The hydrophilic effect

In this chapter, we discuss why and how water structure changes near hydrophilic objects. We follow this with a chapter on the other extreme the hydro-phobic effect. Familiar examples of hydrophilic objects are charged ions such as Na and Cl . Solvation of such ions is important in many areas of chemistry and biology. 

Hydrophilic interaction is operative not only in solvating small rigid ions, but also in stabilizing extended structures such as DNA, proteins, and inorganic extended surfaces such as silica, mica, and zeolites. In the first two examples (proteins and DNA), both hydrophobic and hydrophilic interactions operate synergistically to stabilize the structure. In the case of several common extended objects such as silica and mica surfaces [1,2], it is primarily the hydrophilic interaction that dominates. 

Here the surface atoms can form strong HBs with water molecules and exert influence on the extended HB network of water. Another important class of systems is aqueous binary mixtures, where both hydrophobic and hydrophilic interactions together determine many of the unusual properties exhibited by these systems. The hydrophilic effect is partly responsible for water being such a good solvent for a large number of polar molecules. Hydrophilic interaction also finds great use in industry, as in hydrophilic chromatography. 

Water confined between two hydrophilic objects forms an interesting and important system with unique properties. Sometimes the amount of water molecules confined between two hydrophilic surfaces is rather small, consisting only of a few tens (or even fewer) of water layers. In such cases, the stmctural arrangement of water molecules can become quite distorted compared with the bulk stmcture. Also, the order imposed by each hydrophilic surface can propagate inwards and counter each other. Water s ability to form many isomorphic structures is tested in such a situation, as we discuss below. 

In this chapter, we shall discuss different systems where hydrophilic interaction plays important roles. 

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LBKE can be further modified to capture the multicomponent/multiphase phenomena in GDL as well as GC. This modification also allows modeling the hydrophilic effect such as the bubble transport phenomenon. Lu and Wang visualized the bubble phenomenon in situ using the... 

A hydrophilic molecule or a hydrophilic group of a molecule is generally polar and capable of H-bonding, enabling it to dissolve more readily in water than in oil or other hydrophobic solvents. It has a strong affinity with water tending to dissolve in, mix with, or be wetted by water. When two solute molecules repel each other in water it is called hydrophilic interaction. However there is no phenomenon known as the hydrophilic effect. 

Rate comparisons at different temperature regimes demonstrated that the hydrophilic effect was stronger in dioxane than that in dimethyl-acetamide. Quaternizations of CMPS with triethylamine, N-2-hydroxyethyl-dimethylamine or N,N-bis-hydroxyethylmethylamine conducted in DMF, also exhibited stepwise acceleration. ... 

Table 9 Parameters for the Hydrophilic Effect of Pblar Moieties...

We have previously used the Microtox test to determine the acute toxicities of several series of chlorobenzenes, -phenols, -anilines, -nitrobenzenes, and -pyridines (Kaiser and Ribo 1985 Ribo and Kaiser 1983). For each of these series, a major dependence of the toxicity on the octanol/water partition coefficient (log P) was demonstrated. However, additional parameters, such as the hydrophilic effect parameter (V ) were required to reduce the variation between the different groups of congeners. 

With TiOj photocatalyst alone, the superhydrophilicity disappears shortly once the exposure of the surface to UV light is stopped. When the photocatalyst is combined with silica- or silicon-based chemical compounds that have siloxane bonding, the hydrophilic effect of the surface continues for a long time even in the daik, as seen in Fig. 4.2 [42]. 

Now let us consider the non-electrolytes. Here we have two very distinct types of behaviour. There are the so-called hydro-phobic, and the hydrophilic effects. The hydrophobic effect can be shown schematically from a consideration of the thermodynamics of hydrocarbon solutions. Usually a non-ideal solution arises because the two components either strongly attract each other or strongly repel each other the effects are shown in the enthalpy. Figure 8 shows various types of behaviour, as reflected in the excess thermodynamic functions (Rowlinson, 1969). The drawn out lines are free energies, the broken lines are enthalpies and the dotted lines are the entropy curves. A positive free energy means a positive deviation from ideal behaviour. In normal systems AG follows the AH curve fairly benzene-MeOH. In... 

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