EFFECT OF VESICLE SIZE ON THE HEAT-CAPACITY ANOMALY AT THE GEL TO LIQUID-CRYSTALLINE PHASE-TRANSITION IN UNILAMELLAR VESICLES OF DIMYRISTOYLPHOSPHATIDYLCHOLINE

Dynamic heat capacity has been measured near the gel to liquid-crystal line phase transition of small unilamellar vesicle (SW) samples of dim yristoylphosphatidylcholine with a vesicle size of 30 nn. The heat cap acity showed a very broad peak that is qualitatively similar to that o bserved in the large unilamellar vesicle (LUV) samples with a vesicle size of 100 nm reported earlier. Quantitatively, the heat capacity ano maly for SUV samples differs markedly hom that for LUV samples. The ha lfwidth of the anomaly in SUV's is about 1.1 K, which is about three t imes that in LUV's, and the peak height in SUV's is about 30% of that in LUV's. The data on SUV and LUV samples have been analysed in a unif ied manner. it has been pointed out that the curvature of the vesicle surface acts in a similar way to an external field that drives the tra nsition from first order to critical and then to supercritical.