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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 rele...

In this study, the evolution of the scattering function of silica-filled styrene-butadiene copolymer rubbers (SBRs) under a continuous uniaxial strain cycle is investigated in situ with a complemen...

In this work we present a fundamental analysis based on small-angle scattering, linear rheology and differential scanning calorimetry (DSC) experiments of the role of different hydrogen bonding (H-bonding) types on the structure and dynamics of chain-end modified poly(ethylene glycol) (PEG) in bulk. As such bifunctional PEG with a molar mass below the entanglement mass Me is symmetrically end-functionalized with three different hydrogen bonding (H-bonding) groups: thymine-1-acetic acid (thy), diamino-triazine (dat) and 2-ureido-4[1H]-pyrimidinone (upy). A linear block copolymer structure and a Newtonian-like dynamics is observed for PEG-thy/dat while results for PEG-upy structure and dynamics reveal a sphere and a network-like behavior, respectively. These observations are concomitant with an increase of the Flory–Huggins interaction parameter from PEG-thy/dat to PEG-upy that is used to quantify the difference between the H-bonding types. The upy association into spherical clusters is established by the Percus–Yevick approximation that models the inter-particle structure factor for PEG-upy. Moreover, the viscosity study reveals for PEG-upy a shear thickening behavior interpreted in terms of the free path model and related to the time for PEG-upy to dissociate from the upy clusters, seen as virtual crosslinks of the formed network. Moreover, a second relaxation time of different nature is also obtained from the complex shear modulus measurements of PEG-upy by the inverse of the angular frequency where G’ and G’’ crosses from the network-like to glass-like transition relaxation time, which is related to the segmental friction of PEG-upy polymeric network strands. In fact, not only do PEG-thy/dat and PEG-upy have different viscoelastic properties, but the relaxation times found for PEG-upy are much slower than the ones for PEG-thy/dat. However, the activation energy related to the association dynamics is very similar for both PEG-thy/dat and PEG-upy. Concerning the segmental dynamics, the glass transition temperature obtained from both rheological and calorimetric analysis is similar and increases for PEG-upy while for PEG-thy/dat is almost independent of association behavior. Our results show how supramolecular PEG properties vary by modifying the H-bonding association type and changing the molecular Flory–Huggins interaction parameter, which can be further explored for possible applications.

Reinforcement of elastomers by colloidal nanoparticles is an important application where microstructure needs to be understood-and, if possible, controlled-if one wishes to tune macroscopic mechanical properties. Here, the three-dimensional structure of large aggregates of nanometric silica particles embedded in a soft polymeric matrix is determined by small angle neutron scattering. Experimentally, the crowded environment leading to strong reinforcement induces a strong interaction between aggregates, which generates a prominent interaction peak in the scattering. We propose to analyze the total signal by means of a decomposition in a classical colloidal structure factor describing aggregate interaction and an aggregate form factor determined by a reverse Monte Carlo technique. The result gives new insight to the shape of aggregates and their complex interaction in elastomers. For comparison, fractal models for aggregate scattering are also discussed.

The far-reaching interplay between the speciation of polyoxometalates (POMs) in the liquid phase and the POM adsorption characteristics on substrate surfaces yet remains to be understood. The significance of this interplay is however paramount because it indicates the degree of technical applicability of solvent-processable POM molecules. Herein, we target this fundamentally important issue, shedding light on the "POM-counterion-solvent" and "POM-counterion-solvent-substrate" processes. We effectively combine the results from small-angle X-ray scattering in solution with surface sensitive scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements and present on this basis a semi-quantitative analysis which provides an excellent correlation between both approaches. The MeCN-solution speciation of a tris(alkoxo)-ligated Wells-Dawson-type polyoxoanion - explored as a representative of commonly negatively charged POM-based inorganic-organic nanostructures - is strikingly connected with the growth of porous two-dimensional molecular layers on highly oriented pyrolytic graphite (HOPG). Low water amounts dramatically transform intermolecular relationships toward hierarchical agglomeration that inhibits the layer formation on HOPG. The obtained findings lay the groundwork for a mechanistic study of controlled nucleation and growth of POM nanostructures on weakly interacting surfaces.

