Comment on "Anomalous structural recovery in the near glass transition range in a polymer glass: Data revisited in light of temperature variability in vacuum oven-based 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, T-g, by accounting for the presence of different relaxation mechanisms active in glass equilibration

Effect of environmental humidity on the ionic transport of poly(ethylene oxide) thin films by local dielectric spectroscopy

The effect of humidity on the ionic transport in the amorphous phase of poly(ethylene oxide) thin films has been studied by via local dielectric spectroscopy. We explored a controlled humidity range between 15 %RH and 50 %RH. AFM-based local dielectric imaging allowed to obtain simultaneously the thin films topography and the corresponding dielectric contrast maps. No humidity effect on the film topography was observed whereas large variation of the dielectric signal could be detected. In addition, we observed a clear dielectric contrast in different locations on the thin film surface. At selected regions with high contrast in the dielectric maps, we performed nanoDielectric Spectroscopy (nDS) measurements covering the frequency range from 5 Hz to 100 kHz. By modeling these spectroscopy results, we quantified the conductivity of the amorphous phase of the semicrystalline poly(ethylene oxide) films. The crystalline fraction of the PEO thin films was extracted and found to be about 36%, independently of humidity. However, the average conductivity increased by a factor of 25 from 2×10- 10 to 5×10-9 S/cm, by changing environmental humidity in the explored %RH range.This work was supported by the European Union: EUSMI, H2020-INFRAIA-2016-1, PROJECT 731019. A. A. acknowledges funding from Spanish Government “Ministerio de Ciencia, Innovacion y Universidades” (PGC2018-094548-B-I00 (MCIU/AEI/FEDER, UE)), and Basque Government (IT-1175-19). D. E. M. acknowledges financial support via the “Juan de la Cierva – Incorporación” grant (IJCI-2017-31600, MCIU – Spain)

Dynamics of Confined Short-Chain alkanol in MCM-41 by Dielectric Spectroscopy: Effects of matrix and system Treatments and Filling Factor

The dynamics of n-propanol confined in regular MCM-41 matrix with the pore size Dpore = 40 Å, under various matrix conditioning and sample confining conditions, using broadband dielectric spectroscopy (BDS), is reported. First, various drying procedures with the capacitor filling under air or N2 influence the BDS spectra of the empty MCM-41 and the confined n-PrOH/MCM-41 systems, but have a little effect on the maximum relaxation time of the main process. Finally, various filling factors of n-PrOH medium in the optimally treated MCM-41 system lead to unimodal or bimodal spectra interpreted in terms of the two distinct dynamic phases in the confined states.This research was funded by the EUSMI/Horizon 2020 grants: E181200215 and E 180300076 and E180300077 and by the Slovak Research and Development Agency (SRDA) under the contract No. APVV-16-0369. And J.B. was funded by the VEGA Agency, Slovakia with Grant No. 2/0030/16

Intra- vs Intermolecular Cross-Links in Poly(methyl methacrylate) Networks Containing Enamine Bonds

The molecular dynamics of a copolymer composed of methyl methacrylate (MMA) and (2-acetoacetoxy)ethyl methacrylate (AEMA) monomers and the influence on it of intra-to intermolecular cross-links of AEMA units with ethylenediamine (EDA) was studied by combining dielectric relaxation experiments and thermal investigations. The dielectric spectra of the non-cross-linked copolymer show three dynamical processes: a slow relaxation (alpha) and a faster (beta), both dominated by the MMA dynamics, and an even faster secondary relaxation (gamma) reflecting the AEMA dynamics. Already for low cross-linking densities, the gamma process is very much affected and eventually disappears, increasing the cross-linking density. The secondary beta relaxation however was nearly unaffected by cross-linking. The effect of cross-linking on the alpha relaxation was very pronounced with an important increasing of the glass transition temperature Tg. There was also an increase of the dynamic heterogeneity and the relaxation intensity when increasing the cross-linking density (up to the maximum explored, 9 mol % EDA). The quality of the average time scale and Tg value have similarities in behavior for intra-and intermolecular cross linking, but clear differences in the dynamic heterogeneities where observed. These differences can be interpreted in connection with the sparse internal structure of the collapsed single chains obtained by intramolecular cross-linking.We gratefully acknowledge Grant PGC2018-094548-B-I00 funded by MCIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe", the Grants IT-1175-19 and IT-1566-22 from Eusko Jaurlaritza (Basque Government) and the Open Access funding provided by University of Basque Country

