Interface/surface properties

Davis, J.A., and Feckie, J.O., 1978. Surface ionization and complexation at the oxide/water interface Surface properties of amorphous iron hydroxide and adsorption of metal ions. J. Colloids Interfacial Sci., v. 67, pp. 90-107. 

Krolil, H.U., Stifter, T., Waschipky, H., Weishaupt, K., Hild, S. and Marti, O., Pulsed force mode a new method for the investigation of surface properties. Surf. Interface Anal, 27(5-6), 336-340 (1999). 

The dry adhesive films on the two substrates to be joined must be placed in contact to develop adequate autoadhesion, i.e. diffusion of polymer rubber chains must be achieved across the interface between the two films to produce intimate adhesion at molecular level. The application of pressure and/or temperature for a given time allows the desired level of intimate contact (coalescence) between the two adhesive film surfaces. Obviously, the rheological and mechanical properties of the rubber adhesives will determine the degree of intimacy at the interface. These properties can be optimized by selecting the adequate rubber grade, the nature and amount of tackifier and the amount of filler, among other factors. 

AB diblock copolymers in the presence of a selective surface can form an adsorbed layer, which is a planar form of aggregation or self-assembly. This is very useful in the manipulation of the surface properties of solid surfaces, especially those that are employed in liquid media. Several situations have been studied both theoretically and experimentally, among them the case of a selective surface but a nonselective solvent [75] which results in swelling of both the anchor and the buoy layers. However, we concentrate on the situation most closely related to the micelle conditions just discussed, namely, adsorption from a selective solvent. Our theoretical discussion is adapted and abbreviated from that of Marques et al. [76], who considered many features not discussed here. They began their analysis from the grand canonical free energy of a block copolymer layer in equilibrium with a reservoir containing soluble block copolymer at chemical potential peK. They also considered the possible effects of micellization in solution on the adsorption process [61]. We assume in this presentation that the anchor layer is in a solvent-free, melt state above Tg. The anchor layer is assumed to be thin and smooth, with a sharp interface between it and the solvent swollen buoy layer. 

The present model takes into account how capillary, friction and gravity forces affect the flow development. The parameters which influence the flow mechanism are evaluated. In the frame of the quasi-one-dimensional model the theoretical description of the phenomena is based on the assumption of uniform parameter distribution over the cross-section of the liquid and vapor flows. With this approximation, the mass, thermal and momentum equations for the average parameters are used. These equations allow one to determine the velocity, pressure and temperature distributions along the capillary axis, the shape of the interface surface for various geometrical and regime parameters, as well as the influence of physical properties of the liquid and vapor, micro-channel size, initial temperature of the cooling liquid, wall heat flux and gravity on the flow and heat transfer characteristics. 

The idealized picture of the flow in a heated micro-channel is shown in Fig. 8.1a. Such flow possesses a number of specific properties due to its unique structure, which forms because of liquid evaporation and the interaction of pure vapor and liquid flows separated by the interface surface. The latter has an infinitely thin surface with a jump in pressure and velocity, while the temperature is equal. One can... 

In the previous sections, we have seen how computer simulations have contributed to our understanding of the microscopic structure of liquid crystals. By applying periodic boundary conditions preferably at constant pressure, a bulk fluid can be simulated free from any surface interactions. However, the surface properties of liquid crystals are significant in technological applications such as electro-optic displays. Liquid crystals also show a number of interesting features at surfaces which are not seen in the bulk phase and are of fundamental interest. In this final section, we describe recent simulations designed to study the interfacial properties of liquid crystals at various types of interface. First, however, it is appropriate to introduce some necessary terminology. 

Surface forces measurement is a unique tool for surface characterization. It can directly monitor the distance (D) dependence of surface properties, which is difficult to obtain by other techniques. One of the simplest examples is the case of the electric double-layer force. The repulsion observed between charged surfaces describes the counterion distribution in the vicinity of surfaces and is known as the electric double-layer force (repulsion). In a similar manner, we should be able to study various, more complex surface phenomena and obtain new insight into them. Indeed, based on observation by surface forces measurement and Fourier transform infrared (FTIR) spectroscopy, we have found the formation of a novel molecular architecture, an alcohol macrocluster, at the solid-liquid interface. 

The anisotropy in the physicochemical surface properties and differences in the surface topography of S-layer lattices allowed the determination of the orientation of the monolayers with respect to different surfaces and interfaces. Since in S-layers used for crystallization studies the outer surface is more hydrophobic than the inner one, the protein lattices were generally oriented with their outer face against the air-water interface [120,121]. Crystallization studies with the S-layer protein fromB. coagulansE i Nl at different lipid monolayers [122] revealed that the S-layer lattice is attached to lipid monolay-... 

The popular applications of the adsorption potential measurements are those dealing with the surface potential changes at the water/air and water/hydrocarbon interface when a monolayer film is formed by an adsorbed substance. " " " Phospholipid monolayers, for instance, formed at such interfaces have been extensively used to study the surface properties of the monolayers. These are expected to represent, to some extent, the surface properties of bilayers and biological as well as various artificial membranes. An interest in a number of applications of ordered thin organic films (e.g., Langmuir and Blodgett layers) dominated research on the insoluble monolayer during the past decade. 

The appreciation of the importance of adsorption phenomena at liquid interfaces is probably as old as human history, since it is easily recognized in many facets of everyday life. It is not surprising that liquid interfaces have been a favorite subject of scientific interest since as early as the eighteenth century [3,4], From an experimental point of view, one obvious virtue of the liquid interfaces for studying adsorption phenomena is that we can use surface tension or interfacial tension for thermodynamic analysis of the surface properties. The interfacial tension is related to the adsorbed amount of surface active substances through the Gibbs adsorption equation. 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

The surface tension defined above was related to an interface that behaved mechanically as a membrane stretched uniformly and isotropically by a force which is the same at all points on the surface. A surface property defined this way is not always applicable to the surfaces of solids and the surface energy of planar surfaces is defined to take anisotropy into account. The surface energy is often in the literature interchanged with surface tension without further notice. Although this may be useful in practice, it is strictly not correct. 

Ultrahigh vacuum surface spectroscopies can provide far greater breadth and depth of information about surface properties than can yet be achieved using in situ spectroscopies at the aqueous/metaI interface. Application of the vacuum techniques to electrochemical interfaces is thus desirable, but has been plagued by questions of the relevance of the emersed, evacuated surfaces examined to the real electrochemical interfaces. This concern is accentuated by surface scientists observations that in UHV no molecular water remains on well-defined surfaces at room temperature and above (1). Emersion and evacuation at room temperature may or may not produce significant changes in electrochemical interfaces, depending.on whether or not water plays a major role in the surface chemistry. 

Davis, J. A., and J. O. Leckie (1978a), "Surface Ionization and Complexation at the Oxide/Water Interface. II. Surface Properties of Amorphous Iron Oxyhydroxide and Adsorption of Metal Ions," J. Colloid Interface Sci. 67, 90-107. 

---