Abstract
So far, the near-surface ordering of microemulsions was focused on lamellar ordering while the bulk microemulsion was bicontinuous. In a series of different non-ionic surfactants the near-surface ordering of microemulsions at a hydrophilic silicon surface was studied using grazing incidence small angle neutron scattering. For the surfactant C8E3, most likely a gyroid structure was found at the solid–liquid interface, while the more efficient surfactants find lamellar ordering up to lamellar capillary condensation. The ranges for near-surface ordering are deeper than the bulk correlation lengths. These findings point towards theories that use directional order parameters that would lead to deeper near-surface ordering than simple theories with a single scalar order parameter would predict. Rheology experiments display high viscosities at very low shear rates and, therefore, support the existence of a directional order parameter.
Highlights
In theories of liquid crystals [1,2,3,4] and of granular media [5,6,7,8], a directive field is often needed to describe the various liquid crystalline ordered phases
For diblock copolymers [9] (Grain boundaries of diblock copolymers have been analyzed experimentally [10, 11]) and microemulsions [12,13,14], a wide range of phenomena can be explained on the basis of a single order parameter describing the local concentration of one species versus the other, i.e. monomer A vs. B or water vs. oil
The local bulk order extends with in a correlation volume of (2ξ)3 ≈ (200 Å)3 of approx. 2 × 2 × 2 domains, which is connected to a second order parameter
Summary
In theories of liquid crystals [1,2,3,4] and of granular media [5,6,7,8], a directive field is often needed to describe the various liquid crystalline ordered phases. For diblock copolymers [9] (Grain boundaries of diblock copolymers have been analyzed experimentally [10, 11]) and microemulsions [12,13,14], a wide range of phenomena can be explained on the basis of a single order parameter describing the local concentration of one species versus the other, i.e. monomer A vs B or water vs oil. This is a result of a high degree of symmetry. A high degree of symmetry is assumed, and so only three parameters remain essential,
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