Polyester monofilaments were treated by a pulsed surface electrical discharge in nitrogen at atmospheric pressure, to increase their adhesion to an epoxy resin matrix. The treatment resulted in an eight-fold increase in adhesive strength, without any change in mechanical properties of the monofilaments. It is concluded that polar group interactions, rather than increased surface area, are responsible for the improved adhesive strength.

The surface free-energies of the polyethers, polyethylene glycol, polypropylene glycol, polyepichlorohydrin, and polybutylene glycol, their mixtures and their random and block copolymers were determined by means of the pendant drop method. In all cases, except that of random copolymers, surface excesses of the low surface-energy component have been found. In the mixtures of homopolymers the behavior of surface excess isotherms depends on the molecular weight of the two components, while in block copolymers it depends on the degree of polymerization of the base unit. The Belton and Evans Equation for perfect solutions and the Prigogine equation for r-mer solutions have been applied to the experimental data.

The surface tension and surface entropies of different molecular weight polyethylene glycols and polypropylene glycols have been measured. The surface entropy of a mixture of polyethylene glycol and polypropylene glycol and that of block copolymers have also been determined. In the case of homopolymers, there is no effect of molecular weight on surface free energy and the increase in free energy on passing from the interior to the surface is due mainly to the heat content with the entropic contribution being very small.

In the case of a mixture of homopolymers and block copolymers, a minimum is observed when surface entropy is plotted against composition. At any particular composition, the surface entropy of a mixture is higher than that of a block copolymer of the same composition.

The effect and interrelationship between primary (segmental backbone) and secondary (side chain) molecular motions on thrombogenesis, independent of morphological order/disorder, crystallinity, and/or associated water is elucidated using an amorphous hydrophobic polymer of poly-[(trifluoroethoxy) (fluoroalkoxy)phosphazene], PNF. The results indicate that thrombogenesis for an amorphous hydrophobic polymer is sensitive and dependent on the degrees and types of primary and secondary molecular motions at the polymer interface.

The chemical species created in a low-pressure electrical discharge in oxygen attack the polymer at the surface, converting it to gaseous products. This process is interesting because: 1) the chemical changes on the resulting surface facilitate the formation of strong adhesive bonds and provide sites for the chemical attachment of other molecules, 2) significant morphological features lying below the surface may be revealed, 3) polymer can be cleanly removed from surfaces which are resistant to oxidation, and 4) dielectric breakdown frequently is preceded by the attack on the polymer of chemical species created in a corona discharge. Atomic oxygen is an important chemical species created in such a discharge. It reacts with organic substances rapidly at room temperature, but lives long enough in the low-pressure gas that it can be separated from many other reactive species created in the discharge. “Titration” with NO₂ provides a straightforward chemiluminescent means for determining the concentration of atomic oxygen to which the sample is exposed. This paper characterizes the attack of atomic oxygen, perhaps in the presence of long lived but less reactive species such as excited O₂molecules, on polymer surfaces, using electron microscopic observations of known morphological features of polyethylene to observe the changes produced by atomic oxygen. Lamellar polyethylene crystals were attacked both at the edges and the fold surfaces. Layers many microns thick were removed from spherulitic samples and replicas obtained from the surfaces thus exposed. Thick samples were thinned to the point at which they were transparent to an electron beam and interior morphological features were directly observed.

This study systematically characterises a matrix of water-based flexographic inks with respect to their rheology, surface tension and wetting of liquid packaging board, to provide a basis for interpretation and prediction of their printing performance. For all pigment and acrylate polymer vehicles and mixing proportions the inks were shown to be shear thinning and thixotropic, with plastic viscosity, yield stress and storage and loss moduli increasing strongly with content of solution polymer (at comparable solids contents). The solution polymer decreases the static surface tension of the inks, but generally leads to an increase in their equilibrium drop contact angle on the polyethylene- (PE-) coated board due to increase in the ink-board interfacial energy. The solution polymer also decreases the drop spreading rate, and a simple model is tested to express the spreading dynamics in terms of equilibrium contact angle and a rate parameter given by the effective ratio of surface tension to viscosity.

