One of the most important claims for the plasma technique as a surface treatment is that it modifies only a few atomic layers of materials. However, with polymers, this assumption must be carefully verified to keep the bulk mechanical properties constant. Besides the oxidation of the film, with specific plasma conditions such as high power and duration, the polypropylene film structure is also modified in the bulk through vacuum ultraviolet absorption and thermal relaxation. This change is associated with smectic- and amorphous-phase transformation into an α-monoclinic phase, with a rapid rate for the smectic transformation and a slower rate for the amorphous transformation. At the same time, the crystallite size increases, and the polypropylene film texture is planar and moderated (1.7 mrd at the maximum of the distribution, with a discharge power of 100 W and a treatment duration of 10 min). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2007–2013, 2004
https://onlinelibrary.wiley.com/doi/abs/10.1002/polb.20071

Many experiments have been performed globally to investigate ways of improving adhesion to polymers. This paper discusses current atmospheric surface activation systems, appropriate measurements of wettability and adhesion, over-treatment effects and surface analysis techniques relative to optimizing the adhesion of inks, paints, coatings and adhesives to polymer surfaces. Recommendations for improved activation by substrate and application are discussed.

Hydrophobic solid surfaces with controlled roughness were prepared by coating glass slides with an amorphous fluoropolymer (Teflon^® AF1600, DuPont) containing varying amounts of silica spheres (diameter 48 μm). Quasi-static advancing, θ_A, and receding, θ_R, contact angles were measured with the Wilhelmy technique. The contact angle hysteresis was significant but could be eliminated by subjecting the system to acoustic vibrations. Surface roughness affects all contact angles, but only the vibrated ones, θ_V, agree with the Wenzel equation. The contact angle obtained by averaging the cosines of θ_A and θ_R is a good approximation for θ_V, provided that roughness is not too large or the angles too small. Zisman's approach was employed to obtain the critical surface tension of wetting (CST) of the solid surfaces. The CST increases with roughness in accordance with Wenzel equation. Advancing, receding, and vibrated angles yield different results. The θ_A is known to be characteristic of the main hydrophobic component (the fluoropolymer). The θ_V is a better representation of the average wettability of the surface (including the presence of defects).

A new method for the measurement of apparent contact angles at the global energy minimum on real surfaces has been developed. The method consists of vibrating the surface, taking top-view pictures of the drop, monitoring the drop roundness, and calculating the contact angle from the drop diameter and weight. The use of the new method has been demonstrated for various rough surfaces, all having the same surface chemistry. In order to establish the optimal vibration conditions, the proper ranges for the system parameters (i.e., drop volume, vibration time, frequency of vibration, and amplitude of vibration) were determined. The reliability of the method has been demonstrated by the fact that the ideal contact angles of all surfaces, as calculated from the Wenzel equation using the measured apparent contact angles, came out to be practically identical. This ideal contact angle has been compared with three methods of calculation from values of advancing and receding contact angles.

The control of the surface wettability of poly (methyl methacrylate) (PMMA) substrates has been successfully demonstrated using an Ar2* excimer lamp radiating 126 nm vacuum ultraviolet (VUV) light. Each of the samples was exposed to 126 nm VUV light in air over the pressure range of 2×10−4-105 Pa. Although at the process pressures of 10, 103, and 105 Pa, the PMMA surfaces became relatively hydrophilic, the degree of hydrophilicity depended markedly on the pressure. The minimum water contact angles of the samples treated at 10, 103, and 105 Pa were about 50°, 33°, and 64°, respectively. These values were larger than those of PMMA substrates hydrophilized through 172 nm VUV irradiation conducted under the same conditions. On the other hand, after 126 nm VUV irradiation conducted under the high vacuum condition of 2×10−4 Pa, the PMMA substrate surface became carbon-rich, probably due to preferential cross-linking reactions, as evidenced by x-ray photoelectron spectroscopy. This surface was hydrophobic, showing a water contact angle of about 101°. Although the 126 nm VUV-irradiated surfaces appeared relatively smooth when observed by atomic force microscope, very small particles with diameters of 30-60 nm, which probably originated from the readhesion of photodecomposed products, existed on all of the sample surfaces.

