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Polymer Nanocomposites, Polymer Surfaces - Interfaces and Thin Films, Glass Transition, Condensed Matter Physics, Soft Condensed Matter Physics, Experimental Condensed Matter, and 32 moreNano Composites, Innovation, Patents, R&D, Thin Films and Coatings, -Preparation and Characterization of Nanostructured Thin Films, Thin film (Physics), Enthalpic Recovery, Dusan Racko, Dsc Enthalpy Relaxation Definition, Structural Dynamics, Segmental Mobility Polymer, Polymer science, Polymer Physics, Soft Matter, Dielectric Spectroscopy, Complex Fluids, Differential scanning calorimetry, Nano-confinement, Nanoparticles, Polymer Chemistry, Polymer Composites, Thermodynamics, Glass, Polymer, Dynamics, Physical Aging, Polymer Blends, Nanocomposites, Soft Condensed Matter, Glasses, Creep, Non Destructive Testing, and Temperature edit
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The idea of recycling waste materials from such different sectors as textile or automotive has been popular for decades, but today's recycling methods often produce poor quality products that are difficult to reuse. In the specific... more
The idea of recycling waste materials from such different sectors as textile or automotive has been popular for decades, but today's recycling methods often produce poor quality products that are difficult to reuse. In the specific case of thermoset composites the problem is even greater, since once the resin is cured its dissolution is not possible and therefore the recovery of the original fiber and resin becomes practically unfeasible. This work presents recyclable thermoset composites made with fabrics obtained from waste textiles and epoxy or polyurethane resins, whose crosslinking is based on reversible bonds, which confers them the ability to be dissolved in a specific agent, so that both the fiber and the resin can be recovered for subsequent reuse. Taking into account the particularities of the starting raw materials, the manufacturing parameters of the composites and the resin dissolution conditions have been studied and optimized. The work is part of the European p...
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Resumen del trabajo presentado al APS March Meeting, celebrado en Baltimore, Maryland (USA) del 14 al 18 de marzo de 2016.
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By aging, we draw glassy polymer films to a thermodynamic state, the ideal glass, with the entropy of the crystal.
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L'objet de cette étude est l'élaboration de matériaux polymères nanocomposites transparents à matrice polycarbonate, pour des applications dans des domaines tels que la lunetterie ou le vitrage automobile. L'incorporation de... more
L'objet de cette étude est l'élaboration de matériaux polymères nanocomposites transparents à matrice polycarbonate, pour des applications dans des domaines tels que la lunetterie ou le vitrage automobile. L'incorporation de nanoparticules au sein du polycarbonate a été envisagée afin de lui conférer certaines propriétés mécaniques telles qu'une plus grande rigidité, une meilleure stabilité dimensionnelle, une résistance à la rayure plus importante, tout en conservant sa transparence. Le maintien de la transparence du matériau passe d'une part par l'utilisation de particules nanométriques présentant un indice de réfraction proche de celui de la matrice et d'autre part par une trés bonne dispersion de ces particules au sein de la matrice polymère. Ainsi différents types de nanoparticules minérales ont d'abord été sélectionnés puis incorporés dans la matrice polycarbonate. L'évaluation des performances de ces nanocomposites en termes de transparence...
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We have monitored the physical aging of poly (methyl methacrylate)(PMMA)∕ silica nanocomposites, namely the slow evolution occurring to the structure of glasses below the glass transition temperature (Tg), following the time evolution of... more
We have monitored the physical aging of poly (methyl methacrylate)(PMMA)∕ silica nanocomposites, namely the slow evolution occurring to the structure of glasses below the glass transition temperature (Tg), following the time evolution of the enthalpy as measured by differential scanning calorimetry (DSC). We have systematically varied the concentration of silica to provide insight about the influence of the ratio area of silica∕ volume of PMMA on the physical aging process. Our results clearly indicate that physical aging speeds up with ...
