D. Maniglio

The determination of a ‘stable-equilibrium’ contact angle on heterogeneous and rough surfaces

Abstract 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.

Recent theoretical and experimental advancements in the application of van Oss-Chaudury-Good acid-base theory to the analysis of polymer surfaces. I. General aspects

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.

Recent theoretical and experimental advancements in the application of the van Oss–Chaudhury–Good acid–base theory to the analysis of polymer surfaces II. Some peculiar cases

—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.

Bioreactor type and operating conditions influence cell response to polymeric material properties

Petri dish culture is routinely used to test the effect of biomaterial properties on mammalian cells although significant transport resistance hinders the transport of gaseous metabolites to the cells and culture conditions change in time. In this paper we report on the culture in a continuous-flow recycle bioreactor of rat liver cells adherent on hydrophilized polypropylene membranes at increasing ammonia concentrations. Membranes exhibited varying bulk and surface wettability. Rates of all investigated metabolic reactions increased with increasing ammonia concentrations and with increasing surface wettability, at any ammonia concentration. Metabolic differences among cells cultured on membranes with different wettability became more and more evident at increasing ammonia concentrations. Rate dependence on membrane surface wettability changed with the investigated metabolic pathway, being the strongest for urea synthesis. We conclude that culture in continuous-flow bioreactors may enhance cell metabolic activity, their sensitivity towards the material properties and the sensitivity of the biocompatibility test.

A new experimental method to analyse the dewetting properties of polymer surfaces and cationic surfactants

In the present paper a new method able to easily evaluate the critical height of rupture of liquid films on various substrate surfaces is described and commented. It is automatic and based on the different IR reflectance of solids and liquids. Its limits and advantages are analysed. The heights of rupture of water have been measured on different kinds of polymeric solid surfaces as well as on surfaces whose water repellency has been increased by different mixtures of substituted ammonium salts, used as autophobic rinse aids. In both cases the effect of experimental conditions and the value of contact angles measured by the Wilhelmy microbalance have been correlated with the height of rupture. The peculiar sawtooth trend of force versus immersion in Wilhelmy experiments, performed by using some of these autophobic substances solutions, is described and interpreted.