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A recent model for unentangled polymer chains in confinement [M. Dolgushev and M. Krutyeva, Macromol. Theory Simul. 21, 565 (2012)] is scrutinized by small-angle neutron scattering (SANS) with respect to its static prediction, the single-chain structure factor. We find a remarkable agreement although the model simplifies the effect of the confinement to a harmonic potential. The effective confinement size from fits of SANS data with the model agrees well with the actual pore size. Starting from this result we discuss the possibility of an experiment on the dynamic structure factor predicted by the model. It turns out that such an experiment would need a large ratio polymer dimension/pore size which is difficult but not impossible to achieve. [ABSTRACT FROM AUTHOR]

We report a comprehensive study on the molecular conformation and dynamics of very large poly(ethylene oxide) rings in the melt: (i) for all rings, independent of the ring size, by small angle neutron scattering we observe a crossover from a strong Q -dependence at intermediate Q to a Q − 2 dependence at higher Q. Constructing a generic model including a crossover from Gaussian statistics at short distances to more compact structures at larger distances, we find the crossover at a distance along the ring of N e , 0 = 45 ± 2.5 monomers close to the entanglement distance in the linear counterpart. This finding is clear evidence for the predicted elementary loops building the ring conformation. (ii) The radius of gyration R g (N) follows quantitatively the result of numerous simulations. However, other than claimed, the crossover to mass fractal statistics does occur around N ≅ 10 N e , 0 , but up to N ≅ 44 N e , 0 , the relation R g (N) ∼ N 0.39 holds. The self-similar ring dynamics was accessed by pulsed field gradient-NMR and neutron spin echo spectroscopy: we find three dynamic regimes for center of mass diffusion starting (i) with a strong subdiffusive domain ⟨ r c o m 2 (t) ⟩ ∼ t α (0.4 ≤ α ≤ 0.65) , (ii) a second subdiffusive region ⟨ r c o m 2 (t) ⟩ ∼ t 0.75 that (iii) finally, crosses over to Fickian diffusion. The internal dynamics at scales below the elementary loop size is well described by the ring Rouse motion. At larger scales, the dynamics is self-similar and follows very well the predictions of scaling models with a preference for the fractal loopy globule model. Finally, we note that the key results were previously published in the form of two letters [Kruteva et al., ACS Macro Lett. 9, 507–511 (2020) and Kruteva et al., Phys. Rev. Lett. 125, 238004 (2020)]. [ABSTRACT FROM AUTHOR]

The properties of bicontinuous microemulsions, consisting of water, oil, and a surfactant, can be modified by the addition of diblock copolymers (boosting effect) and homopolymers (inverse boosting effect) or a combination of both. Here, the influence of the addition of homopolymers (PEPX and PEOX, X=5k or 10k molecular weight) on the dynamics of the surfactant layer is studied with neutron spin echo spectroscopy (NSE). Combining the results with the previous findings for diblock copolymers allows for a better separation of viscosity and bending modulus effects. With the addition of homopolymers, a significant increase of the relaxation rate compared to the pure microemulsion has been observed. The influence on the bending rigidity κ is measured with NSE experiments. Homopolymer addition reduces κ by up to Δκ≃-0.5kBT, whereas the diblock copolymer yields an increase of κ by ∼0.3kBT. Comparison of the bending moduli that are obtained by analysis of the dynamics to those obtained from small angle neutron scattering (SANS) sheds light on the different renormalization length scales for NSE and SANS. Variation of the surfactant concentration at otherwise constant conditions of homopolymer or diblock-copolymer concentration shows that NSE results are leading to the pure bending rigidity, while the renormalized one is measured with SANS. [ABSTRACT FROM AUTHOR]