Extending an earlier study on short unentangled telechelic poly(ethylene oxide) (PEO2K) chains by Monkenbusch et al. (), we present investigations on the association dynamics of weakly entangled PEO8K using pulsed field gradient nuclear magnetic resonance (PFG-NMR), small angle neutron scattering (SANS) and neutron spin echo (NSE). From PFG-NMR we obtain the average Fickian diffusion coefficients. With increasing temperature, they approach those from the neat unfunctionalized melt indicating diminishing aggregation. A random phase approximation (RPA) evaluation of SANS data results in much weaker aggregation compared to the PEO2K counterpart in agreement with the prediction of Caruthers' law. The picture of mode amplitude suppression as proposed by Monkenbusch et al. is supported. As a consequence of the rather long terminal times of PEO8K compared to the bond lifetimes, the NSE spectra from the functionalized melt may be well approximated by a product of the internal relaxation spectrum of the building block and the modified diffusion dynamics of the aggregates. Finally, the average center of mass diffusion of the ensemble of aggregates is quantitatively described in terms of the structural SANS results and the aggregation statistics extrapolated from earlier work.

We present a study of the structure and dynamics of long-chain syndiotactic polypropylene (s-PP) melts by small-angle neutron scattering (SANS), rheology, neutron backscattering, and neutron spin echo spectroscopy (NSE). From SANS, we determine the characteristic ratio of C-infinity = 11.5, which is larger than that obtained from previous experiments but in good agreement with simulation. Concerning dynamics, in the Rouse regime, neutron backscattering and incoherent NSE revealed Rouse rates that very well agree with each other, demonstrating the consistency of measurements in energy and time space. The single-chain dynamic structure factor was also measured by NSE. As none of the conventional data evaluation schemes for local reptation were successfully applicable, we used the novel extended de Gennes dynamic structure factor [Monkenbusch, M. J. Chem. Phys. 2023, 159, 034902]. We found that s-PP displays a strongly asymmetric tube with an aspect ratio of about 0.5. Allowing for a small non-Gaussianity improves the fit. The scaling properties of the Monkenbusch dynamic structure factor are well fulfilled also for s-PP. Contrary to intuition, the tube asymmetry appears not to be related to chain stiffness at least not in the range of C-infinity = 5 (polyisoprene) and 11.5 (s-PP).

The dynamics of long polymer chains in the presence of nanoparticles have been investigated. The nanocomposites of interest were inspired by tire industry-like rubber materials and consisted of entangled polyisoprene linear chains mixed with chemically pre-treated silica nanoparticles. Combining rheology, dielectric spectroscopy, and neutron spin echo measurements, we measured the modification of the polymer chain dynamics from bulk state to high filler concentration over a broad range of time and length scales. We show that the end-to-end relaxation does not seem to be impacted, whereas the polymer dynamics is significantly slowed down at a very local scale in the presence of nano-fillers. In addition to this length scale dependent different dynamics, additional Neutron Spin Echo spectroscopy experiments and Small Angle Scattering on labelled polymer chains, irreversibly bound to the filler surface and re-dispersed in a fully deuterated matrix, revealed a negligible dynamical behavior of this particular population of localized chains in the rubber layer. The conformational statistics of these chains is that of self-avoiding walk train within a shell that is thinner than the size of the chain. To the best of our knowledge, this work is the first of its kind which measures the single chain form factor in the bound layer of chemically multi-linked chains to the filler surface.

By neutron spin echo spectroscopy, we have studied the center of mass motion of short tracer chains on the molecular length scale within a highly entangled polymer matrix. The center of mass mean square displacements of the tracers independent of their molecular weight is subdiffusive at short times until it has reached the size of the tube d; then, a crossover to Fickian diffusion takes place. This observation cannot be understood within the tube model of reptation, but is rationalized as a result of important interchain couplings that lead to cooperative chain motion within the entanglement volume ∼d^{3}. Thus, the cooperative tracer chain motions are limited by the tube size d. If the center of mass displacement exceeds this size, uncorrelated Fickian diffusion takes over. Compared to the prediction of the Rouse model we observe a significantly reduced contribution of the tracer's internal modes to the spectra corroborating the finding of cooperative rather than Rouse dynamics within d^{3}.