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The aim of this work is to study the effect of gold nanoparticles on the segmental dynamics, glass transition (Tg) and physical aging of polystyrene (PS). To do so, PS/gold nanocomposite samples containing 5 and 15 wt% of 60 nm spherical... more
The aim of this work is to study the effect of gold nanoparticles on the segmental dynamics, glass transition (Tg) and physical aging of polystyrene (PS). To do so, PS/gold nanocomposite samples containing 5 and 15 wt% of 60 nm spherical gold nanoparticles, surface-treated with thiolated-PS, were prepared. The segmental dynamics of PS, as measured by means of broadband dielectric spectroscopy (BDS), was found to be unchanged in the presence of gold nanoparticles. Conversely, the calorimetric Tg of PS ...
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ABSTRACT Physical aging is an ubiquitous phenomenon in glassy materials and originates from the fact that they are generally out-of-equilibrium. Due to the technological and fundamental implications, this phenomenon has been deeply... more
ABSTRACT Physical aging is an ubiquitous phenomenon in glassy materials and originates from the fact that they are generally out-of-equilibrium. Due to the technological and fundamental implications, this phenomenon has been deeply investigated in the last decades especially in glassy polymers. Here we provide a critical review of the latest hot debated themes in the field of physical aging in polymers and polymer nanocomposites. We first summarize the fundamental aspects of physical aging, highlighting its relation with the polymer segmental mobility. A review of the methods employed to monitor physical aging is provided too, in particular those probing the time dependent evolution of thermodynamic variables (or related to) and those probing the (quasi)instantaneous polymer segmental mobility. We subsequently focus our attention on the two following debated topics in the field of physical aging of polymers: i) the fate of the dynamics and thermodynamics of glassy polymers below the glass transition temperature ($T_g$), i.e. the temperature below which physical aging occurs; ii) the modification of physical aging induced by the presence of inorganic nanofillers in polymer nanocomposites. In respect to the former point particular attention is devoted to recent findings concerning possible deviations from the behavior normally observed above $T_g$ of both dynamics and thermodynamics deep in the glassy state. Regarding the effect of the presence of nanofillers on the rate of physical aging, the role of the modification of the polymer segmental mobility and that of purely geometric factors is discussed with particular emphasis on the most recent advances in the topic. The modification of the rate of physical aging in other nanostructured systems, such as polymer thin films, is discussed with particular emphasis on the analogy in terms of large amount interface with polymer nanocomposites.
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We performed a systematic study on the recoverable enthalpy in several glass-forming polymers. We found that after prolonged isothermal physical aging the enthalpy reaches a plateau with values substantially larger than than those... more
We performed a systematic study on the recoverable enthalpy in several glass-forming polymers. We found that after prolonged isothermal physical aging the enthalpy reaches a plateau with values substantially larger than than those corresponding to the enthalpy state extrapolated from the melt state. Enthalpy recovery experiments after up-jumps indicate that the enthalpy state corresponding to the plateau found after simple down-jump experiments is restored after long-term aging. This result is interpreted considering the plateau in the ...
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A method of preparing a transparent polymer material includes mixing mineral nanoparticles selected from nanoparticles of alkaline-earth metal carbonates, alkaline-earth metal sulfates, metallic oxides, oxides of metalloids, and... more
A method of preparing a transparent polymer material includes mixing mineral nanoparticles selected from nanoparticles of alkaline-earth metal carbonates, alkaline-earth metal sulfates, metallic oxides, oxides of metalloids, and siloxanes, and a composition A including at least one thermoplastic polymer in the molten state selected from polycarbonate (PC), polystyrene (PS) and polymethyl methacrylate (PMMA) in order to obtain a master-batch, the mixture of step i) including at least 25% and at most 75% by weight of the mineral nanoparticles. The ...