Self-propelling colloids with finite state dynamics

Endowing materials with the ability to sense, adapt, and respond to stimuli holds the key to a progress leap in autonomous systems. In spite of the growing success of macroscopic soft robotic devices, transferring these concepts to the microscale presents several challenges connected to the lack of suitable fabrication and design techniques and of internal response schemes that connect the materials’ properties to the function of the active units. Here, we realize self-propelling colloidal clusters which possess a finite number of internal states, which define their motility and which are connected by reversible transitions. We produce these units via capillary assembly combining hard polystyrene colloids with two different types of thermoresponsive microgels. The clusters, actuated by spatially uniform AC electric fields, adapt their shape and dielectric properties, and consequently their propulsion, via reversible temperature-induced transitions controlled by light. The different transition temperatures for the two microgels enable three distinct dynamical states corresponding to three illumination intensity levels. The sequential reconfiguration of the microgels affects the velocity and shape of the active trajectories according to a pathway defined by tailoring the clusters’ geometry during assembly. The demonstration of these simple systems indicates an exciting route toward building more complex units with broader reconfiguration schemes and multiple responses as a step forward in the pursuit of adaptive autonomous systems at the colloidal scale.L.A. acknowledges the financial support from the European Soft Matter Infrastructure (EUSMI) proposal number S180600105. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program grant agreement No. 101001514. We thank Alexander Kuehne and Dirk Rommels for their help with particle synthesis and discussion

Disentangling the Calorimetric Glass-Transition Trace in Polymer/ Oligomer Mixtures from the Modeling of Dielectric Relaxation and the Input of Small-Angle Neutron Scattering

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.A. Alegria, A. Arbe, and J. Colmenero acknowledge the Grant PID2021-123438NB-I00 funded by MCIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe", as well as financial support of Eusko Jaurlaritza, codes IT-1175-19 and IT-1566-22, and from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and the Materials Physics Center on behalf of the Department of Education of the Basque Government. Open Access funding provided by University of Basque Country

Broadband Dielectric Spectroscopy Study of Biobased Poly(alkylene 2,5-furanoate)s’ Molecular Dynamics

Abstract Poly(2,5-alkylene furanoate)s are bio-based, smart, and innovative polymers that are considered the most promising materials to replace oil-based plastics. These polymers can be synthesized using ecofriendly approaches, starting from renewable sources, and result into final products with properties comparable and even better than those presented by their terephthalic counterparts. In this work, we present the molecular dynamics of four 100% bio-based poly(alkylene 2,5-furanoate)s, using broadband dielectric spectroscopy measurements that covered a wide temperature and frequency range. We unveiled complex local relaxations, characterized by the simultaneous presence of two components, which were dependent on thermal treatment. The segmental relaxation showed relaxation times and strengths depending on the glycolic subunit length, which were furthermore confirmed by high-frequency experiments in the molten region of the polymers. Our results allowed determining structure–property relations that are able to provide further understanding about the excellent barrier properties of poly(alkylene 2,5-furanoate)s. In addition, we provide results of high industrial interest during polymer processing for possible industrial applications of poly(alkylene furanoate)s.This research was funded by the European Union: EUSMI, H2020-INFRAIA-2016-1, PROJECT 731019, via proposals E171100043 and E171100040. The APC was funded by EUSMI. B.R.-H. and A.A. acknowledge funding from Basque Government (IT-1175-19). D.E.M.-T. acknowledges financial support via the postdoctoral fellowship “Juan de la Cierva–Incorporación” grant (IJCI-2017-31600, MCIU–Spain). G.G., M.S. and N.L. and A.M. acknowledge financial support via the framework COST Action FUR4Sustain, CA18220, supported by COST (European Cooperation in Science and Technology)

Microscopic versus Macroscopic Glass Transitions and Relevant Length Scales in Mixtures of Industrial Interest

We have combined X-ray diffraction, neutron diffraction with polarization analysis, small-angle neutron scattering (SANS), neutron elastic fixed window scans (EFWS), and differential scanning calorimetry (DSC) to investigate polymeric blends of industrial interest composed by isotopically labeled styrene–butadiene rubber (SBR) and polystyrene (PS) oligomers of size smaller than the Kuhn length. The EFWS are sensitive to the onset of liquid-like motions across the calorimetric glass transition, allowing the selective determination of the “microscopic” effective glass transitions of the components. These are compared with the “macroscopic” counterparts disentangled by the analysis of the DSC results in terms of a model based on the effects of thermally driven concentration fluctuations and self-concentration. At the microscopic level, the mixtures are dynamically heterogeneous for blends with intermediate concentrations or rich in PS, while the sample with highest content of the fast SBR component looks as dynamically homogeneous. Moreover, the combination of SANS and DSC has allowed determining the relevant length scale for the α-relaxation through its loss of equilibrium to be ≈30 Å. This is compared with the different characteristic length scales that can be identified in these complex mixtures from structural, thermodynamical, and dynamical points of view because of the combined approach followed. We also discuss the sources of the non-Gaussian effects observed for the atomic displacements and the applicability of a Lindemann-like criterion in these materials.We thank Marc Couty for fruitful discussions and Karine Vernay (Michelin Advanced Research) for dSBR synthesis. The authors acknowledge Grant PID2021-123438NB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, as well as financial support of Eusko Jaurlaritza (code: IT1566-22) and from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and the Materials Physics Center on behalf of the Department of Education of the Basque Government. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)