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 to the association/breakage dynamics of the transient bonds with characteristic time ∼1 s at T=−25 °C. In the parallel dielectric investigation, the reversible branched structure is still evident from the comparison with the corresponding permanent combs and allows the distinction between fixed arms relaxation and the lifetime. A α∗ process of the thy-thy association is likewise detected. The time scale of the supramolecular association makes the thy-DAT pair an ideal candidate for the development of responsive materials that combine permanent and transient linkages for novel applications and self-healing properties

In this work, the structural properties of pristine and phosphoric acid doped poly(2,5-benzimidazole) membranes have been investigated by small angle neutron- and X-ray scattering, X-ray diffraction, polarized light microscopy and transmission electron microscopy. The results of our investigation demonstrate formation of crystalline regions with a fractal-like distribution upon aging on length scales ranging from sub-nm up to some micrometres. Transport properties of phosphoric acid doped poly(2,5-benzimidazole) membrane measured by pulsed-field-gradient nuclear magnetic resonance spectroscopy reveal proton self-diffusion coefficients of the system.

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 oct...

The understanding of the molecular state of vanadium-oxo clusters (polyoxovanadates, POVs) in solution and on surface is a key to their target application in catalysis as well as molecular electronics and spintronics. We here report the results of a combined experimental and computational study of the behavior of nucleophilic polyoxoanions [VIV10VV8O42(I)]5– charged balanced by Et4N+ in water, in a one-phase organic solution of N,N-dimethylformamid (DMF) or acetonitrile (MeCN), in a mixed solution of MeCN–water, and at the hybrid liquid–surface interface. The molecular characteristics of the compound (NEt4)5[V18O42(I)] (1) in the given environments were studied by microspectroscopic, electrochemical, scattering, and molecular mechanics methods. Contrary to the situation in pure water, where we observe great agglomeration with a number of intercalated H2O molecules between POVs that are surrounded by the Et4N+ ions, no or only minor agglomeration of redox-active POVs in an unprecedented cation-mediated fas...

Nanocomposite materials based on highly stable encapsulated superparamagnetic iron oxide nanocrystals (SPIONs) were synthesized and characterized by scattering methods and transmission electron microscopy (TEM). The combination of advanced synthesis and encapsulation techniques using different diblock copolymers and the thiol-ene click reaction for cross-linking the polymeric shell results in uniform hybrid SPIONs homogeneously dispersed in a poly(ethylene oxide) matrix. Small-angle X-ray scattering and TEM investigations demonstrate the presence of mostly single particles and a negligible amount of dyads. Consequently, an efficient control over the encapsulation and synthetic conditions is of paramount importance to minimize the fraction of agglomerates and to obtain uniform hybrid nanomaterials.

We present results from very long (on the order of several microseconds) atomistic molecular dynamics (MD) simulations 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 ∼5300 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 ...

Scattering techniques with neutrons and X-rays are powerful methods for the investigation of the hierarchical structure of reinforcing fillers in rubber matrices. However, when using only X-ray scattering, the independent determination of the filler response itself sometimes remains an issue because of a strong parasitic contribution of the ZnO catalyst and activator in the vulcanization process. Microscopic characterization of filler-rubber mixtures even with only catalytic amounts of ZnO is, therefore, inevitably complex. Here, we present a study of silica aggregates dispersed in an SBR rubber in the presence of the catalyst and show that accurate partial structure factors of both components can be determined separately from the combination of the two scattering probes, neutrons, and X-rays. A unique separation of the silica filler scattering function devoid of parasitic catalyst scattering becomes possible. From the combined analysis, the catalyst contribution is determined as well and results to be prominent in the correction scheme. The experimental nano-structure of the ZnO after the mixing process as the by-product of the scattering decomposition was found also to be affected by the presence or absence of silica in the rubber mixture, correlated with the shear forces in the mixing and milling processes during sample preparation. The presented method is well suited for studies of novel dual filler systems.

