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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.

We have measured both the static and dynamic structure factors of a single dendrimer with small-angle x-ray scattering ͑SAXS͒ and neutron spin-echo spectroscopy under good solvent conditions with the aim of finding a consistent correlation between the structural properties of dendrimers and their dynamic behavior. The samples under investigation were star-burst polyamidoamine dendrimers with generations gϭ0 to 8 in dilute methanol solutions. A model independent approach employing inverse Fourier transformation and square root deconvolution methods has been used to analyze the SAXS data to obtain the pair distance distribution function p(r) and the radial excess electron density profile ⌬ (r). In addition, we formulated a model that takes both the colloidal ͑globular, compact shape with form polydispersity or fuzzy surface͒ as well as the loose, polymeric ͑self-avoiding random walk͒ character of dendrimers into account. With this model we were able to describe the spectra of all dendrimer generations consistently. Parameters discussed as a function of the dendrimer generation are, among others, the correlation length of the density fluctuations ͑blob radius͒ , the radius of gyration R g , the sphere radius R s , the form polydispersity s or analogously, the width of the fuzzy surface region 2 f . Both the model-independent approach and the model fits reveal that at least down to the third generation the dendrimers exhibit a rather compact, globular shape. These findings are in agreement with the dynamic results obtained by NSE spectroscopy which probes length scales both larger and much smaller than the dimension of a single dendrimer. The method reveals that the dynamics throughout is dominated by the center-of-mass diffusion-the internal dynamics is suppressed. The diffusion coefficients obtained are close to the values calculated from the Stokes-Einstein relation using the sphere radius R s determined from the SAXS spectra. Dynamically, the dendrimers behave like ''hard'', solid spheres.

We present neutron spin echo experiments that address the much debated topic of dynamic phenomena in polymer melts that are induced by interacting with a confining surface. We find an anchored surface layer that internally is highly mobile and not glassy as heavily promoted in the literature. The polymer dynamics in confinement is, rather, determined by two phases, one fully equal to the bulk polymer and another that is partly anchored at the surface. By strong topological interaction, this phase confines further chains with no direct contact to the surface. These form the often invoked interphase, where the full chain relaxation is impeded through the interaction with the anchored chains. The investigation of liquids under nanoconfinement has been a topic of intense scientific scrutiny for decades [1]. The issues are glass transition, crystallization, and phase separation under confinement [2,3]. Recently, this interest has been amplified by the rising of nanotechnology that aims to create new properties by modifying materials at the nanoscale. Polymers are of particular interest since they offer a large range of applications such as coatings, lubrication, nanocomposites, and in the field of biological macromolecules, biosensors [4].Close to a confining surface, the conformations of a polymer are significantly restricted [5]. In addition, the interactions with the surface will strongly affect the dynamics. Related issues such as adsorption, friction, network formation, effects on the entanglement density, and polymer density changes under confinement have been studied [6][7][8][9]. The importance of these phenomena thereby depends on the type of polymer, the specificity of the interactions, and the topology of the confinement. In particular, experimental results have been interpreted in terms of the formation of a glassy polymer layer close to surfaces [7]. Furthermore, the existence of an interphase with properties between those of the glassy layer and the bulk has been hypothesized [10][11][12].A large number of experimental studies have focused on nanoparticles dispersed in a polymer matrix. Whereas for noninteracting polymers significant effects only occur at high particle loadings, the addition of nanoparticles that interact with a polymer matrix induces dramatic property changes for the resulting polymer nanocomposite [7,9,10,13,14]. In particular, it has been reported that the interaction between OH groups on the surface of nanoparticles and locally polar poly(ethylene oxide) (PEO) or polydimethylsiloxane (PDMS) chains lead to the formation of a glassy polymer layer [7,10,13]. Theoretical work and computer simulations of chain adsorption as a function of adsorption strength reveal the existence of different chain conformations including trains, loops, and tails [14].Here, we present an investigation on the dynamics of PDMS chains confined in anodic aluminum oxide (AAO) nanopores. We find that PDMS adsorbs at the surface. However, the formed layer is internally highly mobile and not at all glassy. The siz...

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