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact of the early years of the ESS, and provide a solid base for completion and further expansion of the facility.

We present a structural and dynamic study on the simplest supramolecular hetero-association, recently investigated by the authors to prepare architectural homogeneous structures in the melt state, based on the bio-inspired hydrogen-bonding of thymine/diaminotriazine (thy–DAT) base-pairs. In the combination with an amorphous low Tg poly(butylene oxide) (PBO), no micellar structures are formed, which is expected for nonpolar polymers because of noncompatibility with the highly polar supramolecular groups. Instead, a clear polymer-like transient architecture is retrieved. This makes the heterocomplementary thy–DAT association an ideal candidate for further exploitation of the hydrogen-bonding ability in the bulk for self-healing purposes, damage management in rubbers or even the development of easily processable branched polymers with built-in plasticizer. In the present work, we investigate the temperature range from Tg + 20 °C to Tg + 150 °C of an oligomeric PBO using small-angle X-ray scattering (SAXS) and linear rheology on the pure thy and pure DAT monofunctionals and on an equimolar mixture of thy/DAT oligomers. The linear rheology performed at low temperature is found to correspond to fully closed-state dimeric configurations. At intermediate temperatures, SAXS probes the equilibrium between open and closed states of the thy–DAT mixtures. The temperature-dependent association constant in the full range between open and closed H-bonds and an enhancement of the monomeric friction coefficient due to the groups is obtained. The thy–DAT association in the melt is more stable than the DAT–DAT, whereas the thy–thy association seems to involve additional long-lived interactions.

A key ingredient within theories focusing on the rheology of entangled polymers is the way how the topological constraints of an entangled chain are lifted by unconstrained segments, i.e., how the constraining tube is dilated. This important question has been addressed by directly measuring the tube diameter d at the scale of the tube by neutron spin echo spectroscopy. The tube diameter d and plateau modulus G_{N}^{0} of highly entangled polyethylene oxide (PEO) chains of volume fraction c that are diluted by low molecular PEO show a concentration dependence d∝c^{a/2} and G_{N}^{0}∝c^{1+a} with an exponent a close to 4/3. This result allows the clear discrimination between different theoretical models that predict 4/3 or other values between 1 and 2 and provides an important ingredient to tube model theories.

We present a detailed small-angle neutron scattering investigation of mixtures of poly(ethylene oxide) (PEO)/polyhedral oligomeric silsesquioxane (POSS) hybrids, a popular nanofiller, addressing the conformation of the model-grafted nanoparticles as well as their influence on the linear polymer matrix in which they are embedded. The nanofiller has a well-defined graft arm length and is monomolecular. Because of the identical chemical nature of the grafted arm and matrix chains, it can be considered as an ideal athermal mixture. We have introduced a random phase approximation approach with general application possibilities for-Other grafted nanofillers, combining the star-like and particle-like characteristics of the POSS nanofiller. The size of the nanofiller remained unaffected and Gaussian upon mixing with linear Chains of various lengths, and no aggregation of the nanofiller was observed. This turns the POSS-based nanocomposite into an interesting model compound. The mixtures of PEO chains with the octafunctional PEO-POSS nanofiller were found to resemble those of a Micellar system whereas within experimental uncertainty the radius of gyration of the embedding matrix remained basically unaltered despite some tendency toward shrinking.

