment with ethylenediamine and allylamine decreased the O/N ratio. On the other hand, the O/N ratio was increased by hydrolysis treatment. The s...
TL;DR: In this paper, the authors used force microscopy in the tapping mode to image liquid structures on solid substrates with a resolution in the nanometer range by using an artificially patterned wettability.
Abstract: Liquid structures on solid substrates have been imaged with a resolution in the nanometer range by scanning force microscopy in the tapping mode. Using Substrates with an artificially patterned wettability, characteristic features in the three-phase contact line were induced, which allow the contact line tension to be determined. The values in the range of -1 x 10-10 N obtained for sessile droplets of hexaethylene glycol arc consistent with theoretical predictions.
TL;DR: In this article, the authors developed a method where bulk polystyrene was melted and formed into drop-shaped surfaces with a cylindrical shaft, and they found that cohesive failure occurred and the surfaces were locally damaged.
Abstract: Interfacial properties of bulk polymer samples have been characterized by direct measurements of long-range and adhesion forces using a non-interferometric bimorph surface forces apparatus. For this purpose, we developed a method where bulk polystyrene was melted and formed into drop-shaped surfaces with a cylindrical shaft. In the case of very smooth polystyrene samples, the adhesion in air and water was very strong and when brought into contact, cold welding of the polymers sometimes took place. Upon separation, it was found that cohesive failure occurred and the surfaces were locally damaged. In the case of less flat polystyrene surfaces, the adhesion increased with the applied (external) load to a saturation value. We attribute this to local flattening of nanometer-sized protrusions. The long-range interaction in water is dominated by a weak electrostatic double-layer force. At separations below about 10 nm, an attractive force component predominates the interaction. The adhesion in aqueous solutions ...
TL;DR: The surface isoelectric point of an oxide-covered Ta-implanted A1 surface lies between that of Al2O3 and Ta2O5 as mentioned in this paper, and the acid-base properties of various polymers, including a commercially available pressure-sensitive adhesive, were determined by measuring the contributions γS + and γ S − to the solid surface free energy using the contact angle app...
Abstract: The surface isoelectric point for native air-formed oxide films on various metals has been determined by measurement of contact angles at the hexadecane/ aqueous solution interface as a function of the pH of the aqueous phase. Application of Young's equation, the Gibbs equation, and surface equilibria conditions for hydroxylated oxide films leads to a mathematical expression which shows that the contact angle goes though a maximum at the isoelectric point of the oxide. The experimentally determined values for the oxide films on aluminum, chromium, and tantalum are within one to three pH units of the reported isoelectric points for the corresponding bulk oxide powders. The surface isoelectric point of an oxide-covered Ta-implanted A1 surface lies between that of Al2O3 and Ta2O5. The acid-base properties of various polymers, including a commercially available pressure-sensitive adhesive, were determined by measuring the contributions γS + and γS - to the solid surface free energy using the contact angle app...
TL;DR: In this article, the elastic modulus and failure strength of the adhesive as well as the tensile load capability of the tubular single lap adhesively bonded joint were experimentally and theoretically investigated with respect to the volume fraction of filler and the environmental temperature.
Abstract: When an adhesively bonded joint is exposed to a high environmental temperature, the tensile load capability of the adhesively bonded joint decreases because the elastic modulus and failure strength of the adhesive decrease In this paper, the elastic modulus and failure strength of the adhesive as well as the tensile load capability of the tubular single lap adhesively bonded joint were experimentally and theoretically investigated with respect to the volume fraction of filler and the environmental temperature Two types of fillers - Al2O3 (alumina) and chopped fiber E glass - were used From the experiment, it was found that the elastic modulus and failure strength of the adhesive increased in accordance with the increase of volume fraction of the filler and decreased with the environmental temperature rise It was also found that the tensile load capability of the tubular single lap adhesively bonded joint decreased as the environmental temperature increased; however, it had no correlation with the volu
TL;DR: In this paper, the modifications induced by excimer laser irradiation of poly(ether ether ketone) (PEEK) surfaces have been investigated as a function of the laser process parameters for laser fluences below the material ablation threshold.