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.

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 T-g + 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.

Nanoscale 11(9), 3847-3854 (2019). doi:10.1039/C8NR10018G, Published by RSC Publ., Cambridge

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&ndash, 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&ndash, 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 &deg, C to Tg + 150 &deg, 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&ndash, 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&ndash, DAT association in the melt is more stable than the DAT&ndash, DAT, whereas the thy&ndash, 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 $d\ensuremath{\propto}{c}^{a/2}$ and ${G}_{N}^{0}\ensuremath{\propto}{c}^{1+a}$ 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.

In this work we present the synthesis of poly(1,2-butylene oxide) (PBO) functionalized with the complementary hydrogen bond forming groups 2,4-diaminotriazine (DAT) and thymine. PBO is a rubbery polymer. Due to its semi-polar nature PBO is expected to suppresses non-directed cluster formation of the supramolecular groups but not influence their directed interactions. For the synthesis of backbone functionalized polymers we developed a procedure which allowed randomly copolymerizing BO with 1,2-epoxy-7-octene using anionic ring opening polymerization with potassium tert-butanolate as initiator. The vinyl groups were converted to OH-groups by oxidation. In addition, PBO with one alcoholic end group was obtained by homopolymerization of BO. For the variant with OH-groups at both chain ends a procedure was developed which was based on the cleavage of the tert-butyl initiator group. In all the polymers the alcohol groups were basically quantitatively transformed into NH2-groups. DAT and thymine functionalities were attached to the NH2-groups again in almost quantitative conversion. All reaction steps were monitored by 1H-NMR using pyridine-d5 as solvent. This method allowed determining the conversions of the different synthesis steps with high precision. The materials were examined in linear rheology in order to study the effect of the hydrogen-bonds on the dynamics of the resulting supramolecular structures. The results corroborate the exclusive existence of directed interactions between the supramolecular groups.

We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as a function of the number of entanglements Z. In the unentangled regime η0,linear/η0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/η0,ring = 2. In the entanglement regime, the Z-dependence of ring viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 < Z < 20, η0,linear/η0,ring Z1.2±0.3, is weaker than the scaling prediction (η0,linear/η0,ring Z1.6±0.3) and the simulations (η0,linear/η0,ring Z2.0±0.3). Nevertheless, the present collection of state-of-the-art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year-old problem.

In this work we present a combined analysis of small-angle neutron scattering, linear rheology and pulsed field gradient nuclear magnetic resonance spectroscopy experiments on the supramolecular association and chain structure of well-defined telechelically modified poly(ethylene glycol) (PEG) in the bulk. Oligomeric PEG was functionalized with directed heterocomplementary hydrogen-bonding end-groups, thymine (Thy) and diaminotriazine (DAT). The polarity of the backbone polymer is comparable to the end groups and avoids clustering of the groups basing on energetic arguments. Their linear association behavior in the ideal melt state was investigated on the microscopic/molecular level as a function of temperature. By means of a selective labeling scheme, which should ideally lead to the formation of alternating hydrogeneous-deuterated building block sequences if the hydrogen bonding reaction is exclusively heterocomplementary, we showed that the Thy–DAT association is dominant and a Thy–Thy homoassociation ...

We revisit the nonuniversal aspect of polymer dynamics by considering both new and existing data on the zero-shear viscosity and linear viscoelastic response of various polymers, each with a wide range of molecular weights. Analysis of the zero-shear viscosity data in terms of the packing length p, whose role in entanglements has been discussed previously by Fetters and co-workers, reveals a behavior that is irreconcilable with our current understanding based on the tube model. Specifically, we find that the transition regime between Rouse and pure reptation dynamics, currently understood as the regime where contour length fluctuations are active, systematically shrinks as the packing length of the polymer increases. Further, we find that the slope of the loss moduli in the high-frequency wing of the terminal peak of well-entangled systems also decreases from the common −0.25 to −0.125 with increasing p. This is contrary to the single expected value of −0.25 from tube models which include contour length f...

