Spontaneous Formation of Vesicles of Diblock Copolymer EO₆BO₁₁ in Water:  A SANS Study

Abstract

Small angle neutron scattering (SANS) is used to study the structures formed in water by a diblock copolymer EO6BO11 (having 6 ethylene oxide, EO, and 11 butylene oxide, BO, units). The data show that polymer solutions over a broad concentration range (0.05-20 wt %) contain vesicular structures at room temperature. Interestingly, these vesicles could be formed without any external energy input, such as extrusion, which is commonly required for the formation of other block copolymer or lipid vesicles. The EO6BO11 vesicles are predominantly unilamellar at low polymer concentrations, whereas at higher polymer concentrations or temperatures there is a coexisting population of unilamellar and multilamellar vesicles. At a critical concentration and temperature, the vesicular structures fuse into lyotropic arrays of planar lamellar sheets. The findings from this study are in broad agreement with the work of Harris et al. (Langmuir, 2002, 18, 5337), who used electron microscopy to identify the vesicle phase in the same system.

Microfluidic light scattering as a tool to study the structure of aqueous polymer solutions

“…This function estimated a mean size of ∼9 µm, which is an observed three orders of magnitude higher than their respective membrane thicknesses. We also conclude, using information gathered from SANS studies [29] that the polymer EO 6 BO 11 can exhibit both unilamellar and giant multilamellar vesicles when dissolved in water at low concentrations. The addition of a third component, a 0.1 M KBr (aq) solution, resulted in the formation of vesicles at a lower observed polymer composition.…”

“…The vesicle size observed by SALS and subsequent inverse Fourier transformation (IFT) is approximately three orders of magnitude greater than the vesicle membrane thickness (which has been observed using SANS techniques [29]): on the order of microns compared to nanometers. SANS studies suggested the existence of smaller unilamellar vesicles.…”

SANS from Polymers—Review of the Recent Literature

“…They are cataloged into broad categories that include polymer solutions, 2-9 copolymers, [10][11][12][13][14][15][16][17][18][19] polymer blends, 20-23 branched or grafted polymers, 24-32 polymer gels, [33][34][35][36][37][38][39][40] polymer networks, [41][42][43][44][45][46][47][48] polymer micelles, 49-63 polymeric nanomaterials, [64][65][66][67][68][69][70] and polymer membranes. [71][72][73][74][75][76][77] Of these papers, about half are briefly summarized in order to represent the breadth of ongoing research.…”

Stability of Uni‐ and Multillamellar Spherical Vesicles

“…[31] Previous efforts, to the best of our knowledge, are limited to studies of vesicles with discrete and very few numbers of lamellae (e.g., two bilayers). [40] More effort has been focused on understanding the transition between uni-(L 4 phase) and multilamellar (onion or L a phase) vesicles by varying key experimental parameters, including amphiphile concentration, [41,42] shear fields, [5,43,44] bending rigidity, polarizability of the aqueous medium (such as changing the Hamakar constant), ionic concentration, and/or temperature. [45,46] Herein, we report a study on the stability of monocomponent lipid spherical vesicles in uni-and multilamellar configurations, which may also coexist.…”