The basic types of liquid surfaces

These remarks, which are trivial for every reader, with even a minimal experience in working with solvents, have been added here to justify our choice of not trying to give a schematic overview, and also to justify the extremely schematic presentation of the unique specific more advanced subject we shall here consider, the interfacial properties of liquids. 8.9.1 THE BASIC TYPES OF LIQUID SURFACES 

The surface of a liquid is often represented as a very small fraction of the liquid specimen, and it may be neglected. This statement is not of general validity, however, and often the surface plays a role in some cases, the dominant role. To be more specific, it is convenient to consider a classification of liquid surfaces, starting from a crude classification, and introducing more details later. 

The potentials used to describe these interfaces are those used to describe bulk liquids. The differences stay in the choice of the thermodynamical ensemble (grand canonical ensembles are often necessary), in the boundary conditions to be used in calculations, and in the exphcit introduction in the model of some properties and concepts not used for bulk liquids, like the surface tension. Much could be said in this preliminary presentation of liquid/gas interfaces, but we postpone the few aspects we have decided to mention, because they may be treated in comparison with the other kind of surfaces. 

Liquid/hquid smfaces regard, in general, a couple of liquids with a low miscibility coefficient, but there are also cases of one-component systems presenting two distinct Uquid phases, for which there cordd be interest in examining the interfacial region at the coexistence point, or for situations out of the thermodynamical equilibrium. 

If the second component of the liquid system has a low miscibiUty with the first, and its molar ratio is low, it is easy to find situations in which this second component is arranged as a thin layer on the surface of the main component with a depth reducing, in the opportune conditions, to the level of a single molecule. This is a situation of great practical importance 

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For some types of wetting more than just the contact angle is involved in the basic mechanism of the action. This is true in the laying of dust and the wetting of a fabric since in these situations the liquid is required to penetrate between dust particles or between the fibers of the fabric. TTie phenomenon is related to that of capillary rise, where the driving force is the pressure difference across the curved surface of the meniscus. The relevant equation is then Eq. X-36,... 

For future studies on MOF-based slurry systems, there is basic selection of criteria that needs to be satisfied by both MOF and the liquid solution. The selection of the MOF possessing the appropriate pore size for the preparation of the slurry system is very important to guarantee that the size of the liquid is large enough and does not occupy the pores which leaves no space for C02 to adsorb. Moreover, the structural stability of the MOF in the aqueous solution is essential so that it does not lose its porous framework nor its surface area. The selection of the liquid candidate is crucial, as it should not provide any extra mass transfer resistance for C02 molecules. Further, experimental and computational investigations are still required to understand the separation mechanism in slurry mixtures and to have insight into the different types of interactions between the gas, liquid, and solid materials. 

Figure 3.14 The two basic types of membrane protein ciystals. Type I stacks of membranes containing two-dimensionally crystalline membrane proteins, which are then ordered in the third dimension. Type II a membrane protein crystallised with detergents bound to its hydrophobic surface. The polar surface part of the membrane proteins is indicated by broken lines. The symbols for liquids and detergents are the same as in figure 3.13. From Deisenhofer and Michel (1989) with the permission of the authors, EMBO J, Oxford University Press and copyright The Nobel Foundation (1989).

The subject of liquid crystals has now grown to become an exciting interdisciplinary field of research with important practical applications. This book presents a systematic and self-contained treatment of the physics of the different types of thermotropic liquid crystals - the three classical types, nematic, cholesteric and smectic, composed of rod-shaped molecules, and the newly discovered discotic type composed of disc-shaped molecules. The coverage includes a description of the structures of these four main types and their polymorphic modifications, their thermodynamical, optical and mechanical properties and their behaviour under external fields. The basic principles underlying the major applications of liquid crystals in display technology (for example, the twisted and supertwisted nematic devices, the surface stabilized ferroelectric device, etc.) and in thermography are also discussed. 

The basic idea of on-chip DNA hybridization assays is to integrate assay operations such as sequential sample loading, transportation, mixing, incubation, and detection on a single microfluidic chip. Although the microfluidics-based DNA hybridization assays share the same basic principle, the formats of these assays vary. Generally, the present-day formats of the on-chip DNA hybridization assays remain the main types directed liquid flow-based on-chip DNA hybridization assays, surface-based on-chip DNA hybridization assays, bead-based on-chip DNA hybridization assays, and the on-chip DNA hybridization assays with membrane/film-based transducer. 

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