Abstract: The modifications induced by excimer laser irradiation of poly(ether ether ketone) (PEEK) surfaces have been investigated as a function of the laser process parameters for laser fluences below the material ablation threshold. In the case of 193 nm laser treatment, a significant increase in the adhesion properties of PEEK was obtained due to the formation of new polar and reactive groups on the surface. The extent of these reactive groups has to be controlled since their presence in high concentration may also have a negative effect on the mechanical properties of the treated surface. Laser treatments using 248 nm radiation did not result in a significant increase in the adhesion properties of PEEK. This probably results from thermal degradation of the surface at this laser wavelength.
TL;DR: In this article, the weldability of similar and dissimilar thermoplastics with the use of ultrasonic welding and compares the experimental results with those obtained previously by using the heated tool method are discussed.
Abstract: This paper discusses the weldability of similar and dissimilar thermoplastics with the use of ultrasonic welding and compares the experimental results with those obtained previously by using the heated tool method. Theoretical discussions presented on the effects of diffusion, solubility parameter, surface tension, contact pressure, thermal expansion, thermal dissipation, and vibration transmissibility are used for comparing weldability. Weld strength-to-bulk strength ratios and the ultimate extension values for the welded specimens are compared for assessing the weld efficiency, and therefore the quality of autohesion (self-adhesion), and adhesion. In experiments with ultrasonic welding, the horn down speed is varied to assess, indirectly, the effect of contact force during welding. A sandwich weld structure and the effects of specimen length on the weld strength are also studied for ultrasonic applications to assess these geometrical effects. It is shown that a threshold length exists for weld specimens...
TL;DR: In this article, the impact of surface roughness on the hydrophobic attractive forces between polyethylene spheres and silanated silica surfaces was investigated using atomic force microscopy (AFM).
Abstract: Recently, substantial research effort has been devoted to the study of non-DLVO forces between hydrophobic surfaces. However, the significance of surface roughness in the analysis of these hydrophobic attractive forces has not been given sufficient consideration and research is now in progress to attend to this issue. Fused silica plates covered with adsorbed octadecyltrichlorosilane (OTS) were characterized by water contact angle measurements and atomic force microscopy (AFM). Surfaces with different surface coverages and different contact angles were obtained by variation of the adsorption time. OTS formed patches on the silica surfaces, the lateral size and height of hich depended on the adsorption time. Such surfaces exhibit differences in roughness at the subnanometer level. Using the AFM colloidal probe technique, forces between a polyethylene sphere and silanated silica surfaces were measured in water. Long-range attractive forces were found, usually referred to as hydrophobic forces. The resulting force vs. distance curves were fitted with a double exponential function. The magnitude of the short-range part of the force curves seems to correlate with water contact angles at silanated silica surfaces. On the other hand, the range of the long-range force correlates with the roughness of the silanated silica surface. These results with silanated silica surfaces were compared with the AFM results for polyethylene and graphite surfaces and on the basis of these experimental efforts, it appears that the nature of these hydrophobic attractive forces is related to surface roughness.
TL;DR: In this article, fine particles were extracted from bitumen froth by heptane and the partition of the extracted solids in aqueous, organic, and interphases was measured, and the wettability of the solids by water in various diluents was evaluated from contact angle measurements.
Abstract: Production of synthetic crude oil from oil sands deposits in northern Alberta involves open pit mining, mixing the mined ore with water, extraction of aerated bitumen from the slurry, removal of water and solids from the froth formed, and upgrading heavy bitumen to liquid hydrocarbons. The success of the froth treatment operation, aimed at removal of fine solids and water from the bituminous froth, depends on the control of wettability of fine solids by the aqueous phase. Fine solids were extracted from bitumen froth by heptane. The partition of the extracted solids in aqueous, organic, and interphases was measured, and the wettability of the solids by water in various diluents was evaluated from contact angle measurements. The effect of diluent composition, sample drying, and surface washing on the wettability and fine particle partition was examined. The partition of fine particles correlated well with their wettabilities, and the results were found to be useful for interpreting the observations from fr...
TL;DR: In this article, the effect of surfactants on the adhesion of latex films was investigated at various peel rates, and the main latex polymer was a methyl methacrylate (MMA)/ethyl acrylate copolymer synthesized in the presence of a hydrophilic polyester.
