LIPIDIC COMPOSITE-MATERIALS - INTERFACE MODIFYING AGENT EFFECT ON BULK AND SURFACE-PROPERTIES

Blends of an amphiphilic polymer and a low molecular weight lipidic co mponent with and without an interface modifying agent (IMA) were prepa red. The bulk composition of the blends was analysed using differentia l scanning calorimetry (DSC); surface mapping was performed using a we ttability test. In the binary system, a eutectic at T=47.5 degrees C w as detected for each blend with the lipidic component; the surface ana lysis showed a surface excess of the more lipophilic component. No mod ification in the eutectic temperature was detected upon addition of an IMA (ternary system), whereas composition of the eutectic point was s hifted towards higher percentages of the lipidic component. Moreover, the surface excess of the lipidic constituent was decreased. An evalua tion of these finding indicated that: (i) at normal operative temperat ures (T=body temperature), two separated phases are present in the com posite material. The composition of each phase is predetermined by the experimental one; (ii) the surface composition does not reflect the b ulk composition, with a surface excess of the more lipophilic componen t; (iii) IMA acts as a compatibilizing agent, modifying both the eutec tic point and the surface composition. It is thus shown how slight mod ifications of the bulk composition can cause large changes on the mate rial surfaces.