In the present work, rubber-toughened polypropylenes (TPOs) with different properties of the rubbery phase, consisting in different degrees of rubber dispersion and different levels of rubber crystallinity, were considered. The flame-treated surfaces of these materials and their interfaces with a commonly used primer were studied by dynamic contact angle (DCA) analysis using seven liquids and by scanning probe microscopy (SPM). The contact angle data were analysed using the concepts and the equations of the surface free energy acid-base component theory. A new approach consisting in the use of a large number of probe liquids and of a proper mathematical method is proposed; it allows higher precision in the determination of the surface energy components and the work of adhesion, the reduction of possible artefacts, and the calculation of standard deviations of obtained quantities. It was found that: (i) the characteristics of the flame-treated surfaces were largely independent of the composition and morphology of the rubbery dispersed phase; (ii) the flaming effect was better shown by receding angles and the observed hysteresis allowed a quantitative evaluation of the surface heterogeneity induced by the flame process; and (iii) the flame treatment induced fragmentation of the macromolecules with the production of fragments, soluble in all the test liquids, depending on their surface tension and their acid-base character, as shown by repeated DCA immersions. A comparison has been made with the ASTM 2578-67 method ('swab'). The SPM analysis, both in contact and in 'force spectroscopy' modes, confirmed the surface model obtained by the DCA data.

The common measurement of the contact angle is performed in conditions not corresponding to true equilibrium states and gives non-equilibrium values, the advancing and receding contact angles. To solve this problem, a very simple experimental device, based on the Wilhelmy experiment, is proposed in the present paper. It is able to transfer mechanical energy to the three-phase system in a controlled way through a simple loudspeaker; the analysis of some common surfaces is made through this method showing as a new stable minimum of the surface free energy can be attained, independent on the initial conditions and corresponding to a value of the contact angle intermediate between the advancing and receding ones. A comparison is developed with literature results on heterogeneous and rough surfaces, some ‘first-order’-approximation equations proposed in the literature are examined and compared with the new results. A simple but useful theoretical treatment is also compared with the experimental results to allow a more detailed, although qualitative-level, analysis. An important consequence with respect to the calculations of solid surface free energies is indicated.

The acid-base theory as developed by van Oss, Chaudury and Good is a powerful tool to analyze the surface free energy of polymeric materials; however, some problems are encountered in its application and some authors have shown that these problems can be theoretically solved considering this theory as an example of the so-called LFER theories. From this point of view, the definition of a well-defined scale of acid-base strength and the use of a wide and well-equilibrated, appropriate set of liquids is very important. In the present paper some recent results are presented which are based on the mathematical approach discussed by Della Volpe and Siboni in previous papers. The treatment is developed as a list of questions, Frequently Asked Questions (FAQs), whose theoretical implications are discussed using numerical examples chosen from the literature. Some literature data, collected by the opponents of the acid-base theory and recently published, are re-analysed using these methods, showing that they constitute a well-defined set to calculate, with a good precision, the acidbase components of the considered materials and the interfacial energies of liquids used. The present paper is the premise of a second one, in which a set of contact angles data collected by the authors and by other researchers will be analysed following the principles discussed here.

The acid-base theory of surfaces, as proposed by van Oss, Chaudhury and Good, comнmonly suffers from a series of problems (apparent too high basicity of surfaces, results depending on the choice of liquid triplets, etc.). These problems can be solved if and only if a great attention is paid to the mathematical properties of the equations on which the theory is based. Two of these problems are analysed in detail in the present paper: the choice of the acid-base scale using water as a reference, and the use of the 'equilibrium' contact angle instead of the adнvancing contact angle.

The measurement of contact angles and, thus, determination of solid surface tension has been considered for years as a “comedy of errors”, but in recent years the introduction of more sophisticated techniques and of computer-controlled devices, along with a general better understanding of surface structures, has led to a greater precision and accuracy of measurements. However, it is common to neglect the difference between the advancing contact angle and the Young’s angle or to underestimate the role and significance of receding contact angles. In previous papers an experimental procedure has been developed, called the Vibration Induced Equilibrium Contact Angle (VIECA), applied to a Wilhelmy experiment, which appeared to be able to provide a really stable and equilibrium-like value: this procedure was based on previous, rare literature attempts at providing an operational and satisfactory definition of equilibrium contact angle. The VIECA results seem to be related to the advancing and receding values through simple, but approximate, relations. Moreover, the VIECA appears to be independent of the roughness and heterogeneity of the surfaces analysed in the majority of cases. In the present paper, the VIECA method is extended to the sessile drop technique and comparison is made with the common advancing or “static” estimates of contact angle. A theoretical modelling of the physical situation induced by the application of mechanical vibrations to the meniscus or to the drop is proposed. The main consequence of these results is that the contact angles on common surfaces for common liquids are overestimated; a more subtle consequence is the effect on the evaluation of the surface free energy via the most common semiempirical models.

