Shear-Induced Transformation of Polymer-Rich Lamellar Phases to Micron-Sized Vesicles

Abstract

In the present work, we study the shear-induced transformation of polymer-rich lamellar phases into vesicles. The evolution of vesicle size is studied by different scattering techniques, rheology, and microscopy methods. The lamellar phase found in the system D2O/o-xylene/Pluronic PE9400/C8TAB can be fully transformed to multilamellar vesicles (MLVs) by applying shear. The size of the MLVs is proportional to the inverse square root of the shear rate. Hence, the polymer-based quaternary system behaves similar to lamellar phases based on small surfactant molecules. Additionally, we found a growth effect leading to a size increase of the vesicles after shearing was stopped.

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

“…Similarly, cross-polarised optical microscopy indicates presence of disordered lamellar sheets before shear and an ordered isotropic phase indicated by the change in optical texture. 35,36 This is corroborated by fast Fourier transform (FFT) analysis after shearing, displaying the characteristic cloverleaf pattern indicative of formation of spherical objects. 4,[34][35][36] The size of the vesicles was estimated to be 3 mm.…”

“…35,36 This is corroborated by fast Fourier transform (FFT) analysis after shearing, displaying the characteristic cloverleaf pattern indicative of formation of spherical objects. 4,[34][35][36] The size of the vesicles was estimated to be 3 mm. Microscopy images recorded over the duration of the experiment indicate that the onset of cloverleaf pattern development is around 20 min into the experiment (Fig.…”

“…5b) taken after the constriction across the middle of the channel show increased long range ordering with increasing flow rates and oscillatory volumes with the emergence of cloverleaf pattern indicative of spherical objects. 4,[34][35][36] This is further quantified by normalised intensity analysis (obtained by dividing each curve by its baseline intensity value) of FFTs as a function of azimuthal angle (Fig. 5d), which shows an increase in anisotropy over repeat oscillatory shear cycles.…”

“…The timescales for MLV formations observed with microscopy were approximately the same as timescales observed by rheo-SALS in literature. 35…”

“…4 Numerous experimental reports have considered the effect of shear field, stress and rate, on various model systems (nonionic, 4,21,23,24 cationic 25,26 and anionic 27,28 ), the effect of added co-surfactants 3,29 and salt, 30,31 and the effect of oscillatory shear flows. 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.…”