Exploring Hidden Local Ordering in Microemulsions with a Weak Directive Second Order Parameter

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 C 8 E 3 , 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.

Effect of equilibration time on the structural gradient in the vertical direction for bicontinuous microemulsions in Winsor-III and -IV systems

“…One-phase bicontinuous (W IV ) systems, when in contact with polar surfaces such as glass, silicon, and clay, undergo ordering near the solid-BME interface (on a sub-microscale), approaching lamellar structure, especially in the presence of shear, due to the dampening of fluctuations. [24][25][26][27][28] Less efficient surfactants produce bicontinuous phases with gyroid structure near the solid surface. 27 A second objective for the current study is to observe whether similar changes occurred for the bicontinuous phase isolated from the SDS/pentanol W III system and placed in a quartz cell, near the bottom, quartz-BME interface.…”

“…[24][25][26][27][28] Less efficient surfactants produce bicontinuous phases with gyroid structure near the solid surface. 27 A second objective for the current study is to observe whether similar changes occurred for the bicontinuous phase isolated from the SDS/pentanol W III system and placed in a quartz cell, near the bottom, quartz-BME interface. Such heterogeneity in structure in the vertical direction can affect the properties of nanomaterials formed using BME templates and the diffusive mass transfer rate across interfaces and within the BME phase, which can affect the performance of W III systems for separations and other applications; for example, the performance and properties of nanomaterials formed using bicontinuous templates can be affected.…”