2 research outputs found
Self-Assembly of Condensable “Bola-Amphiphiles” in Water/Tetraethoxysilane Mixtures for the Elaboration of Mesostructured Hybrid Materials
The self-assembly of condensable
amphiphile molecules in water
is an attractive approach for the synthesis of mesostructured hybrid
materials. In this article, we focus on aminoundecyltriethoxysilane
(AUT), a condensable “bola-amphiphile”, i.e., an amphiphilic
molecule possessing two polar heads on both sides of an aliphatic
chain. In the present case, one side is a condensable triethoxysilane,
and the other side is an amino group. We report on the self-assembly
of AUT in mixtures of water and tetraethoxysilane (TEOS). In situ
small-angle X-ray scattering (SAXS) measurements allowed us to follow
the evolution of the structure from the liquid state up to the solid
material formed upon catalytic polycondensation. Depending on the
medium composition, hexagonal or lamellar structures can be observed
in the final material. These observations allowed us to propose a
model for the self-assembly of AUT in water/TEOS mixtures that we
were able to validate by simulations of the SAXS profiles. By taking
advantage of the modularity of such a system, it proves possible to
prepare in a simple way various structured hybrid materials possessing
a high number of available organic functions without using sacrificial
surfactant molecules
Synergism by Coassembly at the Origin of Ion Selectivity in Liquid–Liquid Extraction
In liquid–liquid extraction, synergism emerges
when for
a defined formulation of the solvent phase, there is an increase of
distribution coefficients for some cations in a mixture. To characterize
the synergistic mechanisms, we determine the free energy of mixed
coassembly in aggregates. Aggregation in any point of a phase diagram
can be followed not only structurally by SANS, SAXS, and SLS, but
also thermodynamically by determining the concentration of monomers
coexisting with reverse aggregates. Using the industrially used couple
HDEHP/TOPO forming mixed reverse aggregates, and the representative
couple U/Fe, we show that there is no peculiarity in the aggregates
microstructure at the maximum of synergism. Nevertheless, the free
energy of aggregation necessary to form mixed aggregates containing
extracted ions in their polar core is comparable to the transfer free
energy difference between target and nontarget ions, as deduced from
the synergistic selectivity peak