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The non-exponential character of the structural relaxation is considered one of the hallmarks of the glassy dynamics, and in this context, the relatively narrow shape observed by dielectric techniques for polar glass formers has attracted the attention of the community for long time. This work addresses the phenomenology and role of specific non-covalent interactions in the structural relaxation of glass-forming liquids by the study of polar tributyl phosphate. We show that dipole interactions can couple to shear stress and modify the flow behavior, preventing the occurrence of the simple liquid behavior. We discuss our findings in the general framework of glassy dynamics and the role of intermolecular interactions.

By using time-of-flight neutron spectroscopy with polarization analysis, we have separated coherent and incoherent contributions to the scattering of deuterated tetrahydrofuran in a wide scattering vector (Q)-range from meso- to inter-molecular length scales. The results are compared with those recently reported for water to address the influence of the nature of inter-molecular interactions (van der Waals vs hydrogen bond) on the dynamics. The phenomenology found is qualitatively similar in both systems. Both collective and self-scattering functions are satisfactorily described in terms of a convolution model that considers vibrations, diffusion, and a Q-independent mode. We observe a crossover in the structural relaxation from being dominated by the Q-independent mode at the mesoscale to being dominated by diffusion at inter-molecular length scales. The characteristic time of the Q-independent mode is the same for collective and self-motions and, contrary to water, faster and with a lower activation energy (≈1.4 Kcal/mol) than the structural relaxation time at inter-molecular length scales. This follows the macroscopic viscosity behavior. The collective diffusive time is well described by the de Gennes narrowing relation proposed for simple monoatomic liquids in a wide Q-range entering the intermediate length scales, in contraposition to the case of water.

The conformation of poly(methyl methacrylate) (PMMA)-based single-chain nanoparticles (SCNPs) and their corresponding linear precursors in the presence of deuterated linear PMMA in deuterated dimethylformamide (DMF) solutions has been studied by small-angle neutron scattering (SANS). The SANS profiles were analyzed in terms of a three-component random phase approximation (RPA) model. The RPA approach described well the scattering profiles in dilute and crowded solutions. Considering all the contributions of the RPA leads to an accurate estimation of the single chain form factor parameters and the Flory–Huggins interaction parameter between PMMA and DMF. The value of the latter in the dilute regime indicates that the precursors and the SCNPs are in good solvent conditions, while in crowding conditions, the polymer becomes less soluble.

[EN] We have investigated an all-polymer nanocomposite (NC) consisting of single-chain nanoparticles (SCNPs) immersed in a matrix of linear chains of their precursors (25/75% composition in weight). The SCNPs were previously synthesized via "click" chemistry, which induces intramolecular cross-links in the individual macromolecules accompanied by a slight shift (5-8 K) of the glass transition temperature toward higher values and a broadening of the dynamic response with respect to the raw precursor material. The selective investigation of the dynamics of the NC components has been possible by using properly isotopically labeled materials and applying quasielastic neutron scattering techniques. Results have been analyzed in the momentum transfer range where the coherent scattering contribution is minimal, as determined by complementary neutron diffraction experiments with polarization analysis. We observe the development of dynamic heterogeneity in the intermediate scattering function of the NC components, which grows with increasing time. Local motions in the precursor matrix of the NC are accelerated with respect to the reference bulk behavior, while the displacements of SCNPs' hydrogens show enhanced deviations from Gaussian and exponential behavior compared with the pure melt of SCNPs. The resulting averaged behavior in the NC coincides with that of the pure precursor, in accordance with the macroscopic observations by differential scanning calorimetry (DSC) experiments.

Recent efforts, fostered by a pioneering work by us, have shown the of multiple steps in the recovery of equilibrium of glasses. Jin and McKenna raise concerns regarding the validity of such scenario alleging that the multiple recovery steps would be an artifact arising from poor temperature control in the oven used for isothermal glass equilibration. We critically discuss Jin and McKenna arguments from both the viewpoints of scrutinizing previous literature data and that of the temperature control in the oven. In doing so, we provide compelling arguments that Jin and McKenna conjectures are unjustified and point out the need for efforts to describe glass dynamics significantly below the glass transition temperature, Tg, by accounting for the presence of different relaxation mechanisms active in glass equilibration.

