Static and dynamic wetting behavior of triglycerides on solid surfaces

Triglyceride wetting properties on solid surfaces of different hydrophobici ties were investigated using three different methods, namely, the sessile d rop method for static contact angle measurements, the Wilhelmy method for d ynamic contact angle measurements, and the captive bubble method to investi gate thin triglyceride film stability. For solid surfaces having a surface free energy higher than the surface tension of triglycerides (tributyrin, t ricaprylin, and triolein), a qualitative correlation was observed between w etting and solid/triglyceride relative hydrophobicities. On surfaces presen ting extreme hydrophobic or hydrophilic properties, medium-chain triglyceri des had a behavior similar to that of long-chain unsaturated ones. On a hig h-energy surface (glass), tricaprylin showed an autophobic effect subsequen t to molecular adsorption in trident conformation an the solid, observed wi th the three methods. Thin triglyceride films between an air bubble and a s olid surface were stable for a short time, for solids with a surface free e nergy larger than the triglyceride surface tension. If the solid surface ha d a lower surface free energy, the thin film collapsed after a time interva l which increased with triglyceride viscosity. (C) 2000 Academic Press.