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The aging-time dependence of the segmental relaxation time of poly(vinyl acetate) (PVAc) in the glassy state is investigated in the bulk polymer and its nanocomposites with silica (SiO 2). These systems present identical segmental dynamics, when this is probed in the equilibrium supercooled liquid by broadband dielectric spectroscopy. An acceleration of the physical aging process of PVAc with SiO 2 was detected by monitoring the enthalpy recovery through differential scanning calorimetry. The segmental relaxation time during physical aging, followed by means of BDS, has been shown to increase more rapidly the higher the SiO 2 concentration in PVAc is. Thermally stimulated depolarization current experiments show that this is the case over the whole probed glassy state. This means that nanocomposites displaying a relatively slow segmental mobility evolve toward equilibrium more rapidly than the bulk. Furthermore, despite the faster increase in the relaxation time with aging time, so-called self-retardation, the nanocomposites and their bulk counterpart reach the same values of equilibrium relaxation time. These findings not only confirm the assumption of identical equilibrium dynamics even in the aging regime for all nanocomposites and bulk polymers, proposed in previous works, but also highlight the fact that the physical aging rate is not determined solely by the polymer segmental dynamics, the amount of interface being an additional relevant parameter. © 2012 American Physical Society. ; The authors acknowledge the University of the Basque Country and Basque Country Government (Ref. No. IT-436-07, Departamento de Educación, Universidades e Investigación; and the Spanish Minister of Education (Grant No. MAT 2007-63681) for their financial support. V.M.B. acknowledges the CSIC for the JAE-Doc contract, cofinanced by the European Social Fun. ; Peer Reviewed

The physical aging process, namely the spontaneous evolution of the thermodynamic state occurring in glasses, has been monitored in poly(methyl methacrylate) (PMMA)/silica and polystyrene (PS)/silica nanocomposites following the time evolution of the enthalpy by means of differential scanning calorimetry (DSC). The effect on physical aging of the content of silica particles has been investigated in detail varying it over a wide range. Our results indicate accelerated physical aging in the nanocomposites in comparison to the corresponding pure polymer. Furthermore the acceleration is generally more pronounced in nanocomposites presenting a high silica content. This result cannot be attributed to a difference in molecular mobility of the polymers in the nanocomposites in comparison to pure PMMA and PS, since broadband dielectric spectroscopy (BDS) indicates no effect of silica nanoparticles on the polymer segmental dynamics. Moreover, calorimetric measurements reveal a reduction of the heat capacity jump at T g for the nanocomposites, as well as lower experimentally recoverable enthalpy values. This may result from the faster non-isothermal evolution of the glass state when cooling down the samples from their liquid state. To account for these experimental results the acceleration of physical aging has been rationalized in the framework of the diffusion of free volume holes model as previously proposed. This is able to adequately catch the dependence of the physical aging rate on silica content, determining the area of nanoparticles to the volume of polymer, that is the relevant variable within the diffusion model. © 2012 Published by Elsevier Ltd. ; The authors acknowledge the University of the Basque Country and Basque Country Government (Ref. No. IT-436-07, Depto. Educación, Universidades e Investigación and Spanish Minister of Education (Grant No. MAT 2007-63681) for their support. ; Peer Reviewed

9 páginas, 5 figuras, 3 tablas.-- Trabajo presentado al "MACRO2010: 43rd IUPAC World Polymer Congress" celebrado en Glasgow (U.K.) del 11 al 16 de julio de 2010. ; The spontaneous thermodynamically driven densification, the so-called physical aging, of glassy poly(mehtyl methacrylate) (PMMA) and its nanocomposites with silica has been described by means of the free volume holes diffusion model. This mechanism is able to account for the partial decoupling between physical aging and segmental dynamics of PMMA in nancomposites. The former has been found to be accelerated in PMMA/silica nanocomposites in comparison to "bulk" PMMA, whereas no difference between the segmental dynamics of bulk PMMA and that of the same polymer in nanocomposites has been observed. Thus, the rate of physical aging also depends on the amount of interface polymer/nanoparticles, where free volume holes disappear after diffusing through the polymer matrix. The free volume holes diffusion model is able to nicely capture the phenomenology of the physical aging process with a structure dependent diffusion coefficient. ; The authors acknowledge the University of the Basque Country and Basque Country Government (Ref. No. IT- 436-07, Depto. Educación, Universidades e Investigación) and Spanish Minister of Education (Grant Nos. MAT 2007- 63681 and CSD2006-00053) for their support. The support of the Basque Government within the Etortek program is also acknowledged. ; Peer reviewed