The supramolecular assembly of metal-porphyrin hexamers with bidentate ligands in chloroform solutions is demonstrated by UV/Vis and 1H NMR-titrations, and Small Angle Neutron Scattering (SANS) experiments. Titrations of zinc porphyrin hexamer Zn1 with 1,4-diazabicyclo[2,2,2]octane (DABCO) revealed that at a DABCO/Zn1 molar ratio of 3, intermolecular sandwich complexes are formed, which can be considered as "circular-shaped porphyrin ladders". These supramolecular complexes further aggregate into larger polymeric stacks, as a result of a combination of cooperativity effects, π-π stacking interactions, and chelate effects. The presence of rodlike assemblies in solution, formed by assembly of Zn1 and DABCO, is confirmed by SANS-experiments. Using a model for cylindrical assemblies, curve fitting calculations reveal that rods with an average length of 26 nm and a radius of 30-35 Å were formed, corresponding to columnar stacks of approximately 30 hexamer molecules. In contrast, the metal-free hexamer H21 did not form extended assemblies due to the absence of coordinative intermolecular interactions.

We report the preparation and structural and mechanical characterization of a tough supramolecular hydrogel, based exclusively on hydrophobic association. The system consists of a multiblock, segmented copolymer of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA) building blocks. A series of copolymers containing 2K, 4K, and 8K PEG were prepared. Upon swelling in water, a network is formed by self-assembly of hydrophobic DFA units in micellar domains, which act as stable physical cross-link points. The resulting hydrogels are noneroding and contain 75–92 wt % of water at swelling equilibrium. Small-angle neutron scattering (SANS) measurements showed that the aggregation number of micelles ranges from 2 × 102 to 6 × 102 DFA units, increasing with PEG molecular weight. Mechanical characterization indicated that the hydrogel containing PEG 2000 is mechanically very stable and tough, possessing a tensile toughness of 4.12 MJ/m3. The high toughness, processability, and ease of preparation make these hydrogels very attractive for applications where mechanical stability and load bearing features of soft materials are required.

The combination of a set of complementary techniques allows us to construct an unprecedented and comprehensive picture of the internal structure, temperature dependent swelling behavior, and the dependence of these properties on the cross-linker concentration of microgel particles based on N-vinylcaprolactam (VCL). The microgels were synthesized by precipitation polymerization using different amounts of cross-linking agent. Characterization was performed by small-angle neutron scattering (SANS) using two complementary neutron instruments to cover a uniquely broad Q-range with one probe. Additionally we used dynamic light scattering (DLS), atomic force microscopy (AFM), and differential scanning calorimetry (DSC). Previously obtained nuclear magnetic resonance spectroscopy (NMR) results on the same PVCL particles are utilized to round the picture off. Our study shows that both the particle radius and the cross-link density and therefore also the stiffness of the microgels rises with increasing cross-linker content. Hence, more cross-linker reduces the swelling capability distinctly. These findings are supported by SANS and AFM measurements. Independent DLS experiments also found the increase in particle size but suggest an unchanged cross-link density. The reason for the apparent contradiction is the indirect extraction of the parameters via a model in the evaluation of DLS measurements. The more direct approach in AFM by evaluating the cross section profiles of observed microgel particles gives evidence of significantly softer and more deformable particles at lower cross-linker concentrations and therefore verifies the change in cross-link density. DSC data indicate a minor but unexpected shift of the volume phase transition temperature (VPTT) to higher temperatures and exposes a more heterogeneous internal structure of the microgels with increasing cross-link density. Moreover, a change in the total energy transfer during the VPT gives evidence that the strength of hydrogen bonds is significantly affected by the cross-link density. A strong and reproducible deviation of the material density of the cross-linked microgel polymer chains toward a higher value compared to the respective linear chains has yet to be explained.