The polymer dynamics in blends of long and short chains spans several decades in time and the understanding of the effect of the short chains on the relaxation mechanism of the long chains due to constraint release requires the combination of microscopic and macroscopic techniques. While the longtime dynamics can be accessed by mechanical or dielectric spectroscopy (DS), its relation to the microstructural details requires the application of theoretical models. In contrast, neutron spin echo (NSE) measures directly the dynamic structure factor reflecting the process of constraint removal at the molecular scale. Here the comparison of NSE and DS results in a model blend of short and long polyisoprene enables the exploration of the entire time regime showing that constraint release leads to a dilation of the confining tube. We show the description of the dynamic tube dilation using a simple model in which the time controlling the tube dilation for the long chain is the terminal time of the short chain.

We investigate by neutron scattering and calorimetry a mixture of styrene-butadiene rubber (SBR) and a commercial resin. The neat materials present a large dynamic contrast, having SBR a much lower glass-transition temperature than the resin. The focus is to exploit neutron scattering selectivity in an isotopically labelled sample where deuterated SBR is the majority component. This direct insight into the resin atomic motions within the mixture allows determining the ‘microscopic’ glass transition of the resin in the presence of the a priori much more mobile SBR. This transition takes place in the vicinity of the initial calorimetric glass transition temperature, mainly dictated by the majority component.

We present a combined study by quasielastic neutron scattering (QENS), differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS) on poly(tetrahydrofuran-co-epichlorohydrin) copolymers, to see how their composition can be used to tune their crystallizability and to elucidate the impact of this factor on the dynamical properties. QENS reveals a strong effect on the local dynamics upon cooling down, where the local motions of a sample that remains in the supercooled state at lower temperatures are less Gaussian and slower than those in a sample that crystallizes a few degrees below. This can be attributed to the enhancement of local heterogeneities in the former, which could be a determining factor preventing crystallization.

Begins are usually difficult and most of the times the first experience is crucial in determining the long-term development of an incursion in a new field. Our team had the great opportunity of meeting Bernhard Frick as local contact in our first neutron scattering experiments in the late 80’s. Since then, the collaboration with Bernhard has resulted in a plethora of exciting investigations mainly centered on polymer dynamics, but covering diverse aspects that include tunneling and rotations of methyl groups, segmental motions, local processes involved in secondary relaxations, etc. With our own ageing, the complexity of the systems investigated has also increased along these years. The joint investigations cover from homopolymers to polymer blends and, more recently, novel materials based on single-chain nanoparticles. This talk will be a journey along the main achievements of our (still living) collaboration with Bernhard.

The main challenge for the preparation of protein single-chain nanoparticles (SCNPs) is the natural complexity of these macromolecules. Herein, we report the suitable conditions to produce "neat" bovine serum albumin (BSA) single-chain nanoparticles (SCNPs) from partially denatured BSA, which involves denaturation in urea and intramolecular cross-linking below the overlap concentration. We use two disuccinimide ester linkers containing three and six methylene spacer groups: disuccinimidyl glutarate (DSG) and disuccinimidyl suberate (DSS), respectively. Remarkably, the degree of internal cross-linking can be followed simply and efficiently via 1H NMR spectroscopy. The associated structural changes-as probed by small-angle neutron scattering (SANS)-reveal that the denatured protein has a random-like coil conformation, which progressively shrinks with the addition of DSG or DSS, thus allowing for size control of the BSA-SCNPs with radii of gyration down to 5.4 nm. The longer cross-linker exhibits slightly more efficiency in chain compaction with a somewhat stronger size reduction but similar reactivity at a given cross-linker concentration. This reliable method is applicable to a wide range of compact proteins since most proteins have appropriate reactive amino acids and denature in urea. Critically, this work paves the way to the synthesis of "neat", biodegradable protein SCNPs for a range of applications including nanomedicine.

Recent efforts, fostered by a pioneering work by us, have shown the of multiple steps in the recovery of equilibrium of glasses. Jin and McKenna raise concerns regarding the validity of such scenario alleging that the multiple recovery steps would be an artifact arising from poor temperature control in the oven used for isothermal glass equilibration. We critically discuss Jin and McKenna arguments from both the viewpoints of scrutinizing previous literature data and that of the temperature control in the oven. In doing so, we provide compelling arguments that Jin and McKenna conjectures are unjustified and point out the need for efforts to describe glass dynamics significantly below the glass transition temperature, T-g, by accounting for the presence of different relaxation mechanisms active in glass equilibration.

