The effect of film thickness and surface preparation techniques on contact angles of water, 1-bromonaphtalene, and n-hexadecane on Teflon^® AF 1600 polymeric surfaces is studied. It was found that contact angles of water on different thicknesses of spin-coated films ranging from 27 nm to 420 nm are essentially constant. This is due to the homogeneity and smoothness of the coating layers as shown by the scanning force microscopy of the samples. Furthermore, the contact angle measurements with these three liquids on both dip-coated and spin-coated films suggested that the film preparation technique does not affect contact angles dramatically. Interestingly, slightly higher contact angles on dip-coated surfaces were measured. It is also argued that the anomaly of the water contact angle—in the sense that the measured contact angle is much higher than the expected ideal value—is due to specific interactions between water and Teflon^®.

Accurate surface tension of Teflon^® AF 1600 was determined using contact angles of liquids with bulky molecules. For one group of liquids, the contact angle data fall quite perfectly on a smooth curve corresponding to γ_sv = 13.61 mJ/m², with a mean deviation of only ±0.24 degrees from this curve. Results suggest that these liquids do not interact with the solid in a specific fashion. However, contact angles of a second group of liquids with fairly bulky molecules containing oxygen atoms, nitrogen atoms, or both deviate somewhat from this curve, up to approximately 3 degrees. Specific interactions between solid and liquid molecules and reorientation of liquid molecules in the close vicinity of the solid surface are the most likely causes of the deviations. It is speculated that such processes induce a change in the solid–liquid interfacial tension, causing the contact angle deviations mentioned above. Criteria are established for determination of accurate solid surface tensions.

Surfaces and interfaces exhibit a rich variety of phase transitions. While some of these phase transitions also occur in the bulk, others involve coupling between surface and bulk degrees of freedom; consequently the surface phase diagram may be rather complex even for simple Ising like systems. In these lectures I will introduce the generic 4-dimensional surface phase diagram (bulk and surface couplings, bulk and surface fields) of Ising like systems and discuss bulk vs. surface criticality. I will start with a review of surface thermodynamics and scaling of interfaces with emphasis on wetting phenomena. Then Landau mean-field theory is used to calculate the global surface phase diagram. The effects of thermal fluctuations are discussed using the capillary wave Hamiltonian: The correlation functions are calculated using Ornstein-Zernike theory for systems with short and long-range forces. Finally, I will comment on the status of the renormalization group results for 3-dimensional short-range critical wetting that are at odds with the results of simulations of the Ising model and of a recent experiment.

A remote atmospheric pressure discharge working with ambient air is used for the near room temperature treatment of polymer foils and textiles of varying thickness. The envisaged plasma effect is an increase in the surface energy of the treated material, leading, e.g., to a better wettability or adhesion. Changes in wettability are examined by measuring the contact angle or the liquid absorptive capacity. Two regimes of the remote atmospheric pressure discharge are investigated: the glow regime and the streamer regime. These regimes differ mainly in power density and in the details of the electrode design. The results show that this kind of discharge makes up a convenient non-thermal plasma source to be integrated into a treatment installation working at atmospheric pressure.

This article attempts to give an overview of atmospheric plasma sources and their applications. The aim is to introduce, in a first part, the main scientific background concerning plasmas as well as the different atmospheric plasma sources (description, working principle). The second part focuses on the various applications of the atmospheric plasma technologies, mainly in the field of surface treatments.Thus this paper is meant for a broad audience: non-plasma-specialized readers will find basic information for an introduction to plasmas whereas plasma spectroscopists who are familiar with analytical plasmas may be interested in the synthesis of the different applications of the atmospheric pressure plasma sources.

For determination of wettability of rough surfaces using the contact angle hysteresis approach and equilibrium contact angles, some new surfaces with controlled roughness were prepared. The influence of the binder nature and size of primary particles of silica powders on surface roughness and wettability of the newlydeveloped films was investigated using optical microscopy, profilometry, SEM and measurement of contact angles of water. Using the silicate binder and silica powders with primary particles of 9 nm, 40 nm and 4 μm, surface hierarchical structures were obtained. The maximal value of the roughness parameter Rq= 366.3 nm was obtained for the sample with silica microparticles of 4 μm. Wettability of the synthesized films was determined mostly by the binder crystals formed on the surface and their ability to interact with hexamethyldisilazane (HMDS). It is well characterised by equilibrium contact angles.

