THE STUDY OF THE MICROENCAPSULATED DYE RELEASE FROM SOYBEAN LECITHIN LIPOSOMES A.L.F.Baptistaa,P.J.G.Coutinhob,M.E.C.D.Real Oliveirab,J.I.N.Rocha Gomesa aUniversidade do Minho - Departamento de Engenharia Têxtil - Campus de Azurem -4800 Guimarães-Portugal bUniversidade do Minho - Departamento de Física - Campus de Gualtar - 4700 Braga-Portugal The objective of our work has been the microencapsulation of dyes with lecithin from soybean, with the formation of liposomes, as a substitute for synthetic auxiliaries so as to improve the quality of the effluent. Current scenarios promote the disintegration and leakage of the liposomes, such as, changes in temperature, acidity, the use of surfactants, etc. Since dyeing process is a mix of all these parameters, we pretended to study each one separately. INTRODUCTION Rhodamine 6G Equilibrium binding constant of rhodamine in soybean lecithin: Equilibrium dimerization constant in aqueous media: Equilibrium dimerization constant in lipid media: MODELIZATION Structural parameters lext=lint=10 Å; Rext=8000 Å; Rint=7950 Å Mass balance equation Conversion factors from bulk to local concentration Where: { } - local concentration [ ] - bulk concentration TEMPERATURE AND SURFACTANT EFFECT ON THE CONTROL RELEASE OF THE DYE TEMPERATURE FITTED PARAMETERS SURFACTANT/TEMPERATUE % DYE RELEASE pH EFFECT CONTROL RELEASE OF THE DYE pH FITTED PARAMETERS % DYE RELEASE PROTECTION TO MEMBRANE INTERIOR EXTERNAL pH 12 EXTERNAL pH 3 Carbofluoresceina CONCLUSIONS The temperature, the surfactant and pH induce a release of the encapsulated dye resulting in rhodamine dilution and consequently alterations in the dimerization/binding equilibrium. The amount of dye released induced by temperature changes was greater in the presence of surfactant. Changes in pH at constant temperature induces a release of dye similar as the one obtained with changes in temperature. In acid conditions we found a very fast initial dye release which doesn’t occur in basic ones. Using carboxyfluoresceine, as a pH fluorescence probe, we concluded that the liposome membrane doesn’t protect the liposome interior from changes on the external pH although in acid conditions there is a residual protection effect. ACKNOWLEDGE TO FUNDAÇÃO PARA A CIENCIA E TECNOLOGIA FOR IT SUPPORT TO THIS PROJECT