The performance of water-based acrylic flexographic inks laboratory printed on three different polymer-coated boards, namely coated with LDPE, OPP and PP, have been analysed and interpreted. The print quality and resistance properties obtained were related to varying ink formulation, in particular choice of emulsion polymer and presence of silicone additive in the vehicle, as well as varying levels of corona pretreatment. Print mottle and adhesion were worst on PP, while wet (water) rub and scratch resistance were worst on OPP and PE, respectively. However, these properties could be greatly influenced by the ink formulation, more so than corona level. In general addition of silicone improved scratch resistance, due to reduction in polar energy component of the print surface, but at the expense of worsened wet rub resistance. The emulsion polymer giving best resistance performance was generally found to give poorest optical properties, presumably due to more limited resolubility on press.

In this study, polyimide was treated by atmospheric pressure dielectric barrier discharge plasma using a helium and/or helium-oxygen mixture gasses. The polyimide was placed between copper electrodes with dielectric material installed on the cathode electrode. To investigate the surface treatment, the plasmas as a function of power, treatment time, and plasma gasses were introduced on the polyimide substrate. The experimental results show that the polyimide treated by dielectric barrier discharge plasma increases the wetting property. This property can be attributed to the surface roughness and the water compatible functional groups. The roughness increases by helium plasma treatment and can be further improved by increasing plasma power or the presence of oxygen in the helium-oxygen mixture plasma. On the other hand, the plasma surface treatment led to formation of oxygen related functional groups of -C=O and -OH.

In this study, the surfaces of ultrahigh molecular weight polyethylene (UHMWPE), poly(ethylene terephthalate) (PET), and polytetrafluoroethylene (PTFE) films were treated with a helium-water vapor plasma at atmospheric pressure and room temperature. Surface changes related to hydrophilicity, chemical funtionalization, surface energy, and adhesive strength after plasma treatment were investigated using water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS), and mechanical T-peel tests. Results indicate increased surface energy accompanied with enhanced hydrophilicity. WCA decreased by 36, 50, and 16% for UHMWPE, PET, and PTFE, respectively, after only 0.4 s treatment. For UHMWPE, it is shown that the surface functionalization can be tailored depending on the plasma exposure time. Aging studies performed for these three polymers show the stability of the surface groups as indicated by a small increase in WCA values of plasma treated samples which can be attributed to cross-linking of surface and subsurface polymer chains. XPS analysis of the surfaces show increased oxygen content via the formation of polar, hydroxyl-based functional groups. Furthermore, major changes in the polymer structure of PET are observed, possibly due to the opening of the aromatic rings caused by the plasma energetic species. T-peel test results show an 8, 7.5, and 400-fold increase in peel strength for UHMWPE, PET, and PTFE, respectively. Most importantly, it is shown that water-vapor based plasmas can be a promising, “green,” inexpensive route to promote the surface activation of polymers.

The interfacial tension along the boundary formed between two immiscible polymer liquids has been measured by the pendant drop method. The polymers employed for the study are polyethylene, polydimethylsiloxane, poly(ethylene oxide), polytetrahydrofuran, poly(vinyl acetate) and an ethylene-vinyl acetate copolymer. Surface tensions of these polymers (against air) were also determined by the same technique. The values of interfacial tension between polyethylene and each of the five polar polymers, together with the surface tension data, were utilized to calculate the separate contributions to the surface tension by dispersion and dipole interaction forces, in accordance with the procedure proposed by Fowkes. The interfacial tension between two polar polymers was then analyzed in terms of these separate components of forces. An empirical relation has been shown to correlate the dipole interaction term in interfacial tension with the individual dipole force components of the two polar polymers involved.