Phase Coexistence in a Dynamic Phase Diagram

Abstract

Metastability and phase coexistence are important concepts in colloidal science. Typically, the phase diagram of colloidal systems is considered at the equilibrium without the presence of an external field. However, several studies have reported phase transition under mechanical deformation. The reason behind phase coexistence under shear flow is not fully understood. Here, multilamellar vesicle (MLV)-to-sponge (L3 ) and MLV-to-Lα transitions upon increasing temperature are detected using flow small-angle neutron scattering techniques. Coexistence of Lα and MLV phases at 40 °C under shear flow is detected by using flow NMR spectroscopy. The unusual rheological behavior observed by studying the lamellar phase of a non-ionic surfactant is explained using (2) H NMR and diffusion flow NMR spectroscopy with the coexistence of planar lamellar-multilamellar vesicles. Moreover, a dynamic phase diagram over a wide range of temperatures is proposed.

Dynamic phase diagram of soft nanocolloids

“…by changing γ int . 29,30 There a temperature dependent transition from planar lamellae to multilamellar vesicles (MLVs) was observed. 10,25 Later, Lonetti et al extended this approach to the study of binary mixtures of ultra-soft colloids and linear polymers.…”

Rheo‐NMR in food science—Recent opportunities

“…A particular well‐studied example are nonionic surfactant systems of the C n E m type (“n” is the unit number of the chain group and “m” the unit number of the head group). It exhibits a rich phase behavior both in the static and the dynamic range . For these systems, a continuous application of shear can induce the formation of MLVs from an originally aligned lamellar phase, first observed in a sodium dodecyl sulfate/pentanol/water/decane system under steady‐state shear .…”

“…These MLVs often consist of a hierarchy of many closed layers and are thus often referred to as “onions.” However, the formation of MLVs under shear is far from being fully understood to date. Consequently, many experimental studies have recently investigated C n E m systems with different “n” and “m” values and under various thermal conditions giving insight on finer details on the MLV formation process. However, only a very few studies have considered different kinds of shear deformations, as for example, flow reversal or oscillatory shear in the case of an sodium bis(2‐ethyl‐1‐hexyl)sulfosuccinate (AOT) brine system.…”

Lamellar-to-MLV transformation in SDS/octanol/brine examined by microfluidic-SANS and polarised microscopy

“…4,28,32 Predominant analytical techniques include rheology, 33,34 scattering, 21,22,34,35 optical microscopy 35,36 and 2 H NMR. 4,[37][38][39][40] In this work, we consider tubular flow, in continuous and oscillatory modes, and both wall shear and extensional (viz. contraction-expansion) flows, motivated by their industrial relevance in complex fluid processing (e.g., through nozzles and continuous flow reactors) and academic importance.…”