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Physical mixtures of a BN polymeric precursor with oxides such as MgO, A l z 0 3 , and TiOl have been found to yield crystalline, tightly adherent coatings of hexagonal BN on the oxide surface, after appropriate heat treatments. In every instance, the BN (0001) basal planes are parallel to the oxide surface. Generally, the coating conforms very well to the contours of the oxide surface. However, an exception was the silica surface where no coatings were observed. It appears that the surface silanols condense to form siloxanes at high temperatures, yielding a surface that is unreactive and unable to bind to the BN. Modification of the silica surface by incorporation of a monolayer of titania dramatically alters the ability of the silica to stabilize BN coatings. It was found that stable BN coatings could be obtained when the silica surfaces were thus modified. [

Enthalpies of solution of five amino acids, glycine, l-alanine, l-valine, l-serine, and l-threonine in aqueous solutions of three quarternary ammonium surfactants, [C n H2n+1(CH3)2NCH2CH2OH]Br (n = 12, 14, 16), have been measured at 298.15 K with a microcalorimeter. Enthalpies of transfer of amino acids from water to aqueous surfactant solutions have been derived. It has been observed that, at relatively low concentrations of the surfactant solutions, amino acids are still in the water phase and mainly interact with the hydrophilic head groups of the surfactant molecules. With an increase of the concentration of the surfactant solutions, the microenvironment of amino acids changes, and the molecules might insert into the micelles and interact with the hydrophobic tail groups of the surfactant molecules. The results are discussed in terms of a delicate balance of hydrophobic and hydrophilic interactions and differences in the molecular structure of amino acids.