Contact angles interactions wettability

The change in surface wettability (measured by the contact angle) with concentration for the three surfactants is plotted in Fig. 2.54 (Zhang and Manglik 2005). The contact angle reaches a lower plateau around the CMC where bilayers start to form on the surface. Wettability of non-ionic surfactants in aqueous solutions shows that the contact angle data attains a constant value much below CMC. Direct interactions of their polar chain are generally weak in non-ionics, and it is possible for them to build and rebuild adsorption layers below CMC. The reduced contact an-... 

In this chapter, we concentrate on the role of the intermolecular interactions at interfaces based on the surface dynamics, the surface free energy at a given temperature and the surface energy (or enthalpy) of a solid. Contact angle and gas chromatographic techniques are respectively chosen for the studies of wettability and adsorption phenomena because of their simplicity and clearness. The degree of adhesion at interfaces between unlike solid substances is also discussed from a viewpoint of intermolecular interactions. 

These surface modifications were performed in "pure" micro-wave (2.45 GHz, "single-mode") or in combined microwave/ radio frequency (2.45 GHz/13.56 MHz, "dual-frequency") plasma. Important systematic changes of the surface composition, wettability, and adhesion of thin metal films were observed for different substrate bias values, and for the different gases. The modified surface-chemical structure is correlated with contact angle hysteresis of water drops this helps to identify which surface characteristics are connected with the wettability heterogeneity and with adhesive bonding properties, and how they are influenced by plasma-surface interactions. 

Another approach to increasing the contact angle and hence improving the accuracy of substrate materials is desirable if there is to be confidence that there has been no chemical interaction that may have affected the liquid surface. 

Experimentally, the measurement of contact angles is somewhat tricky, hence absolute values should not be considered too seriously. In particular, there is generally a difference between the an e found when the liquid advmices over the solid, and the angle found when the liquid recedes this is because the previous condition of the surface affects its wettability. But a series of measurements made under the same conditions certainly indicates the right ordering of fiber materials with regard to interaction with water. 

The problem of the interactions between membrane and absorbent solution interests, for instance, the removal of CO2. Reactive absorption liquids, such as amines, that are used for this type of removal, usually wet polyolefin membranes. Wettability depends on the surface tension of the liquid, membrane material, contact angle, and pore properties of the membrane. Possible solutions to this problem are to employ more resistant membrane materials, to use different absorbent liquids, and to deposit a nonporous layer on the membrane surface that prevents any passage of the liquid through pores. In order to do not increase too much the resistance to the mass transport, the layer has to be thin and highly permeable to the gaseous species. The dense skin can be useful also for avoiding any possible contamination of the feed gas by the absorbent (Figure 38.4). 

Measurement of contact angles on solids yields data that reflect the thermodynamics of a liquid/solid interaction. These data can be used to estimate the surface tension of the solid. For this purpose, drops of a series of liquids are formed on the solid surface and their contact angles are measured. Calculations based on these measurements produce a parameter (critical surface tension, surface tension, surface free energy etc.), which quantifies the characteristic of the solid surface and its wettability. 

In order to investigate the interaction of different types of cells in terms of the surface hydrophilicity/ hydrophobicity of polymeric materials, Chinese hamster ovaries (CHO), fibroblasts, and bovine aortic endothehal cells (EC) were cultured for 1 and 2 days on the PE wettability chemogradient surfaces. The maximum adhesion and growth of the cells appeared around a water contact angle of 50 to 55°... 

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