The surface structure and properties of poly(vinyl alcohol)-poly(dimethylsiloxane), PVAL-PDMS, graft copolymers with the controlled PDMS graft chain length as well as chain distribution were studied. The surface of the graft copolymer was examined by XPS technique and was found to be covered with essentially pure PDMS graft component even in only 5 mole% siloxane unit content. The contact angle measurement was carried out with the water-in-air technique for PVAL—PDMS graft copolymers as well as the graft copolymer/PVAL homopolymer blends and the significant surface accumulation of PDMS graft component was confirmed with the graft copolymer/PVAL blend of less than 1 mole% of siloxane unit content. In contact with water, PVAL—PDMS graft copolymer surface was found to transform its surface morphology remarkably, which was noticed by the contact angle measurement with the air-in-water technique, where the contact angle of PVAL—PDMS graft copolymer surface was found to differ from that of pure PDMS—coated surface.

These lecture notes discuss some theoretical approaches for the prediction of the structure, thermodynamics, and dynamics of polymers at interfaces, with emphasis on self-consistent field (SCF) methods. We begin with simple models for the conformational statistics of unperturbed chains and derive the Edwards diffusion equation for a Gaussian thread in a field. We then describe a simple lattice-based approach for a polymer melt at a flat interface and results from its application. Next, we discuss mixing energetics in the lattice model and outline an extension of the lattice-based SCF theory to treat copolymers at interfaces. Correspondences are pointed out between lattice-based and continuous SCF approaches, the latter making use of the Edwards diffusion equation. As an example of continuous formulations we present Helfand and Tagami’s elegant analytical solution for a flat interface between two immiscible polymers in the limit of very large molecular weights. Following Fredrickson et al., we outline a general fieldtheoretic approach for the mesoscopic modelling of inhomogeneous polymer systems. Using a symmetric diblock copolymer as an example, we show how a saddle point approximation reduces this formalism to a SCF theory and discuss the phase diagram obtained through continuous SCF by Matsen and Schick. As an example of scaling considerations, we derive expressions for the chain length dependence of the long period of the lamellar phase of the diblock copolymer. The latter part of the notes focusses on applications and comparisons with experiment. We discuss the structure of polymer/polymer and solid/polymer interfaces in the presence of diblock copolymers. We then briefly review a hierarchical theoretical/simulation approach for exploring adhesion at a solid/polymer interface strengthened by chains terminally grafted to the solid.

In the study reported in this paper, a series of reproducible conditions were employed to uniformly functionalize nylon 6 surfaces using a commercially available, low-frequency (40 kHz), low-pressure plasma system, utilizing oxygen plasma as a reactive gas. Initially, the plasma-treated samples were investigated using static contact angle measurements, showing a progressive increase in wettability with increasing plasma activation time between 10 and 40 s. Such an increase in wettability (and therefore increase in adhesive capabilities of the surfaces) was attributed to the creation of surface C-OH, C=O, and COOH groups. These surface-chemical modifications were characterized using x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). Surface radical densities were also shown to increase following plasma activation, having been quantified using a radical scavenging method based on the molecule 2,2-diphenyl-1-picrylhydrazyl (DPPH). The samples were imaged and analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), to confirm that there had been no detectable alteration to the surface roughness or morphology. Additionally, the “hydrophobic recovery” or “ageing” of the activated polymer samples, post-plasma treatment, was also investigated in terms of wettability and surface-chemistry, with the wettability of the sample surfaces decreasing over time due to a reduction in surface-oxygen concentration.

This study describes experiments to quantify polymer surface energy changes after exposure to atmospheric plasma. Atmospheric plasma treatment permits surface functionalization at near-ambient temperatures. Polyethylene and polystyrene are treated with an atmospheric plasma unit. The increased surface energy and improved wetting characteristics lead to a significant adhesion improvement with adhesives that cannot be used without surface treatment.

The water vapor permeability of glass-bead-filled phenoxy films was shown to depend strongly on the degree of interfacial interaction between the filler and matrix; the greater the adhesion, the lower the permeability. Scanning electron microscopy (SEM) was used to characterize the glass surface and the corresponding degree of adhesion between the filler and polymer matrix. Maximum interaction between the acidic phenoxy and glass filler was obtained when the glass had been treated with an aminopropyltriethoxysilane, which yielded a basic surface overall. Retention of the cellosolve acetate solvent was also reduced by the glass filler, especially by the more basic glass. The dynamic mechanical properties were affected primarily by the presence of residual solvent.

The gas-phase reactions of ozone with CH bonds in methane, ethane, propane (secondary CH bond), and isobutane (tertiary CH bond) have been studied by semiempirical AM1 method. Reactions proceed through biradical transition state and lead to alkyl and hydrotrioxyl HOOO radicals. The latter immediately decomposes into molecular oxygen and hydroxyl radical HO. The formation of hydrotrioxides ROOOH in gas-phase reactions between ozone and hydrocarbons is shown to be highly improbable.