The line energy associated with the triple phase contact line is a function of local surface defects (chemical and topographical); however, it can still be calculated from the advancing and receding contact angles to which those defects give rise. In this study an expression for the line energy associated with the triple phase contact line is developed. The expression relates the line energy to the drop volume, the interfacial energies, and the actual contact angle (be it advancing, receding, or in between). From the expression we can back calculate the equilibrium Young contact angle, θ ₀, as a function of the maximal advancing, θ _A, and minimal receding, θ _R, contact angles. To keep a certain maximal hysteresis between advancing and receding angles, different line energies are required depending on the three interfacial energies and the drop's volume V. We learn from the obtained expressions that the hysteresis is determined by some dimensionless parameter, script K sign, which is some normalized line energy. The value of script K sign required to keep a constant hysteresis (θ _A - θ _R) rises to infinity as we get closer to θ ₀ = 90°.

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.

The present invention provides a method of modifying the surface of a polymeric substrate, e.g., to improve the wettability of the polymer film surface and/or alter the metal adhesion properties of the surface of the substrate by exposing the substrate to a flame. The flame is supported by an oxidizer and fuel mixture that includes an effective amount, for modifying the polymeric substrate, of at least one sulfur-containing compound that functions as a fuel substitute. In addition, substrates are provided that have increased wettability or increased metal adhesion performance.

A new plasma-based micropatterning technique, here referred to as plasma printing, combines the well known advantages given by the nonequilibrium character of a dielectric barrier discharge (DBD) and its operation inside small gas volumes with dimension between tens and hundreds of micrometres. The discharge is run at atmospheric pressure and can be easily implemented for patterned surface treatment with applications in biotechnology and microtechnology. In this work the local modification of dielectric substrates, e.g. polymeric films, is addressed with respect to coating and chemical functionalisation, immobilisation of biomolecules and area-selective electroless plating.

Abstract Application of a pulsed high negative voltage (approx. 10 us pulse width, 300-900 pulses per second (pps)) to a substrate is found to induce discharge and thereby increase the ion current of an inductively coupled plasma. This plasma source ion implantation (PSII) technique is investigated as a surface modification method for poly (ethylene terephthalate)(PET) films using Ar, N2 and CZHZ gases. PSII treatment of PET with N2 and Ar gases is found to change the color of the PET film, effectively increasing the near-ultraviolet absorption. The effects of the treatment using N2 and Ar gases on the chemical bonding of C, H and O are examined by X-ray photoelectron spectroscopy (XPS). PSII treatment with CZHQ gas is shown to produce a thin diamond-like carbon film on the PET surface. The layer is shown to be smooth by scanning electron microscopy, and the structure is analyzed by XPS and laser Raman spectroscopy. The treatment using CZHZ gas effectively reduces the oxygen transmission rate by up to 100 times that of unmodified PET film at a carbon film thickness of only 70-300 mm.

The effects of exposure to [72 nm ultraviolet (UV) excimer light in ambient air on the wettability and surface free energy of polymer films were investigated from contact angle measurements. The polymer films used were polyethylene (PE), polypropylene (PP), poly (ethylene terephthalate)(PET), nylon 6 (Ny6) and polyimide (Pl). As a measure of the wettability, the water contact angle was determined by the sessile drop and the Wilhelmy methods. For all films, considerable increase in wettability was accomplished by UV exposure within a few tens of seconds. After the UV exposure, a decrease in the wettability, the hydrophobic recovery, was observed over a time period of several days. Even after the recovery, the wettability was sufficiently higher compared to that before the UV exposure. The Lifshitz-van der Waals component and Lewis acid-base parame-ters of the surface free energy of the films were determined by contact angle measurements using certain probe liquids. The base parameter was found to increase considerably by the UV exposure. XPS analysis and AFM observation of the film surfaces showed that such increases in the wettability and the surface free energy were due to the increased atomic oxygen concentration at the film surfaces. The effect of the UV exposure on particle deposition onto PP and PET in water was also examined using spherical polyethylene and nylon 12 particles. The apparent equilibrium number of particles deposited on the polymer substrate decreased drastically after UV exposure. The particle deposition behavior was explained well in terms of the free energy change due to deposition, which was calculated from various surface free energies.

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated using pulsed KrF (248 nm) excimer laser in air and in diethylenetriamine (DETA), to improve their adhesion to epoxy resin. The effects of fluence, number of pulses and the treatment environment were explored. Topographical and chemical changes on the fiber surface were characterized using several techniques, including X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic wettability measurements. SEM micrographs and AFM images revealed that the surface roughness of fibers increased after the laser treatment and was a function of the fluence (energy density) of the laser beam and number of pulses. The XPS data indicated that oxygen and nitrogen were incorporated on the fiber surfaces making them more polar. The dynamic wettability data confirmed the presence of polar groups on the fiber surfaces. The UHMWPE fiber/epoxy resin interfacial shear strength (IFSS) increased by up to 600% for some treatment conditions. Introduction of polar groups and increased surface roughness are two main factors that contribute to the increased adhesion (IFSS) of the UHMWPE fiber/epoxy resin system significantly.

