Contact angle measurement has wide application in studying the wettability of a surface. This paper presents a contact angle measurement system developed using simple apparatus. The system consists of a bespoke measurement software, USB microscope, motorized linear position slider and a sample holder with back lighting system. The advantages of this system include user friendly, compact size, allow manual and automatic measurements and cost effective. This system is established with the contact angle and surface tension measurement experiment which is based on Fox-Zisman theory. Different probe liquids were suggested and the critical surface tension of polydimethylsiloxane (PDMS) and polyimide were determined using both the software and the hardware system developed.

An RTV silicone and high density polyethylene are exposed in an activated gas plasma for varying times and varying conditions. Both oxygen and argon are used. Changes in critical surface tension of wetting as determined by contact angle measurements are reported. Bondability of the treated surfaces is evaluated with both the aged bonds and aged surfaces prior to bonding being evaluated. In contradiction to some of the recent work reported in the literature on the effect of activated inert gas on surface characteristics, contact angles always decreased on the materials studied indicating an increase in surface energy. The significance of the results on present adhesion theories is discussed.

In atmospheric pressure corona systems, the densities of electrons and ions determine the level of treatments. Here, the electron and ion densities in a corona plasma are evaluated for a DC positive-polarity wire discharge in dry air at atmospheric pressure, in the coaxial wire-cylinder geometry. We use a new numerical iterative approach to solve the coupled equations for the electric field and charge densities. The role of electron diffusivity is discussed and the influence of the charge distribution between electrodes on the electric field strength and on the plasma region is analyzed.

Many approaches have been used to infer the surface tension of solids from liquid contact angles. In most cases the different methods have not been verified by independent means because of the inherent difficulty in directly measuring a solid surface tension. This paper examines a range of diverse experiments which, together with appropriate thermodynamic models, permit such an independent verification to be made.

As part of an ongoing study, the focus has been on two methods of interpreting contact angles which often yield conflicting results; namely, the equation of state approach and the theory of surface tension components. The previous work has led to the conclusion that the latter approach is incorrect. In this paper the accuracy of these two methods is examined in a strictly empirical way through the interpretation of a wide body of experimental results. It is seen that the predictions of the equation of state approach are in much closer agreement with the various experiments than are those derived from the Fowkes equation.

Striking a balance between applied and theoretical research, this work details many of the uses of wettability and interprets experimental data from a variety of viewpoints, including the ‘separation of forces’ and the ‘equation of state approaches.’

The determination of solid and solid-liquid surface tensions is of importance in a wide range of problems in pure and applied science. There exist, at present, many indirect approaches for obtaining these values because it is not possible to measure directly surface tensions involving a solid phase. These various methods are often in considerable disagreement, both quantitatively and from a theoretical standpoint. The problem persists since most of these approaches have not been tested objectively through the prediction of physical phenomena which could be independently observed and thus used to validate the various theories.

The accurate measurement of contact angles is essential in many areas of applied surface thermodynamics. As was seen in Chapters 3 and 5, the contact angle provides a unique means of determining solid-vapor and solid-liquid surface tensions. The range of applications of this measurement is remarkable, both as a simple tool to assess, for example, the cleanliness of surfaces, and as a highly sensitive scientific measurement aimed at providing information on the solid surface tension and the physical state of the surface. When first encountered, the measurement of contact angles appears to be quite straightforward. This apparent simplicity is, however, very misleading, and experience has shown that the acquisition of thermodynamically significant contact angles requires painstaking effort. This chapter addresses the many practical issues pertaining to the measurement of contact angles and liquid surface tensions, including the preparation of suitable solid surfaces and measuring liquids.

The behavior of a silicone sealant during its application, from its extrusion from the carнtridge to the completion of the joint, has been identified as a key feature for professional applicators. This feature called “ease of use’* is very complex and includes many different criteria such as the ease of extrusion and joint smoothing, the aesthetic of surface finish, the stringing, and the action of a tooling aid (aqueous solution of surfactant) during the smoothing operation. Several of these criteнria seem directly linked to surface properties of the uncured sealant. In an attempt to translate these subjective properties into quantitative measurements in the laboratory and to understand the underнlying parameters that can be used to control these features, the surface energy of uncured sealants was measured using the solid-liquid contact angle technique. The surface energy data were further correlated with ratings collected from professional applicators with regards to ease-of-use criteria. A correlation was also built between the contact angle values obtained with various tooling aid soluнtions against the surface of the sealant and the ease of smoothing obtained by using these tooling aids at the application stage. The evolution of the contact angle of a water droplet at the surface of uncured sealant with time provided some insights in the understanding of the migration and/or reнorientation of polar entities from the sealant bulk to the sealant surface.

