Bending elastic properties of a block copolymer-rich lamellar phase doped by a surfactant: a neutron spin-echo study

Abstract

The influence of the short alkyl-chain ionic surfactant OTAB on the dynamic behavior of an inverse block copolymer-rich lamellar phase was investigated by neutron spin-echo spectroscopy (NSE). The observed intermediate scattering function can be described by a sum of two contributions. For high scattering vectors the model of Zilman-Granek plus a slow diffusional mode can be used to describe the experimental data and the bending elastic modulus k for a polymer-rich membrane is calculated. At low scattering vectors the relaxation curves are strongly influenced by de Gennes narrowing arising from the structure factor of the L a phase. Hence, the computed relaxation rates in this q-range are inversely proportional to the static structure factor. The present study demonstrates the necessity to directly investigate the dynamic behavior of lamellar phases and that an analysis of the width of the Bragg peaks can be insufficient to derive information about the single membrane elasticity, especially when both k and B depend on the composition of the membrane.

Influence of Li-Salt on the Mesophases of Pluronic Block Copolymers in Ionic Liquid

“…The low value of η indicates a rather rigid bilayer structure. 46 Analysis of Phase Transitions by DSC Measurements. While the SAXS data demonstrate the existence and structural parameters of ordered structures in the ternary mixtures, they do not provide evidence as to whether additional bulk phases (i.e., of pure IL) are coexisting with the structures identified in Figure 1.…”

“…However, even though the variation of the lamellar spacing is not immense, it can be said that a small decrease can be observed with increasing IL content. The low value of η indicates a rather rigid bilayer structure …”

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

“…In systems where B̅ and κ change in an antiproportional way, no modification of η might occur despite of changes in κ. 81 The modified Caillétheory can also be applied to a concentrated phase of MLVs because on the local scale analyzed by SAXS, it cannot be distinguished from a planar lamellar phase.…”

“…The Caillé parameter describing the rigidity of the bilayer consists of the Boltzmann constant k B , the absolute temperature T , the interlamellar spacing d , the bulk modulus of compression B̅ related to the membrane–membrane interactions, and the bilayer bending rigidity κ. η gives information about the elastic properties, but elastic constants cannot be extracted easily from the value of η. In systems where B̅ and κ change in an antiproportional way, no modification of η might occur despite of changes in κ . The modified Caillé theory can also be applied to a concentrated phase of MLVs because on the local scale analyzed by SAXS, it cannot be distinguished from a planar lamellar phase.…”

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

“…5,19 Experimentally, the formation of MLVs has been described by the emergence of intermediate multilamellar cylinder (MLC) phase [20][21][22] in continuous shear flow or a direct emergence of MLVs with oscillatory flows. 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.…”