We have disentangled the contributions to the glass transition as observed by differential scanning calorimetry (DSC) on simplified systems of industrial interest consisting of blends of styrene-butadiene rubber (SBR) and polystyrene (PS) oligomer. To do this, we have started from a model previously proposed to describe the effects of blending on the equilibrium dynamics of the alpha-relaxation as monitored by broadband dielectric spectroscopy (BDS). This model is based on the combination of self -concentration and thermally driven concentration fluctuations (TCFs). Considering the direct insight of small-angle neutron scattering on TCFs, blending effects on the alpha-relaxation can be fully accounted for by using only three free parameters: the self-concentration of the components q)self SBR and q)selfPS) and the relevant length scale of segmental relaxation, 2Rc. Their values were determined from the analysis of the BDS results on these samples, being that obtained for 2Rc approximate to 25 angstrom in the range usually reported for this magnitude in glass-forming systems. Using a similar approach, the distinct contributions to the DSC experiments were evaluated by imposing the dynamical information deduced from BDS and connecting the component segmental dynamics in the blend above the glass-transition temperature Tg (at equilibrium) and the way the equilibrium is lost when cooling toward the glassy state. This connection was made through the alpha-relaxation characteristic time of each component at Tg, tau g. The agreement of such constructed curves with the experimental DSC results is excellent just assuming that tau g is not affected by blending.

We have investigated an all-polymer nanocomposite (NC) consisting of single-chain nanoparticles (SCNPs) immersed in a matrix of linear chains of their precursors (25/75% composition in weight). The SCNPs were previously synthesized via “click” chemistry, which induces intramolecular cross-links in the individual macromolecules accompanied by a slight shift (5–8 K) of the glass transition temperature toward higher values and a broadening of the dynamic response with respect to the raw precursor material. The selective investigation of the dynamics of the NC components has been possible by using properly isotopically labeled materials and applying quasielastic neutron scattering techniques. Results have been analyzed in the momentum transfer range where the coherent scattering contribution is minimal, as determined by complementary neutron diffraction experiments with polarization analysis. We observe the development of dynamic heterogeneity in the intermediate scattering function of the NC components, which grows with increasing time. Local motions in the precursor matrix of the NC are accelerated with respect to the reference bulk behavior, while the displacements of SCNPs’ hydrogens show enhanced deviations from Gaussian and exponential behavior compared with the pure melt of SCNPs. The resulting averaged behavior in the NC coincides with that of the pure precursor, in accordance with the macroscopic observations by differential scanning calorimetry (DSC) experiments.

The folding of certain proteins (e.g., enzymes) into perfectly defined 3D conformations via multi-orthogonal interactions is critical to their function. Concerning synthetic polymers chains, the “folding” of individual polymer chains at high dilution via intra-chain interactions leads to so-called single-chain nanoparticles (SCNPs). This review article describes the advances carried out in recent years in the folding of single polymer chains into discrete SCNPs via multi-orthogonal interactions using different reactive chemical species where intra-chain bonding only occurs between groups of the same species. First, we summarize results from computer simulations of multi-orthogonally folded SCNPs. Next, we comprehensively review multi-orthogonally folded SCNPs synthesized via either non-covalent bonds or covalent interactions. Finally, we conclude by summarizing recent research about multi-orthogonally folded SCNPs prepared through both reversible (dynamic) and permanent bonds.

The folding of certain proteins (e.g., enzymes) into perfectly defined 3D conformations via multi-orthogonal interactions is critical to their function. Concerning synthetic polymers chains, the “folding” of individual polymer chains at high dilution via intra-chain interactions leads to so-called single-chain nanoparticles (SCNPs). This review article describes the advances carried out in recent years in the folding of single polymer chains into discrete SCNPs via multi-orthogonal interactions using different reactive chemical species where intra-chain bonding only occurs between groups of the same species. First, we summarize results from computer simulations of multi-orthogonally folded SCNPs. Next, we comprehensively review multi-orthogonally folded SCNPs synthesized via either non-covalent bonds or covalent interactions. Finally, we conclude by summarizing recent research about multi-orthogonally folded SCNPs prepared through both reversible (dynamic) and permanent bonds.

