Self-assembled monolayers (SAMs) of alkylsiloxanes on elastomeric PDMS (polydimethylsiloxane) were used as model systems to study interactions between surfaces. Surface free energies (γsv) of these chemically modified surfaces were estimated by measuring the deformations that resulted from the contact between small semispherical lenses and flat sheets of the elastomer under controlled loads. The measured surface free energies correlated with the surface chemical compositions of the SAMs and were commensurate with the values estimated from the measurements of contact angles. This study provides direct experimental evidence for the validity of estimates of the surface free energies of low-energy solids obtained from contact angles.

A method of preparing modified surfaces, referred to as soft-landing, is described in which intact polyatomic ions are deposited from the gas phase into a monolayer fluorocarbon surface at room temperature. The ions are trapped in the fluorocarbon matrix for many hours. They are released, intact, upon sputtering at low or high energy or by thermal desorption, and their molecular compositions are confirmed by isotopic labeling and high-resolution mass measurements. The method is demonstrated for various silyl and pyridinium cations. Capture at the surface is favored when the ions bear bulky substituents that facilitate steric trapping in the matrix.

The magnitude of the hydrophobic effect, as measured from the surface area dependence of the solubilities of hydrocarbons in water, is generally thought to be about 25 calories per mole per square angstrom (cal mol^-1 Å^-2). However, the surface tension at a hydrocarbon-water interface, which is a "macroscopic" measure of the hydrophobic effect, is ≈72 cal mol^-1 Å^-2. In an attempt to reconcile these values, alkane solubility data have been reevaluated to account for solute-solvent size differences, leading to a revised "microscopic" hydrophobic effect of 47 cal mol^-1 Å^-2. This value, when used in a simple geometric model for the curvature dependence of the hydrophobic effect, predicts a macroscopic alkane-water surface tension that is close to the macroscopic value.

Interfacial interactions underpin phenomena ranging from adhesion to surface wetting. Here, we describe a simple, rapid, and robust approach to modifying solid surfaces, based on an ultrathin cross-linkable film of a random copolymer, which does not rely on specific surface chemistries. Specifically, thin films of benzocyclobutene-functionalized random copolymers of styrene and methyl methacrylate were spin coated or transferred, then thermally cross-linked on a wide variety of metal, metal oxide, semiconductor, and polymeric surfaces, producing a coating with a controlled thickness and well-defined surface energy. The process described can be easily implemented and adapted to other systems.

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.

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.

Recent advances in surface science have led to a broad interest in wetting and/or spreading characterization of solid surfaces. Wettability of a solid surface can be defined as the tendency of a liquid to spread over the surface which is measured in terms of an angle, ie, contact angle between the tangent drawn at the triple point between the two phases (liquid and vapor) and the substrate surface. Reproducible and accurate measurements of the contact angle from the experiments are crucial in order to analyze the spreading behavior of a substrate. Spreading is greatly affected by different factors including liquid properties, substrate properties, and system/operating conditions. Here, different types of spreading phenomena in terms of drop evaporation on reactive/non-reactive surfaces and correct measures to obtain accurate contact angles in such scenarios are presented.

Surface science, which comprises the preparation, development and analysis of surfaces, is of utmost importance in both fundamental and applied sciences as well as in engineering and industrial research. During our research in the field of coatings/surfaces and coating materials, the analyses of wetting of coating materials and the coatings themselves led us to the field of dynamically performed drop shape analysis. We focussed our research efforts on the main problem of the surface science community, which is to determine the correct and valid definition and measurement of contact angles. So we developed the high-precision drop shape analysis (HPDSA) and three statistical contact angle determination procedures. HPDSA involves complex transformation of images from dynamic sessile drop experiments to x-y-coordinates and opens up the possibility of a physically meaningful calculation of curvature radii. This calculation of radii is the first step to an “assumption-free” link to the Laplace equation, which can deepen the understanding of the interface between the liquid and the vapour in relation to different properties and conditions (temperature, experimental technique, surface, etc.). The additional benefit of a tangent-free calculation of contact angles is presented in our 2014 and 2016 published papers. To fulfil the dire need for a reproducible contact angle determination/definition, we developed three procedures, namely, overall, global, and individual statistical analyses, which are based on, but not restricted to, HPDSA . . .

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.

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.

Cellulose is a biodegradable, renewable, flexible, inexpensive biopolymer that is abundant in nature. However, due to its hydrophilicity, applications of cellulose (paper) in the handling of liquids are severely limited. Appropriate plasma-or glow discharge-assisted processing sequences can be used to modify the surface of cellulose/paper so that the interaction of liquids with these surfaces can be altered. In particular, nanostructures associated with crystalline regions of cellulose fibers can be uncovered by plasma-enhanced etching; subsequent plasma-enhanced fluorocarbon film deposition (~ 100 nm) converts the surface into a superhydrophobic (static water contact angle> 150o; receding contact angle< 8o) state. Similar results can be obtained by depositing diamond-like carbon films on the plasmaetched surface, in spite of the inherently hydrophilic nature of diamond-like carbon itself. In addition, droplet adhesion and mobility can be controlled; depending on the etch cycle parameters, the paper surface can be rendered ‘roll-off’or ‘sticky’superhydrophobic. Use of a commercial printer to generate hydrophobic ink patterns on superhydrophobic paper surfaces allows controlled movement, transfer and storage of water or other aqueous liquids on the paper surface. These basic functionalities can be combined to design simple two-dimensional lab-on-paper (LOP) devices. Finally, by controlling both the cellulose fiber size and spacing, and depositing a fluorocarbon film, paper surfaces can be rendered superomniphobic, repelling both polar and apolar liquids.

