The influence of u.v. irradiation on the surface morphology of some commercial polymers was investigated using scanning electron microscopy (SEM). The photodegraded samples exhibited a high degree of surface damage. The formation of cracks and holes resulting from the degradation and evolution of volatile products was observed. In polymers undergoing photocrosslinking, the agglomeration of particles was clearly seen. Polymer photodegradation in the presence of hydrogen peroxide as an acceleration agent revealed its etching action.

This paper discusses a recently developed surface energetics criterion for adhesive bonding and fracture and its applications in such diverse areas as structural adhesive bonding, fiber reinforced composites, biomaterials development, and lithographic printing. The theoretical relations describe systematic methods for the surface energy analysis of solid adhesive and adherend surfaces. The surface tension properties for the adhesive and adherend can then be introduced into a modified Griffith fracture mechanics relation to obtain predictions of bond strength under varied conditions of liquid or gas phase immersion such as water and dry air.

A new definition for work of adhesion W_a is applied to computationally define the dispersion γ_s^d and polar γ_s^d components of the solid surface tension γ_s = γ_s^d + γ_s^d for twenty-five low energy substrates. These calculated surface properties are correlated with surface composition and structure. Surface dipole orientation and electron induction effects are respectively distinguished for chlorinated and partially fluorinated hydrocarbons. Published values for critical surface tension of wetting γ_c are correlated with both γ_s^d and γ_s.

Wettability measurements and surface energy analysis are applied to isolate the (London-d) and (Keesom-p) polar contributions to solid-vapor surface tension γ_sv=γ^d _sv + γ^p _sv of surface treated graphite fibers. Surface treatments include metal coatings with Al, Cu, and Ni, chemically reducing heat treatments in H₂ and vacuum, and films of highly chlorinated polymers such as polyhexachlorobutadiene and polychloral. This study shows that the highly polar surface properties γ^p _sv|γ_sv ≃ γ^d _sv|γ_sv ≃ 0.50 of commercial graphite fibers can be modified by surface treatment to display dominant dispersion character with γ^d _sv|γ_sv ≃ 0.79 to 0.92 without substantial reduction in total surface energy γ_sv. For adsorption bonded fiber/matrix interfaces a new method of mapping the surface energy effects of an immersion phase upon the Griffith fracture energy γ_G is applied to define criteria for strong interfacial bonding under both air and water immersion.

Average values for dispersion γ_s^d and polar γ_s^d contributions of the solid surface tension γ_s γ_s^d + γ_s^p for poly(methylene oxide) (PMO) and Na-treated polytetrafluoroethylene (PTFE) are determined by a new computational analysis of wettability data. PMO displays γ_s^d equals; 21.8 ± 0.9 and γ_s^p = 11.5 ± 1.5 dyn/cm while Na-treated PTFE displays γ_s^d = 36.1 ± 3.0 and γ_s^p = 14.5 ± 2.9 dyne/cm. These surfaces present the highest fractional surface polarity p_s = γ_s^p/γ_s = 0.29-0.35 yet encountered for organic polymers or oriented monolayers. These unusual surface tension properties are correlated with surface chemistry and adhesion phenomena.

This report applies recently developed surface energy and fracture mechanics relations to the analysis of bioadhesion and biocompatibility. The dispersion α and polar β components of 190 biological and implant surfaces are analysed. The surface energetics relations between bioadhesion and biocompatibility point out that a strongly adsorbed plasma protein film on the implant surface provides the best blood compatibility and low thrombogenic effects. The surface energy relations provide means of selecting optimum implant surface properties and mapping on surface energy diagrams the three phase interactions which define bioadhesion.