We investigate the effect of intra-molecular cross-links on the properties of polymer bulks. To do this, we apply a combination of thermal, rheological, diffraction, and neutron spin echo experiments covering the inter-molecular as well as the intermediate length scales to melts of single-chain nano-particles (SCNPs) obtained through ‘click’ chemistry. The comparison with the results obtained in a bulk of the corresponding linear precursor chains (prior to intra-molecular reaction) and in a bulk of SCNPs obtained through azide photodecomposition process shows that internal cross-links do not influence the average inter-molecular distances in the melt, but have a profound impact at intermediate length scales. This manifests in the structure, through the emergence of heterogeneities at nanometric scale, and also in the dynamics, leading to a more complex relaxation behavior including processes that allow relaxation of the internal domains. The influence of the nature of the internal bonds is reflected in the structural relaxation that is slowed down if bulky cross-linking agents are used. We also found that any residual amount of cross-links is critical for the rheological behavior, which can vary from an almost entanglement-free polymer bulk to a gel. The presence of such inter-molecular cross-links additionally hinders the decay of density fluctuations at intermediate length scales.

We present an investigation by molecular dynamics (MD)-simulations of the coherent dynamic structure factor, S(Q, t) (Q: momentum transfer), of liquid water at the mesoscale (0.1 Å−1 ≤ Q ≤ Qmax) [Qmax ≈ 2 Å−1: Q-value of the first maximum of the static structure factor, S(Q), of water]. The simulation cell—large enough to address the collective properties at the mesoscale—is validated by direct comparison with recent results on the dynamic structure factor in the frequency domain obtained by neutron spectroscopy with polarization analysis [Arbe et al., Phys. Rev. Res. 2, 022015 (2020)]. We have not only focused on the acoustic excitations but also on the relaxational contributions to S(Q, t). The analysis of the MD-simulation results—including the self- and distinct contributions to the diffusive part of S(Q, t)—nicely explains why the relaxation process hardly depends on Q in the low Q-range (Q ≤ 0.4 Å−1) and how it crosses over to a diffusion-driven process at Q ≈ Qmax. Our simulations also give support to the main assumptions of the model used to fit the experimental data in the above mentioned paper. The application of such a model to the simulation S(Q, t) data delivers (i) results for the relaxation component of S(Q, t) in agreement with those obtained from neutron experiments and (ii) longitudinal and transverse hydrodynamic-like components with similar features than those identified in previous simulations of the longitudinal and transverse current spectra directly. On the other hand, in general, our MD-simulations results of S(Q, t) qualitatively agree with the viscoelastic transition framework habitually used to describe inelastic x-ray scattering results.

Single-Chain Nano-Particles (SCNPs) obtainedby intra-molecular cross-linking of linear macromolecules (precursors) are emerging soft nano-objects showing unique and remarkablephysicochemical, rheological, and sensing properties as a result of their locally collapsed structure and ultrasmall size. During last years, we havestudied the properties of systems based on SCNPs, including dilute and crowded solutions, bulks and all-polymer nano-composites with SCNPs asfillers (see, e. g.). Diverse techniques have been combined, including small angle scattering, quasielastic neutron scattering and coarse-gainedmolecular dynamics simulations. Here we present the results on the properties of SCNPs in solution and how they develop upon crowding their environment, with the all-polymer nano-composite as limit. In solution, SCNPs obtained through standard synthesis routes adopt sparsemorphologies. Crowding induces compaction of the SCNPs and in the limit case of the nano-composite, the observed conformation of the SCNPresembles that of a crumpled globule. Furthermore, the impact of the presence of SCNPs on the dynamics of an entangled polymer matrix isaddressed. In the dynamically asymmetric system investigated, we observe a slowing down of the Rouse-like dynamics as well as a pronouncedincrease of the explored volume of the (faster) matrix linear chains. The latter effect is attributed to the particular topology (internalcompartmentation) of the slow SCNP filler component.