Contact angle hysteresis was measured for a variety of liquids on condensed monolayers of 17-(perfluoroheptyl)heptadecanoic acid adsorbed on polished chromium. The hysteresis was shown to be simply related to the molecular volume of the liquid and to result from the penetration of liquid molecules into the porous monolayer. However, contact angle hysteresis was negligible when the average diameter of the liquid molecules was larger than the average cross-sectional diameter of the intermolecular pores. It is shown that it is possible to estimate intermolecular pore dimensions of such adsorbed monolayers by contact angle hysteresis measurements on a series of liquids having gradations in molecular volume. The results of this investigation reveal that liquid penetration, even into pores of molecular dimensions, is a cause of significant contact angle hysteresis, and it is also shown how liquids can be selected for contact angle investigations on organic solid surfaces so that there will be freedom from this source of hysteresis. The results also suggest that under these experimental conditions, liquid water, on the average, behaves as if it were associated in clusters of about six water molecules. Similarly, both ethylene glycol and glycerol behave as associated clusters of about two molecules.

It was shown that when polyurethanes designed for use in biopolymer applications were immersed in orienting fluids, significant increases in their non-dispersive surface energies took place. The kinetics of the surface energy response were found to be a function of the immersion medium's acid-base interaction potential. Restructuring from the as-cast state, similar to that reported for two-component polyurethane adhesives, occurs in response to thermodynamic demands and is attributable to a preferential concentration of low energy segments in the surface region. Since shifting surface energies in polyurethanes may pose problems in biological applications, an attempt was made to crosslink the surface of the polymers by the use of cold, microwave plasma discharges with Argon as the treatment gas. Plasma treatments proved to be successful, in that polyurethane surfaces so modified responded much more weakly to changes in the polarity of contact media.

The effects of oxygen plasma treatment on ultra-high-modulus polyethylene monofilaments have been investigated with particular reference to their adhesion to epoxy resins. The adhesion strength was monitored by pull-out tests, and the effects on the monofilaments was also studied by contact angle measurements, determination of gel content and scanning electron microscopy. The results of this investigation suggest that there are three contributions to the improvements in adhesion obtained from the plasma treatment. First, at comparatively short treatment times there is a general oxidation of the surface. Secondly, at intermediate treatment times cross-linking of the surface occurs, which increases the cohesive strength of the fibre surface. Finally, at long exposure times there is a pitting of the surface, which could give rise to a mechanical keying effect but may also reduce the fibre strength.

The dispersive component of the surface free energy, the nondispersive interaction, with polar liquids were determined for cellulose, cellulose acetate and cellulose grafted with alkyl ketene dimer (AKD). and were calculated in the dry state as well as the fully hydrated state by the two liquid contact angle method. was found to be independent of AKD coverage. Iⁿ_sw was found to be highly dependent on AKD coverage and differed significantly between the dry and fully hydrated states. Using the work of adhesion as a criterion, it was postulated that in the dry state, the AKD molecule renders the cellulose hydrophobic, and undergoes surface restructuring in the hydrated state leading to a hydrophilic surface.

The relationship between wetting and pressure-sensitive adhesion was studied using an adhesive composed of poly(butyl acrylate) and various adherends of different surface tension. The amount of adhesive deposit was determined quantitatively by tracer technique although the unbonding process was apparently observed as interface failure. The adhesive force and amount of deposit were both dependent on the critical surface tension of the adherends. Maximum tack value and contamination were observed with adherends whose critical surface tension was close to that but a little higher than that of the adhesive. The adhesive force obtained was lower than cohesive strength of adhesive. From this evidence, a mechanism for pressure-sensitive adhesion was discussed: the bond breaks in the addesive mass around the very minute spots where interaction is at work between adhesive and adherend. Inasmuch as the density of the minute spots per unit area depends on the surface tension, the adhesive force also depends on the surface tension.

The wettability of stereospecific poly(methacrylates) was studied. In the wettability of poly(methacrylates) having bulky substituents such as phenyl and chloroethyl groups, it was found that the critical surface tensions for isotactic polymers were low compared to those for attactic polymers. The steric effect of the bulky substituent on wetting was also discussed.

This paper investigates the surface modification of Parylene-C thin films under various oxygen plasma treatment conditions, such as power intensity (50:400 W) and exposure time (1:20 min). The extent of hydrophilicity was investigated through contact angle measurements, and correlations between treatment parameters, film thickness, restoration of hydrophobicity and etching rates were experimentally established. We also demonstrate the selective modification of Parylene-C films, facilitating distinct hydrophilic and hydrophobic areas with μm-resolution that can be exploited in self-alignment applications.

