Structure of pluronic based lamellar phases and their rheological properties

Großkopf S. Structure of pluronic based lamellar phases and their rheological properties. Bielefeld: Universität Bielefeld; 2019

Dynamics of proteins confined in non-ionic bicontinuous microemulsions: a FCS study.

Wrede O, Großkopf S, Seidel T, Hellweg T. Dynamics of proteins confined in non-ionic bicontinuous microemulsions: a FCS study. Physical chemistry chemical physics : PCCP. 2019;21(12):6725-6731.In our present work we present an approach which allows one to confine proteins in structurally nearly identical bicontinuous microemulsions with systematically decreasing water domain size. It is shown that sub-diffusive behaviour occurs already at water domain sizes below 13 nm. However, above 13 nm normal diffusion is seen. Moreover, we compare protein diffusion in microemulsions to the transport of a much smaller fluorescent dye

Pluronic-based lamellar phases: influence of polymer architecture on bilayer bending elasticity

Großkopf S, Fouquet P, Wiehemeier L, Hellweg T. Pluronic-based lamellar phases: influence of polymer architecture on bilayer bending elasticity. Molecular Physics. 2021: e1893400.In this study, we investigate the influence of the block copolymer architecture on the bending elasticity of polymer-rich lamellar phases. In detail, we study the polymer-rich system water/o-xylene/Pluronic triblock copolymer/C8TAB and change the polymer while keeping the mass ratios constant. We use neutron spin echo measurements (NSE) to determine κ. With the measurements we determine the relaxation rate Γqz,ZG of the bilayer bending mode and subsequently calculate the bilayer bending modulus κ using the Zilman-Granek approach [Zilman et al., Phys. Rev. Lett. 77, 4788–4791 (1996)]. Moreover, we have investigated the lamellar phases via small-angle X-ray scattering (SAXS) and have analysed the data with the modified Caillé theory to obtain the Caillé parameter η. Based on κ the bulk compression modulus B can be calculated. Increasing values of κ are found with increasing EO and PO block size in the range of 3.8 to 13.4 kBT. The computed values of B are in the range of 103 to 105 Pa

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

Brinkkotter M, Geisler R, Großkopf S, Hellweg T, Schonhoff M. Influence of Li-Salt on the Mesophases of Pluronic Block Copolymers in Ionic Liquid. The journal of physical chemistry. B. 2020;124(42):9464–9474.We study the complex mixture of a polyethylene oxide-b-polypropylene oxide-b-polyethylene oxide triblock copolymer (Pluronic F127) with ionic liquid (IL) and Li-salt, which is potentially interesting as an electrolyte system with decoupled mechanical and ion-transport properties. Small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) are employed to scrutinize the phase structures and elucidate the ternary phase diagram. These data are combined with the ion diffusivities obtained by pulsed field gradient (PFG) nuclear magnetic resonance (NMR). Analyzing the partial ternary phase diagram of F127/LiTFSI/Pyr14TFSI, hexagonal, lamellar, and micellar mesophases are identified, including two-phase coexistence regions. While the PPO block is immiscible with the liquid, and forms the backbone of the mesostructured aggregates, the PEO blocks are not well miscible with the IL. Poorly solvated, the latter may still crystallize. At a higher IL content, PEO is further solvated, but a major solvation effect occurs due to addition of Li-salt. Li ions promote solubilization of the PEO chains in the IL, since they coordinate to the PEO chains. This was identified as the mechanism of a transition of the mesostructures, with increasing Li-salt content changing from a hexagonal to a lamellar and further to a micellar phase. In summary, both, the amount of IL and its compatibility with the PEO block, the latter being controlled by the Li-salt amount, influence the compositions of the formed mesophases and the ion diffusion in their liquid regions

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

Großkopf S, Tiersch B, Koetz J, Mix A, Hellweg T. Shear-Induced Transformation of Polymer-Rich Lamellar Phases to Micron-Sized Vesicles. Langmuir. 2019;35(8):3048-3057.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

UV cross-linked smart microgel membranes as free-standing diffusion barriers and nanoparticle bearing catalytic films

Dirksen M, Brändel T, Großkopf S, et al. UV cross-linked smart microgel membranes as free-standing diffusion barriers and nanoparticle bearing catalytic films. RSC Advances. 2021;11(36):22014-22024