Most printing inks used in major printing processes such as lithography, gravure, and flexography contain organic solvents. Some of these solvents, e.g., toluene, are toxic and can be harmful to humans. Both environmental and workplace safety considerations exert growing pressure on the printing industry to limit the use of toxic organic solvents. Due to this pressure, the share of water-based liquid printing inks in packaging printing (including corrugated) has achieved a respectable level of about 50%. In newspaper printing the share is estimated at about 10 to 15% of the total. To prepare for a possible ban on the use of toxic organic solvents, the printing industry is exploring the viability of water-based 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.

Gravity-induced sagging can amplify variations in goniometric measurements of the contact angles of sessile drops on super-liquid-repellent surfaces. The very large value of the effective contact angle leads to increased optical noise in the drop profile near the solid–liquid free surface and the progressive failure of simple geometric approximations. We demonstrate a systematic approach to determining the effective contact angle of drops on super-repellent surfaces. We use a perturbation solution of the Bashforth–Adams equation to estimate the contact angles of sessile drops of water, ethylene glycol, and diiodomethane on an omniphobic surface using direct measurements of the maximum drop width and height. The results and analysis can be represented in terms of a dimensionless Bond number that depends on the maximum drop width and the capillary length of the liquid to quantify the extent of gravity-induced sagging. Finally, we illustrate the inherent sensitivity of goniometric contact angle measurement techniques to drop dimensions as the apparent contact angle approaches 180°.

Electret charging methods on the basis of gas discharge in air offer many advantages, including a very simple arrangement, no direct contact to the electret surface, and no restrictions on charging temperature. For discharge in air two arrangements are in use: (1)discharge in a parallel air gap and (2) corona discharge. A comparison of both methods, showing significant similarities, is given.

Starting with investigations of charging in a parallel air gap, the practical knowledge is applied to the more complex corona charging. The characteristics of equilibrum electret voltage and its dependence on applied voltage are measured and interpreted theoretically. The influence of deviations in gap spacing on electret voltage is discussed. Electrical breakdowns of the electret foil affect the results. Therefore the role of breakdown is investigated in more detail.

The spreading of surfactant solutions over hydrophobic surfaces is considered from both theoretical and experimental points of view. Water droplets do not wet a virgin solid hydrophobic substrate. It is shown that the transfer of surfactant molecules from the water droplet onto the hydrophobic surface changes the wetting characteristics in front of the drop on the three-phase contact line. The surfactant molecules increase the solid–vapor interfacial tension and hydrophilize the initially hydrophobic solid substrate just in front of the spreading drop. This process causes water drops to spread over time. The time of evolution of the spreading of a water droplet is predicted and compared with experimental observations. The assumption that surfactant transfer from the drop surface onto the solid hydrophobic substrate controls the rate of spreading is confirmed by our experimental observations.

A plasma treatment that renders asymmetric polysulfone membranes permanently hydrophilic is reported. Our modification strategy entails treating these membranes downstream from an inductively coupled rf plasma source. Contact angle measurements confirm that the membranes are completely wettable with water as a result of H₂O plasma treatment. More importantly, the hydrophilic modification is permanent as plasma-treated membranes remain wettable for more than 16 months after plasma treatment. This treatment achieves the desired change in wettability for microporous as well as ultrafiltration polysulfone membranes, illustrating the universality of this method. XPS analysis of treated membranes demonstrates this dramatic change in wettability is a result of chemical changes in the membrane induced by plasma treatment. Moreover, the membrane modification is complete as the plasma penetrates the thickness of the membrane, thereby modifying the entire membrane cross-section.