Network dynamics in nanofilled polymers

It is well accepted that adding nanoparticles (NPs) to polymer melts can result in significant property improvements. Here we focus on the causes of mechanical reinforcement and present rheological measurements on favourably interacting mixtures of spherical silica NPs and poly(2-vinylpyridine), complemented by several dynamic and structural probes. While the system dynamics are polymer-like with increased friction for low silica loadings, they turn network-like when the mean face-to-face separation between NPs becomes smaller than the entanglement tube diameter. Gel-like dynamics with a Williams-Landel-Ferry temperature dependence then result. This dependence turns particle dominated, that is, Arrhenius-like, when the silica loading increases to similar to 31 vol%, namely, when the average nearest distance between NP faces becomes comparable to the polymer's Kuhn length. Our results demonstrate that the flow properties of nanocomposites are complex and can be tuned via changes in filler loading, that is, the character of polymer bridges which 'tie' NPs together into a network.We thank Leon Serc (ETH Zurich) for help with FTIR. Enlightening discussions with Ulrich Jonas are gratefully acknowledged. Partial support has been provided by the EU FP7 (ETN Supolen GA-607937, Infrastructure ESMI GA-262348) and the Greek General Secretariat for Research and Technology (Thalis-380238 COVISCO). M.R. acknowledges financial support from the National Science Foundation under grants DMR-1309892, DMR-1436201 and DMR-1121107, the National Institutes of Health under grants P01-HL108808 and 1UH2HL123645 and the Cystic Fibrosis Foundation. D.Z., S.G., R.H.C. and S.K.K. gratefully acknowledge the National Science Foundation grant DMR-1408323 for financial support

How confinement affects the nucleation, crystallization and dielectric relaxation of poly(butylene succinate) and poly(butylene adipate) infiltrated within nanoporous alumina templates

This work describes the successful melt infiltration of poly(butylene succinate) (PBS) and poly(butylene adipate) (PBA) within 70 nm diameter anodic aluminum oxide (AAO) templates. The infiltrated samples were characterized by SEM, Raman, and FTIR spectroscopy. The crystallization behavior and crystalline structure of both polymers, bulk and confined, were analyzed by differential scanning calorimetry (DSC) and grazing incidence wide angle x-ray scattering (GIWAXS). DSC revealed that a change in the nucleation process occurred from heterogeneous nucleation for bulk samples, to homogeneous nucleation for infiltrated PBA, and to surface-induced nucleation for infiltrated PBS. GIWAXS results indicate that PBS nanofibers crystallize in the α-phase, as well as their bulk samples. However, PBA nanofibers crystallize just in the β-phase, whereas PBA bulk samples crystallize in a mixture of α- and β-phases. The crystal orientation within the pores was determined, and differences between PBS and PBA were also found. Finally, broadband dielectric spectroscopy (BDS) was applied to study the segmental dynamics for bulk and infiltrated samples. The glass temperature was found to significantly decrease in the PBS case upon infiltration while that of PBA remained unchanged. These differences were correlated with the higher affinity of PBS to the AAO walls as compared to PBA, in accordance with their nucleation behavior (surface-induced versus homogeneous nucleation respectively).POLYMAT and ICTP-CSIC Institutions acknowledge financial support from the Spanish Ministry of Science, Innovation, and Universities (MAT2017-83014-C2-1-P and MAT2017-83014-C2-2-P). M.S. gratefully acknowledges the award of a PhD fellowship by POLYMAT Basque Center for Macromolecular Design and Engineering. J.M. acknowledges support from the Provincial Council of Gipuzkoa under the program Fellow Gipuzkoa and “Fomento San Sebastián” in the framework program “Retorno del Talento Local” Donostia up! 2016. G.L, D.W., and A.J.M acknowledge the support from the National Natural Science Foundation of China (51820105005, 21873109) and National Key R&D Program of China (2017YFE0117800). G.L. acknowledges the support from the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2015026). This work has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 778092. The UPV/EHU team gratefully acknowledges the financial contribution of the Basque Government through grants IT1309-19 and IT1175- 19