Polar and dispersion surface free energy (SFE) can be determined with the Owens-Wendt method. Thereby, contact angles (CAs) of at least two liquids with known surface tension (ST) components are measured. The ST components can either be determined through experiment or drawn from literature. However, it is important to know how big the difference is between SFE component values that have been calculated with experimentally-determined ST values or values derived from literature. In this study, STs of different test liquids were analyzed by Pendant Drop method and the components by CA measurement on a non-polar surface. CAs on different polymer surfaces were measured to calculate SFE components with the Owens-Wendt method. The calculations conducted were either based on experimentally-determined ST parts or different sets of values found in the literature. The findings of the survey show that, depending on the set of literature values used, the SFE results deviate significantly from the values obtained from experiment. Expressing this deviation in figures, in extreme cases the polar part differs for some polymers by -100% to +100%, with the dispersion component spanning -50% to +43%. In comparison, the expected relative uncertainties exhibited by the experimentally-determined ST values are about 15% for the polar and approximately 5% for the dispersion SFE part. Hence, the results show that the SFE uncertainty can be reduced significantly by means of analyzing the ST parts experimentally.

A dielectric barrier discharge in a corona process configuration is used to treat the surface of fluoropolymers in a nitrogen–organic precursor environment. The surface chemistry, thickness, and water contact angle of the deposited coatings are measured and used to build up an output matrix to be correlated with an input matrix built using electrical parameters of the discharge, the gas mixture chemical composition, and spectroscopic parameters measured in both the infrared and ultraviolet–visible emission spectral regions. A partial least-squares regression (PLSR) model enables determining the most important plasma parameters to drive the coating physicochemical characteristics. From the PLSR model, it is determined that the plasma electrical parameters drive the surface modification process, at the expense of other plasma characteristics such as gas flow, gaseous precursor concentration, nitrogen vibrational temperature, and the level of gaseous precursor conversion within the plasma.

Poor adhesion continues to be a problem for manufacturers of laminated packaging. Therefore, the aim of this research was to study the effect of flame treatment, the type of coating, and starch application on the adhesion force of polyethylene/paperboard. The force of adhesion was determined using the peel test method; the paper surface energy was assessed by contact angle analysis; and paperboard roughness was determined by profilometer. The flame treatment did not affect the surface roughness but significantly increased the paperboard surface energy. The paperboard coated with polar latex showed much higher surface energy than the paperboard coated with nonpolar latex. The adhesion force of polyethylene presented a linear correlation to the surface energy of the paperboard. Therefore, the surface energy of paperboard is an excellent indication of its adhesion force to polyethylene, and this represents a very reliable and practical method in terms of quality control in the paper industry for producing laminated packages.

Wetting, the process of water interacting with a surface, is critical in our everyday lives and in many biological and technological systems. The contact angle is the angle at the interface where water, air and solid meet, and its value is a measure of how likely the surface is to be wetted by the water. Low contact-angle values demonstrate a tendency of the water to spread and adhere to the surface, whereas high contact-angle values show the surface’s tendency to repel water. The most common method for surface-wetting characterization is sessile-drop goniometry, due to its simplicity. The method determines the contact angle from the shape of the droplet and can be applied to a wide variety of materials, from biological surfaces to polymers, metals, ceramics, minerals and so on. The apparent simplicity of the method is misleading, however, and obtaining meaningful results requires minimization of random and systematic errors. This article provides a protocol for performing reliable and reproducible measurements of the advancing contact angle (ACA) and the receding contact angle (RCA) by slowly increasing and reducing the volume of a probe drop, respectively. One pair of ACA and RCA measurements takes ~15–20 min to complete, whereas the whole protocol with repeat measurements may take ~1–2 h. This protocol focuses on using water as a probe liquid, and advice is given on how it can be modified for the use of other probe liquids.

This chapter describes an application of plasma in printed substrates and the influence of plasma treatment on polymers and polymeric composites, their printability and prints quality. Plasma is one of the physical methods of surface modification that includes, among others, corona, flame, and laser treatment. Contrary to the corona treatment, plasma activation enables very uniform modification. Due to the attributes of polymers, particularly their thermal sensitivity, their modification is almost exclusively done using cold plasma, which described in depth in this chapter. Additionally, the changes induced in the material are explained. Especially substrate wettability and its roughness are of paramount importance, impacting printability significantly. Moreover, the influence of selected parameters of plasma treatment on surface modification is presented. Due to the fact that changes induced in the material surface are not permanent, the chapter also goes into more detail about the aging process in relation to the type of polymer, conditions of plasma activation, and storage.