Abstract: The glass transition temperature ($ T_g $) of polymer thin films has been a subject of controversy in the last two decades.(Pseudo) thermodynamic determinations of $ T_g $ generally suggest a significant depression, whereas the... more
Abstract: The glass transition temperature ($ T_g $) of polymer thin films has been a subject of controversy in the last two decades.(Pseudo) thermodynamic determinations of $ T_g $ generally suggest a significant depression, whereas the molecular mobility is found to be unchanged. The present study clarifies this apparent controversy by assuming that the $ T_g $ in thin films is determined not only by the molecular mobility but also by the thickness of the film. This hypothesis is supported by the analysis of literature results on polystyrene ...
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1. A method of preparing a transparent polymer material, characterized in that it comprises steps i) and ii) in any order, the steps consisting in: i) mixing: mineral nanoparticles having a form factor strictly greater than 1.0, the form... more
1. A method of preparing a transparent polymer material, characterized in that it comprises steps i) and ii) in any order, the steps consisting in: i) mixing: mineral nanoparticles having a form factor strictly greater than 1.0, the form factor being determined as described in the description; and • a polymer matrix comprising a quantity of at least 80% by weight of a polycarbonate (PC) first thermoplastic polymer and of a second transparent thermoplastic polymer other than the first thermoplastic polymer; in order to obtain a mixture; and ii) heating the polymer matrix to ...
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Process for preparing a transparent polymeric material comprising the steps indifferent unorden ie consisting ii: i. mixing: - mineral nanoparticles having a form factor strictly greater than 1.0, being determined factorde manner as... more
Process for preparing a transparent polymeric material comprising the steps indifferent unorden ie consisting ii: i. mixing: - mineral nanoparticles having a form factor strictly greater than 1.0, being determined factorde manner as described in the description, and - a polymer matrix comprising an amount of at least 80 mass% of a first polimerotermoplastico polycarbonate (PC), and a second transparent thermoplastic polymer different from thermoplastic primerpolimero, to obtain a mixture, ii. heat alone or mixed polymer matrix, in the state fundido.para obtain the transparent polymeric material, the mixture i an amount low enough al5 mass% of nanoparticles having a form factor comprising strictly greater than 1.0, and not involving the etapai mineral nanoparticles as obtained premix with a thermoplastic polymer melt elegidoentre polycarbonate (PC), polystyrene (PS) and polymethyl methacrylate (PMMA).
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We investigate the kinetics of enthalpy recovery in stacked glassy polystyrene (PS) films with thickness from 30 to 95 nm over a wide temperature range below the glass transition temperature (T g). We show that the time evolution toward... more
We investigate the kinetics of enthalpy recovery in stacked glassy polystyrene (PS) films with thickness from 30 to 95 nm over a wide temperature range below the glass transition temperature (T g). We show that the time evolution toward equilibrium exhibits two mechanisms of recovery, in ways analogous to bulk PS. The fast mechanism, allowing partial enthalpy recovery toward equilibrium, displays Arrhenius temperature dependence with low activation energy, whereas the slow mechanism follows pronounced super-Arrhenius temperature dependence. In comparison to bulk PS, the time scales of the two mechanisms of recovery are considerably shorter and decreasing with the film thickness. Scaling of the equilibration times at various thicknesses indicates that the fast mechanism of recovery is compatible with the free volume holes diffusion model. Conversely, the slow mechanism of recovery appears to be accelerated with decreasing thickness more than predicted by the model and, therefore, its...
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Trash-2-Cash is an EU funded project under the Horizon 2020 research programme. The project started in June 2015 and will be running until the end of November 2018. It applies Design-Driven Material Innovation (DDMI) as a tool for... more
Trash-2-Cash is an EU funded project under the Horizon 2020 research programme. The project started in June 2015 and will be running until the end of November 2018. It applies Design-Driven Material Innovation (DDMI) as a tool for development routes within design, materials research and manufacturing of new materials, services and products. The overall objective of the Trash-2-Cash project is to develop new materials and products via creative design from waste materials and industrial side-products or by-products from the textile and paper industries and to promote development within the creative sector by providing technology solutions for exploitation of waste streams and design for recycling. 18 partners from 10 countries formed a cross-disciplinary team of designers, material researchers, and manufacturers in combination with specialists on behavioural research and cost and environmental assessments. Having all these specialists on board means that waste materials can be used to...