A new version of axisymmetric drop shape analysis (ADSA) called ADSA-NA (ADSA-no apex) was developed for measuring interfacial properties for drop configurations without an apex. ADSA-NA facilitates contact angle measurements on drops with a capillary protruding into the drop. Thus a much simpler experimental setup, not involving formation of a complete drop from below through a hole in the test surface, may be used. The contact angles of long-chained alkanes on a commercial fluoropolymer, Teflon AF 1600, were measured using the new method. A new numerical scheme was incorporated into the image processing to improve the location of the contact points of the liquid meniscus with the solid substrate to subpixel resolution. The images acquired in the experiments were also analyzed by a different drop shape technique called theoretical image fitting analysis-axisymmetric interfaces (TIFA-AI). The results were compared with literature values obtained by means of the standard ADSA for sessile drops with the apex. Comparison of the results from ADSA-NA with those from TIFA-AI and ADSA reveals that, with different numerical strategies and experimental setups, contact angles can be measured with an accuracy of less than 0.2°. Contact angles and surface tensions measured from drops with no apex, i.e., by means of ADSA-NA and TIFA-AI, were considerably less scattered than those from complete drops with apex. ADSA-NA was also used to explore sources of improvement in contact angle resolution. It was found that using an accurate value of surface tension as an input enhances the accuracy of contact angle measurements.

In this work particular attention has been paid to the aging behavior of biaxially oriented polypropylene (BOPP) film surfaces modified with the acrylic acid (AAc) corona discharge treatment previously reported. Three different corona energies of 15.3, 38.2 and 76.4 kJ/m² were studied. The surface properties of treated films during 90 days of aging were compared with those of normal air-corona treated films prepared with the same corona energies. The surface chemical compositions of aged films were analyzed by curve-fitting of the ATR-FTIR spectra. The wettabilities of all aged films were monitored by water contact angle and surface free energy measurements. The change of surface topology of air- and AAc-corona treated films was investigated at 1 day, 7 days and 90 days of aging using the technique. In addition, the surface adhesions of aged films were determined with the T-peeling test. The results showed that the amount of polar functional groups on the surface of aged films had changed. However, the aged films of the AAc-corona treated films still showed greater wettability than did the air-corona treated films and could retain high surface hydrophilicity for more than 90 days of aging under ambient condition. The surface topology of both types of aged films changed after aging from a globular structure to a flatter surface, due to mobility of the deposited polymer layer. The AAc-corona treated films showed rougher surfaces due to the influence of poly(acrylic acid) deposition and they could retain the improved surface wettability despite the change in surface topography. The adhesion peel forces of aged films decreased slightly due to the topological changes. A mechanism for the change in surface topography and in chemical functionality of each type of aged film is proposed.

In this work, the acrylic acid (AAc)-corona discharge was carried out on biaxially oriented polypropylene (BOPP) films by introducing AAc vapor into the corona region of a normal corona treater. Three different corona energies of 15.3, 38.2 and 76.4 kJ/m² were studied. Surface properties of treated films were compared with those of air-corona treated films prepared with the same corona energies. The change in chemical composition on the film surface was characterized by curve-fitting of the ATR-FTIR spectra. The wettability of treated films, before and after aging in different environments, was observed by water contact angle and surface free energy. The surface morphology of air- and AAc-corona treated films was investigated using SEM and AFM techniques. Adhesion of the treated films to some other substrate was determined with the T-peeling test. It was found that the hydrophilicity of all treated films increased with increasing corona energy. AAc-corona treated films showed greater wettability than did the air-corona treated films and could retain the surface hydrophilicity for more than 90 days of aging under ambient conditions. The surface morphology of BOPP films changed after corona treatment into a globular structure. The AAc-corona treated films showed rougher surfaces due to surface oxidation and polymer formation, whereas, air-corona treated films displayed a similar structure but of smaller size due to the formation of low molecular weight oxidized materials (LMWOM) arising from the degradation of BOPP films. AAc-corona treated films showed greater peel strength than did the air-corona treated films.

The changes of contact angle (θ) and surface free energy (γS) under low-temperature air plasma in the polymers of different chemical structure and polarity (polyethylene, PE; polypropylene, PP; poly(ethylene terephtalate), PET and poly(methyl methacrylate), PMMA) pointed out to the greater effect of short-time plasma action (5–15 s) on these parameters as compared to longer times of exposure.

