Alain Carre

Study of acid/base properties of oxide, oxide glass, and glass-ceramic surfaces

Abstract The points of zero charge, pH0, of 25 oxides were first calculated from the well-known Parks theory and then in developing a new approach based on the ionization potential of the corresponding metals. The theoretical values were found in good agreement with literature data and with experimental results obtained in using a method of adsorption of colored indicators. Afterward, the study of acid/base properties of glasses and glass-ceramics was undertaken and a simple additive relationship allowing the calculation of their points of zero charge from their compositions was established and experimentally verified with the colored indicator method. The concept of surface molar composition ensues from the theoretical model. The effect of mechanical surface treatments on the acid/base properties of the materials was related to the role of alkaline and alkaline-earth oxides in the silica network and in particular to the weakening of the glass structure by these elements. As a consequence, a mechanical action on glass and glass-ceramic surfaces increases the alkalinity.

Molecular interactions between DNA and an aminated glass substrate.

With the development of DNA arrays, the immobilization of DNA strands onto solid substrates remains an essential research topic. DNA arrays have potential applications in DNA sequencing, mutation detection, and pathogen identification. DNA bound to solid substrates must still be accessible and retain the ability to hybridize with its complementary strands. One technology to produce these arrays involves linking DNA molecule probes to a silanized substrate in microspot patterns and exposing them to a solution of fluorescently labeled samples of DNA targets. The behavior of both the target and probe DNA and their interactions with each other at the substrate surface, particularly with respect to molecular interactions, are poorly understood at the present time. The objective of this work is to model simply the interface interactions between DNA and glass slides modified with an aminosilane (gamma-aminopropyltriethoxysilane, APTS). In aqueous solutions, DNA behaves as a polyacid over a wide range of pH. A glass substrate treated with APTS is positively or negatively charged, depending on the pH. A model of the surface charge of APTS-treated glass has been developed from results of wetting experiments performed at various pH. It has been demonstrated that the surface charge of APTS-treated glass is well described by a model of constant capacitance of the electrical double layer. A good correlation between experimental data on DNA retention at various pHs and the variation of the surface charge of the APTS-treated glass is obtained. This provides an indication of the role of ionic interactions in the adsorption of DNA molecules onto aminated glass slides.

How Substrate Properties Control Cell Adhesion. A Physical–Chemical Approach

Most living cells derived from solid tissues require an adhering surface to live in vitro conditions. A good understanding of the relationships between the behavior of cells and the physicochemical properties of substrates such as the surface free energy, the surface polarity, the presence of functional groups and surface charges is of prime importance for the optimization of adhesion, spreading and proliferation of cells. Polystyrene and treated polystyrene surfaces were characterized by determining their surface free energies using wettability measurements. The knowledge of the surface properties of the culture substrates provides a good view of the influence of the substrate properties on cell adhesion. However, this study shows that it is not directly the surface free energy of materials that controls cell adhesion but rather the interfacial free energy between the culture medium and the substrate. The interfacial free energy between the culture medium and the solid surface controls the adsorption of serum components that may inhibit or promote cell adhesion. One of the components inhibiting cell adhesion is serum albumin. The results indicate that the adsorption of serum albumin is related to the interfacial free energy between the culture medium and the substrate. Hydrophilic substrates, such as plasma treated polystyrene substrates, have a lower interfacial free energy with water than hydrophobic polystyrene leading to a lower adsorption of proteins inhibiting cell adhesion. In addition, it is observed that there is a competition between proteins inhibiting (serum albumin) and proteins promoting cell adhesion (such as fibronectin).

Wettability Techniques to Monitor the Cleanliness of Surfaces

Publisher Summary In the broad spectrum of contamination control, a major concern is the presence of organic contamination on various inorganic surfaces. In order to control surface contamination of materials, a rapid-detection method is required that does not adversely affect the surface. Wettability measurements provide a convenient and rapid method for probing the outermost surface of a material. The technique is highly surface specific, generally exceeding the sensitivity of electron spectroscopies and is sensitive to a fraction of a monolayer. The most widely used quantitative measure of wettability is the contact angle. When a drop of a liquid with a sufficiently small size is placed on a smooth, flat, homogeneous solid substrate, the drop takes the shape of a spherical cap. The shape of the drop approximates that of a spherical cap when the forces other than the surface tension become negligible. Each solid and liquid (and vapor phase) combination gives rise to a specific degree of wettability. The parameter defining the wettability is the observed contact-angle; the lower the contact angle, the higher the wettability. This angle is measured between a tangent to the liquid surface where it meets the solid substrate and the plane of the solid substrate. It is found that any test of surface cleanliness involving wettability by water cannot be used on metal surfaces that have an indeterminate oxide layer. It is tempting to assume that any clean metal oxide surface would be hydrophilic, but even this rule may have some exceptions.

Determination of the molecular area on a liquid surface from thermodynamic functions : application to alkanes

A method is proposed to calculate the molecular area on the surface of a liquid from thermodynamic parameters such as the molar internal energy, the surface free energy, and the surface entropy. When the method is applied to the series of normal alkanes, it allows calculation of the area of the molecules on these liquid surfaces and to deduce the orientation of these molecules. Moreover, the molecular areas of the first terms of the alkane series and of hydrogen are also obtained by extrapolation.