The glass transition temperature (Tg) of polymer thin films has been a subject of intense debate in the last two decades. (Pseudo)thermodynamic determinations, such as calorimetry and ellipsometry, generally suggest a significant... more
The glass transition temperature (Tg) of polymer thin films has been a subject of intense debate in the last two decades. (Pseudo)thermodynamic determinations, such as calorimetry and ellipsometry, generally suggest a significant depression of Tg, whereas the dynamic Tg, measured by techniques such broadband dielectric spectroscopy and AC-calorimetry directly probing the molecular mobility, is found to be unchanged. The present
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The glass transition temperature ($ T_ {g}) $ of polymer thin films has been a subject of intense debate in the last two decades.(Pseudo) thermodynamic determinations, such as calorimetry and ellipsometry, generally suggest a significant... more
The glass transition temperature ($ T_ {g}) $ of polymer thin films has been a subject of intense debate in the last two decades.(Pseudo) thermodynamic determinations, such as calorimetry and ellipsometry, generally suggest a significant depression of $ T_ {g} $, whereas the dynamic $ T_ {g} $, measured by techniques such broadband dielectric spectroscopy and AC-calorimetry directly probing the molecular mobility, is found to be unchanged. The present study provides a resolution to this controversy on polystyrene by ...
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The effect of gold nanoparticles on the segmental dynamics, glass transition ($T_{g})$ and physical aging of polystyrene (PS) was studied in PS/Gold nanocomposites samples containing 5 and 15 wt.{\%} of 60 nm spherical gold nanoparticles,... more
The effect of gold nanoparticles on the segmental dynamics, glass transition ($T_{g})$ and physical aging of polystyrene (PS) was studied in PS/Gold nanocomposites samples containing 5 and 15 wt.{\%} of 60 nm spherical gold nanoparticles, surface-treated with thiolated-PS. While the segmental dynamics of PS, as assessed by broadband dielectric spectroscopy (BDS), was found to be unchanged in presence of gold nanoparticles, the calorimetric $T_{g}$ of PS was shown to decrease with increasing the amount of nanoparticles in the samples. Furthermore, the ...
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The physical aging of polystyrene (PS) free standing films has been investigated as a function of the films thickness, ranging from several microns to tens of nanometers. In this range of thicknesses, unchanged segmental dynamics in... more
The physical aging of polystyrene (PS) free standing films has been investigated as a function of the films thickness, ranging from several microns to tens of nanometers. In this range of thicknesses, unchanged segmental dynamics in comparison to the bulk was previously reported. This study has been carried out through differential scanning calorimetry (DSC), by following the enthalpy recovery to monitor the physical aging process at different temperatures. The temperature marking the onset of non-equilibrium effects, that is the onset of the glass transtion temperature, $T_g^{on}$, was also assessed, at different cooling rates. An acceleration of the physical aging process, and consequently a depression of $T_g^{on}$, is found with decreasing the films thickness, already for thicknesses in the micrometer range. Moreover, the onset of non-equilibrium effects is shown to be cooling rate dependent, this being more pronounced when the PS films get thinner. The thickness effects on the typical signatures of the out-of-equilibrium dynamics of the films, namely their physical aging and $T_g^{on}$, can be well accounted for by assuming an equilibration mechanism based on volume holes diffusion toward the interfaces of the films. The temperature dependence of the diffusion coefficient obtained within this framework is found to crossover from VFT to Arrhenius when decreasing the temperature. The implications of these results are discussed.
