The organization of cationic or anionic organic and inorganic molecular species to produce three-dimensional periodic biphase arrays is described. The approach uses cooperative nucleation of molecular inorganic solution species with surfactant molecules and their assembly at low temperatures into liquid-crystal-like arrays. The organic/inorganic interface chemistry makes use of four synthesis routes with (S+I-), (S-I+), (S+X-I+), and (S-M+I-) direct and mediated combinations of surfactant (cationic S+, anionic S-) and soluble inorganic (cationic I+, anionic I-) molecular species. The concepts can be widely applied to generate inorganic oxide, phosphate or sulfide framework compositions. Distinct lamellar, cubic silica mesophases were synthesized in a concentrated acidic medium (S+X-I+), with the hexagonal and the cubic phases showing good thermal stability. For the hexagonal mesostructured silica materials high BET surface areas (>1000 m₂/g) are found. Hexagonal tungsten(V1) oxide materials were prepared in the presence of quaternary ammonium surfactants in the pH range 4-8. Cubic (Ia3d) and hexagonal antimony(V) oxides were obtained by acidifying (pH = 6-7) homogeneous solutions of soluble Sb(V) anions and quaternary ammonium surfactants at room temperature (S+I-). Using anionic surfactants, hexagonal and lamellar lead oxide mesostructures were found (S-I+). Crystalline zinc phosphate lamellar phases were obtained at low synthesis temperatures (4°C) and lamellar sulfide phases could be also readily generated at room temperature. The synthesis procedure presented is relevant to the coorganization of organic and inorganic phases in biomineralization processes, and some of the biomimetic implications are discussed

I1I. SUPPLENIEN TARY NO &ES

A model that makes use of the cooperative organization of inorganic and organic molecular species into three dimensionally structured arrays is generalized for the synthesis of nanocomposite materials. In this model, the properties and structure of a system are determined by dynamic interplay among ion-pair inorganic and organic species, so that different phases can be readily obtained through small variations of controllable synthesis parameters, including mixture composition and temperature. Nucleation, growth, and phase transitions may be directed by the charge density, coordination, and steric requirements of the inorganic and organic species at the interface and not necessarily by a preformed structure. A specific example is presented in which organic molecules in the presence of multiply charged silicate oligomers self-assemble into silicatropic liquid crystals. The organization of these silicate-surfactant mesophases is investigated with and without interfacial silicate condensation to separate the effects of self-assembly from the kinetics of silicate polymerization.

Multinuclear (2H, 13C, 29Si, 81Br) magnetic resonance spectroscopy, small-angle X-ray scattering, and polarized optical microscopy techniques have been used to investigate molecular and mesoscopic organization in silicate−surfactant lyotropic liquid crystals with hexagonal and lamellar morphologies under highly alkaline conditions. Such systems cooperatively self-assemble following the addition of a basic aqueous solution containing anionic silicate oligomers (e.g., double-four-ring species) to an isotropic micellar solution of cationic surfactant molecules (e.g., cetyltrimethylammonium bromide). Important similarities and differences are shown to exist between multicomponent silicate−surfactant and conventional binary lyotropic liquid crystals. Under highly alkaline conditions, the silicate−surfactant systems possess the characteristics of ordinary lyotropic liquid crystalline systems, though the balance of forces underlying their self-assembly is complicated by the richness of the aqueous silicate chemistry. This is the first comprehensive description of lyotropic silicate−surfactant liquid crystalline behavior, from which detailed insight is obtained into the molecular factors governing inorganic−organic mesophase formation in aqueous media.

Macroscopic orientational ordering of the pores of condensed hexagonal mesostructured silica (MCM-41) was achieved through alignment of an unpolymerized, hexagonal, lyotropic silicate-surfactant liquid crystal in a high magnetic field. This alignment was preserved after polymerization of the silicate species by acid treatment. Subsequent calcination to remove the surfactant yielded a mesoporous silica solid that retained both macroscopic pore alignment and mesoscale periodicity. Potential applications of such liquid crystal processing strategies range from the formation of anisotropic silica-based bulk ceramics to the production of oriented mesoporous thin films for chemical sensors, separations, catalysis, or host-guest applications.T h e recent discovery (I ) that inorganic silicate and organic surfactant precursors can self-organize (2) to form ordered materials with nanometer-scale periodicities has created exciting avenues for the synthesis of nanostructured materials. Ordered inorganic-surfactant composites have been made with a wide variety of transition metal (3, 4) and main group oxides and phosphates (5, 6, 7, 8 ) as well as metal chalcogenides (9). These composites have been shown to consist of aggregates of assembled surfactant molecules that interact covalently (3,8,10) or electrostatically (1, 6, 8 ) with an inorganic framework. For densely cross-linked inorganic mesostructures, it is frequently possible to remove the organic surfactant from the inorganic-surfactant composite by calcination or ion exchange to produce an ordered, mesoporous inorganic material with unifo~m pore sizes ranging from 20 to over 100 A in diameter (1 ).Many uses have been proposed for these mesoporous materials (1 1, 12), most notably catalysis, separations, and chemical sensing of molecules that are too large for processing with crystalline zeolite molecular siev$s, which generally have smaller (2 to 15 A ) micropores. Mesoporous solids may also be used as host matrices for optically (13,14) or electrically active (15) species. Many of these applications, however, are hindered by the fact that many mesoporous solids have to date been produced only as powders (16, 17) with small domain sizes (-1 pm) that have no orientational alignment of the pores over macroscopic length scales. Progress in orienting these materials has been made by growing thin films of mesoporous silicates at surfaces or interfaces (1 8-2 1 ), but the interface generally determines the alignment of the pores and frequently produces pores with orientations that are not desirable for the envisioned applications (1 8, 19). In particular, the synthesis of mesoporous p6mm hexagonal (MCM-41) films with pores that are perpendicular to the plane of the film is a desirable goal (1 6).The formation of silica meso~hase solids under basic conditions (1) has been shown to proceed by the cooperative organization of solution-phase silicate and surfactant species coupled with inorganic polymerization (22). Under the appropriate conditions, however, mesophase self-assemb...