According to the general guidelines presented in the accompanying paper, some relevant examples of common polymer surfaces are analysed and discussed; a number of polymers commercially available or laboratory synthesized have been analysed. In particular, the case of poly(vinyl chloride) (PVC), often considered as peculiar in the literature, is fully analysed on the basis of a new set of well-prepared samples, whose compositions were checked by high-vacuum spectroscopies. 'Equilibrium' contact angles, obtained by a new experimental technique, are presented. The results are, however, preliminary, because the final set of liquids used is not so 'well equilibrated' as possible, from the point of view of acid–base properties. The contact angle data obtained are analysed in a non-linear way to calculate the acid–base components of all the liquids and solids. The results are discussed and compared with those obtained from liquid–liquid interfaces presented in the accompanying paper. The physico-chemical features of these samples have also been compared with the adhesion properties of some bacterial cells, commonly found as infective agents on biomaterials surfaces of medical devices, in order to rationalize these results within the theoretical framework of acid–base theory.

The overwhelming basicity of all analysed surfaces strongly dependent on the choice of liquid triplet used for contact angle measurements and the negative values sometimes obtained for the square roots of the acid-base parameters can be summarized as the main problems arising from the application of the Good-van Oss-Chaudhury (GvOC) theory to the calculation of Lewis acid-base properties of polymer surfaces from contact angle data. This paper tries to account for these problems, namely: (1) the Lewis base, or electron donor component, is much greater than the Lewis acid or electron-acceptor component because of the reference values for water chosen in the original GvOC theory. A direct comparison of the acidic component with the basic one of the same materials has no meaning. A new reference scale for water which is able to overcome this problem is suggested. For the calculation of acid-base components, a best-fit approach is proposed which does not require any starting information about the liquids or polymers and can yield estimates of the acid-base parameters for both the liquids and the polymers involved; (2) the strong dependence of the value of the acid-base components on the three liquids employed is due to ill-conditioning of the related set of equations, an intrinsic and purely mathematical feature which cannot be completely cured by any realistic improvement in experimental accuracy. To reduce or eliminate the effect, one only needs a proper set of liquids, representative of all kinds of different solvents; (3) the negative coefficients appear as a simple consequence of measurement uncertainty, combined with the possible ill-conditioning of the equation set. We cannot exclude, however, that in some cases they could have a different origin.

This paper considers the correctness of the application of Good–van Oss theory (vOGT) to the calculation of acid–base components of solid surface free energies. Theory equations are written in a matrix form, and their application is analyzed particularly from a mathematical point of view. A calculation procedure similar to the approach used for other scales of acid–base strength is suggested to obtain in a straightforward manner the necessary material coefficients. The chemical consequences of these considerations are also discussed. The acceptability of current experimental literature data and the validity of the calculations obtained from them by the proposed method are considered, showing the origin of some inconsistencies in current results. Some general considerations regarding the difficulties commonly encountered in the application of vOGT are also discussed, and it is shown that they can be rationalized or eliminated with more acid solvents being included in the solvent set and the properties of the reference solvent being correctly chosen. The difficulties encountered in correctly expressing the acid properties of some polymers are closely examined. Finally, some indications are given of the future possible developments of vOGT.

Unprinted, unsized, and sized security papers (SP) were treated under SiCl₄−, O₂−, and CF₄-cold plasma conditions. The plasma treatments were carried out in a stainless steel, parallel plate RF (30 kHz) reactor. The influence of plasma parameters, such as RF power, pressure, and treatment time, on the surface properties of plasma-modified security paper was examined. The newly gained surface characteristics were evaluated by Wilhelmy wettability measurements, x-ray photoelectron spectroscopy (ESCA), and scanning electron microscopy (SEM). Statistical experimental designs were used to understand the interactive effects of the plasma parameters. It was found that short treatment times and low RF power values produced the highest wettability with both SiCl₄ and O₂ plasmas regardless of the sizing. Printing and durability characteristics of the plasma-treated substrates were equivalent or superior to the standard samples. Mechanisms of plasma-induced surface modifications are discussed for the paper substrates.

