1
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Málek J. How to Distinguish Nonexponentiality and Nonlinearity in Isothermal Structural Relaxation of Glass-Forming Materials. J Phys Chem B 2024; 128:8074-8083. [PMID: 39115114 PMCID: PMC11345833 DOI: 10.1021/acs.jpcb.4c02226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2024] [Revised: 07/15/2024] [Accepted: 07/16/2024] [Indexed: 08/23/2024]
Abstract
The nonexponentiality and nonlinearity are two essential features of the structural relaxation in any glass-forming material, which seem to be inextricably bound together by the material time. It is shown that the temperature down-jump and up-jump experiments of the same magnitude ΔT = T0 - T to the same temperature T provide a clue for their separation. The isothermal structural relaxation can be quantified using the stabilization period on the logarithmic time scale log(tm/t0). It is described as the sum of the nonexponentiality term 1.181/ß and the nonlinearity term (σ/2.303)ΔT for the temperature down-jump, and as their difference for the temperature up-jump. The material parameter σ = -(∂lnτ/∂Tf)i quantifies variation of the relaxation time with structural changes at the inflection point of the relaxation curve and is formulated for the most widely used phenomenological models. The asymmetry of approach to equilibrium after the temperature down-jump and up-jump was first described by Kovacs in 1963. A detailed analysis of this asymmetry is provided, and a simple method for the estimation of the parameters characterizing the nonexponentiality (ß) and nonlinearity (σ) is proposed. The applicability of this method is tested using previously reported isothermal experimental data as well as calculated data for aging of polymers and other glass-forming materials. This concept illuminates differences in structural relaxation kinetics in a simple and consistent way that can be useful in the design of novel materials and the evaluation of their physical aging treatment.
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Affiliation(s)
- Jiří Málek
- Department of Physical Chemistry,
Faculty of Chemical Technology, University
of Pardubice, Studentská
573, Pardubice 532 10, Czech Republic
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2
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Charif I, Doulache N, Gourari A, Rodrigue D, Giroux Y, Cherfi R. Physical aging of
PC
:
PS
blends: Dynamic mechanical analysis and nuclear magnetic resonance studies. POLYM ENG SCI 2022. [DOI: 10.1002/pen.26117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Imane Charif
- Laboratory of Material Physics, Department of Materials, Faculty of Physics University of Science and Technology Algiers Algeria
| | - Naima Doulache
- Laboratory of Material Physics, Department of Materials, Faculty of Physics University of Science and Technology Algiers Algeria
| | - Azeddine Gourari
- Laboratory of Material Physics, Department of Materials, Faculty of Physics University of Science and Technology Algiers Algeria
| | - Denis Rodrigue
- Department of Chemical Engineering Laval University Quebec Canada
| | - Yann Giroux
- Department of Chemical Engineering Laval University Quebec Canada
| | - Rabah Cherfi
- Laboratory of Material Physics, Department of Materials, Faculty of Physics University of Science and Technology Algiers Algeria
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3
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Jin S, McKenna GB. 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*. POLYM ENG SCI 2022. [DOI: 10.1002/pen.25911] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Shuang Jin
- Department of Chemical and Biomolecular Engineering North Carolina State University Raleigh North Carolina USA
- Department of Chemical Engineering Texas Tech University Lubbock Texas USA
| | - Gregory B. McKenna
- Department of Chemical and Biomolecular Engineering North Carolina State University Raleigh North Carolina USA
- Department of Chemical Engineering Texas Tech University Lubbock Texas USA
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4
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Yoon H, Hinton ZR, Heinzman J, Chase CE, Gopinadhan M, Edmond KV, Ryan DJ, Smith SE, Alvarez NJ. The effect of pyrolysis on the chemical, thermal and rheological properties of pitch. SOFT MATTER 2021; 17:8925-8936. [PMID: 34546280 DOI: 10.1039/d1sm00594d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Pitch-based carbon fibers are of considerable interest as high-performance materials. There are reports over the last several decades detailing (i) methods of improving pitch-based carbon fiber performance, and (ii) reducing the cost of production via novel processing techniques. However, there remain considerable challenges in producing high-performance pitch-based carbon fibers consistently on an industrial scale. This is arguably due to the difficulty of scaling the melt-spinning process to compensate for variability in pitch feedstock quality and a lack of understanding of processing-structure-performance relationships. This work focuses on the early stages of heat treatment (pyrolysis) of isotropic pitch and its effect on the chemical, thermal, and rheological properties of the pitch, which help determine its processability. More specifically, we quantify significant changes in chemical structure, Mw, Tg, Ts, and shear and extensional rheology as a function of pyrolysis time at 400 °C. The extensional rheology, in particular, shows that the 'stretchability' of the pitch samples strongly depends on pyrolysis severity, and is important for characterizing 'drawability'. Using a novel analysis of the uniaxial stretching kinematics, we show an isothermal 'drawability window' that allows for the largest axial and radial Hencky strains at constant rate. We hypothesize that this extensional drawability window could facilitate the successful processing of pitch into high quality fiber, minimizing the trial-and-error approach currently used in the field.
