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Two poly(ethylenepropylene)–poly(ethylethylene) (PEP-PEE) diblock copolymer melts, containing 25% and 83% by volume PEP, were investigated using small-angle neutron scattering (SANS) and rheological measurements. The SANS measurements were performed with the aid of an in situ shearing device operated directly in the neutron beam. Each sample was observed to possess three equilibrium phases: two ordered phases at low temperature and a disordered phase at elevated temperatures. The low and high temperature ordered phases have been evaluated to be hexagonally packed (hex) cylinders and body centered cubic (bcc) spheres, respectively. Application of a large amplitude dynamic shear deformation to the hex phase leads to well-aligned cylinders, with a specific crystallographic orientation relative to the shear plane. Upon heating through the cylinder-to-sphere transition, the bcc phase grows epitaxially, with the [111] direction coincident with the original cylinder axis, leading to a well-defined twinned microstructure. SANS measurements performed while the bcc specimens were dynamically sheared revealed a rich compliment of microstructural rearrangements, with the twinned state appearing at low and high shear rates, and two-dimensional disordering at intermediate shear rates.

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Structural studies on aqueous solutions of PEO-PPO-PEO block copolymers show three phases as the temperature is varied. At low 7\ the tri-block units are dissolved Gaussian chains. As T is increased still more unimers aggregate in micelles, until a volume fraction of 0.52 is reached. The micelles then crystallize in a body-centered-cubic lattice. Upon the application of a small shear, the high-jT polycrystalline phase abruptly transforms into a single crystal, characterized by only quasi-long-range order in bond length, but true long-range correlations in the bond angle.

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Phospholipid bilayers host and support the function of membrane proteins and may be stabilized in disk-like nano structures allowing for unprecedented solution studies of assembly, structure and function of membrane proteins. Based on small-angle neutron scattering in combination with variable temperature studies of synchrotron small-angle x-ray scattering on nanodiscs1 in solution we show that the fundamental nanodisc unit, consisting of a lipid bilayer surrounded by amphiphilic scaffold proteins, posses intrinsically an elliptical shape. The temperature dependence of the curvature of the nanodiscs prepared with two different phospholipid types (DLPC and POPC) shows that it is the scaffold protein that determines the overall elliptical shape and that the nanodiscs become more circular with increasing temperature. Our data also show that the hydrophobic bilayer thickness is to a large extent dictated by the scaffolding protein and adjusted to minimize the hydrophobic mismatch between protein and phospholipid. Our conclusions result from a new comprehensive and molecular based model of the nanodisc structure and the use of this to analyze the experimental scattering profile from nanodiscs. The model paves the way for future detailed structural studies of functional membrane proteins encapsulated in nanodiscs.

We have studied the aggregation behavior of polyethylene−poly(ethylenepropylene) (PE−PEP) diblock copolymers dissolved in decane. For this purpose PE−PEP diblock copolymers of various molecular weights, compositions, and degrees of deuteration were synthesized via an anionic route. The structure and morphology of the aggregates was studied by small angle neutron scattering varying both the contrast as well as the polymer labeling. We found a hierarchy of structures:  The PE component crystallizes in lamellar sheets (thickness 40−80 Å) surrounded on both sides by a PEP brush which exhibits a close to parabolic density profile. Different aggregates form macroaggregates of needlelike shape with the PE lamellar planes in the long direction. This macroaggregation is well described by a paracrystalline structure factor. The structural parameters depending on composition and molecular weights can be well understood in terms of a free energy of formation based on a scaling model. A quantitative evaluation of the different contributions to the free energy reveals an important role of defect structures resulting from the ethylene side branches in the polyethylene component. Finally, we show in a semiquantitative approach that the van der Waals energy between the brushes is large enough to facilitate macroaggregation.