Polymer dynamics under cylindrical confinement featuring a locally repulsive surface: A quasielastic neutron scattering study

Interaction between Filler and Polymeric Matrix in Nanocomposites: Magnetic Approach and Applications

In recent years, polymer nanocomposites produced by combining nanofillers and a polymeric matrix are emerging as interesting materials. Polymeric composites have a wide range of applications due to the outstanding and enhanced properties that are obtained thanks to the introduction of nanoparticles. Therefore, understanding the filler-matrix relationship is an important factor in the continued growth of this scientific area and the development of new materials with desired properties and specific applications. Due to their performance in response to a magnetic field magnetic nanocomposites represent an important class of functional nanocomposites. Due to their properties, magnetic nanocomposites have found numerous applications in biomedical applications such as drug delivery, theranostics, etc. This article aims to provide an overview of the filler-polymeric matrix relationship, with a special focus on magnetic nanocomposites and their potential applications in the biomedical field.

A decade of innovation and progress in understanding the morphology and structure of heterogeneous polymers in rigid confinement

When confined in nanoscale domains, polymers generally encounter changes in their structural, thermodynamics and dynamics properties compared to those in the bulk, due to the high amount of polymer/wall interfaces and limited amount of matter. The present review specifically deals with the confinement of heterogeneous polymers (i.e. polymer blends and block copolymers) in rigid nanoscale domains (i.e. bearing non-deformable solid walls) where the processes of phase separation and self-assembly can be deeply affected. This review focuses on the innovative contributions of the last decade (2010-2020), giving a summary of the new insights and understanding gained in this period. We conclude this review by giving our view on the most thriving directions for this topic.

Disentangling of complex polymer dynamics under soft nanoscopic confinement

We discuss the complex interplay between host and guest dynamics for a polymer in soft confinement by a droplet-phase microemulsion. Intermediate scattering functions obtained by neutron spin echo spectroscopy are first analysed by means of an effective diffusion coefficient. From its dependence on the absolute of the scattering vector q we concluded a sophisticated model for the systems dynamics taking both polymer and microemulsion contributions into account. Global fitting of this model to the intermediate scattering functions at all measured q-values and all investigated confinement sizes eventually allows for a precise disentangling of the pure polymer dynamics in confinement from the overlaying microemulsion dynamics. Validity of our approach is further supported by numerical random walk calculations.

Elucidating the impact of extreme nanoscale confinement on segmental and chain dynamics of unentangled poly(cis-1,4-isoprene)

Broadband dielectric spectroscopy is employed to probe dynamics in low molecular weight poly(cis-1,4-isoprene) (PI) confined in unidirectional silica nanopores with mean pore diameter, D, of 6.5 nm. Three molecular weights of PI (3, 7 and 10 kg/mol) were chosen such that the ratio of D to the polymer radius of gyration, R_g, is varied from 3.4, 2.3 to 1.9, respectively. It is found that the mean segmental relaxation rate remains bulk-like but an additional process arises at lower frequencies with increasing molecular weight (decreasing D/R_g. In contrast, the mean relaxation rates of the end-to-end dipole vector corresponding to chain dynamics are found to be slightly slower than that in the bulk for the systems approaching D/R_g ∼ 2, but faster than the bulk for the polymer with the largest molecular weight. The analysis of the spectral shapes of the chain relaxation suggests that the resulting dynamics of the 10kg/mol PI confined at length-scales close to that of the R_g are due to non-ideal chain conformations under confinement decreasing the chain relaxation times. The understanding of these faster chain dynamics of polymers under extreme geometrical confinement is necessary in designing nanodevices that contain polymeric materials within substrates approaching the molecular scale.

Neutron spin echo monitoring of segmental-like diffusion of water confined in the cores of carbon nanotubes

Following the stream of increasing scientific interest in condensed-matter systems under ultra-hydrophobic confinement, the present work reports the first incoherent neutron spin echo assessment of the dynamics of water axially confined inside single-wall carbon nanotubes of diameter d∼ 1.4 nm. At the time scale of nanoseconds, two water populations are retrieved, whose relative proportion matches the one expected for a concentric shell + chain arrangement with cylindrical symmetry. The time dependence of the mean square displacement related to the external component is found to be subdiffusive, with peculiar resemblance to segmental diffusion typical of entangled polymeric systems.

Polymer dynamics under confinement

We review recent neutron scattering work and related results from simulation and complementary techniques focusing on the microscopic dynamics of polymers under confinement. Confinement is either realized in model porous materials or in polymer nanocomposites (PNC). The dynamics of such confined polymers is affected on the local segmental level, the level of entanglements as well as on global levels: (i) at the segmental level the interaction with the surface is of key importance. At locally repulsive surfaces compared to the bulk the segmental dynamics is not altered. Attractive surfaces slow down the segmental dynamics in their neighborhood but do not give rise to dead, glassy layers. (ii) Confinement generally has little effect on the inter-chain entanglements: both for weakly as well as for marginally confined polymers the reptation tube size is not changed. Only for strongly confined polymers disentanglement takes place. Similarly, in PNC at higher NP loading disentanglement phenomena are observed; in addition, at very high loading a transition from polymer caused topological constraints to purely geometrical constraints is observed. (iii) On the more global scale NSE experiments revealed important information on the nature of the interphase between adsorbed layer and bulk polymer. (iv) Polymer grafts at NP mutually confine each other, an effect that is most pronounced for one component NP. (v) Global diffusion of entangled polymers both in weakly and strongly attractive PNC is governed by the ratio of bottle-neck to chain size that characterizes the 'entropic barrier' for global diffusion.