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Affiliation(s)
- Heedong Yoon
- Chemical and Biological Engineering Department, Drexel University, 3141 Chestnut St., Philadelphia, PA, 19104, USA.
| | - Zachary R Hinton
- Chemical and Biological Engineering Department, Drexel University, 3141 Chestnut St., Philadelphia, PA, 19104, USA.
| | - James Heinzman
- Chemical and Biological Engineering Department, Drexel University, 3141 Chestnut St., Philadelphia, PA, 19104, USA.
| | - Clarence E Chase
- Corporate Strategic Research, ExxonMobil Research and Engineering Company, 1545 Route 22 E., Annandale, NJ, 08801, USA
| | - Manesh Gopinadhan
- Corporate Strategic Research, ExxonMobil Research and Engineering Company, 1545 Route 22 E., Annandale, NJ, 08801, USA
| | - Kazem V Edmond
- Corporate Strategic Research, ExxonMobil Research and Engineering Company, 1545 Route 22 E., Annandale, NJ, 08801, USA
| | - Daniel J Ryan
- Analytical Sciences Laboratory, ExxonMobil Research and Engineering Company, 1545 Route 22 E., Annandale, NJ, 08801, USA
| | - Stuart E Smith
- Corporate Strategic Research, ExxonMobil Research and Engineering Company, 1545 Route 22 E., Annandale, NJ, 08801, USA
| | - Nicolas J Alvarez
- Chemical and Biological Engineering Department, Drexel University, 3141 Chestnut St., Philadelphia, PA, 19104, USA.
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5
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Zhao X, Grassia L, Simon SL. Mobility of Pressure-Densified and Pressure-Expanded Polystyrene Glasses: Dilatometry and a Test of KAHR Model. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c00983] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Xiao Zhao
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409, United States
| | - Luigi Grassia
- Department of Engineering, University of Campania Luigi Vanvitelli, Aversa 81031, Italy
| | - Sindee L. Simon
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
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Czerniecka-Kubicka A, Zarzyka I, Pyda M. Long-Term Physical Aging Tracked by Advanced Thermal Analysis of Poly( N-Isopropylacrylamide): A Smart Polymer for Drug Delivery System. Molecules 2020; 25:E3810. [PMID: 32825687 PMCID: PMC7503768 DOI: 10.3390/molecules25173810] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 08/17/2020] [Accepted: 08/18/2020] [Indexed: 02/01/2023] Open
Abstract
Poly(N-isopropylacrylamide) (PNIPA), as a smart polymer, can be applied for drug delivery systems. This amorphous polymer can be exposed on a structural recovery process during the storage and transport of medicaments. For the physical aging times up to one year, the structural recovery for PNIPA was studied by advanced thermal analysis. The structural recovery process occurred during the storage of amorphous PNIPA below glass transition and could be monitored by the differential scanning calorimetry (DSC). The enthalpy relaxation (recovery) was observed as overshoot in change heat capacity at the glass transition region in the DSC during heating scan. The physical aging of PNIPA was studied isothermally at 400.15 K and also in the non-isothermal conditions. For the first time, the structural recovery process was analyzed in reference to absolute heat capacity and integral enthalpy in frame of their equilibrium solid and liquid PNIPA.
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Affiliation(s)
- Anna Czerniecka-Kubicka
- Department of Experimental and Clinical Pharmacology, Medical College of Rzeszow University, The University of Rzeszow, 35-310 Rzeszow, Poland
| | - Iwona Zarzyka
- Department of Chemistry, Rzeszow University of Technology, 35-959 Rzeszow, Poland; (I.Z.); (M.P.)
| | - Marek Pyda
- Department of Chemistry, Rzeszow University of Technology, 35-959 Rzeszow, Poland; (I.Z.); (M.P.)