The structure and linear viscoelastic behavior of four different model star polymer melts were investigated experimentally. The star polymers were prepared via different synthetic routes based on atom transfer radical polymerization (ATRP). Stars with small elongated (linear backbone) cores exhibited slight differences in the asymmetry of the core, which however did not affect the rheological properties significantly. The relaxation behavior of these stars with an asymmetric core was well-described by available tube models. On the other hand, stars with large cross-linked cores exhibited a core–shell morphology and their stress relaxation was dominated by a power-law decay over about 8 decades, akin to gel-like soft systems. This behavior reflected their liquid-like ordering and small intercore distances, and bares analogueies to that of interpenetrating soft colloids and microgels.

Viscoelastic solids such as rubber exhibit a complex elastic modulus E(ω), which depends on the frequency ω of the applied stress or strain. The modulus E(ω) can often be determined in a wide frequency range by performing measurements in a limited frequency range for many different temperatures, and then shift the frequency segments horizontally along the frequency axis to obtain a continuous master curve. We show that one can use the spectral representation of E(ω) (or 1/E(ω)), which obeys causality, to determine the optimal shifting procedure, and to test the accuracy of the measured data and the calculated master curve.

The self-assembly of achiral and chiral porphyrin trimers based on benzene triscarboxamide in solution is studied with the help of NMR, FT-IR, UV-vis, and CD spectroscopy. These studies revealed that in apolar solvents the porphyrin trimers self-assembled in columnar stacks via a combination of hydrogen bonding and π-π stacking interactions. While the critical aggregation constant is about 0.2 mM in chloroform, aggregation already occurs at micromolar concentrations in n-hexane. Small angle neutron scattering (SANS) studies in chloroform, toluene, and n-hexane confirmed aggregation of the trimers into columnar stacks. In chloroform and n-hexane, but not in toluene, the trimers gelated the solvent. In chloroform the stacks of the achiral trimer were found to contain on average about 70 molecules, while in toluene the stacks were much smaller and contained on average 7-9 molecules. In n-hexane the SANS studies revealed that the chiral trimer formed a gel with an average mesh size of the transient network of chains of approximately 90 nm, with chains being built up from effective cylindrical aggregates with an average length of 20 nm.

We present a neutron scattering analysis of the structure and dynamics of PEO polymer rings with a molecular weight 2.5 times higher than the entanglement mass. The melt structure was found to be more compact than a Gaussian model would suggest. With increasing time the center of mass (c.o.m.) diffusion undergoes a transition from sub-diffusive to diffusive behavior. The transition time agrees well with the decorrelation time predicted by a mode coupling approach. As a novel feature well pronounced non-Gaussian behavior of the c.o.m. diffusion was found that shows surprising analogies to the cage effect known from glassy systems. Finally, the longest wavelength Rouse modes are suppressed possibly as a consequence of an onset of lattice animal features as hypothesized in theoretical approaches.

We present a small angle neutron scattering (SANS) study of the association of heterocomplementary telechelic polypropylene glycol (PPG) polymers, bearing either diaminotriazine (DAT) or thymine (Thy) stickers as end-groups, both in the melt and in dilute solution. The SANS data are critically examined for the architecture and morphology as well as relative extent of linear assembly in the apolar solvent toluene. A random phase approximation (RPA) approach, adapted for a supramolecularly assembled multiblock copolymer is presented, which allows to extract the interaction parameters between the constituents and the medium. From the proposed approach, which describes very well heterocomplementary hydrogen-bonding telechelic polymers in both diluted toluene solution and in the melt, we conclude that linear association prevails.

The relaxation time spectrum in blends of architecturally different polymers with strongly disperse time scales has been investigated by their time-dependent small angle neutron scattering signal a...

Nanocomposites in general have gained importance in current products, leading to improved performance of these complex compound materials. The structure of the solid particles is not limited in terms of shape in advance, but their specific function is tightly connected to their shape. Scattering experiments are often employed to supervise production routes and the final performance, but not all possibilities of scattering experiments are exploited due to several reasons: engineers need to enter the unknown stage of scattering experiments, and the scattering experts need to simplify their experience to simple, usable recipes that are applicable and reliable. This process is still ongoing, and the authors hope to contribute to this highly interesting journey.

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 (α-process and α∗-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.