Polyolefins such as polyethylene, polypropylene and their copolymers have excellent bulk physical/chemical properties, are inexpensive and easy to process. Yet they have not gained considerable importance as speciality materials due to their inert surface. Polyethylene in particular holds a unique status due to its excellent manufacturer- and user-friendly properties. Thus, special surface properties, which polyethylene does not possess, such as printability, hydrophilicity, roughness, lubricity, selective permeability and adhesion of micro-organisms, underscore the need for tailoring the surface of this valuable commodity polymer. The present article reviews some of the existing and emerging techniques of surface modification and characterisation of polyethylene. Surface modification of polymers, polyethylene in particular, has been extensively studied for decades using conventional tools. Although some of these techniques are still in use, they suffer from distinct shortcomings. During the last two decades, different means of surface modification have been thoroughly explored. The increasing expectancy for smart materials in daily life has, of late, sharply influenced research in the area of surface modification. Technologies that involve surface engineering to convert inexpensive materials into valuable finished goods have become even more important in the present scenario. In this review article we have attempted to broadly address almost all conventional and modern techniques for the surface modification of different physical forms and chemical compositions of polyethylene. This article will hopefully stimulate further research in this area and result in the development of polyolefins with multi-functional and responsive surfaces, which would ultimately lead to the commodities of polyolefins with smart surfaces.

The surface chemistry and surface energies of materials are important to performance of many products and processes—sometimes in as yet unrecognized ways. This article has been written for the researchers who wish to calculate solid surface energy (SE) from contact angle data. In this article, we describe various methods of calculations and their assumptions. The theoretical and experimental approaches for understanding the solid surface free energy using various methods are discussed in this article. Researchers concerned with many fields such as printing, dyeing, coating, adhesion, pharmaceuticals, composite materials, textiles, polymers, and ceramics should have interest in this topic. SE calculated by various methods for polyethylene surface treated in air plasma is discussed. Using contact angle data, the values of surface roughness using Wenzels equation, have been obtained and correlated to surface roughness calculated from AFM data.
© 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 https://onlinelibrary.wiley.com/doi/abs/10.1002/app.27446

Of the several techniques available for the surface modification, plasma processing has proved to be very appropriate. The low temperature plasma is a soft radiation source and it affects the material only over a few hundred Å deep, the bulk properties remaining unaffected. Plasma surface treatment also offers the advantage of greater chemical flexibility. PET films are widely used for packaging and electrical insulation. The studies of adhesion and printability properties are important. In the present study PET films are treated in air plasma for different time of treatment. The improvement in adhesion is studied by measuring T-peel and Lap shear strength. In addition, printability of plasma treated PET films is studied by cross test method. It has been found that printability increases considerably for plasma treatment of short duration. Therefore it is interesting to study the surface composition and morphology by contact angle measurement, ESCA and AFM. Surface energy and surface roughness can be directly correlated to the improvement in above-mentioned surface related properties. It has been found that the surface oxidation occurs containing polar functional groups such as CO, COO. A correlation of all such observations from different techniques gives a comprehensive picture of the structure and surface composition of plasma treated PET films.

We have used Time of Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) in combination with X-ray photoelectron spectroscopy (XPS) to study chemical changes taking place at the surface of pure cellulose paper samples treated in N2 plasma for periods of time up to 60 seconds. High resolution TOF-SIMS spectra permit the detection of various functionalities containing nitrogen, even following very brief (∼2s) plasma exposure. Correlations between chemistry and surface properties, such as water wettability, are presented and discussed.

In modern technology, there is a constant need to solve very complex problems and to fine-tune existing solutions. This is definitely the case in modern medicine with emerging fields such as regenerative medicine and tissue engineering. The problems, which are studied in these fields, set very high demands on the applied materials. In most cases, it is impossible to find a single material that meets all demands such as biocompatibility, mechanical strength, biodegradability (if required), and promotion of cell-adhesion, proliferation, and differentiation. A common strategy to circumvent this problem is the application of composite materials, which combine the properties of the different constituents. Another possible strategy is to selectively modify the surface of a material using different modification techniques. In the past decade, the use of nonthermal plasmas for selective surface modification has been a rapidly growing research field. This will be the highlight of this review. In a first part of this paper, a general introduction in the field of surface engineering will be given. Thereafter, we will focus on plasma-based strategies for surface modification. The purpose of the present review is twofold. First, we wish to provide a tutorial-type review that allows a fast introduction for researchers into the field. Second, we aim to give a comprehensive overview of recent work on surface modification of polymeric biomaterials, with a focus on plasma-based strategies. Some recent trends will be exemplified. On the basis of this literature study, we will conclude with some future trends for research.

An experimental study of the wettability of rough surfaces over an extremely wide range of roughness is described. The theoretical wettability behavior of an idealized, rough surface agrees well with that of real surfaces. The theoretically predicted minimum in the curve of receding contact angle vs. roughness, for systems of high intrinsic contact angle, is experimentally verified.

A modified Wilhelmy plate technique has been developed for the measurement of surface tensions of viscous polymers. The method requires no knowledge of liquid density and provides a means of assuring a zero contact angle for the polymer on the plate. The surface tensions of several silicone polymers with viscosities as high 106 centipoises have been measured. The method has also been used to determine the surface tensions of several molten polyethylenes as a function of temperature over the range 115° to 215°C.