The existence of an ideal glass and the resolution to the Kauzmann paradox is a long-standing open question in materials science. To address this problem, we exploit the ability of glasses with large interfacial area to access low energy states. We submit aggregates of spheres of a polymeric glass former to aging well below their glass transition temperature, Tg; and characterize their thermodynamic state by calorimetry, and the vibrational density of state (VDOS) by inelastic neutron scattering (INS). We show that, when aged at appropriate temperatures, glassy spheres attain a thermodynamic state corresponding to an ideal glass in time scales of about one day. In this state, the boson peak, underlying the deviation from the Debye level of the VDOS, is essentially suppressed. Our results are discussed in the framework of the link between the macroscopic thermodynamic state of glasses and their vibrational properties.

We investigate the effect of intra-molecular cross-links on the properties of polymer bulks. To do this, we apply a combination of thermal, rheological, diffraction, and neutron spin echo experiments covering the inter-molecular as well as the intermediate length scales to melts of single-chain nano-particles (SCNPs) obtained through ‘click’ chemistry. The comparison with the results obtained in a bulk of the corresponding linear precursor chains (prior to intra-molecular reaction) and in a bulk of SCNPs obtained through azide photodecomposition process shows that internal cross-links do not influence the average inter-molecular distances in the melt, but have a profound impact at intermediate length scales. This manifests in the structure, through the emergence of heterogeneities at nanometric scale, and also in the dynamics, leading to a more complex relaxation behavior including processes that allow relaxation of the internal domains. The influence of the nature of the internal bonds is reflected in the structural relaxation that is slowed down if bulky cross-linking agents are used. We also found that any residual amount of cross-links is critical for the rheological behavior, which can vary from an almost entanglement-free polymer bulk to a gel. The presence of such inter-molecular cross-links additionally hinders the decay of density fluctuations at intermediate length scales.

Combining neutron scattering and fully atomistic molecular dynamics simulations allows unraveling structural and dynamical features of polymer melts at different length scales, mainly in the intermolecular and monomeric range. Here we present the methodology developed by us and the results of its application during the last years in a variety of polymers. This methodology is based on two pillars: (i) both techniques cover approximately the same length and time scales and (ii) the classical van Hove formalism allows easily calculating the magnitudes measured by neutron scattering from the simulated atomic trajectories. By direct comparison with experimental results, the simulated cell is validated. Thereafter, the information of the simulations can be exploited, calculating magnitudes that are experimentally inaccessible or extending the parameters range beyond the experimental capabilities. We show how detailed microscopic insight on structural features and dynamical processes of various kinds has been gained in polymeric systems with different degrees of complexity, and how intriguing questions as the collective behavior at intermediate length scales have been faced.

167 p., Las llamadas nanopartículas unicadena ("single-chain nanoparticles", SCNPs) se obtienen mediante enlazamiento puramente intramolecular de precursores poliméricos. Hay un interés creciente en estos sistemas debido a sus prometedoras aplicaciones en catálisis, biomedicina, sensores, nanocompuestos, etc. El conocimiento de su estructura y dinámica, que controlan en gran parte su respuesta al entorno, es aún escaso. Esta tesis supone un importante avance en dicho conocimiento al investigar tres problemas de interés fundamental y práctico aún inexplorados. Mediante técnicas de simulación computacional se estudia y demuestra: 1) La posibilidad de controlar la topología (en particular la compacidad) de las SCNPs usando anillos como precursores en disoluciones concentradas de anillos inertes (con interacciones puramente estéricas). 2) La respuesta de las SCNPs al flujo de cizalla, cubriendo todo el intervalo desde alta dilución hasta disolución concentrada. Las SCNPs muestran una respuesta independiente de su topología concreta, únicamente ligada a su arquitectura de tipo red polimérica. A diferencia del caso simple de cadenas lineales, la respuesta es diferente a ambos lados de la concentración de solapamiento, este efecto estando ligado a las interacciones topológicas que evitan la concatenación de los anillos presentes en su arquitectura. 3) La competición entre enlaces intra- e intermoleculares en disoluciones de SCNPs con enlaces reversibles, y la obtención de geles reversibles basados en SCNPs, con redes estables altamente dinámicas y evitando la separación de fases a concentraciones de interés.