[Abstract] The present work aims to provide insights on recent findings indicating the presence of multiple equilibration mechanisms in physical aging of glasses. To this aim, we have investigated a glass forming polyether, poly(1-4 cyclohexane di-methanol) (PCDM), by following the evolution of the enthalpic state during physical aging by fast scanning calorimetry (FSC). The main results of our study indicate that physical aging persists at temperatures way below the glass transition temperature and, in a narrow temperature range, is characterized by a two steps evolution of the enthalpic state. Altogether, our results indicate that the simple old-standing view of physical aging as triggered by the α relaxation does not hold true when aging is carried out deep in the glassy state. ; D.C. research was funded by MICINN-Spain and FEDER-UE, grant PGC2018-094548-B-I00; and the Basque Government, grant IT-1175-19. J.M. thanks MICINN /FEDER for grant Ref. PGC2018-094620-A-I00 ; Eusko Jaurlaritza; IT-1175-19

This article belongs to the Special Issue Recent Developments on Calorimetry and Thermal Analysis of Polymers and Nanocomposites. ; The present work aims to provide insights on recent findings indicating the presence of multiple equilibration mechanisms in physical aging of glasses. To this aim, we have investigated a glass forming polyether, poly(1-4 cyclohexane di-methanol) (PCDM), by following the evolution of the enthalpic state during physical aging by fast scanning calorimetry (FSC). The main results of our study indicate that physical aging persists at temperatures way below the glass transition temperature and, in a narrow temperature range, is characterized by a two steps evolution of the enthalpic state. Altogether, our results indicate that the simple old-standing view of physical aging as triggered by the α relaxation does not hold true when aging is carried out deep in the glassy state. ; D.C. research was funded by MICINN-Spain and FEDER-UE, grant PGC2018-094548-B-I00; and the Basque Government, grant IT-1175-19. J.M. thanks MICINN /FEDER for grant Ref. PGC2018-094620-A-I00. ; Peer reviewed

The colloidal stability of metal nanoparticles is tremendously dependent on the thermal behavior of polymer brushes. Neat polyethylene glycol (PEG) presents an unconventional upper critical solution temperature in ethanol, where phase segregation and crystallization coexist. This thermal behavior translated to a PEG brush has serious consequences on the colloidal stability in ethanol of gold nanoparticles (AuNPs) modified with PEG brushes upon cooling. We observed that AuNPs (13 nm diameter) stabilized with conventional linear PEG brushes (Mn = 6 and 11 kg mol−1) in ethanol suffer from reversible phase separation upon a temperature drop over the course of a few hours. However, the use of a polymer brush with cyclic topology as a stabilizer prevents sedimentation, ensuring the colloidal stability in ethanol at −25 °C for, at least, four months. We postulate that temperature-driven collapse of chain brushes promotes the interpenetration of linear chains, causing progressive AuNP sedimentation, a process that is unfavorable for cyclic polymer brushes whose topology prevents chain interpenetration. This study reinforces the notion about the importance of polymer topology on the colloidal stability of AuNPs. ; We gratefully acknowledge support from the Spanish Ministry "Ministerio de Ciencia, Innovación y Universidades" (PGC2018-094548-B-I00, MICINN/FEDER, UE, and PID2019-111772RB-I00), Basque Government (IT-1175-19 and PIBA 2018-34) and Diputación Foral de Guipúzcoa (RED 2018). ; Peer reviewed

Despite the growing application of nanostructured polymeric materials, there still remains a large gap in our understanding of polymer mechanics and thermal stability under confinement and near polymer-polymer interfaces. In particular, the knowledge of polymer nanoparticle thermal stability and mechanics is of great importance for their application in drug delivery, phononics, and photonics. Here, we quantified the effects of a polymer shell layer on the modulus and glass-transition temperature (T) of polymer core-shell nanoparticles via Brillouin light spectroscopy and modulated differential scanning calorimetry, respectively. Nanoparticles consisting of a polystyrene (PS) core and shell layers of poly(n-butyl methacrylate) (PBMA) were characterized as model systems. We found that the high T of the PS core was largely unaffected by the presence of an outer polymer shell, whereas the lower T of the PBMA shell layer decreased with increasing PBMA thickness. The surface mobility was revealed at a temperature about 15 K lower than the T of the PBMA shell layer. Overall, the modulus of the core-shell nanoparticles decreased with increasing PBMA shell layer thickness. These results suggest that the nanoparticle modulus and T can be tuned independently through the control of nanoparticle composition and architecture. ; E.K., B.G., and G.F. acknowledge the financial support by ERC Advanced Grant Smartphon (No. 694977). B.G. acknowledges the support from the First Team project (POIR.04.04.00-00- 5D1B/18-00) granted by the Foundation for Polish Science. R.D.P. acknowledges the support of the National Science Foundation (NSF) Materials Research Science and Engineering Center Program through the Princeton Center for Complex Materials (DMR-1420541) and NSF CBET1706012. D.C. acknowledges financial support from the Basque Government (Grant No. IT-1175-19).