The non-reversion effect of θ changes caused by plasma in PE and PP suggests that the oxidation processes mainly decide about values in nonpolar polymers. The significantly greater θ changes in PE than those in PP indicate that the side groups present in the main chains impede oxidation of such a polymer by plasma.

The reversion of θ changes in PET and in PMMA, and return of these values to almost the initial ones after 10 min storage proves that the main reason for θ changes in polar polymers is a certain alteration of the chain conformation.

These changes, taking place after longer plasma treatment, suggest that the side ester groups in PMMA retard the above-mentioned conformational transformations. Then, in both kinds of polymers (polar and nonpolar) the structure of macrochain decides about the efficiency of reaction caused by plasma, and at the same time the side groups retard not only the oxidation processes but the conformational changes as well.

In this study the effect of low temperature plasma (LTP) treatment of cotton fabric for ink-jet printing was investigated. Owing to the specific printing and conductivity requirements for ink-jet printing, none of the conventional printing chemicals used for cotton fabric can be directly incorporated into the ink formulation. As a result, the cotton fabric requires treatment with the printing chemicals prior to the stage of ink-jet printing. The printing chemicals as a treatment to cotton fabric are applied by the coating method. The aim of this study was to investigate the possibility and effectiveness of applying LTP pre-treatment to enhance the performance of treatment paste containing sodium alginate, to improve the properties of the ink-jet printed cotton fabric. Experimental results revealed that the LTP pre-treatment in conjunction with the ink-jet printing technique could improve the final properties of printed cotton fabric.

Polyester and polyamide fabrics were treated with plasma under atmospheric pressure for different durations, 3, 5 and 7 s. The wettability of polyester and polyamide fabrics, measured in terms of contact angle and longitudinal wicking, was improved after plasma treatment. The oxygen content of the fabrics was increased indicating that hydrophilic groups had been introduced into the fabric leading to the improved wettability. However, there was no obvious improvement in dryability because bulk properties of the fibres did not change. Moreover, with the help of plasma treatment, water repellency of the fabrics was greatly improved when water repellency finishing agent was added.

Argon plasma-pretreated polytetrafluoroethylene (PTFE) films were subjected to further surface modification by near-UV light-induced graft copolymerization with acrylic acid (AAc), sodium salt of styrenesulfonic acid (NaSS), and N,N-dimethylacrylamide (DMAA). The surface compositions and microstructures of the modified films were characterized by angle-resolved X-ray photoelectron spectroscopy (XPS). A stratified surface microstructure with a significantly higher substrate-to-graft chain ratio in the top surface layer than in the subsurface layer was always obtained for PTFE surface with a substantial amount of the hydrophilic graft. The stratified surface microstructure was consistent with the observed hysteresis in advancing and receding water contact angles. The graft yield increased with Ar plasma pretreatment time and monomer concentration. Covalent immobilization of trypsin on the AAc polymer-grafted PTFE films was facilitated by water-soluble carbodiimide (WSC). The effective enzyme activities increased initially with increasing surface concentration of the grafted AAc polymer but became saturated at a moderate AAc polymer concentration. The immobilized enzyme could still retain close to 30% of its original activity. Solution-coating of the polymeric acid-modified PTFE films with the emeraldine (EM) base of polyaniline readily resulted in an interfacial charge transfer interaction and a semiconductive PTFE surface.

Plasma treatment effectively alters the surface of textiles and reduces the need for using environmentally hazardous chemicals. Applications of the technology include enhancing wettability, adhesiveness of polymer surface, and anti-felting properties of wool fibers, as well as improving dyeing properties, and sterilization. Free radicals generated on the surface can induce further crosslinking or polymerization.

Surface modification of textile fibers using gas plasma is a useful tool in altering the wettability, adhesiveness, and dyeability of synthetic polymer-based textiles. Plasma treatment is also effective for biomedical applications such as sterilization. Antibacterial properties can be achieved by subsequent grafting.

