Interface interfacial//phenomena

Davies, J.T. and Rideal, E.K. Adsorption at Liquid Interfaces Interfacial Phenomena. Academic Press New York, 1961, pp. 154—216. 

Whether a polymer is hydrophilic or hydrophobic can be explained by the X interaction. However, why the air/hydrogel interface of a gelatin hydrogel is hydrophobic cannot be explained by x interaction because it is a strictly interfacial phenomenon that is governed by the interfacial interaction. The strictly interfacial phenomena could be explained by 7 interaction. The first term in Eq. (25.1) is x interaction and the second term is 7 interaction. The overall rate of surface dynamic change is, therefore, dependent on both 7 interaction and x interaction [7]. Thus,... 

Johnson D. The discovery-development interface has become the new interfacial phenomenon. Drug Discov Today 1999 4(12) 535-6. 

In dilute solutions of surface-active agents, the amount of change in any interfacial phenomenon produced by the adsorption of surfactant at the interface is a function of the concentration of surfactant absorbed at the interface. Thus efficiency is determined by the ratio of surfactant concentration at the interface to that in the bulk (liquid) phase, Cinterface/CbUik- This ratio is determined by the free... 

Since the effect of a surfactant on an interfacial phenomenon is a function of the concentration of surfactant at the interface, we can define the effectiveness of a surfactant in adsorbing at an interface as the maximum concentration that the surfactant can attain at that interface, i.e., the surface concentration of surfactant at surface saturation. The effectiveness of adsorption is related to the interfacial area occupied by the surfactant molecule the smaller the effective cross-sectional area of the surfactant at the interface, the greater its effectiveness of adsorption. Effectiveness of adsorption, therefore, depends on the structural groupings in the surfactant molecule and its orientation at the interface. Another parameter characterizing the performance of surfactants, important in high-speed interfacial phenomena such as wetting and spreading, is the rate of adsorption of the surfactant at the relevant interface(s). This will be discussed in Section IV of Chapter 5. 

Adhesion is an interfacial phenomenon that occurs at the interfaces of adherends and adhesives. This is the fact underlying the macroscopic process of joining parts using adhesives. An understanding of the forces that develop at the interfaces is helpful in the selection of the right adhesive, proper surface treatment of adherends, and effective and economical processes to form bonds. This chapter is devoted to the discussion of the thermodynamic principles and the work of adhesion that quantitatively characterize the surfaces of materials. Laboratory techniques for surface characterization have been described which allow an understanding of the chemical and physical properties of material surfaces. 

One of the most relevant, if not the most relevant, coUoidal and interfacial phenomenon in life sciences is bioadhesion, that is, the joining together of surfaces of which at least one is of biological nature. Usually, bioadhesion involves the association of a biological cell (including bacterial cells) with the surface of a living or an inanimate substratum. In the special case where the adhesion is between particles of comparable size, it may be referred to as aggregation, and adhesion at a gas-liquid interface is also called flotation. 

When a multicomponent system is exposed to an interface, there is a change in the concentration profile at the interfacial region. If the concentration of one or more of the components at interface increases, then these components are said to adsorb at that interface and the phenomenon is known as adsorption. Conversely, when there is a decrease in the concentration of one or more of the components at the interface the phenomenon is called depletion. 

Lipases (EC 3.1.1.3) belong to the second group of PET hydrolases. Lipases, in general, catalyze the hydrolysis of long chain water-insoluble triglycerides [7, 15]. Their activity is greatly increased at the water-lipid interface, a phenomenon described as interfacial activation [35]. The active site of lipases is buried in a short polypeptide chain (lid) [21, 46]. Upon adsorption at the lipid-water interface, the movement of the lid exposes the active site and increases the hydrophobicity of the surface of the enzyme around the catalytic site [12]. In contrast, the catalytic site of cutinases is not covered by a lid, but is directly exposed to the solvent. 

As one example, consider the interfacial phenomenon between ceramic and copper wiring. If the material or process conditions of the ceramic and copper are inappropriate, various macro and micro flaws occur. For example, in the firing process, minute pores are formed at the interface. Possible causes of the formation of the pores are (1) mismatch of the firing and shrinkage behaviors of the conductor and ceramic, (2) insufficient adherence between the conductor and ceramic in the laminating process, (3)... 

In addition, the amount of mthenium oxide dissolved in the glass is very little at less than 0.5%, and since interface reactions between ruthenium oxide and glass are not observed, the impact of the interfacial phenomenon on the value of resistance is small [21, 22]. 

The activity of lipases in catalyzing the hydrolysis of ester bonds in water-insoluble triglycerides is maximal only when the enzyme is adsorbed at the oil-water interface— a phenomenon known as interfacial activation [59]. Elucidation of the structure and function of several lipases revealed the explanation [60]. All have a general core structure, known as the a/b core and a catalytic triad made up of serine, histidine, and aspartic acid amino acid residues. Common to all structures is a hydrophobic lid covering the active site. During interfacial activation, the lid is opened, revealing an even more hydrophobic surface. Thus, for a lipase to work in water, it must first penetrate the lipid phase for activation. 

From the hydrolases toolbox, probably lipases have been the most demanding catalysts for synthetic application. Their natural funchon involves the hydrolysis of triacylglycerol ester bonds, compoimds that are poorly soluble in water. Thus, the reaction usually occurs in an organic-aqueous interface. This phenomenon involving the conformational change of the selected lipase is called interfacial achvahon [35], and it provides an inherent affinity for hydrophobic media to the enzyme. 

Other aspects of interfacial science and chemistry are examined by Owen and Wool. The former chapter deals with a widely used chemistry to join disparate surfaces, that of silane coupling agents. The latter chapter describes the phenomenon of diffusion at interfaces, which, when it occurs, can yield strong and durable adhesive bonds. Brown s chapter describes the micromechanics at the interface when certain types of diffusive adhesive bonds are broken. The section on surfaces ends with Dillingham s discussion of what can be done to prime surfaces for adhesive bonding. 

The several industrial applications reported in the hterature prove that the energy of supersonic flow can be successfully used as a tool to enhance the interfacial contacting and intensify mass transfer processes in multiphase reactor systems. However, more interest from academia and more generic research activities are needed in this fleld, in order to gain a deeper understanding of the interface creation under the supersonic wave conditions, to create rehable mathematical models of this phenomenon and to develop scale-up methodology for industrial devices. 

Interfacial behavior of different silicones was extensively studied, as indicated in Section 3.12.4.6. To add a few more examples, solution behavior of water-soluble polysiloxanes carrying different pendant hydrophilic groups, thus differing in hydrophobicity, was reported.584 A study of the aggregation phenomena of POSS in the presence of amphiphilic PDMS at the air/water interface was conducted in an attempt to elucidate nanofiller-aggregation mechanisms.585 An interesting phenomenon of the spontaneous formation of stable microtopographical surface domains, composed primarily of PDMS surrounded by polyurethane matrix, was observed in the synthesis of a cross-linked PDMS-polyurethane films.586... 

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