We find that nitrogen plasma treatment of micro/nanofibrillated cellulose films increases wettability of the surface by both liquid polar water and nonpolar hexadecane. The increased wetting effect is more pronounced in the case of polar liquid, favouring the use of plasma treated micro/nanofibrillated cellulose films as substrates for a range of inkjet printing including organic-based polar-solvent inks. The films were formed from aqueous suspensions of progressively enzymatic pretreated wood-free cellulose fibres, resulting in increased removal of amorphous species producing novel nanocellulose surfaces displaying increasing crystallinity. The mechanical properties of each film are shown to be highly dependent on the enzymatic pretreatment time. The change in surface chemistry arising from exposure to nitrogen plasma is revealed using X-ray photoelectron spectroscopy. That both polar and dispersive surface energy components become increased, as measured by contact angle, is also linked to an increase in surface roughness. The change in surface free energy is exemplified to favour the trapping of photovoltaic inks.

Highly hydrophobic surfaces have numerous useful properties; for example, they can shed water, be self-cleaning, and prevent fogging (1, 2). Surface hydrophobicity is generally characterized with contact angle (CA) goniometry. With a history of more than 200 years (3), the measurement of CAs was and still is considered the gold standard in wettability characterization, serving to benchmark surfaces across the entire wettability spectrum from superhydrophilic (CA of 0°) to superhydrophobic (CA of 150° to 180°). However, apart from a few reports [e.g., (4–8)], the inherent measurement inaccuracy of the CA goniometer has been largely overlooked by its users. The development of next-generation liquid-repellent coatings depends on raising awareness of the limitations of CA measurements and adopting more sensitive methods that measure forces.

Surface treatment of monofilaments of polypropylene (PP), poly (ethylene terephthalate) (PET), and polyamide-6 (PA-6) was carried out by corona discharge. The process was conducted with an inter-electrode distance of 4 mm and treatment time in the range of 10 s to 120 s using a wire-plan system under controlled ambient conditions. The samples, before and after corona, were characterized through contact angle measurements, water absorption, Fourier transform infrared spectroscopy/attenuated total reflectance (FT-IR/ATR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). After corona, the PP, PET, and PA-6 samples showed water absorption degrees of 9.4%, 8.5%, and 9.1%, respectively. Meanwhile, their dynamic contact angles reduced by 29.6% (PP), 27.9% (PET), and 18.6% (PA-6), while their corresponding surface energies were 71.1 mJ/m², 77.4 mJ/m², and 75 mJ/m², respectively. The FT-IR/ATR, SEM, and DSC results showed that corona treatment effectively improves the wettability of polymeric surfaces through oxidation and surface morphology alteration, but does not affect the bulk thermal properties.

Corona and chemical treatment worked cooperatively for increasing and stabilizing the polyethylene film surface energy. Gentle and varied corona discharge treatment conditions were applied for each polyethylene film to reach 40 dynes/cm. A rather low blending amount of additive could stabilize the film surface energy obviously. Compared with neat PE film, of which the surface energy decreased to 36 dynes/cm at the 12th day, films blended with 1000 ppm A7-OH or PE-PEG 4k -PE showed stable surface energy (36–38 dynes/cm) over 150 days. The influence of industrial applied slipping agent was investigated as well. Morphological and chemical changes were studied by X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscope (AFM). The surface energy was determined by the dyne pens. Mechanism investigation of hydrophilization and hydrophobic recovery processes showed that proper crystallization behavior and enough C[dbnd]O groups on the film surface guarantee satisfactory stability of the surface energy.

The carbon fibers (CFs) reinforced polytetrafluoroethylene (PTFE) composites have been modified using proton irradiation, and the surface energy, hardness and tribological properties have been investigated before and after irradiation. The CFs increased the hardness and the wear resistance. Proton irradiation led to defluorination and carbonization of the CF/PTFE composite surface, and decreased the surface wettability and the surface energy. The irradiation depth was 820 nm from the material surface calculated with SRIM software package. In addition, the wear resistance was improved after proton irradiation. Proton irradiation improved the wear resistance of the composite and induced the material transfer from Cu alloy surface to CF/PTFE. These significant improvements could enable potential applications in aeronautics and smart medical materials.