The combination of dielectric and mechanical spectroscopies is very powerful. However, it is not quite clear in your paper how the time scales of your supramolecular combs compare from these two spectroscopies. Maybe you can make a plot of the temperature dependence of the time scales for arm retraction and for terminal relaxation that are obtained by these two methods? That would really help the reader understand not only how they compare but what temperature ranges can be studied for these two vital time scales....

The micellar system based on cetylpyridinium chloride (CPyCl) and sodium salicylate (NaSal) in brine solution is investigated on both macro- and micro-length scales through rheology and scattering measurements. The linear viscoelasticity of the system and its structural parameters are explored by systematically changing the amount of NaSal over an extremely wide range of concentrations, thus producing salt-to-surfactant molar ratios from zero to about 8.5. As a result, the well-known non-monotonic behaviour of the zero-shear rate viscosity as a function of salinity can be connected to micellar morphological changes, whose driving force is represented by the simultaneous binding and screening actions of NaSal. The viscosity behaviour can be seen as a direct consequence of consecutive lengthening/shortening of the contour length, where the micelles attempt to minimize the electrostatic charge density on their surface. Along similar lines, the scattering measurements of the semidilute solutions show that the local stiffness of the micellar chain changes with increasing salt content influencing the elasticity of the resulting network. Within this general view, the branching of the micelles can be seen as a side effect attributable to the main character of the play, namely, the binding salt NaSal, whereas the overall dynamics of the system is driven by the considerable changes in the entanglement density of the micellar network.

The shear flow dynamics of linear and branched wormlike micellar systems based on cetylpyridinium chloride and sodium salicylate in brine solution is investigated through rheometric and scattering techniques. In particular, the flow and the structural flow response are explored via velocimetry measurements and rheological and rheometric small-angle neutron scattering (SANS) experiments, respectively. Although all micellar solutions display a similar shear thinning behavior in the nonlinear regime, the experimental results show that shear banding sets in only when the micelle contour length L[over ¯] is sufficiently long, independent of the nature of the micellar connections (either linear or branched micelles). Using rheometric SANS, we observe that the shear banding systems both show very similar orientational ordering as a function of Weissenberg number, while the short branched micelles manifest an unexpected increase of ordering at very low Weissenberg numbers. This suggests the presence of an additional flow-induced relaxation process that is peculiar for branched systems.

The chain and association dynamics of supramolecular polymer ensembles decisively determines their properties. Using neutron spin echo (NSE) spectroscopy we present molecular insight into the space and time evolution of this dynamics. Studying a well characterized ensemble of linearly associating telechelic poly(ethylene glycol) melts carrying triple H-bonding end groups, we show that H-bond breaking significantly impacts the mode spectrum of the associates. The breaking affects the mode contributions and not the relaxation times as was assumed previously. NSE spectra directly reveal the so far intangible H-bond lifetimes in the supramolecular melt and demonstrate that for both the microscopic and the macroscopic dynamics of the supramolecular ensemble the instantaneous average of the ${M}_{w}$ distribution governs the system response at least as long as the Rouse picture applies.

We present a systematic investigation of well-characterized, experimentally pure polystyrene (PS) rings with molar mass of 161 000 g/mol in dilute solutions. We measure the ring form factor at θ - and good-solvent conditions as well as in a polymeric solvent (linear PS of roughly comparable molar mass) by means of small-angle neutron scattering (SANS). Additional dynamic light scattering (DLS) measurements support the SANS data and help elucidate the role of solvent quality and solution preparation. The results indicate the increase of ring dimensions as the solvent quality improves. Furthermore, the experimental form factors in both θ -solvent and linear matrix behave as ideal rings and are fully superimposable. The nearly Gaussian conformations of rings in a melt of linear chains provide evidence of threading of linear chains through rings. The latter result has implications for the dynamics of ring-linear polymer mixtures.

