The charging of arachidic
acid Langmuir monolayers as a function
of subphase pH and monovalent ion concentration below 100 mM was investigated
using vibrational sum frequency spectroscopy. Molecular information
was obtained by targeting the vibrational modes of the carboxylic
acid headgroups, alkyl chains, and water molecules in the immediate
surface and diffuse double layers. The surface charge in the monolayer
was experimentally determined by monitoring the hydrated carboxylate
stretching modes. The charging behavior was found to be in excellent
agreement with that predicted by Gouy–Chapman theory using
a thermodynamic pK
a of 5.1 ± 0.2.
This resulted in an apparent pK
a of ∼10.8
when the only ions present in solution were those associated with
adjusting the pH. Water molecules with a preferred orientation in
the immediate surface region were found to primarily interact with
the uncharged carboxylic acid moiety, decreasing in number as the
monolayer further deprotonated. Contributions from water molecules
in the diffuse double layer, partly aligned by the exponentially decaying
surface electric field, closely followed the predictions of a recently
proposed theoretical framework that accounts for interference and
screening effects. Finally, the charging of the monolayer was experimentally
found to be independent of the identity of either the monovalent cation
(i.e., Li+, Na+, Rb+) or anion (i.e.,
F–, Cl–, I–)
at low salt concentrations.
Control over morphology and internal mesostructure of surfactant templated silicas remains a challenge, especially when considering scaling laboratory syntheses up to industrial volumes. Here we report a method combining emulsification with the evaporation-induced self-assembly (EISA) method for preparing spherical, mesoporous silica particles. This emulsion and solvent evaporation (ESE) method has several potential advantages over classic precipitation routes: it is easily scaled while providing superior control over stoichiometric homogeneity of templating surfactants and inorganic precursors, and particle sizes and distributions are determined by principles developed for manipulating droplet sizes within water-in-oil emulsions. To demonstrate the method, triblock copolymer P104 is used as a templating amphiphile, generating unusually well-ordered 2D hexagonal (P6mm) mesoporous silica, while particle sizes and morphologies were controlled by varying the type of emulsifier and the method for emulsification.
Three dimensional silica photonic crystals with the gyroid minimal surface structure have been synthesized. The butterfly Callophrys rubi was used as a biotemplate. This material represents a significant addition to the small family of synthetic bicontinuous photonic crystals.
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