PHASE-SEPARATION IN MICROCAPSULE MEMBRANES COMPOSED OF SOYBEAN LECITHIN, CHOLESTEROL, STEARIC-ACID AND POLYVINYLPYRROLIDONE

A phase diagram of a soybean lecithin (SL)-cholesterol (CH)stearic aci d (SA) system incorporating 42% polyvinylpyrrolidone was estimated by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) an d polarizing microscopy in order to relate it to the dissolution and d isintegration properties of microcapsules whose membranes consisted of these compounds. At the weight ratio of SL:CH = 4:1, SL:SA = 4:1 or S L:CH:SA = 3:1:1, SL liquid crystalline phase (SL(LCP)) dissolved the m aximum amount of CW and/or SA without any other crystalline phases det ected on DSC and XRD. The existence of SL(LCP) was confirmed by observ ation under polarizing microscope: mixtures remained anisotropic over 20-90 degrees C or SA-containing anisotropic phases became isotropic a t 70-80 degrees C without any peaks on DSC. With increase in CH and/or SA, these were separated from SL(LCP) dissolving CH and/or SA. The se parated CH (CH(c)) was found to have the same crystalline structure as the parent CH from XRD. The separated SA, in contrast, showed two typ es of XRD patterns: one had the same pattern as the parent SA (SA(c)) and the other had a pattern with some peaks shifted to shorter spacing s (SA(c')). The mixtures gave a phase diagram with six regions, each o f which had the following phase(s): 1) SL(LCP); 2) SL(LCP) and (CH(c); 3) SL(LCP), CH(c) and SA(c'); 4) CH(c), SA(c') and SA(c); 5) SA(c) an d SA(c'); 6)SL(LCP) and SA(c'). It was not clear whether SL(LCP) was p resent in the fourth and fifth zones or not.