Using dielectric spectroscopy experiments performed at multiple temperatures and frequency ranges, we demonstrate how the chemotherapy drug paclitaxel changes the dynamic properties of water in a breast cancer cell line (MCF-7). From the measured data, we present evidence that treatment with paclitaxel leads to a slight increase in activation energy in a relaxation related to bulk-like water. More importantly, we also observe that paclitaxel changes the constraining imposed by the biological interfaces on hydration water, whose single-particle dynamics becomes slower and with higher activation energy. These variations are only observable after freezing the dynamics from other cellular components, such as proteins and DNAs, regardless of the state of the cells, that is, treated or not treated or even if the cells are no longer viable. Therefore, changes in water dynamics could be detected prior to those related to the global dynamics within the cellular environment.

Single-chain polymer nanoparticles (SCNPs) are soft nano-objects consisting of uni-macromolecular chains collapsed to a certain degree by intramolecular crosslinking. The similarities between the behaviour of SCNPs and that of intrinsically disordered proteins suggest that SCNPs in concentrated solutions can be used as models to design artificial micro-environments, which mimic many of the general aspects of cellular environments. In this work, the self-assembly into SCNPs of an amphiphilic random copolymer, composed by oligo(ethylene glycol)methyl ether methacrylate (OEGMA) and 2-acetoacetoxy ethyl methacrylate (AEMA), has been investigated by means of the dielectric relaxation of water. Direct evidence of segregation of the AEMA repeating units is provided by comparison with the dielectric relaxation of water in similar solutions of the linear hydrophilic polymer, P(OEGMA). Furthermore, the results of comparative studies with similar water solutions of an amphiphilic block copolymer forming multi-chain micelles support the single-chain character of the self-assembly of the random copolymer. The overall obtained results highlight the suitability of the dielectric spectroscopy to confirm the self-assembly of the amphiphilic random copolymers into globular like core–shell single-chain nanoparticles at a concentration well above the overlap concentration.

Combining neutron scattering and fully atomistic molecular dynamics simulations allows unraveling structural and dynamical features of polymer melts at different length scales, mainly in the intermolecular and monomeric range. Here we present the methodology developed by us and the results of its application during the last years in a variety of polymers. This methodology is based on two pillars: (i) both techniques cover approximately the same length and time scales and (ii) the classical van Hove formalism allows easily calculating the magnitudes measured by neutron scattering from the simulated atomic trajectories. By direct comparison with experimental results, the simulated cell is validated. Thereafter, the information of the simulations can be exploited, calculating magnitudes that are experimentally inaccessible or extending the parameters range beyond the experimental capabilities. We show how detailed microscopic insight on structural features and dynamical processes of various kinds has been gained in polymeric systems with different degrees of complexity, and how intriguing questions as the collective behavior at intermediate length scales have been faced.

By means of the recent implementation of neutron polarization analysis on a wide-angle time-of-flight spectrometer, we have been able to separately measure coherent and incoherent dynamic structure factors of heavy water with sub-meV resolution in a wide scattering vector (Q) range. The observed decorrelation of collective fluctuations at mesoscales hardly depends on Q. In the crossover towards intermolecular scales, the coherent dynamics is nicely described by the convolution of a Q-independent mode and diffusion, in addition to collective excitations.

In recent decades, self-confinement effects arising from the folding of individual synthetic polymer chains to single-chain nanoparticles (SCNPs) have been exploited for the construction of efficient enzyme-mimetic catalysts, improved drug delivery nanosystems and innovative sensing nanomaterials, among other uses. Remarkably, the imperfect folding of a unimolecular synthetic chain to a functional soft nano-object resembles – to some extent – the folding of a protein to its native, functional state. However, the huge possibilities that can be deployed by determining how external confinement modulates the structure, dynamics and properties of SCNPs have not been totally appreciated yet. In this article, after considering the opportunites that internal confinement in SCNPs offers for catalysis; encapsulation, transport and delivery of therapeutic cargos; and sensing, targeting and bioimaging applications, as well as other diverse advanced applications, we try to provide a unifying vision of what is the expected effect of external confinement – as imposed under different geometrical constraints as well as in solution, in the melt state, on surfaces and in membranes – on the size, shape and, hence, potential functionality/foreseen applications of SCNPs. We anticipate a plethora of opportunities that open up arising from external confinement of SCNPs: from innovative purification techniques and improved all-polymer nanocomposites, to smart responsive surfaces and new topological nanostructures.

