セッケンの比熱測定による相転移の研究

概要

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The phase transition of crystalline form of typical sodium soaps, ranging from sodium laurate (C<SUB>12</SUB>) to sodium stearate (C<SUB>18</SUB>), were studied by the measurement of change in the specific heat. It is known from the previous X-ray diffraction studies that sodium soap molecules align parallel to the long axes of their hydrocarbon chain and the ionic ends are adjacent to each other, thus they form the bimolecular laminate. By using the above-mentioned model, the relation of the van der Waals force acting between the adjacent hydrocarbon chains and the Coulomb force acting between the ionic layers or adjacent molecules is clarified. From this, it is shown that the balance of two sorts of forces acting between two molecules is altered by the length of paraffinic carbon chain. In sodium laurate, Coulomb force acting between the adjacent hydrocarbon chains is strongnger than van der Waals force acting between the ionic ends of the adjacent layer, and then the behavior of phase transition of sodium laurate is similar to the ionic crystal. In the myristate and palmitate, the balance between the two forces is kept generally and they show the similar behavior in the change of phase transition. In sodium stearate, the thermal behavior is different from other soaps because of that the thermal motion is complicated.
社団法人日本油化学会の論文