NMR-Studien an grenzflächenaktiven Verbindungen in kosmetisch relevanten Systemen

In this work surfactant systems of cosmetically interest are examined by static and dynamic NMR-methods in order to get more insight in stabilization mechanisms of emulsions used for cosmetic products. Cosmetic oil in water emulsions with a stearyl phosphate emulsifier were examined by means of static and dynamic 31P NMR techniques in order to characterize the molecular properties of the emulsifier in situ. The interfacially bound emulsifier can be detected by high resolution NMR spectroscopy, whereas the excess emulsifier exists as a solid lipid phase not detectable by this technique. The emulsions and the emulsifier raw material were examined by solid state cross polarization magic angle spinning (CPMAS) NMR spectroscopy to prove the existence of solid emulsifier phases in the emulsions. By applying dynamic 31P NMR methods to the interfacially bound emulsifier, information about the molecular dynamics at the interface was obtained. The results of the T1 and T2 relaxation time measurements indicate a restricted motion of the molecules which is dependent on the oil droplet size in the emulsions. This was verified by NMR pulsed gradient spin echo (PGSE) self-diffusion measurements on emulsions with different droplet sizes. In conclusion it can be stated that only about 4% of the emulsifier are bound at the interface while the excess forms solid lipid phases. The coverage of the interface seems to be independent of the emulsifier concentration. The molecular mobility of the emulsifier at the interface indicates the two dimensional environment of the molecules on the droplets surface. These results are checked by 13C NMR spectroscopic examinations on emulsions with more complex emulsifier systems. Surfactant systems show in general several molecular populations with different dynamic behaviour detectable by NMR techniques. The exchange rate between the different molecular states determines if the states can be detected separately in the NMR spectrum or if the signals coalesce to one line