Crystal structures of binary systems of saturated fatty acids

Data on crystal lattices of 13 different mixtures of the system palmitic acid:stearic acid (C₁₆/C₁₈) could be obtained by means of X-ray and electron diffraction. The modification occurring in all concentrations was found to be in conformity with the known γ₄- or C-form of the pure components. It is characterized by the fact that, in mixtures with 95-60 mol % stearic acid, the shorter chained palmitic acid molecules may be incorporated in the crystal lattice of pure stearic acid without dimension c of the unit cell being changed. In concentration ranges of 50–20% C₁₈-molecules, one form of mixture which proves to be stable is characterized by constancy of nearly all unit cell parameters of various mixture ratios. From SP10 to SP0, the lattice constants of pure palmitic acid are mainly obtained. The occurrence of C₁₈-molecules of up to 10% in the unit cell of palmitic acid results in a slight decrease of the angle β by 1–2^o and an enlargement of the distance to neighbored molecules.