Applying small-angle neutron scattering (SANS) on isotopically labeled samples, we have characterized the thermally driven concentration fluctuations (TCFs), one of the main factors in the phenomenology of blend dynamics, in mixtures of styrene–butadiene rubber (SBR) and oligomers of polystyrene (PS) with different compositions. This system displays a large dynamic asymmetry and is thus a good model to explore the tunability of properties of interest in the rubber industry. The SANS experiments, complemented with neutron diffraction with polarization analysis, have allowed one to determine the UCST behavior of the blend and establish its phase diagram. We find a close vicinity of the spinodal and vitrification lines for intermediate concentrations and samples rich in PS. This induces the freezing of the correlation length for TCF when decreasing the temperature and also has an impact on the reported dielectric response of these mixtures. Furthermore, we have deduced the relevant length scale for segmental relaxation from the comparison of SANS and dielectric results. The values found (≈1.5–2 nm) are close to the Kuhn lengths of the components. The relevance of nanometric length scales in this system could also be tentatively attributed to an underlying nanodomain structure associated with the segregation of phenyl rings and main chains, supported by complementary X-ray diffraction experiments.

We present a small-angle neutron scattering (SANS) and neutron spin echo investigation on the structure and dynamics of irreversible single-chain nanoparticles (SCNPs) in dilute solution. SCNPs are ultra-small soft nano-objects obtained by intramolecular folding/collapse of individual linear polymer chains (precursors). SANS has demonstrated the compaction of macromolecules upon creation of internal cross-links, although their conformation is far from a globular topology. To describe the dynamic structure factor of the SCNPs in solution, we have taken into account their dual polymer/nanoparticle character and applied theoretical approximations based on the Zimm model. The study reveals relaxation of internal degrees of freedom but clearly slowed down with respect to the precursor counterparts. This effect is attributed to the internal friction associated to the compartmentation in domains within the macromolecule. We discuss the structural and dynamical similarities of SCNPs with disordered proteins, in particular with intrinsically disordered proteins. The high internal friction in both cases seems to be associated to the existence of internal domains.

The mechanical characterization of rubber materials at the frequencies relevant for the tire function during braking (about 1 MHz) is extremely challenging. On the other hand, dielectric relaxation experiments provide a suitable tool for the analysis of relaxation phenomena over a broad frequency range with high sensitivity. Here we show that by analyzing dielectric relaxation experiments in the framework of a simple model the mechanical relaxation of simplified industrial systems based on mixtures of a styrene butadiene rubber (SBR) with a polystyrene oligomer can be anticipated, at least for the SBR rich mixtures that are more relevant for development of tire polymers. The model needs the description of the dielectric and mechanical relaxation processes of the single components of the mixture and uses concepts and ideas introduced in the past for describing the segmental dynamics of athermal polymer blends. The model description of dielectric relaxation experiments on the mixtures provides a quantification of the thermal fluctuations of concentration in the blends. With this input, the mechanical relaxation of the mixtures are calculated using well established equations for the mechanical properties of composite materials. The present approach should be helpful in a rational design of the rubber material depending on the specific requirements.

More than 100 years after Debye proposed his model for the dielectric relaxation of monoalcohols (MA), some fundamental questions about their dynamics and its relation with the supramolecular structures created by hydrogen bonding remain not fully understood. The recent detection of the dynamics of hydrogen bonded aggregates by techniques other than dielectric spectroscopy is leading to novel insights and opening new questions. In particular it was recently reported that the shear response of some MA present three relaxation components, at variance with their apparent bimodal dielectric response. We show by mixing an archetype MA with LiCl that both shear and dielectric measurements are consistent with the presence of three separated contributions. Results are discussed in the more general context of MAs with non-exponential slow dielectric relaxations. In particular, we propose the recently reported third process as the origin of the unusual broadening of the Debye-like dielectric relaxation of some MAs.

The impact of purely intramolecular cross-linking on the properties of a polymer melt is studied by neutron diffraction and quasielastic incoherent and coherent neutron scattering on a system composed exclusively of single-chain nanoparticles. As a reference, a parallel study is presented on the melt of the linear precursor chains’ counterpart. Associated with structural heterogeneities provoked by the internal compartmentalization due to cross-links, a dramatic slowing down of the relaxation of density fluctuations is observed at intermediate length scales.