We use small-angle neutron scattering to measure the molecular stretching in polystyrene melts undergoing steady elongational flow at large stretch rates. The radius of gyration of the central segment of a partly deuterated polystyrene molecule is, in the stretching direction, increasing with the steady stretch rate to a power of about 0.25. This value is about half of the exponent observed for the increase in stress value σ, in agreement with Gaussian behavior. Thus, finite chain extensibility does not seem to play an important role in the strongly non-linear extensional stress behavior exhibited by the linear polystyrene melt.

The rheological behavior of poly(ethylene-alt-propylene) (PEP), polydimethylsiloxane (PDMS) and polyisoprene (PI, two molecular weights: 70k and 200k) melts containing polyhedral oligomeric silsesquioxane (POSS) molecules was investigated by means of small angle scattering (SAXS and SANS) and oscillatory shear rheology. The dependence of the nanocomposite viscosity on the polymer–particle solubility and polymer molecular weight was studied. At high filler fractions all polymers exhibited hydrodynamic reinforcement of the plateau modulus quantified by a Guth Gold relation. Additionally, the PEP and PI70k systems showed a transition from liquid-like to solid-like rheological behavior. SAXS results enabled us to relate this behavior to the formation of a POSS network or POSS particle jamming, respectively. At low filler degrees, the zero shear viscosity of the nanocomposites was strongly dependent on the polymer solubility and entanglement number. We observed a viscosity decrease in the filled PDMS and PI200...

Using small-angle neutron scattering, the unperturbed chain dimensions of a series of poly(alkylene oxide)s (PAO’s) were studied as a function of side-chain length. The PAO’s were obtained using anionic ring-opening polymerization methods. The deuterated monomers were synthesized from commercially available precomponents. A systematic decrease of the chain dimensions with increasing length of the side chains was found. We also compare the PAO’s with the chemically very similar poly(olefin)s with respect to the characteristic ratio C∞, the chain dimensions, and the packing length as a function of the molecular weight per backbone bond. In doing so, we found significant differences between the static properties of the two systems.

The amphiphilic copolymers of the Pluronic family are known to be excellent dispersants for single-walled carbon nanotubes (SWCNT) in water, especially F108 and F127, which have rather long end-blocks of poly(ethylene oxide) (PEO). In this study, the structure of the CNT/polymer hybrid formed in water is evaluated by measurements of small-angle neutron scattering (SANS) with contrast variation, as supported by cryo-transmission electron microscopy (cryo-TEM) imaging. The homogeneous, stable, inklike dispersions exhibited very small isolated bundles of carbon nanotubes in cryo-TEM images. SANS experiments were conducted at different D(2)O/H(2)O content of the dispersing solvent. The data for both systems showed surprisingly minimal intensity values at 70% D(2)O solvent composition, which is much higher than the expected value of 17% D(2)O that is based on the scattering length density (SLD) of PEO. At this near match point, the data exhibited a q(-1) power law relation of intensity to the scattering vector (q), indicating rodlike entities. Two models are evaluated, as extensions to Pederson's block copolymer micelles models. One is loosely adsorbed polymer chains on a rodlike CNT bundle. In the other, the hydrophobic block is considered to form a continuous hydrated shell on the CNT surface, whereas the hydrophilic blocks emanate into the solvent. Both models were found to fit the experimental data reasonably well. The model fit required special considerations of the tight association of water molecules around PEO chains and slight isotopic selectivity.

By the use of small angle neutron scattering, the chain conformation in a polymer nanocomposite was studied as a function of the nanoparticle fraction for two different molecular weights. A repulsive system was realized in mixing poly(ethylene−propylene) and hydrophobically modified silica. All nanocomposite SANS data exhibit a pronounced scattering peak at intermediate momentum transfers, which is closely connected with the particle structure. Even under contrast matching conditions, the hydrophobic surface layer of the nanoparticles was found to contribute significantly to the scattering signal. In particular, in the short chain matrix the peak origin is exclusively related to direct particle scattering. In the long chain matrix, an additional peak contribution is present. Possible origins include void correlation scattering or polymer correlation scattering. We show unambiguously that the conformation of short chains with a molecular weight of 3000 g/mol is not visibly disturbed by the presence of the ...