Confinement effects on water structure in membrane lyotropic phases

Abstract

The change of the water structure in aqueous solutions of the tri-ethyleneglycol mono n-decyl ether (C(10)E(3)) was studied by micro Raman scattering. The results obtained on the O-H stretching band show that the behavior of the hydrogen bonding (H-bonds) water network can be used as a probe to follow the lamellar (L(α)) to sponge (L(3)) phase transition. In the lamellar phase, the stack of the surfactant molecules aggregated into a two-dimensional structure (membrane) acts as a soft confinement system for the H-bond water network of which the regular tetrahedral structure is perturbed. The change of the planar organization of the membranes to a highly disordered and infinite array of bilayers in the sponge phase amplifies the surface of contact between amphiphilic surfactant and water molecules which drives a strong disruption of the regular tetrahedral H-bonding water network.

Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

“…In geochemistry, it determines the influence of hydrous silica gel coatings on the long-term weathering rates of silicate glasses and minerals 8,9 , these rates being important unknowns in studies of soil formation 10 and global carbon cycling 11 and in predicting the fate of CO 2 12,13 and high-level radioactive waste in geological repositories 14,15 . From a theoretical perspective, the question is compelling because hydrophilic silica nanopores can be readily fabricated with well-controlled structural features (the materials listed above have an amorphous SiO 2 matrix, silanol surface functional groups, cylindrical pores, and pore diameters that can be varied from about 1 nm to more than 100 nm [1][2][3][4]6 ) for probing the new physics of water that occur due to finite-size effects, a frontier research area with broad implications in catalysis 16 , biology 17,18 , nanofluidics 19,10 , membrane science 2`, and the geosciences [21][22][23] . Theoretical models of transport and chemistry in water-filled nanopores routinely rely on the simplifying approximation that water properties are not modified by confinement 19 , but this approximation is expected to fail in nanoporous media where pore size approaches the diameter of a water molecule 20 .…”

“…Theoretical models of transport and chemistry in water-filled nanopores routinely rely on the simplifying approximation that water properties are not modified by confinement 19 , but this approximation is expected to fail in nanoporous media where pore size approaches the diameter of a water molecule 20 . Studies of water in hydrophilic nanopores carried out with a range of techniques (thermoporometry 1,24 , capillary imbibition 25 , surface force apparatus 22,26 , infrared and Raman spectroscopy 4,17,18,21,27 , NMR spectroscopy 28 , X-ray and neutron diffraction 6,[29][30][31] , quasi-elastic neutron 4 scattering 2,32 , molecular dynamics simulations 26,[33][34][35][36] ) show that this failure occurs in pores narrower than ~20 nm and can be classified into two regimes. The first regime occurs in pores that are about 2 to 20 nm wide and results from "surface water" [water with structure and dynamics distinct from those of bulk liquid water, found within up to three statistical monolayers (~0.9 nm) from hydrophilic surfaces 34,35 ] constituting a nonnegligible part of the pore water 25,27,34 .…”

Confinement of a Nonionic Surfactant Membrane Within a Montmorillonite as a New Way to Prepare Organoclay Materials

“…, above the critical micellar concentration (CMC) experimentally determined at 7.5 × 10 -4 mol L -1 , displaying a lamellar phase as revealed by both optical and diffraction data 15 . The solution was homogenized at 500 rpm using a magnetic stir bar at room temperature for several days in order to reach an equilibrium state, which was properly checked by phase contrast microscopy measurements as it was explained in more details elsewhere 15 .…”

“…The solution was homogenized at 500 rpm using a magnetic stir bar at room temperature for several days in order to reach an equilibrium state, which was properly checked by phase contrast microscopy measurements as it was explained in more details elsewhere 15 . A clay suspension solution was then poured into the surfactant solution.…”

“…Nonionic surfactants containing n-C n H 2n+1 (OCH 2 CH 2 ) m OH (abbreviated as C n E m ) can self-assemble to form bicontinuous structures made of amphiphilic bilayers 14 . In particular, the C 10 E 3 (tri-ethylene glycol mono n-decyl ether) and water system forms internal structures organized by surfactant bilayers such as the lamellar (L α ) characterized by a stack of surfactant molecules aggregated into a two dimensional structure [12][13][14][15] . interlayer space of a Na-montmorillonite, resulting in the state of the lyotropic liquid crystal in a lamellar phase points out the possible link between bulk surfactants molecular structures and the way they pack in the internal structure of the clay mineral [12][13][14] .…”