The objectives of this work were to identify, develop and compare methods for opti-mized welding of polypropylene using the ultrasonic method. The methods considered include: modification of surface polarity by grafting monomers onto polypropylene backbone, thermal and chemical surface pretreatments and surface pretreatment by excimer laser ablation. The weld joint tensile strength was chosen as the optimization criterion for ultrasonic welding. The thermal properties and weld morphology obtained using Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM), respectively, were correlated to weld strength. It was determined that proper surface modification improved material weldability. The results suggest that increased polarity and roughness and decreased melting temperature and heat of melting increase the weld strength.

The theoretical analysis of electrostatic interactions and ion redistribution in the close vicinity of the three-phase contact line shows their important role in the Langmuir wetting process. To provide a sufficient rate for the ion transfer, which is intended to neutralize the interfacial charge, the concentration and potential distributions deviate from the equilibrium. As a consequence, during the deposition process the adhesion work, and hence the contact angle, are defined by the local ionic concentrations near the three-phase contact line. The concentration profiles and the electro-diffusion ion fluxes induced during the Langmuir wetting process are strongly dependent on the subphase composition and on the monolayer properties. The results of the analysis are in a good agreement with the experiments.

Polystyrene (PS) and polyethylene (PE) samples were treated with argon and oxygen plasmas. Microwave electron cyclotron resonance (ECR) was used to generate the argon and oxygen plasmas and these plasmas were used to modify the surface of the polymers. The samples were processed at different microwave powers and treatment time and the surface modification of the polymer was evaluated by measuring the water contact angle of the samples before and after the modification. Decrease in the contact angle was observed with the increase in the microwave power for both polystyrene and polyethylene. Plasma parameters were assessed using Langmuir probe measurements. Fourier transform infrared spectroscopy showed the evidence for the induction of oxygen-based functional groups in both polyethylene and polystyrene when treated with the oxygen plasma. Argon treatment of the polymers showed improvement in the wettability which is attributed to the process called as CASING, on the other hand the oxygen plasma treatment of the polymers showed surface functionalization. Correlation between the plasma parameters and the surface modification of the polymer is also discussed.

Devices are presented which allow determination of unknown surface properties through the creation of a channel capillary, comprised in part of the subject surface or surfaces, and measurement of the capillary pressure created by a test fluid within the resultant channel. In various embodiments of the invention, a channel is created in a reference material which is bonded, through some mechanism, to the test surface in order to create a narrow capillary channel. In other embodiments of the invention, the capillary channel is created with test surfaces on either side of standoff strips which space the surfaces a precise distance from one another. Methods are presented for using these capillaries through immersion, along their length, in a bath of test fluid, such that the resultant fluid level provides a measure of capillary pressure. Being, in part, a consequence of the contact angle between the test fluid and the surface or surfaces under consideration, the capillary pressure is a convenient measure of surface properties inherently related to printability, affinity for adhesives, surface contamination by foreign substances, surface roughness, and the like. Devices are presented which allow measurement of test fluid height within the capillary, both in situations where a static equilibrium is achieved, and in situations where a dynamic contact angle is operative as the fluid rises or falls within the capillary.

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.

This paper describes the photochemical surface modification of polystyrene (PS) substrates using vacuum ultraviolet (VUV) light 172 nm in wavelength. We have particularly focused on the effects of atmospheric pressure during VUV irradiation on the obtained surface's wettability and the stability of the wettability, in addition to its chemical structure, morphology, and photooxidation rate. Samples were photoirradiated with VUV light under pressures of 10, 10(3), or 10(5) Pa. Although, in each case, the originally hydrophobic PS surface became highly hydrophilic, the final water-contact angle and photooxidation rate depended on the atmospheric pressure. The samples treated at 10 Pa were less wettable than those prepared at 10(3) and 10(5) Pa due to the shortage of oxygen molecules in the atmosphere. The minimum water-contact angles of the samples treated at 10, 10(3), and 10(5) Pa were about 8 degrees, 0 degrees, and 0 degrees, respectively. With the samples prepared at 10 and 10(3) Pa, photooxidation reactions proceeded in the topmost region closest to the surface, while at 10(5) Pa photooxidation was found to be greatly enhanced in the deeper regions, as evidenced by angle-resolved X-ray photoelectron spectroscopy. Photoetching rates were determined through atomic force microscope observation of microstructured PS samples prepared by a simple mesh-contact method. As estimated from AFM images of the latticed microstructures obtained, the rates of samples prepared at 10(3) and 10(5) Pa were about 1.5 and 1.3 nm/min, respectively. However, no photoetched features were observable on the sample surface prepared at 10 Pa. Hydrophilic stability also varied greatly depending on atmospheric pressure. The hydrophilicity of samples treated at 10 and 10(3) Pa gradually decreased as they were exposed to air. On the other hand, the sample surface prepared at 10(5) Pa showed excellent hydrophilicity even after being left in air for 30 days.

