Characterizing Size and Porosity of Hollow Nanoparticles: SAXS, SANS, TEM, DLS, and Adsorption Isotherms Compared

A combination of experimental methods, including transmission and grazing incidence small-angle X-ray scattering (SAXS and GISAXS), small-angle neutron scattering (SANS), transmission electron microscopy (TEM), dynamic light scattering (DLS), and N₂ adsorption–desorption isotherms, was used to characterize SiO₂/TiO₂ hollow nanoparticles (HNPs) of sizes between 25 and 100 nm. In the analysis of SAXS, SANS, and GISAXS data, the decoupling approximation and the Percus–Yevick structure factor approximation were used. Brunauer–Emmett–Teller, <i>t</i>-plot, and a spherical pore model based on Kelvin equation were applied in the treatment of N₂ isotherms. Extracted parameters from the scattering and TEM methods are the average outer and inner diameters and polydispersity. Good agreement was achieved between different methods for these extracted parameters. Merits, advantages, and disadvantages of the different methods are discussed. Furthermore, the combination of these methods provided us with information on the porosity of the shells of HNPs and the size of intrawall pores, which are critical to the applications of HNPs as drug delivery vehicles and catalyst supports

Induction of Thermotropic Bicontinuous Cubic Phases in Liquid-Crystalline Ammonium and Phosphonium Salts

Two series of wedge-shaped onium salts, one ammonium and the other phosphonium, having 3,4,5<b>-</b>tris­(alkyloxy)­benzyl moieties, exhibit thermotropic bicontinuous “gyroid” cubic (Cub_bi) and hexagonal columnar liquid-crystalline (LC) phases by nanosegregation between ionophilic and ionophobic parts. The alkyl chain lengths on the cationic moieties, anion species, and alkyl chain lengths on the benzyl moieties have crucial effects on their thermotropic phase behavior. For example, triethyl-[3,4,5-tris­(dodecyloxy)­benzyl]­ammonium hexafluorophosphate forms the thermotropic <i>Ia</i>3̅<i>d</i> Cub_bi LC phase, whereas an analogous compound with trifluoromethanesulfonate anion shows no LC properties. Synchrotron small-angle diffraction intensities from the <i>Ia</i>3̅<i>d</i> Cub_bi LC materials provide electron density maps in the bulk state. The resulting maps show convincingly that the <i>Ia</i>3̅<i>d</i> Cub_bi structure is composed of three-dimensionally interconnected ion nanochannel networks surrounded by aliphatic domains. A novel differential mapping technique has been applied successfully. The map of triethyl-[3,4,5-tris­(decyloxy)­benzyl]­ammonium tetrafluoroborate has been subtracted from that of the analogous ammonium salt with hexafluorophosphate anion in the <i>Ia</i>3̅<i>d</i> Cub_bi phases. The differential map shows that the counteranions are located in the core of the three-dimensionally interconnected nanochannel networks. Changing from trimethyl- via triethyl- to tripropylammonium cation changes the phase from columnar to Cub_bi to no mesophase, respectively. This sensitivity to the widened shape for the narrow end of the molecule is explained successfully by the previously proposed semiquantitative geometric model based on the radial distribution of volume in wedge-shaped molecules. The LC onium salts dissolve lithium tetrafluoroborate without losing the <i>Ia</i>3̅<i>d</i> Cub_bi LC phase. The Cub_bi LC materials exhibit efficient ion-transporting behavior as a result of their 3D interconnected ion nanochannel networks. The <i>Ia</i>3̅<i>d</i> Cub_bi LC material formed by triethyl-[3,4,5-tris­(decyloxy)­benzyl]­phosphonium tetrafluoroborate shows ionic conductivities higher than the analogous <i>Ia</i>3̅<i>d</i> Cub_bi material based on ammonium salts. The present study indicates great potential of Cub_bi LC nanostructures consisting of ionic molecules for development of transportation nanochannel materials