- Department of Biophysics, Poznan University of Medical Sciences, 60-780 Poznan, Poland
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Ngai KL, Capaccioli S, Wang LM. Segmental α-Relaxation for the First Step and Sub-Rouse Modes for the Second Step in Enthalpy Recovery in the Glassy State of Polystyrene. Macromolecules 2019. [DOI: 10.1021/acs.macromol.8b02125] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- K. L. Ngai
- CNR-IPCF, Università di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
- State Key Lab of Metastable Materials Science and Technology and College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei 066004, China
| | - Simone Capaccioli
- CNR-IPCF, Università di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
| | - Li-Min Wang
- State Key Lab of Metastable Materials Science and Technology and College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei 066004, China
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Sasaki K, Takatsuka M, Kita R, Shinyashiki N, Yagihara S. Enthalpy and Dielectric Relaxation of Poly(vinyl methyl ether). Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b00780] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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9
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Grassia L, Koh YP, Rosa M, Simon SL. Complete Set of Enthalpy Recovery Data Using Flash DSC: Experiment and Modeling. Macromolecules 2018. [DOI: 10.1021/acs.macromol.7b02277] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Luigi Grassia
- Department of Industrial
and Information Engineering, Università degli Studi della Campania “Luigi Vanvitelli”, Via Roma 19, 81031 Aversa (CE), Italy
| | - Yung P. Koh
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
| | - Mattia Rosa
- Department of Industrial
and Information Engineering, Università degli Studi della Campania “Luigi Vanvitelli”, Via Roma 19, 81031 Aversa (CE), Italy
| | - Sindee L. Simon
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
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10
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11
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McKenna GB, Simon SL. 50th Anniversary Perspective: Challenges in the Dynamics and Kinetics of Glass-Forming Polymers. Macromolecules 2017. [DOI: 10.1021/acs.macromol.7b01014] [Citation(s) in RCA: 102] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Gregory B. McKenna
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
| | - Sindee L. Simon
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
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12
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13
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14
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Affiliation(s)
- Evelyn Lopez
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
| | - Sindee L. Simon
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
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15
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Burgess SK, Mubarak CR, Kriegel RM, Koros WJ. Physical aging in amorphous poly(ethylene furanoate): Enthalpic recovery, density, and oxygen transport considerations. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/polb.23648] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Steven K. Burgess
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology; Atlanta Georgia 30332
| | | | | | - William J. Koros
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology; Atlanta Georgia 30332
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16
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Liu G, Zuo Y, Lin J, Zhao D. Study on enthalpy relaxation of glassy polystyrene using a structure-dependent Kohlrausch stretch exponent combined with coupling model. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2014; 37:20. [PMID: 25052065 DOI: 10.1140/epje/i2014-14063-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Revised: 03/24/2014] [Accepted: 06/17/2014] [Indexed: 06/03/2023]
Abstract
In this paper the enthalpy relaxation of polystyrene (PS) was restudied using a structure-dependent Kohlrausch stretch exponent β with incorporation of a coupling model (CM). The structure dependence of β is described in 3 semi-phenomenological equations. The temperature and structure dependence of the relaxation time of the Johari-Goldstein (JG) relaxation (τ JG) is presented using the traditional Tools-Narayanaswamy-Moynihan (TNM) and Adam-Gibbs-Vogel (AGV) equations. The fitting results of heat capacity data are much better than the conventional TNM and Adam-Gibbs (AG) models when the structure dependence of β is described using an exponential equation and τ JG is calculated using the AGV equation, although there are one fewer fitting parameters in the new model. The results indicate that both the structure dependence of β and the CM model may play considerable roles in the investigation on the structure relaxation process in polymers around the glass transition.
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Affiliation(s)
- Guodong Liu
- Institute of Polymer Science and Engineering, Hebei University of Technology, 300130, Tianjin, China,
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17
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Koh YP, Simon SL. Enthalpy Recovery of Polystyrene: Does a Long-Term Aging Plateau Exist? Macromolecules 2013. [DOI: 10.1021/ma4011236] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Yung P. Koh
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
| | - Sindee L. Simon
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409-3121, United States
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18
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Boucher VM, Cangialosi D, Alegría A, Colmenero J. Enthalpy Recovery of Glassy Polymers: Dramatic Deviations from the Extrapolated Liquidlike Behavior. Macromolecules 2011. [DOI: 10.1021/ma2018233] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Virginie M. Boucher
- Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastián, Spain
| | - Daniele Cangialosi
- Centro de Física de Materiales (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain
| | - Angel Alegría
- Centro de Física de Materiales (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain
- Departamento de Física de Materiales, Universidad del País Vasco (UPV/EHU), Apartado 1072, 20080 San Sebastián, Spain
| | - Juan Colmenero
- Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastián, Spain
- Centro de Física de Materiales (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain
- