Discontinuities in the Coefficients of Thermal Expansion of Long Chain Fatty Acids

抄録

The labile d₂₀₀ of the C form, d₀₂₀ of the B form, and d₁₀₀ of the A form for stearic and lauric acids by the changes in temperature were measured from -40°C to near their melting points by the X-ray powder diffraction method. Plots of the side spacing against the temperature showed distinct discontinuities corresponding to the existence of the second order transitions in long chain fatty acids rather than the polymorphic transition. These discontinuities in the coefficients of thermal expansion were observed at the following temperatures : stearic acid-C form, 30°C ; B form, 20°C and lauric acid-C form, 15°C ; A form, 8°C. The coefficients of expansion above the discontinuous points were equal to 1.5 to 2.7 times as great as those below.