Search

A new mesoporous structure, silicate spherulite, has been produced in dilute surfactant and silicate solutions. The spherulites were formed from radially arranged rod-like micelles. The surfactant molecules in the rod-like micelles can be removed by heat treatment to leave a unique mesoporous material with radially arranged channels for easy access. Although the spherulite morphology has been observed in the nucleation and growth of polymeric crystals for a long time, it has not been reported in surfactant solutions. Similar to the polymeric materials, the surfactant spherulites are most likely the fingerprints of the early nucleation process in the preparation of ordered mesophase silicates.

Steric stabilization of small unilamellar vesicles composed of dipalmitoyl phosphatidylglycerol (DPPG) is achieved by the incorporation of nonylphenol poly(ethylene oxide) ethers at varying mol%. Nonylphenol poly(ethylene oxide) ethers with an average of either 10.8 (NP 10 or 50 (NP 50 ethylene oxide groups are incorporated into vesicles at between 2.5 and 10 mol%. Vesicle aggregation is induced by the addition of either NaCl or CaCl 2 with the effective diameter of the vesicle dispersion measured as a function of time using photon correlation spectroscopy. The addition of between 5 and 20 mol% NP 10 to DPPG vesicles increases dispersion stability 10-fold in the presence of NaCl but only 2-fold in the presence of CaCl 2 . Dispersion stability is increased 100-fold with the addition of 10–20 mol% NP 50 in NaCl and 1000-fold in the presence of CaCl 2 . Vesicle aggregation is found to be reversible with 5 mol% added NP 50 in NaCl but only partially reversible in the presence of CaCl 2 . The hydrophobic nonylphenol moiety of NP 50 is found to be critical for imparting dispersion stability when compared to the addition of pure poly(ethylene oxide) to vesicles.

A non-aqueous synthesis route broadens the spectrum of useful precursors and the range of compositions which can be achieved in the synthesis of ordered, mesoporous multicomponent materials. A formamide solution of surfactant (cetyltrimethylammonium chloride/hydroxide) allows for distribution of a water-sensitive metal oxide precursor prior to reaction. Hydrolysis of the metal oxide precursor and phase separation to the pure oxide are controlled by adding limited amounts of water. Subsequent addition of a second metal oxide source as an aqueous solution initiates the reactions leading to a mixed oxide having ordered mesopores. Ordered mesoporous titanium silicates having final Ti/Si mole ratios in excess of 1/20 are synthesized.

Two aspects of phospholipid vesicle aggregation are examined: the low rate at which it occurs, even at high electrolyte concentrations, and its unusual temperature dependence. A comparison of experimental data with theoretical calculations suggests that phospholipid vesicles aggregate into a shallow minimum, resulting in weak, reversible aggregation. The incorporation of a hydration effect gives the total interaction potential the necessary features for such behavior. The temperature dependence of the aggregation kinetics appears to result from a temperature dependence of the effective Hamaker constant and the hydration parameters.