The contact angles θ of dispersion (D), polar (P) and hydrogen bonding (H) liquids on poly(vinylidene fluoride-co-hexafluoroacetone) (P(VDF-HFA); HFA content 6.5, 8.3 and 10.4 mol%) were measured. The critical surface tensions γ_c of P(VDF-HFA) were evaluated by the Zisman plot (cos θ versusγ_L), Young-Dupre-Good-Girifalco plot $\text{(1 +}\text{cos}\text{θ versus}\text{1}\text{γ}{}^{0.5}{}_{\mathrm{<mtext>L</mtext>}}\text{)}$ and the log(1 + cos θ) versus log (γ_L) plot. The following results were obtained: the γ_c values of P(VDF-HFA) evaluated for the P liquids were larger than those for the D and H liquids; the γ_c values estimated by the Zisman plot were smaller than those obtained by the other plots; the surface tension γ_s values of P(VDF-HFA) revealed a minimum at the HFA content of 8.3 mol%. It was expected that P(VDF-HFA) with HFA = 8.3 mol% induced surface segregation most easily.

Rough PDMS surfaces comprising 3 μm hemispherical bumps and cavities with pitches ranging from 4.5 to 96 μm have been fabricated by photolithographic and molding techniques. Their wetting and dewetting behavior with water was studied as model for print surfaces used in additive manufacturing and printed electronics. A smooth PDMS surface was studied as control. For a given pitch, both bumpy and cavity surfaces exhibit similar static contact angles, which increase as the roughness ratio increases. Notably, the observed water contact angles are shown to be consistently larger than the calculated Wenzel angles, attributable to the pinning of the water droplets into the metastable wetting states. Optical microscopy reveals that the contact lines on both the bumpy and cavity surfaces are distorted by the microtextures, pinning at the lead edges of the bumps and cavities. Vibration of the sessile droplets on the smooth, bumpy, and cavity PDMS surfaces results in the same contact angle, from 110°-124° to ∼91°. The results suggest that all three surfaces have the same stable wetting states after vibration and that water droplets pin in the smooth area of the rough PDMS surfaces. This conclusion is supported by visual inspection of the contact lines before and after vibration. The importance of pinning location rather than surface energy on the contact angle is discussed. The dewetting of the water droplet was studied by examining the receding motion of the contact line by evaporating the sessile droplets of a very dilute rhodamine dye solution on these surfaces. The results reveal that the contact line is dragged by the bumps as it recedes, whereas dragging is not visible on the smooth and the cavity surfaces. The drag created by the bumps toward the wetting and dewetting process is also visible in the velocity-dependent advancing and receding contact angle experiments.

Plasma surface treatment of plastics is definitely not new, nor is it commonplace. What is a plasma and what can it do is the subject of the following paper. A plasma is an excited gas, not unlike the aurora borealis. The excited particles that comprise the plasma bombard materials placed within their environment causing permanent change to their surface properties. By the judicious selection of process gas(es) and process parameters, the surface can be reengineered to fit specific needs. This paper presents quantitative analytical data on the chemical changes to the surface of polyethylene subjected to a plasma.

To many people, plasma is a laboratory curiosity or limited in scale. Few know that plasma is a commercial process used daily in the treatment of fabrics, non-woven webs and film. This paper reviews applications and processes used to modify materials up to 60 in. in width in a roll-to-roll plasma system. The applications are quite varied. Sometimes, the process is simply to change the surface energy, while at other times, far more sophisticated processes, such as plasma-enhanced chemical vapor deposition (PECVD) processes, are employed to provide a chemical barrier or alter the tribological properties. As will be seen in this review presentation, plasma is extremely versatile and applicable to high-volume web applications.

The virtues of chemical inertness and low surface energy which make polytetrafluoroethylene (PTFE) a valuable engineering polymer also account for the difficulty in achieving structural adhesive bonds. While plasma surface treatment has proven to be the most effective means of maximizing strength and permanence of adhesive bonds with the most inert of engineering polymers, a simple plasma treatment has proven elusive for PTFE. The following studies evaluate two very different plasma processes, activation and deposition, as a means to achieve reliable and high-strength structural adhesive bonds. Sodium naphthalene-etched PTFE is used as a control. Presented are ESCA data which support a theory that improvement is limited by a weakened boundary layer of the PTFE.