Hypothesis: Both the surface free energy (γ) and solubility (δ) parameters of substances are related to their cohesive energies which are decided by intermolecular interactions, and there should be some intrinsic relationships between the two parameters. Understanding of the γ-δ correlations is of great fundamental and practical importance. Several empirical γ-δ equations have been proposed so far, but their application to solids is limited. This is because the molar volume (V~) as a parameter exists in these equations while the V~ of solids is commonly hard to be obtained. Hence, the development of γ-δ equations without the parameter V~ is essential for solids.

Method: The γ and δ data of 21 solids including polymers and layered solid materials were chosen, and possible γ-δ relationships were systematically explored using the parameter data of solids by a trial and error fitting method.

Finding: Six γ-δ equations without the parameter V~ are proposed. The γ parameters include total (γ_t), dispersive (γ_d), and polar (γ_p) ones, and the δ parameters include the Hildebrand parameter (δ_t) and the Hansen dispersive (δ_d), polar (δ_p), and hydrogen-bonding (δ_h) ones. Interestingly, the so-obtained V~-free γ-δ equations are also valid for most liquids including nonpolar and polar ones. These γ-δ equations can provide a way to estimate non-measurable parameters from measurable parameters for solid materials, which is beneficial to the application of the characteristic parameters (γ and δ) for solid material engineering.

In order to determine the surface free energy of a solid, it is necessary to measure contact angles of a variety of liquids on a given solid. The models investigated, here, include those proposed by Zisman, Kwok and Neumann; Owens and Wendt; van Oss, Chaudhury and Good, as well as Chen and Chang. In this chapter, the relative merits of these models are explored. The use of an overdetermined data set allows one to assess the statistical quality of the model and the estimated parameters. Liquids that show unusual behaviors (eg stick-slip) are unsuitable for determination of surface free energy. In this work, it will not be possible to examine the quality of each contact angle measurement. Rather, a relative assessment of various models is made. The results reported here indicate that no more than two adjustable parameters can be statistically justified. The Zisman, Kwok-Neumann models and a version of the van Oss, Chaudhury and Good model where the value of γ+ for the solid surface equals zero appear to be statistically viable. γ+ is the parameter that assesses the acidic character of the surface. These models yield similar values for the total surface free energy of the polymer surfaces.

In this paper, several acrylic pressure-sensitive adhesives (PSAs) were studied through adhesion tension relaxation (ATR) technique introduced by Kasemura and Takahashi. These acrylic PSA samples were also analyzed through static contact angle, surface free energy, dynamic contact angle hysteresis, and peel force measurements. The study has shown that the acrylic PSAs are multicomponent polymeric systems which reorient their surface segments so as to minimize interfacial tension in response to environmental changes. Therefore, it is important to consider the mobility of the surface segments of PSAs in understanding their contact angle hysteresis. Further, the ATR technique has proven to be useful in estimating such mobility.

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.

The wettability of materials depends strongly on their surfaces, and endowing them with expected wetting properties promotes their applications in various fields. In this work, the biodegradable and superhydrophilic poly(butylene succinate) (PBS) nanofibrous membranes were fabricated using a combination of electrospinning and oxygen plasma treatment for the first time. The surface morphologies, chemical composition and wettability of the PBS membrane were investigated. It was found that the plasma etched the fiber surface and the etching depth increased with the plasma treatment time. The membrane became superhydrophilic from hydrophobic upon treated with oxygen plasma and the water droplet could completely spread out within 0.5 s, which was mainly attributed to the introduction of oxygen-containing groups by plasma treatment rather than the enlarged surface roughness. Meanwhile, the speed of water spread out on the modified membrane was closely and reversely related to the density of membrane. The wettability differences between nanofibrous membrane and dense films were also pointed out, and the structure had great influence in the performance. Furthermore, the wetting stability of treated membrane was explored by monitoring the evolution of contact angle. The contact angle gradually increased with days due to the decreasing functional groups, and the ageing rate was dependent on the plasma exposure time. Even though the wettability of membranes changed fast in the first 10 days, surfaces were still remained moderately hydrophilic (contact angle ~50°) after a month. The investigation concentrated on the wettability of PBS nanofibrous membrane treated with oxygen plasma is beneficial to the creation of materials with desirable properties for various applications.