Abstract: In order to study the effect of surfactants on the adhesion of latex films, peel energy versus surfactant concentration curves were established at various peel rates. The main latex polymer was a methyl methacrylate (MMA)/ethyl acrylate (EA) copolymer synthesized in the presence of a hydrophilic polyester. Another polymer, less extensively studied, a styrene/butyl acrylate/methacrylic acid terpolymer, was also used for comparison purposes. The surfactants were either sodium dodecyl sulfate (SDS) or ethoxylated nonyl phenol containing 30 segments of ethylene oxide (NP30). The substrates were glass plates or poly(ethylene terephthalate) films. It was found that with SDS-containing films, whatever the substrate or the polymer, the curves went through a maximum, whereas with NP30 they went through a minimum, at medium or high peel rates. When the peel rate was decreased, the curves flattened out and at zero peel rate (extrapolated values), they became horizontal. The peel energies at zero peel rate were three...
TL;DR: In this article, the theoretical profile for barrel-type droplets on cylinders is considered and the inflection angle in the profile depends on the droplet parameters, such as drop radius and volume dependence.
Abstract: A droplet of liquid placed on a flat high-energy solid surface spreads to give a thin film so that no macroscopic droplet shape exists. On a chemically identical solid surface with only the geometry changed to a cylinder, the same droplet can have an equilibrium conformation. When the equilibrium conformation is of a barrel type, the profile of the droplet changes rapidly in curvature as the three-phase contact line is approached and the direct measurement of the contact angle is difficult. This work considers the theoretical profile for barrel-type droplets on cylinders and discusses how the inflection angle in the profile depends on droplet parameters. Experimental results are reported for poly(dimethylsiloxane) oils on a range of fiber surfaces and these are used to estimate the equilibrium contact angle from the inflection angle. The drop radius and volume dependence of the inflection angle is confirmed.
TL;DR: In this paper, the pull-off of a viscoelastic sphere from a flat substrate is considered and a theoretical description of the dynamics of the pull off of a sphere from solid substrate with allowance for the dependence of the effective work of adhesion on the displacement velocity of contact line is presented.
Abstract: Abstraet-The problem of the pull-off of a viscoelastic sphere from a flat substrate is considered. Current theoretical models are critically treated. It is shown that a theoretical description of the dynamics of the pull-off of a sphere from a solid substrate with allowance for the dependence of the effective work of adhesion on the displacement velocity of contact line can be reduced to the solution of a first-order differential equation. The procedure for a numerical solution to this equation is elaborated. A scheme for analytical evaluation of the main parameters such as the pull-off work or force and the velocity of the crack tip is suggested. Data obtained using approximate formulae and by numerical solution of the problem are compared. The values of the pull-off work and force calculated with approximate formulae and numerical analysis are shown to be in good agreement over seven orders of magnitude.
TL;DR: In this article, the relationship between the molecular structure (as characterized by the stereochemistry and conformations of macromolecules), the functional-group composition, and the wettability of polymer surfaces was investigated.
Abstract: Stereoregular poly(methyl methacrylates) (PMMAs) solvent-cast in the form of films against a glass substrate were employed as model systems for a systematic study of the relationship between the molecular structure (as characterized by the stereochemistry and conformations of macromolecules), the functional-group composition, and the wettability of polymer surfaces. The water wettability of a syndiotactic surface was found to be highly sensitive to the polarity of the adjacent phase in the film-casting process, whereas the wettability of an isotactic surface was invariant to the polarity of the contacting medium. The tacticity-dependent wetting behavior arises from the difference in the extent of functional-group surface segregation or, in other words, from the different surface activity of the different tactic versions of the polymer. This difference, in turn, is associated with fundamental distinctions in the conformational structures energetically allowed for the isotactic and syndiotactic configuratio...
TL;DR: In this paper, a novel procedure for the preparation of hydrophobic spherical particles from thermoplastic materials, such as polyethylene (PE) or fossil resin (FR), is presented.
Abstract: A novel procedure for the preparation of hydrophobic spherical particles from thermoplastic materials, such as polyethylene (PE) or fossil resin (FR), is presented. These particles are particularly useful in the determination of surface forces with the atomic force microscope using the colloidal probe technique. The preparation steps include (i) suspending powdered polymer (PE and FR) in glycerol, (ii) heating the suspension above the melting point of the polymer, (iii) solidification of dispersed PE/FR droplets at a reduced temperature, (iv) filtration of the particles, and (v) washing/drying of the product. Such produced particles of PE and FR had a broad size distribution (2-50 μm) and a spherical shape. The surfaces of these particles were relatively smooth, with a small number of asperities, and/or attached satellite particles or non-spherical debris. Analytical examination of the polymer surface, before and after treatment with hot glycerol, by SEM, AFM, contact angle, XPS, and FTIR measurements rev...