Polymers offer a wide range of bulk physical, chemical and mechanical properties, are inexpensive and are relatively easy to synthesize. However, very often these polymer surfaces do not possess properties needed for application in certain external environments which could be one of the limiting factors in their usage. Polymer surface characterization and modification is of fundamental importance for the good functioning of a composite material and plays a key role in determining successful implementation of the polymer. Tailoring of polymer surface properties such as adhesion, wettability, surface roughness and chemical reliability (including heat-soak) is critical for several applications like decorative coatings, protective films, thin film technologies and biomaterials, to name a few. For these reasons, surface modification techniques which can transform these inexpensive materials into highly valuable finished products have become an important part of the polymer and nanocomposite industries. This chapter reviews the importance and applications of polymer surface modification using corona treatment to enhance adhesion by reporting most recent advancements in the field. Novel corona treatment (type of plasma, pressure, and power) and its potential in several applications is briefly discussed in latter part of this chapter.

Surface modification to improve the adhesion property by means of dry methods such as flame, corona and plasma treatments is commonly used for films, foils and paper-based substrates. The corona discharge treatment technology is explored here and elaborated on. Subjecting the substrate to a corona discharge may provide greater wettability, higher surface free energy, and higher adhesion performance due to the introduction of polar functional groups at the uppermost surface. In addition, the surface roughness of polymeric materials may also be altered during the bombardment by the species in the discharge. The applied corona dosage, or referred to as watt density in the industry, also plays a great role in the level of surface modification.

In this chapter, we present an overview on recent research and development work in the area of atmospheric pressure plasma treatments (APPTs) to generate adhesion-promoting surfaces of polymers used in various applications in automotive, aerospace, packaging, and medical fields. In comparison to the classical “corona treatment” the APPTs provide access to a broader range of industrially interesting surface modifications that are normally better controlled with respect to their physicochemical nature. Thus, application of APPTs may become a superior option for preparing polymer surfaces for adhesive bonding, adhesive-free low-temperature bonding involving homogeneous and heterogeneous substrates, lacquering, or coupling of specific biomolecules, proteins, or cells. APPT technology is, however, not only flexible for tuning surface chemistry but also is flexible with respect to plasma source and equipment design. Versatility of the APPT technology facilitates its integration into a variety of process chains. An example presented here is a hybrid technology combining both APPT and additive manufacturing based on 3D printing processes using fused filament deposition. Inline treatment by quasi-simultaneous execution of printing and APPT can, for instance, increase the adhesion of 3D printed products in print direction (z-Axis) and thus increase the mechanical stability of the printed part. In the medical field such a technology may be attractive for cell growth by promoting treatment of internal surfaces of printed porous scaffolds. In future, products made from biobased or recycled polymers will become increasingly important. APPT technology could become an important enabler for meeting the technical requirements for the adhesion of such products.

Adhesion promotion techniques have wide applications in numerous industries for a wide range of plastic parts, and polyolefin films such as those made of PE, PP, and PET. One method used to modify the surface of these and other polymer products to promote adhesion of inks, coatings, adhesives, metallized paper and films, microorganisms or cells is flame plasma treatment. In addition, flame plasma is used to clean the surface of metals and to roughen the surface of paperboard to enhance adhesion of the polyolefin coating. This chapter describes the theory behind hydrocarbon fired flame plasma surface treatment to promote adhesion of water-based inks, coatings, adhesives, labels and other laminates to polyolefin-based substrates. Critical parameters in flame plasma treatment are flame chemistry, flame geometry, plasma output, and distance of the burner from the part. The interrelationship between these variables, and how to control them for optimum surface treatment, are discussed. A completely new patented process design has been developed and successfully implemented providing significantly improved control of the flame chemistry, while at the same time simplifying the process control and mechanical hardware required. In addition, the new design improves the overall efficiency of the flame plasma treatment process by more accurately controlling air/gas chemistry, simplifying the control valve piping, incorporating a variable frequency drive (VFD) combustion air blower to more accurately control and vary the burner firing rate, i.e., amount of plasma generated, and refining the control algorithms.

The surface treatment of plastics as well as metals or ceramics includes a thorough surface cleaning as an essential step prior to adhesive bonding and coating processes. Besides this, surface activation of polymers is often needed because their surface free energy is too low for durable adhesion of a coating or adhesive. In this chapter various types of UV/Ozone sources with different light spectra as well as the influences of spectra and ozone concentration are investigated and compared. Also the surface wetting and adhesive bond strength as a result of UV/Ozone, atmospheric plasma, or corona treatments on thermoset, thermoplastic, and rubber materials are presented. UV/Ozone treatment was found to show an excellent cleaning performance on all kinds of materials, and especially as a very useful technique for surface functionalisation of polymers, resulting in durable adhesion both for adhesives as well as coatings. This chapter is a condensed overview of over 30 years of experiments done with UV/Ozone treatments at The Delft University of Technology.

Polymers are widely used in different industries ranging from microelectronics, medical, to space. However, polymer materials are seldom used in their pristine state and need selective surface treatment to induce a specific response which is a challenging and complex task. Adhesion enhancement of polymers is one of the major requirements that can be achieved with ion beam technology at low cost. Surface enhancement involves keeping the bulk properties of materials unchanged and modifying only the surface properties to achieve optimum results. In this chapter, we illustrate the use of ion beam technology to modify the surface properties of polymers for potential biomedical and microelectronics applications. This chapter focuses on effects on the adhesion characteristics of different polymeric materials with various optimizable parameters such as type of ion used, ion energy regime (low to medium to high) and the ion fluence range with respect to singly and multi-charged ion beams.