The structural phases of magnetically alignable lipid mixtures were investigated as a function of temperature and lipid concentration using small-angle neutron scattering (SANS). Two systems were examined:  (a) an aqueous mixture of DMPC (dimyristoyl phosphatidylcholine) and DHPC (dihexanoyl phosphatidylcholine) lipids doped with Tm3+ ions resulting in the positive alignment of the system with the applied magnetic field and (b) the above aqueous Tm3+ doped lipid mixture containing a negatively charged lipid, DMPG (dimyristoylphosphatidylglycerol). For both systems, three different scattering patterns were observed corresponding to distinct structural phases at specific temperatures and lipid concentrations. At 45 °C and a lipid concentration of >0.05 g/mL, the high-viscosity liquid crystalline phase was found to be a perforated and possibly undulating lamellar phase consistent with NMR results. Upon dilution (<0.05 g/mL) at the same temperature (45 °C), the perforated lamellar phase transformed into a unilamellar vesicular phase, in which the bilayers may also be perforated. Below about 25 °C, the viscosity decreases considerably and the scattering data suggest that the lamellae present at higher temperatures break up into smaller entities characterized by the bicellar morphology proposed previously for the nondoped system. The structural dimensions of the vesicular and bicellar phases have been determined as a function of lipid concentrations from the SANS data. In the lamellar phase, the influence of Tm3+ ions and DMPG on bilayer structure (e.g., lamellar repeat spacing, bilayer rigidity, and magnetic alignment) were also investigated.

Small-angle neutron scattering (SANS) studies indicate that oil-in-water microemulsions, consisting of aqueous HCl, the nonionic block copolymer surfactant Pluronic P123 (poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide), EO20−PO70−EO20, M av = 5800), 1,3,5-trimethylbenzene (TMB, oil), and ethanol (cosurfactant), are novel colloidal templates that direct the synthesis of mesoporous silica with well-defined ultralarge pores. The sizes of the microemulsion droplets can be controlled by the TMB concentration and by temperature. The microemulsion droplet sizes and the cell sizes of the mesostructured cellular foam (MCF) materials increase linearly with the cube root of the TMB concentration. Increasing the temperature from 40 to 80 °C expands the droplet sizes, which is similar to micellar solutions of Pluronic surfactants in the absence of oil. Ethanol acts as a cosurfactant, increases the TMB solubility of the P123 micelles, and enables swelling of the P123 micelles. Low concentrations of NH4F (8 × 10-3 mol/L) show no significant effect upon the nature of the microemulsions. The polydispersities of the droplet sizes range from 11% to 21%. The microemulsion templates reported in this paper are considered as a valuable addition to existing colloidal templates that direct the synthesis of porous materials. The benefits of the microemulsion templates are (i) their easy preparation by simply mixing water, surfactant, oil, and a cosurfactant, and (ii) the synthesis of ultralarge-pore mesoporous materials with narrow pore size distributions without the need for further processing.