The influence of the gas mixture of oxygen and nitrogen on the treatment efficiency distribution is investigated. The treatment efficiency is evaluated by contact angle measurement on polypropylene (PP) samples placed in varying distance from the coplanar barrier discharge electrode module. A planar electrode operated with 4 kHz signal and power of typically 10–21 W is used for treatment. A strong variation of contact angle as a function of distance from the CDB electrode surface is observed for samples treated 4 s in nitrogen discharge. Contact angle changes within 0.3 mm from 37.9 to 62.5° and it reaches 94.1° for 1.5-mm distance. It is already very close to the value of 103° measured on untreated PP. Much smaller treatment depth is obtained for mixture of nitrogen and oxygen. The experiments are performed without gas flow.fferent plasma treatments in a rf

Ultrahigh molecular weight polyethylene fibres have been treated in nitrogen plasma at atmospheric pressure. The plasma was generated by a pulsed electric discharge on the fibre surface. Fibre/rubber matrix interfacial adhesion was improved substantially by the plasma treatment. Zeta-potential measurements indicate an increase in hydrophilicity and basic groups density on the treated fibre surface. EPR spectrometry study reveals creation of peroxy type radicals by the plasma treatment.

Growing demands on the functionality of technical textiles as well as on the environmental friendliness of finishing processes increase the interest in physically induced techniques for surface modification and coating of textiles. In general, after the application of water-based finishing systems, the textile needs to be dried. The removing of water is energy intensive and therefore expensive. In contrast to conventional wet finishing processes, a plasma treatment is a dry process. The textile stays dry and, accordingly, drying processes can be avoided and no waste water occurs. Plasma treatments represent, therefore, energy efficient and economic alternatives to classical textile finishing processes. Within plasma processes, a high reactive gaseous phase interacts with the surface of a substrate. In principle, all polymeric and natural fibres can be plasma treated. For many years, mainly low-pressure plasma processes have been developed for textile plasma treatment. However, the integration of these processes, which typically run at pressures between 0.1 and 1 mbar, into continuously and often fast-running textile production and finishing lines is complex or even impossible. In addition, due to the need for vacuum technology, low-pressure processes are expensive. The reasons why plasma processes at atmospheric pressure are advantageous for the textile industry are in detail: • The typical working width of textile machines is between 1.5 and 10 meters. Textile-suited plasma modules need to be scalable up to these dimensions, which is easier for atmospheric-pressure techniques.• Textiles have large specific surfaces compared to foils, piece goods or bulk solids. Even with strong pumps, the reduced pressure which is necessary for low pressure plasma will only be reached slowly due to the desorption of adsorbed gases.

This invention relates to a process for treating the surface of a stretched film of a polyester or polypropylene or copolymers or polymer mixtures of the latter containing at least 60 percent by weight, calculated on the total polymer weight, of propylene, in order to improve the adhesion of the film surface to a heatsealable coating, which comprises subjecting the film surface to a corona discharge in an atmosphere consisting essentially of nitrogen or carbon dioxide containing not more than about 15 percent by volume of oxygen, at a film temperature in the range of room temperature to about 25° to 50° C. below the softening point of the stretched film. The invention also relates to the films so treated.

Corona discharge treatment of isotactic polypropylene surfaces in N₂ and CO₂ was investigated by contact angle measurements and ESCA. The electrical characteristics of the discharges as well as the influence of indirect parameters (moment of air contact and ageing time) and direct parameters (applied charge, electrical field strength and film temperature) on the surface modification were determined. These investigations showed that electrons, emitted by photo effect are the dominant charge carriers and the main cause of surface activation. The active species in the surfaces (presumably radicals) can either perform crosslinking and H-abstraction or react with the discharge gas. In the N₂-discharge the polymer radicals can only react with atomic or excited nitrogen whereas in CO₂ they also react with ground state molecules. If the samples are brought into air contact after discharge leftover radicals are oxidized by atmospheric oxygen. In addition a UV-radiation causing activation in a surface layer was found. The bulk of the polymer is not influenced by corona discharge.

The paper investigates the effect of corona discharge (CD) treatment on the properties of surface layer (SL) of polylactide (PLA) film. The modification of PLAwas carried out in the air and helium atmosphere and the results were compared on the basis of the assessment ofwettability, surface free energy (SFE) calculated using Owens-Wendt method aswell as the degree of oxidation (O/C) of the modified SL, determined by photoelectron spectroscopy.

Surface layer of com. polylactide (PLA) was modified with corona discharges and studied for contact angle (H2O, CH2J2) and the geometric structure (at. force microscopy). The surface free energy was caled, by using Owens-Wendt equation. The treatment resulted in a decrease in the contact angle and an Increase in the surface free energy of the PLA film.