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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Neutron spin echo has revealed the single chain dynamic structure factor of entangled polymer chains confined in cylindrical nanopores with chain dimensions either much larger or smaller than the lateral pore sizes. In both situations, a slowing down of the dynamics with respect to the bulk behavior is only observed at intermediate times. The results at long times provide a direct microscopic measurement of the entanglement distance under confinement. They constitute the first experimental microscopic evidence of the dilution of the total entanglement density in a polymer melt under strong confinement, a phenomenon that so far was hypothesized on the basis of various macroscopic observations. DOI: 10.1103/PhysRevLett.104.197801 PACS numbers: 61.41.+e, 62.25.Àg, 78.70.Nx, 82.35.Lr Confinement effects in polymer melts may lead to unusual properties. This concerns both the chain conformation, which may be distorted, as well as chain dynamics, which may be altered due to surface interactions and changes of topology and chain self-density [1][2][3][4]. The understanding of such behavior is not only a scientific challenge but is also important for knowledge-based applications in nanotechnology, such as nanocomposites, coatings, adhesives, etc. [5]. Today, microscopic studies on the chain dynamics under confinement are mainly available through simulations. Only a few experiments have addressed this problem, e.g., the flow of polymers through nanopores, the extensional rheology of nanosized polymer films, the observation of dewetting kinetics of thin films or NMR relaxometry. Chain dynamics is commonly described in terms of the Rouse and the reptation model. The relaxation of the Rouse modes, determined by a balance of viscous and entropic forces, only depends on the chain length and the monomeric friction. In addition, long polymers heavily interpenetrate each other and mutually restrict their motions at long times in forming topological constraints (''entanglements''). In the reptation model the entanglement effect is modeled by a tube of diameter d $ ' ffiffiffiffiffiffi N e p along the coarse grained chain profile confining the chain motion (', monomer length; N e , number of monomers between the entanglements). The dominant motional mechanisms in this model are (i) a curvilinear version of the Rouse motion (local reptation) followed by (ii) the escape of the whole molecule from the tube at long times, the reptation process (see, e.g., [6,7]). The important question that is addressed now both by simulations [2,3,8,9] as well as by a variety of experiments on a macroscopic level [4,[10][11][12] is how these dynamics change under confinement.Basically all simulations available indicate that confinement reduces chain mobility independent of the adhesive potential of the wall. An analysis of the Rouse modes of unentangled chains under confinement reveals a uniform slowing down of all modes which was interpreted by an effective increase of monomeric friction [8]. The consequences for the entanglement density are less...

In this work, we show the effects of nanoconfinement on the crystallization of poly(ethylene oxide) (PEO) nanotubes embedded in anodized aluminum oxide (AAO) templates. The morphological characteristics of the hollow 1D PEO nanostructures were evaluated by scanning electron microscopy (SEM). The crystallization of the PEO nanostructures and bulk was studied with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The crystallization of PEO nanotubes studied by DSC is strongly influenced by the confinement showing a strong reduction in the crystallization temperature of the polymer. X-ray diffraction (XRD) experiments confirmed the isothermal crystallization results obtained by DSC, and studies carried out at low temperatures showed the absence of crystallites oriented with the extended chains perpendicular to the pore wall within the PEO nanotubes, which has been shown to be the typical crystal orientation for one-dimensional polymer nanostructures. In contrast, only planes oriented 33, 45, and 90° with respect to the plane (120) are arranged parallel to the pore's main axis, indicating preferential crystal growth in the direction of the radial component. Calculations based on classical nucleation theory suggest that heterogeneous nucleation prevails in the bulk PEO whereas for the PEO nanotubes a surface nucleation mechanism is more consistent with the obtained results.