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In this work, we have studied the effect of silica particles on the physical aging of nanocomposites based on poly(methyl methacrylate) (PMMA). To do that, we have followed the enthalpyrelaxation by means of differential scanning... more
In this work, we have studied the effect of silica particles on the physical aging of nanocomposites based on poly(methyl methacrylate) (PMMA). To do that, we have followed the enthalpyrelaxation by means of differential scanning calorimetry (DSC). In agreement with previous results carriedout by means of broadband dielectric spectroscopy (BDS), we observe an acceleration of the physical agingprocess of PMMA nanocomposites in comparison to bulk PMMA. The fitting of the enthalpy relaxationresults to the well-known Tool-Narayanaswamy-Moynihan (TNM) model gives rise to equal structuralparameters for all investigated samples, including bulk PMMA. This implies that the molecular mechanism for physical aging in PMMA is not affected by the presence of silica particles.The only parameter changing is the pre-exponential factor setting the time scale of physical aging. The values obtained are correlated to the area/volume ratio of silica particles in the polymer and thereby to the silica interparticle distance in the nanocomposites. This latter observation is an indication that the physical aging process is driven by thediffusion of free volume holes toward polymer interfaces, as already proposed in the past.
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We investigated the kinetics of enthalpy recovery of several glass-forming polymers at temperatures significantly below the glass transition temperature (Tg) and for aging times up to one year. We find a double-step recovery at relatively... more
We investigated the kinetics of enthalpy recovery of several glass-forming polymers at temperatures significantly below the glass transition temperature (Tg) and for aging times up to one year. We find a double-step recovery at relatively low aging temperatures for the longest investigated aging times. The enthalpy recovered after the two-step decay approximately equals that expected by extrapolation from the melt. The two-step enthalpy recovery indicates the presence of two time scales for glass equilibration. The equilibration time of the first recovery step exhibits relatively weak temperature dependence, whereas that of the second step possesses pronounced temperature dependence, compatible with the Vogel-Fulcher-Tammann behavior. These results, while leaving open the question of the divergence of the relaxation time and that of a thermodynamic singularity at a finite temperature, reveal a complex scenario of glassy dynamics.
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Macroscopic volume as well as capacitive dilatometry (CD) measurements have been performed on polystyrene/silica nanocomposites during the course of physical aging below the glass transition temperature (Tg). Our results show that the... more
Macroscopic volume as well as capacitive dilatometry (CD) measurements have been performed on polystyrene/silica nanocomposites during the course of physical aging below the glass transition temperature (Tg). Our results show that the macroscopic volume recovery during physical aging is not affected by the presence of nanofillers, whereas the CD measurements, delivering also information on the polymer matrix density, show acceleration of the recovery with increasing the silica content. Hence, the main outcome of the present work is that the evolution of macroscopic and matrix densities are markedly different in polymer nanocomposites. We interpret these results invoking an equilibration mechanism based on volume holes diffusion. According to this model, excess free volume migration at the polymer/filler interface only modifies the matrix density, thereby explaining the faster recovery detected by CD measurements in comparison to the macroscopic volume one.
Physical aging is a ubiquitous phenomenon in glassy materials and originates from the fact that they are generally out-of-equilibrium. Due to the technological and fundamental implications, this phenomenon has been deeply investigated in... more
Physical aging is a ubiquitous phenomenon in glassy materials and originates from the fact that they are generally out-of-equilibrium. Due to the technological and fundamental implications, this phenomenon has been deeply investigated in the last decades especially in glassy polymers. Here we provide a critical review of the latest hot debated themes in the field of physical aging in polymers and polymer nanocomposites. We first summarize the fundamental aspects of physical aging, highlighting its relationship with the polymer segmental mobility. A review of the methods employed to monitor physical aging is also provided, in particular those probing the time dependent evolution of thermodynamic variables (or related to) and those probing the (quasi)instantaneous polymer segmental mobility. We subsequently focus our attention on the two following debated topics in the field of physical aging of polymers: (i) the fate of the dynamics and thermodynamics of glassy polymers below the glass transition temperature (Tg), i.e. the temperature below which physical aging occurs; (ii) the modification of physical aging induced by the presence of inorganic nanofillers in polymer nanocomposites. With respect to the former point particular attention is devoted to recent findings concerning possible deviations from the behavior normally observed above Tg of both dynamics and thermodynamics deep in the glassy state. Regarding the effect of the presence of nanofillers on the rate of physical aging, the role of the modification of the polymer segmental mobility and that of purely geometric factors are discussed with particular emphasis on the most recent advances in the topic. The modification of the rate of physical aging in other nanostructured systems, such as polymer thin films, is discussed with particular emphasis on the analogy in terms of a large amount of interface with polymer nanocomposites.
