PVD of fatty acids on a cold quartz crystal sensor

A fatty acid mixture of lauric acid and myristic acid was deposited on a cold quartz crystal sensor from the binary vapor phase of the mixture by physical vapor deposition (PVD). The cold quartz crystal sensor could detect a small amount of deposit in real time, and provided the growth rate of the thin solid deposit by the PVD. The composition of lauric acid in vapor phase was fixed at a mole fraction of about 0.5 by controlling the composition of lauric acid in melt phase computed from the vapor–liquid equilibrium (VLE). The growth rate of solid phase in the PVD increased with the elevation of the melt temperature, because the vapor pressure of the melt raised by the temperature elevation was the driving force of the PVD. The composition of lauric acid in the solid phase was considerably lower than that in the vapor, and it was increased as the growth rate in the solid phase rose. The distribution coefficient of lauric acid between solid and vapor phases was much less than that between solid and melt phases. We compared the separation capacity in melt crystallization with that in the PVD using the effective distribution coefficient, and found that the PVD had higher separation capacity.