Near-Surface and Bulk Behavior of Bicontinuous Microemulsions under High-Pressure Conditions

Abstract

The effect of hydrostatic pressure on the structure of a bicontinuous microemulsion in the presence of a solid interface has been studied by X-ray reflectometry and compared to the bulk behavior determined by small-angle X-ray scattering. Surface-induced lamellar ordering is observed close to the hydrophilic interface, which persists upon compression. The lamellar domains are compressed, but the correlation length of lamellar order does not change with pressure. SAXS measurements on the bulk microemulsion revealed an increased order upon pressurization. Although pressure can cause the formation of highly ordered lamellar phases from ordered bicontinuous cubic phases, such a scenario is not observed for the disordered analogue studied here. High pressure increases the stiffness of the interfacial surfactant layer, but this is not sufficient to overcome the loss in conformational entropy that would result from a transition to an ordered lamellar phase. Possible technological and biological implications of our results are briefly discussed.

Properties of Hydrogen-Bonded Liquids at Interfaces

“…This supports reports suggesting an attractive interaction between the AOT layer and the embedded PEG chain [88]. Moreover, Berghaus et al [159] studied the effect of hydrostatic pressure on the structure of a bicontinuous microemulsion in the presence of a confining solid interface by X-ray reflectometry, and compared the results to the bulk behavior determined by SAXS. High pressure has been applied to be able to fine-tune molecular shapes (i.e.…”

“…Although pressure can cause the formation of highly ordered lamellar phases from ordered bicontinuous cubic phases in the bulk, such a scenario is not observed for the disordered analog studied here. High pressure increases the stiffness of the interfacial surfactant layer, but this is not sufficient to overcome the loss in conformational entropy that would result from a transition to an ordered lamellar phase [159].…”

Confined microemulsions: pore diameter induced change of the phase behavior

“…The interaction of a nonionic surfactant microemulsion with a at surface has been studied in many works, [33][34][35][36] including simulations, 37 investigations under shear stress, 38 and at highpressure conditions. 39 In the case of bicontinuous microemulsions, the main difference between the interface and the bulk structure is the planar geometry near an interface, which becomes sponge-like when the distance to the interface increases. Since, in many relevant applications, the surface is rough or even porous, we must also consider the inuence of curved interfaces.…”

Generalized skew-symmetric interfacial probability distribution in reflectivity and small-angle scattering analysis

“…In doing so, it generates an effective ðzÞ profile of a zeroth order of continuity that does not necessarily saturate at the nominal density value in the middle of each layer. This model has found very wide applications when modeling layered structures such as simple liquid interfaces (Lehmkü hler et al, 2009), organic monolayers (Schwendel et al, 2003), inorganic multilayers (Dö ring et al, 2009;Neuhold et al, 2011), microemulsion films (Berghaus et al, 2016), polymer films (Wieland et al, 2011), nanoparticle superlattices (Zhang et al, 2017), lipid and bio-membranes (Tiemeyer et al, 2010;Phan & Shin, 2015;Nowak et al, 2016), and nanoparticle-biomembrane composite films (Wang et al, 2016;Phan et al, 2017). While all PDFs used in these applications are symmetric functions, asymmetric interfacial profiles are required at times, such as liquid/vapor interfaces in critical adsorption phenomena (Zhao et al, 1995), chemicalgradient-induced interfaces (also known as chemical roughness) (Bé ziel et al, 2008;de Silva et al, 2012), and thin or incomplete layers grown, deposited or adsorbed on impermeable hard surfaces (Yim et al, 2000;Gutberlet et al, 2004).…”