Adsorption hysteresis of nitrogen and argon in pore networks and characterization of novel micro- and mesoporous silicas.

We report results of nitrogen and argon adsorption experiments performed at 77.4 and 87.3 K on novel micro/mesoporous silica materials with morphologically different networks of mesopores embedded into microporous matrixes: SE3030 silica with worm-like cylindrical channels of mode diameter of approximately 95 angstroms, KLE silica with cage-like spheroidal pores of ca. 140 angstroms, KLE/IL silica with spheroidal pores of approximately 140 angstroms connected by cylindrical channels of approximately 26 angstroms, and, also for a comparison, on Vycor glass with a disordered network of pores of mode diameter of approximately 70 angstroms. We show that the type of hysteresis loop formed by adsorption/desorption isotherms is determined by different mechanisms of condensation and evaporation and depends upon the shape and size of pores. We demonstrate that adsorption experiments performed with different adsorptives allow for detecting and separating the effects of pore blocking/percolation and cavitation in the course of evaporation. The results confirm that cavitation-controlled evaporation occurs in ink-bottle pores with the neck size smaller than a certain critical value. In this case, the pressure of evaporation does not depend upon the neck size. In pores with larger necks, percolation-controlled evaporation occurs, as observed for nitrogen (at 77.4 K) and argon (at 87.3 K) on porous Vycor glass. We elaborate a novel hybrid nonlocal density functional theory (NLDFT) method for calculations of pore size distributions from adsorption isotherms in the entire range of micro- and mesopores. The NLDFT method, applied to the adsorption branch of the isotherm, takes into account the effect of delayed capillary condensation in pores of different geometries. The pore size data obtained by the NLDFT method for SE3030, KLE, and KLE/IL silicas agree with the data of SANS/SAXS techniques.

Rational design of oligopeptide organizers for the formation of poly(ethylene oxide) nanofibers.

Template pre-organized oligopeptides were conjugated to poly(ethylene oxide) chains yielding peptide-polymer-building blocks that self assemble into fiber-like nanostructures having a maximum length in the range of a micrometer.

Mixed micellar phases of nonmiscible surfactants: mesoporous silica with bimodal pore size distribution via the nanocasting process.

Highly organized mesoporous silica monoliths were reproducibly prepared by nanocasting mixtures of fluorinated nonionic surfactants and micelles of two hydrocarbon block copolymers. It is the special feature of this fluorocarbon/hydrocarbon template mixture that they form not mixed micelles but individual micelles instead. By careful analysis of the pore architectures by gas sorption measurements and transmission electron microscopy in dependence on the relative template concentration, two different situations could be identified: (a) mesoscopically demixed samples and (b) mixed micellar phases where the two different micelles are packed in some type of organized alloy phase. Besides identification of such mixed phases for the first time for fluorocarbon/hydrocarbon mixtures, the resulting porous systems with controlled bimodal pore size distribution might be interesting from a materials perspective.