We present results from very long (on the order of several microseconds) atomistic molecular dynamics (MD) simura'tions for the density, microscopic structure, conformation, and local and segmental dynamics of pure, strictly monodisperse ring and linear poly(ethylene oxide) (PEO) melts, ranging in molar mass from similar to 5300 to similar to 20 000 g/mol. The MD results are compared with recent experimental data for the chain center-of-mass self-diffusion coefficient and the normalized single-chain dynamic structure factor obtained from small-angle neutron scattering, neutron spin echo, and pulse-field gradient NMR, and remarkable qualitative and quantitative agreement is observed, despite certain subtle disagreements in important details regarding mainly internal ring motion (loop dynamics). A detailed normal-mode analysis allowed us to check the degree of consistency of ring PEO melt dynamics with the ring Rouse model and indicated a strong reduction of the normalized mode amplitudes for the smaller mode numbers (compared to the Rouse model scaling), combined with an undisturbed spectrum of Rouse relaxation rates. We have further measured the zero-shear rate viscosity eta(0) of the PEO-5k and PEO-10k rings at several temperatures and extracted their activation energies. These were compared with the activation energies extracted from the MD simulations via analysis of the temperature dependence of the corresponding Rouse relaxation times of the two rings in the same temperature range.

Controlling the mechanical behavior of novel supramolecular materials is of the utmost importance and requires a fundamental understanding of the underlying physical processes. We present a multimethods approach to the dynamics of entangled transient polyisoprene networks. Small-angle neutron scattering (SANS) on randomly functionalized chains shows homogeneous supramolecular melts with Gaussian chain conformations. The H-bond lifetimes (dielectric α*-process) and the rheological response in terms of the loss modulus G″ differ by 2 orders of magnitude in time. Within the concept of a compact random walk (RW), where the random walker (urazole group acting as a sticker) undergoes multiple returns to its starting point and following the concept of theoretical proposed renormalized sticky bond lifetimes, we quantitatively solve this longstanding and unexplained large discrepancy: While the bond opening gives rise to the dielectric response, for rheological relaxation the association with a new partner is relevant. This takes place only after multiple returns to the original binding partner.

The structure and the dynamics of supramolecular comblike polymers in the melt state is studied by a combination of linear rheology, dielectric spectroscopy, and small angle neutron scattering. The system consists of blends of 1,2-polybutyleneoxide (PBO) entangled backbones, randomly functionalized with thymine (thy) and barely entangled PBO graft chains—modified with 2,4-diamino-1,3,5-triazine (DAT) end groups. These bioinspired groups associate into a transiently branched comb architecture through heterocomplementary interaction involving the two different hydrogen bonding groups thy and DAT. In the present manuscript, we focus on the comparison of the macroscopic dynamics of the associating blends and permanent comb analogs. The viscoelastic and dielectric response of covalent and reversible combs are found to be comparable. The viscoelastic response of mixtures of thy-functionalized entangled backbones and DAT-end-modified barely entangled chains show a relaxation mechanism, which is mostly attributed...

Supramolecular groups in polymeric systems lead to responsive materials which are ideally suited for applications in dynamic environments. The key to their advanced properties such as shape-memory or self-healing is the reversibility of secondary interactions which can be triggered by external stimuli such as temperature, light, or pH-value. Controlling the (mechanical) behavior of such systems requires a precise understanding of intrinsic properties. We present a multimethod study of transient polyisoprene networks that were functionalized with different amounts of hydrogen bonding urazole groups. This work aims at understanding rich rheological features on the basis of their microscopic origin. First, the thermorheological simple behavior is validated experimentally. Subsequently, we characterize the underlying microscopic processes by broadband dielectric spectroscopy (alpha-process and a alpha* -process), differential scanning calorimetry (glass transition behavior), and Fourier-transform infrared spectroscopy (thermodynamics of group association/dissociation). Based on these results, the influence of the supramolecular groups on the rheological response is analyzed. The observed features such as the onset of elastomeric properties in the flow regime, a drastic increase in the chain relaxation time with an increasing amount of functional groups, and the occurrence of a second rheological relaxation process, which is the most prominent effect, are discussed and related to their physical origin. (C) 2017 The Society of Rheology.

During the last few decades, broadband dielectric spectroscopy (BDS) has proven to be a very useful technique in the study of the molecular dynamics of materials. The huge frequency range achieved (10–10 Hz) and the possibility of measurements under different temperature, pressure, and environmental conditions allows the observation of a large variety of processes with very different time scales. Within this extraordinary experimental window, molecular and colletive dipolar fluctuations, charge transport and polarization effects take place, in turn determining the dielectric response of the material under study. However, in the last few years, growing interest in nanostructured materials highlighted the need for local measurements.