168 p., Las propiedades dinámicas de los elastómeros en régimen lineal son una de las líneas de investigación centrales de Michelin. La comprensión del efecto del plastificante en la dependencia en temperatura de la relajación mecánica es un punto clave para mejorar el rendimiento de un neumático, en particular aumentar la adherencia durante el frenado y la disminución de la resistencia a la rodadura. De hecho, durante su período de uso, el neumático debe disipar la mayor cantidad de energía posible durante el frenado, sin embargo, debemos minimizar este proceso durante el rodamiento regular. Variar la temperatura de transición vítrea (Tg) del sistema permite modificar el dominio de la frecuencia y la temperatura en el que el material disipa la energía. Los resultados obtenidos en esta tesis doctoral permiten obtener una mejor comprensión de la dinámica de las mezclas de polímeros, así como la predicción de las propiedades mecánicas de alta frecuencia que podrían ser un punto determinante para facilitar una mejora significativa en el diseño de materiales con propiedades deseadas.

Single-chain polymer nanoparticles (SCNPs) obtained through chain collapse by intramolecular cross-linking are attracting increasing interest as components of all-polymer nanocomposites, among other applications. We present a dielectric relaxation study on the dynamics of mixtures of poly(vinyl methyl ether) (PVME) and polystyrene (PS)-based SCNPs with various compositions. Analogous dielectric measurements on a miscible blend of PVME with the linear precursor chains of the SCNPs are taken as reference for this study. Both systems present completely different behaviors: While the blend with the linear precursor presents dynamics very similar to that reported for PVME/PS miscible blends, in the PVME/SCNP mixtures there are an appreciable amount of PVME segments that are barely affected by the presence of SCNPs, which nearly vanishes only for mixtures with high SCNP content. Interestingly, in the frame of a simple two-phase system, our findings point towards the existence of a SCNP-rich phase with a constant PVME fraction, regardless of the overall concentration of the mixture. Moreover, the dynamics of the PVME segments in this SCNP-rich phase display an extreme dynamic heterogeneity, a signature of constraint effects.

The diffusion of polymer chains in miscible polymer blends with large dynamic asymmetry—those where the two blend components display very different segmental mobility—is not well understood yet. In the extreme case of the blend system of poly(ethylene oxide) (PEO) and poly(methyl methacrylate)(PMMA), the diffusion coefficient of PEO chains in the blend can change by more than five orders of magnitude while the segmental time scale hardly changes with respect to that of pure PEO. This behavior is not observed in blend systems with small or moderate dynamic asymmetry as, for instance, polyisoprene/poly(vinyl ethylene) blends. These two very different behaviors can be understood and quantitatively explained in a unified way in the framework of a memory function formalism, which takes into account the effect of the collective dynamics on the chain dynamics of a tagged chain.

Access to completely deuterated single-chain nanoparticles (dSCNPs) has remained an unresolved issue. Herein, the first facile and efficient procedure to produce dSCNPs is reported, which comprises: i) the use of commercially available perdeuterated cyclic ether monomers as starting reagents, ii) a ring-opening copolymerization process performed in bulk to produce a neat dSCNP precursor, iii) a standard azidation reaction to decorate this precursor with azide moieties, and iv) a facile intramolecular azide photodecomposition step carried out under UV irradiation at high dilution providing with highly valuable, completely deuterated soft nano-objects from the precursor. dSCNPs are used to investigate by means of neutron-scattering measurements the form factor (radius of gyration, scaling exponent) of polyethylene oxide (PEO) chains in nanocomposites with different amounts of dSCNPs. Moreover, to illustrate the possibilities offered by the synthetic route disclosed in this communication for potential applications, the significant reduction in viscosity observed in a pure melt of polyether-based single-chain nanoparticles when compared to a melt of the corresponding linear polymer chains is shown.

The conformation of single-chain nanoparticles (SCNPs) in the presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders. A model describing the scattering of aggregating polydisperse SCNPs has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Two different crowders, of low and high molecular weights, are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and shall contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects and in particular the effect of crowding on biomacromolecules.