Poly(ethylene terephthalate) (PET) film surfaces were modified by argon (Ar), oxygen (O₂), hydrogen (H₂), nitrogen (N₂), and ammonia (NH₃) plasmas, and the plasma-modified PET surfaces were investigated with scanning probe microscopy, contact-angle measurements, and X-ray photoelectron spectroscopy to characterize the surfaces. The exposure of the PET film surfaces to the plasmas led to the etching process on the surfaces and to changes in the topography of the surfaces. The etching rate and surface roughness were closely related to what kind of plasma was used and how high the radio frequency (RF) power was that was input into the plasmas. The etching rate was in the order of O₂ plasma > H₂ plasma > N₂ plasma > Ar plasma > NH₃ plasma, and the surface roughness was in the order of NH₃ plasma > N₂ plasma > H₂ plasma > Ar plasma > O₂ plasma. Heavy etching reactions did not always lead to large increases in the surface roughness. The plasmas also led to changes in the surface properties of the PET surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surfaces decreased. Modification reactions occurring on the PET surfaces depended on what plasma had been used for the modification. The O₂, Ar, H₂, and N₂ plasmas modified mainly CH₂ or phenyl rings rather than ester groups in the PET polymer chains to form CO groups. On the other hand, the NH₃ plasma modified ester groups to form CO groups. Aging effects of the plasma-modified PET film surfaces continued as long as 15 days after the modification was finished. The aging effects were related to the movement of CO groups in ester residues toward the topmost layer and to the movement of CO groups away from the topmost layer. Such movement of the CO groups could occur within at least 3 nm from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3727–3740, 2004
https://onlinelibrary.wiley.com/doi/abs/10.1002/polb.20234

The surface degradation and production of low molecular weight oxidized materials (LMWOM) on biaxially oriented polypropylene (BOPP) and low-density polyethylene (LDPE) films was investigated and compared for two different dielectric barrier discharge (DBD) treatment types, namely air corona and nitrogen atmospheric pressure glow discharge (N₂ APGD). Contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) analyses were performed in conjunction with rinsing the treated films in water. It is shown that N₂ APGD treatments of both polyolefins result in much less surface degradation, therefore, allowing for a significantly higher degree of functionalization and better wettability. Hydrophobic recovery of the treated films has also been studied by monitoring their surface energy (γ_s) over a period of time extending up to several months after treatment. Following both surface modification techniques, the treated polyolefin films were both found to undergo hydrophobic recovery; however, for N₂ APGD modified surfaces, γ_s ceases to decrease after a few days and attains a higher stable value than in the case of air corona treated films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1291–1303, 2004
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.21134

Digital printing is increasingly being used for package printing. One of the major techniques of digital printing is dry-toner electrophotography. This paper evaluates the printability of three different extrusion coatings used for packaging boards: low-density polyethylene (PE-LD), ethylene methyl acrylate (E/MA) and polyethylene terephthalate (PET). Extrusion coatings in general have an impervious, chemically inert, nonporous surface with low surface energies that cause them to be non-receptive to bonding with toners. The most common methods used in improving the adhesion properties of polymer coatings are different surface treatments. These increase the surface energy and also provide the polar molecular groups necessary for good bonds between the toner and polymer molecules. The polymer coatings have been modified with electrical corona discharge treatment. The effects of corona on polymer surfaces and the correlation between surface modification and print quality have been evaluated. Results show that sufficiently high surface energy and surface-charge uniformity are necessary for even print quality and toner adhesion. E/MA and PET have the required surface-energy level without the corona treatment, but PE-LD needs surface modification in order to succeed in the electrophotographic process. E/MA also has exceptional surface-charge properties compared with PET and PE-LD. Polym. Eng. Sci. 44:2052–2060, 2004. © 2004 Society of Plastics Engineers.