The Phase Behaviour of Saturated and Unsaturated Monoglycerides and the Influence of Triglyceride on the Aggregation in Hydrophobic System

It is well known that long chain monoglycerides form a metastable α-gel phase (Lβ) on cooling. Despite the inevitable storage problems, this state is frequently employed to stabilise emulsions or to incorporate “active” ingredients in many food and fragrance applications, and is also used for drug delivery. In this work, we have examined the phase behaviour of saturated and unsaturated monoglyceride. Furthermore, the same systems have been studied in mixtures containing liquid triglycerides. In the study, Optical microscopy has been employed as a function of temperature for an initial survey of phase behaviour, and differential scanning calorimetry (DSC) has been used to determine the transition temperatures and enthalpies between mesophases. Surfactant mobility in the various phases was studied by measuring proton nuclear magnetic resonance (NMR) T2 relaxation times in order to characterize the solid phase fraction in the sample. In parallel, small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) have been used to identify the structures of the different mesomorphic phases formed at different temperatures. The study shows various ordered phases are formed by glycerol monostearate (GMS), GMS/oil, glycerol monooleate (GMO), GMO/oil. There are 4 phases associated with GMS, α–gel phase, sub α phase, L2 and β3 crystal. However, when oil is added 5 phases are seen, α–gel phase, sub α phase, β2 crystal, L2 and β3 crystal .Only 2 phases are found for GMO, β1 crystal and L2, while for GMO/oil 3 phases are found, β2 crystal, β1 crystal and L2 . Furthermore, this paper proves that the oil incorporates with sub α phase and α gel phase for GMS, and this is not the case for GMO.</jats:p

Influence of added electrolytes on the lyotropic phase behavior of triethylammoniodecyloxycyanobiphenyl bromide (OCB-C10NEt3Br)

The influence of added electrolytes (NaBr, NaCl, Na2SO4, Na3PO4 Na2HPO4, NaSCN) on the lyotropic mesophase behavior of triethylammoniodecyloxycyanobipenyl bromide (OCB-C10NEt3) has been studied using optical microscopy, X-ray diffraction, and NMR. Optical microscopy was employed to map the existence regions of the lamellar mesophase, while X-ray diffraction gave its interaggregate dimensions, and NMR was employed to monitor water ordering. Only lamellar and micellar phases have been observed. Tn all of the electrolytes except NaSCN, partial miscibility of surfactant and water is induced above a certain concentration. This usually involves the separation of a dilute surfactant solution from a more concentrated one. It does not occur within the extensive lamellar phase region. X-ray diffraction and NMR results demonstrate that the major influence of the electrolytes is to reduce the area per headgroup within the aggregates. The effects of the electrolytes follow the Hofmeister series and are attributed to adsorption or desorption of anions at the aggregate surface rather than to changes in "water structure". Sodium thiocyanate causes the occurrence of a "re-entrant" isotropic phase, in part because the lamellar phase is stabilized to low concentrations. The displacement of OCB groups from the micellar surface by SCN ions is suggested to account for this, which, if valid, offers a potential route to obtaining true amphitropic mesophases (i.e., materials with both thermotropic and lyotropic liquid crystalline order)

Density measurements through the gel and lamellar phase transitionsof di-tetradecanoyl- and di-hexadecanoyl-phosphatidylcholines : observation of slow relaxation processes and mechanisms of phase transitions

Density measurements on aqueous dispersions of C14: 0/C14:0 and C16:0/C16:0 phosphatidylcholines have been carried out to give information on the mechanism of the phase transitions [main transition: lamellar phase (L-alpha) to gel (P-beta'); pre-transition: gel (P-beta') to second gel phase (L-beta')]. Quite remarkably, for both systems we observe that repeated temperature cycles give different measurements, with a slow relaxation to apparent equilibrium, at least for some of the phases. We also observe that there are marked reductions in lipid density just above the main transition that indicate the spontaneous formation of 'lipid patches'. The density measurements allow the calculation of the relative contributions to the phase transitions from changes in van der Waals energy (Delta U-vdW) and chain configurations (Delta U-Rot). Both contribute to the main transition whilst only changes in the van der Waals energy are involved in the pre-transition