We introduce an approach to synthesize macrocyclic poly(ethylene oxide)s containing a pendant protected thiol group (pSH-CPEO), which is demonstrated to be able to attach to gold surfaces without prior deprotection. Our strategy is based on a bimolecular approach by which a di-alkyne molecule derived from thiol-protected 3-mercapto-1,2-propanediol and a series of PEO bis(azides) of M = 2, 6, and 11 kg mol are coupled via copper-catalyzed azide-alkyne cycloaddition. The cyclization reaction was verified by size exclusion chromatography and matrix-assisted laser desorption ionization time of flight mass spectrometry. In addition, we used fast scanning calorimetry to evaluate the glass transition temperature (T) of the synthesized pSH-CPEOs. Thanks to the extremely rapid cooling power of this technique, PEO crystallization can be circumvented and, therefore, its fully amorphous state can be investigated. The results confirmed higher T values for macrocycles compared to their chemically equivalent linear precursors. This result highlights the importance of the chain end in affecting the T of polymers. Finally, to demonstrate the ability of pSH-CPEO to covalently attach to gold surfaces, pSH-CPEO samples were allowed to react with gold-coated glass slides and the surface properties were compared with those of the samples obtained by the reaction of linear α-thiol, ω-methoxy PEO (with and without protection of the thiol group) and gold-coated glass slides. X-ray photoelectron spectroscopy data confirmed the formation of Au-S linkages as well as the removal of the thiol protector group through the quantitative analysis of the chemical composition at the surface. The contact angle data of pSH-CPEO/gold exhibited increased hydrophilicity compared to bare gold and topological effects at the interface. A reaction mechanism between the 2,4-dinitrobenzene-protected thiol group and the gold surface is also proposed. ; We also gratefully acknowledge support from the Spanish Ministry "Ministerio de Ciencia, Innovación y Universidades" (PGC2018-094548-B-I00, MICINN/ FEDER, UE), Basque Government (IT-1175-19 and PIBA 2018- 34), and Diputación Foral de Guipúzcoa (RED 2018).

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG ; [Abstract] Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities. ; This work was supported by the Ministerio de Ciencia e Innovacion/FEDER (under Ref. PGC2018-094620-A-I00 and PGC2018-095411-B-I00, CEX2019-000917-S, and PGC2018-095411-B-100) and the Basque Country Government (Ref. PIBA19-0051). S.M. is grateful to POLYMAT for the doctoral scholarship. The authors thank A. Arbe, A. Alonso-Mateo, and L. Hueso for their support and access to characterization tools. The authors also thank the technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). GIWAXS experiments were performed at BL11 NCD-SWEET beamline at ALBA Synchrotron (Spain) with the collaboration of ALBA staff. J.M and E.F.-G. acknowledge support through the European Union's Horizon 2020 research and innovation program, H2020-FETOPEN 01-2018-2020 (FET-Open Challenging Current Thinking), "LION-HEARTED," Grant Agreement No. 828984. J.M and N.S. would like to thank the financial support provided by the IONBIKE RISE project, which received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 823989. N.S., A.K., and A.B. furthermore are grateful to the U.S. National Science Foundation (NSF) for support via Project No. 1905901 within NSF's Division of Materials Research. A.S. and M.C. acknowledge financial support by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program "HEROIC," Grant Agreement No. 638059. This work was partially carried out at Polifab, the micro- and nanotechnology center of the Politecnico di Milano. C.M. thanks the Knut and Alice Wallenberg Foundation for funding through the project "Mastering Morphology for Solution-borne Electronics." A.I. thanks MICINN for a Personal Técnico de Apoyo contract (PTA2017-14359-I) and gratefully acknowledge the financial support of the Basque Government (Research Groups IT-1175-19) and the MICINN (PGC2018-094548-B-I00, MCIU/AEI/FEDER, UE. Funding for open access charge: Universidade da Coruña/CISUG. ; Gobierno Vasco; PIBA19-0051 ; Gobierno Vasco; IT-1175-19 ; Estados Unidos. National Science Foundation; 1905901