Hydrophobicity, average properties

A fourth solvent structural effect refers to the average properties of solvent molecules near the solute. These solvent molecules may have different bond lengths, bond angles, dipole moments, and polarizabilities than do bulk solvent molecules. For example, Wahlqvist [132] found a decrease in the magnitude of the dipole moment of water molecules near a hydrophobic wall from 2.8 D (in their model) to 2.55 D, and van Belle et al. [29] found a drop from 2.8 D to 2.6 D for first-hydration-shell water molecules around a methane molecule. 

The concept of such an "interface" is hazy since the diameter of any of the microphases is probably very small, most likely below 30 A. A "phase" with such dimension is a small system in the sense of Hill ( ) and the fluctuations of its properties from their averages are large. With this caveat it is still possible to consider the average properties of these microphases and to assume that a small molecule with a hydrophilic and a hydrophobic part is situated, on the average, with its hydrophilic portion in the aqueous microphase and its hydrophobic portion in the hydrophobic microphase of the membrane polymer. 

The transition enthalpies of the s- and p-fractions obtained from the feed with a comonomer molar ratio of 85 15 were equal to 6 and 7 J/g, respectively, i.e. the values are very close. This, therefore, can be indicative of almost the same average length of oligoNVCl blocks. Moreover, as we have already stressed, the fractions also had virtually the same final comonomer composition. However, since the solution properties of these fractions are drastically different, one can draw the conclusion that this is apparently due to a specific distribution of hydrophobic and hydrophilic residues along the polymer chains. In turn, because of all the properties that are exhibited by the s-fraction, this fraction can be considered to be a protein-like copolymer [27]. 

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