We present a small angle neutron scattering (SANS) investigation of a blend composed of a dendritic polymer and a linear matrix with comparable viscosity in start-up of an elongational flow at Tg + 50. The two-generation dendritic polymer is diluted to 10% by weight in a matrix of a long well-entangled linear chains. Both components consist of mainly 1,4-cis-polyisoprene but differ in isotopic composition. The resulting scattering contrast is sufficiently high to permit time-resolved measurements of the system structure factor during the start-up phase and to follow the retraction processes involving the inner sections of the branched polymer in the nonlinear deformation response. The outer branches and the linear matrix, on the contrary, are in the linear deformation regime. The linear matrix dominates the rheological signature of the blend and the influence of the branched component can barely be detected. However, the neutron scattering intensity is predominantly that of the (branched) minority component so that its dynamics is clearly evident. In the present paper, we use the neutron scattering data to validate the branch point withdrawal process, which could not be unambiguously discerned from rheological measurements in this blend. The maximal tube stretch that the inner branches experience, before the relaxed outer arm material is incorporated into the tube is determined. The in situ scattering experiments demonstrate for the first time the leveling-off of the strain as the result of branch point withdrawal and chain retraction directly on the molecular level. We conclude that branch point motion in the mixture of architecturally complex polymers occurs earlier than would be expected in a purely branched system, presumably due to the different topological environment that the linear matrix presents to the hierarchically deep-buried tube sections.

A new dual network elastomer is developed that consists of polybutadiene crosslinked with both permanent and transient bonds. The transient network is formed by the association of urazole groups that are randomly attached to the polymer backbone. Subsequent orthogonal covalent crosslinking through hydrosilylation in the melt state leads to a dual network with variable permanent and transient crosslinking density. Small angle neutron scattering (SANS) investigations show a homogeneous distribution of the transient bonds in both the functionalized polymers and the dual network products. The enhanced mechanical properties of the dual networks compared to conventional polybutadiene elastomers are characterized by stress–strain measurements. The increased toughness can be explained by a protective mechanism where the weaker supramolecular bonds act as sacrificial bonds that dissipate energy.

We review some of our latest contributions in the field of neutron scattering of polymers with linear and non-linear architecture. On the one hand, the reviewed Small Angle Neutron Scattering investigations cover dilute mixtures of dendritic polymers and linear polymers that were investigated during relaxation after a fast step strain or in situ during a strain ramping. The focus was on the otherwise not accessible long time dynamics of the inner branches. The parameters of the model are those of the tube model and include the evolution of liberated chain ends, the size and time dependence of the confining tube diameter and branch-point related dynamics. The case of deformed tube diameters could be obtained from a permanently-linked network state as the limiting case of a deformed melt. On the other hand, recently, cyclic polymers as a special class of branched architectures showed to be of high significance to detect similar features directly from equilibrium measurements by means of quasi-elastic Neutron Spin Echo spectroscopy. We show that by means of polymer rings as a probe different aspects of the tube concept can be distinguished in a unique way.

In this work, an investigation of the hydrogen-bonding mechanism in a transiently branched comb-like polymer system in the melt is reported. The system under investigation consists of a polybutylene oxide (PBO)-based backbone, randomly functionalized with thymine (thy) groups, in combination with shorter PBO graft chains, end-functionalized with diaminotriazine (DAT) groups. The functional groups are able to associate through hydrogen bonding. The heterocomplementary association of these groups leads to the formation of a transiently branched comb-like polymer system. Since recently virtually exclusive heterocomplementary association could be observed in the supramolecular association of telechelically modified oligomeric PEG chains, here we aim to extend the supramolecular assembly mechanism toward branched structures. The present work combines small angle neutron scattering (SANS) experiments on a selectively labeled system with macroscopic dynamics measured in linear rheology response. The association ...