The dynamic wetting behavior of poly(tetrafluoroethylene) (PTFE), polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), nylon 6, poly(ether urethane) (PU), poly(vinyl alcohol) (PVA), and cellulose was studied by the Wilhelmy balance technique at speeds of immersion from 1 to 50 mm/min. The Wilhelmy method was modified so as to determine contact angles without extrapolation of the loop to the zero immersion depth, employing a rectangular flat sample having a rectangular hole. This modification of the method allowed us to determine the advancing and receding contact angles on the very narrow sample area close to the lower (first) and the upper (second) sample-hole boundaries, theta1 and theta2, respectively. The interaction time of the sample part located at the lower boundary with the wetting liquid (water) was twice as long as that of the upper boundary. No difference was observed between the advancing contact angles measured at the lower and the upper parts of the sample (theta(ADV,1) = theta(ADV,2)) for all the Polymers, displaying that the dried polymer surfaces had no difference in wettability along the sample length. However, the lower part of the sample became more hydrophilic than the upper part during the wetting measurement for PET, PU, nylon 6, PVA, and cellulose, resulting in the difference between the receding contact angles (theta(REC,1) < theta(REC,2)). The effect was attributed to the time-dependent surface reorientation of hydrophilic and hydrophobic groups, occurring upon immersion of the polymer sample in water. A close correlation was observed between the hysteresis of the contact angle and the underwater surface reconstruction of polymers: the strongest hysteresis corresponds to the greatest wettability gradient generated by the time-dependent reorientation process. However, even when the effect of reorientation was zero (PTFE, PE, and PP) or very low (cellulose), the observed hysteresis was still as high as 27-degrees. The contribution of the surface reorientation of polar groups to the observed hysteresis was estimated to amount to 0-25-degrees, depending on the chemical structure of the polymer investigated. The speed of the sample immersion had no detectable effect on the wettability of PTFE, PE, and PP. On the other hand, the advancing contact angle on PET, PU, and nylon 6 increased while the receding contact angle decreased, as the immersion speed became higher. This behavior may be accounted for by referring to a model of macromolecular dynamics at the three-phase boundary.

Surfactants — an acronym for surface-active agents — are versatile and ubiquitous chemicals. They are found in industrial areas related to detergents (Hancock 1984; Thayer 1993), pharmaceuticals (Tadros 1984; Attwood and Florence 1983), cosmetics (Ainsworth 1993), paints (Nylen and Sunderland 1965), pesticides (Wada et al. 1983; Tann, Berger and Berger 1992) and oil recovery (Neustalder 1984), to mention a few. Mother Nature used them, long before humans, as major building blocks of biological membranes, taking advantage of the so-called hydrophobic effect (Tanford 1980). This chapter focuses on applications of surfactants in liquid film coating processes, and in particular in coatings involving aqueous solutions, as encountered in the photographic industry.

The effects of the modification of polystyrene (PS), polyethylene (PE), poly(vinyl chloride) (PVC), silicone rubber (SR), and fluorinated ethylene propylene (FEP) copolymer by radio frequency glow discharge in a helium environment were presented in part I. The hydrated polymer surfaces were characterized by XPS, SEM, visual microscopy, and by contact angle measurements. In general, exposure of the polymers to RFGD produced an oxidized hydrophilic surface, yet the roughness of the surface was unaltered by the relatively mild plasma conditions used. In this article, the frictional behavior of oxidized and unoxidized SR, PE, and FEP in distilled water, isotonic saline, and blood plasma environments is examined experimentally. The results are discussed in relation to the properties generally believed to affect frictional phenomena and to the surface properties as determined in part I. Results indicate that RFGD-treated SR generates less friction than untreated SR when dragged across all untreated and treated polymer surfaces, whether the medium is distilled water or an isotonic saline solution. Friction is consistently lower in a blood plasma medium between all surfaces investigated, most probably because of the presence of adsorbed proteins at the polymer interfaces.

Film samples of low-density polyethylene (LDPE) and biaxially oriented poly(propylene) (BOPP) were surface modified by vacuum ultraviolet (VUV) irradiation using a Kr resonant lamp at λ = 123.6 nm in low-pressure ammonia gas, and were then stored in air. The time-dependence of the surface properties was monitored using several complementary surface-sensitive techniques such as contact angle goniometry (CAG), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS), which allows one to determine the surface energy, and chemical composition at different depths. The relative importance of four possible mechanisms involved in surface hydrophobic recovery is discussed, and we show that in our particular case the main mechanism is rotational and/or translational motion of polymer chains and chain segments. This restructuring determines the observed “loss” of functional groups, which occurs within the first few monolayers of the surface (∼1 nm), as shown by the ToF-SIMS results, and which leads to the observed decrease in the surface energy. In the deeper surface regions (∼10 nm) long-lived radicals react with oxygen and water vapor upon exposure to the atmosphere, leading to an increase in the concentration of bound oxygen, as observed by XPS. Finally, CAG measurements show that the hydrophobic recovery is reversible and can be significantly reduced by cross-linking near the surface, as illustrated by depth sensing nano-indentation measurements on BOPP surfaces.