Abstract: The glass transition temperature ($ T_g $) of polymer thin films has been a subject of controversy in the last two decades.(Pseudo) thermodynamic determinations of $ T_g $ generally suggest a significant depression, whereas the... more
Abstract: The glass transition temperature ($ T_g $) of polymer thin films has been a subject of controversy in the last two decades.(Pseudo) thermodynamic determinations of $ T_g $ generally suggest a significant depression, whereas the molecular mobility is found to be unchanged. The present study clarifies this apparent controversy by assuming that the $ T_g $ in thin films is determined not only by the molecular mobility but also by the thickness of the film.
Recent studies have illustrated a decoupling between cooperative segmental mobility and the glass transition temperature (Tg) of thin polymer films and nanocomposites. Here, we use dielectric spectroscopy to probe the cooperative... more
Recent studies have illustrated a decoupling between cooperative segmental mobility and the glass transition temperature (Tg) of thin polymer films and nanocomposites. Here, we use dielectric spectroscopy to probe the cooperative segmental mobility and capacitive dilatometry to determine the Tg of films of polystyrene nanospheres with diameters (d) less than 400 nm. We find that both capacitive dilatometry and calorimetry revealed nearly identical suppressions in Tg as the size of the nanospheres was reduced.
"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 (SiO2). These systems present identical segmental... more
"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 (SiO2). 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 SiO2 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 SiO2 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 previousworks, 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."
The physical aging of polystyrene (PS) free-standing films has been investigated as a function of the films thickness, ranging from several micrometers to tens of nanometers. In this range of thicknesses, unchanged segmental dynamics in... more
The physical aging of polystyrene (PS) free-standing films has
been investigated as a function of the films thickness, ranging from several
micrometers to tens of nanometers. In this range of thicknesses, unchanged
segmental dynamics in comparison to the bulk was previously reported. This
study has been carried out through differential scanning calorimetry (DSC),byfollowing the enthalpy recovery to monitor the physical aging process at different temperatures. The temperature marking the onset of nonequilibrium effects, that is the onset of the glass transtion temperature, Tgon, was also assessed, at different cooling rates. An acceleration of the physical aging process, and consequently a depression of Tgon, is foundwith decreasing the films thickness, already for thicknesses in the micrometer range. Moreover, the onset of nonequilibrium effects is shown to be cooling rate dependent, this being more pronounced when the PS films get thinner. The thickness effects on the typical signatures of the out-of-equilibrium dynamics of the films, namely their physical aging and Tgon, can be wellaccounted for by assuming an equilibration mechanism based on volume holes diffusion toward the interfaces of the films. The temperature dependence of the diffusion coefficient obtained within this framework is found to crossover from Vogel−Fulcher−Tammann (VFT) to Arrhenius when decreasing the temperature. The implications of these results are discussed.
been investigated as a function of the films thickness, ranging from several
micrometers to tens of nanometers. In this range of thicknesses, unchanged
segmental dynamics in comparison to the bulk was previously reported. This
study has been carried out through differential scanning calorimetry (DSC),byfollowing the enthalpy recovery to monitor the physical aging process at different temperatures. The temperature marking the onset of nonequilibrium effects, that is the onset of the glass transtion temperature, Tgon, was also assessed, at different cooling rates. An acceleration of the physical aging process, and consequently a depression of Tgon, is foundwith decreasing the films thickness, already for thicknesses in the micrometer range. Moreover, the onset of nonequilibrium effects is shown to be cooling rate dependent, this being more pronounced when the PS films get thinner. The thickness effects on the typical signatures of the out-of-equilibrium dynamics of the films, namely their physical aging and Tgon, can be wellaccounted for by assuming an equilibration mechanism based on volume holes diffusion toward the interfaces of the films. The temperature dependence of the diffusion coefficient obtained within this framework is found to crossover from Vogel−Fulcher−Tammann (VFT) to Arrhenius when decreasing the temperature. The implications of these results are discussed.
We investigate the segmental dynamics and glass transition temperature (Tg) of polystyrene (PS) thin films. The former is investigated by alternating current (AC) calorimetry and dielectric spectroscopy (BDS). The Tg, underlying the... more
We investigate the segmental dynamics and glass transition temperature (Tg) of polystyrene (PS) thin films. The former is investigated by alternating current (AC) calorimetry and dielectric spectroscopy (BDS). The Tg, underlying the equilibrium to out-of- equilibrium crossover from the supercooled liquid to the glass, is obtained by differential scanning calorimetry (DSC) and capacitive dilatometry (CD).We show that the intrinsic molecular dynamics of PS are independent of the film thickness both for the freestanding and supported films, whereas Tg decreases with film thickness from several microns down to 15 nm. This result is found for complementary methods and in a simultaneous measurement in BDS and CD. This questions the widespread notion that segmental mobility and the equilibrium to out-of-equilibrium transition are, under any experimental conditions, fully interrelated. For thin films, it appears that the molecular mobility and Tg are affected differently by geometrical factors.
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... more
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 Tg for the nanocomposites, as well as lower experimentally recoverable enthalpy values. This may result from the faster non-isothermal evolution of the glass statewhen 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.
Excellent dispersion of functionalized graphene (FG) sheets in polystyrene was achieved relying on the reaction of ‘‘living’’ poly(glycidyl phenyl ether) chains onto graphene sheets. The physical aging of polystyrene was substantially... more
Excellent dispersion of functionalized graphene (FG) sheets in
polystyrene was achieved relying on the reaction of ‘‘living’’
poly(glycidyl phenyl ether) chains onto graphene sheets. The
physical aging of polystyrene was substantially accelerated by
the presence of FG sheets at low filler content, retaining film
transparency and increasing the electrical conductivity.
polystyrene was achieved relying on the reaction of ‘‘living’’
poly(glycidyl phenyl ether) chains onto graphene sheets. The
physical aging of polystyrene was substantially accelerated by
the presence of FG sheets at low filler content, retaining film
transparency and increasing the electrical conductivity.
We performed a systematic study on the recoverable enthalpy in several glassforming polymers. We found that after prolonged isothermal physical aging the enthalpy reaches a plateau with values substantially larger than than those... more
We performed a systematic study on the recoverable enthalpy in several glassforming polymers. We found that after prolonged isothermal physical aging the enthalpy reaches a plateau with values substantially larger than than those corresponding to the enthalpy state extrapolated from the melt state. Enthalpy recovery experiments after up-jumps indicate that the enthalpy state corresponding to the plateau found after simple down-jump experiments is restored after long-term aging. This result is interpreted considering the plateau in the enthalpy as a thermodynamically stable state. We argue on the possible scenarios emerging from this conclusion. In particular, we discuss whether polymer glasses in the achieved thermodynamic state are stable over any time scale, or rather this corresponds to a relative minimum with further evolution at much larger time scales. Finally, the shift factor obtained from aging timetemperature superposition of enthalpy recovery data was found to considerably deviate from the Vogel FulcherTammann equation, normally adequate to describe the segmental mobility above the glass transition temperature (Tg). The deviation of thermodynamics and dynamics from the behavior expected extrapolating the behavior from above Tg has been analyzed within the AdamGibbs framework, which actually relates the relaxation time and a thermodynamic magnitude, namely the configurational entropy. It has been found that, at least semiquantitatively for most of the investigated polymers, the connection between dynamics and thermodynamics holds also below Tg.
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... more
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. © 2011 American
Institute of Physics.
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. © 2011 American
Institute of Physics.
The aim of this work is to study the effect of gold nanoparticles on the segmental dynamics, glass transition (Tg) and physical aging of polystyrene (PS). To do so, PS/gold nanocomposite samples containing 5 and 15 wt% of 60 nm spherical... more
The aim of this work is to study the effect of gold nanoparticles on the segmental dynamics, glass transition (Tg) and physical aging of polystyrene (PS). To do so, PS/gold nanocomposite samples containing 5 and 15 wt% of 60 nm spherical gold nanoparticles, surface-treated with thiolated-PS, were prepared. The segmental dynamics of PS, as measured by means of broadband dielectric spectroscopy (BDS), was found to be unchanged in the presence of gold nanoparticles. Conversely, the calorimetric Tg of PS was shown to decrease with increasing the amount of gold nanoparticles in the samples. Furthermore, by measuring the amount of recovered enthalpy of PS—by means of DSC—after annealing at temperatures below Tg for various aging times, the physical aging was shown to speed up with increasing the nanoparticles weight fraction, i.e. the amount of PS/gold interface in the hybrid material. Thus, the main conclusion of our work is that PS molecular mobility and the out-ofequilibrium
dynamics are markedly decoupled in these nanocomposites. The significant effect of the amount of PS/gold interface on both the physical aging rate of PS and the depression of the calorimetric Tg in the presence of nanoparticles is quantitatively accounted for by a model based on the diffusion of free volume holes towards polymer interfaces, with a diffusion coefficient depending only on the molecular mobility.
dynamics are markedly decoupled in these nanocomposites. The significant effect of the amount of PS/gold interface on both the physical aging rate of PS and the depression of the calorimetric Tg in the presence of nanoparticles is quantitatively accounted for by a model based on the diffusion of free volume holes towards polymer interfaces, with a diffusion coefficient depending only on the molecular mobility.
The present invention relates to a method of preparing a transparent polymer material, comprising the following steps: i) mineral nanoparticles, chosen from alkaline-earth metal carbonate, alkaline-earth metal sulphate, metal oxide,... more
The present invention relates to a method of preparing a transparent polymer material, comprising the following steps: i) mineral nanoparticles, chosen from alkaline-earth metal carbonate, alkaline-earth metal sulphate, metal oxide, metalloid oxide and siloxane nanoparticles, are mixed with a composition A comprising at least one thermoplastic polymer in the molten state chosen from polycarbonate (PC), polystyrene (PS) and polymethyl methacrylate (PMMA), in order to obtain a masterbatch, the mixture resulting from step i) comprising at least 25% and at most 75% by weight of said mineral nanoparticles; and ii) the masterbatch obtained from i) is mixed with a composition B comprising a thermoplastic polycarbonate matrix (mPC) in the molten state, so as to obtain a transparent polymer material comprising at most 10% by weight of said mineral nanoparticles, preferably at most 5% by weight of said mineral nanoparticles.
The present invention relates to a method for preparing a transparent polymer material, including steps i and ii in any order, consisting of: i. mixing together mineral nanoparticles, having a shape factor strictly higher than 1.0, a... more
The present invention relates to a method for preparing a transparent polymer material, including steps i and ii in any order, consisting of: i. mixing together mineral nanoparticles, having a shape factor strictly higher than 1.0, a polymer matrix including at least 80 wt % of a first polycarbonate (PC) thermoplastic polymer, and a second transparent thermoplastic polymer different from the first thermoplastic polymer, in order to obtain a mixture; ii. heating the polymer matrix alone or in a mixture, in a molten state, in order to obtain the transparent polymer material, the mixture of step i including strictly less than 5 wt % of mineral nanoparticles with a shape factor strictly higher than 1.0.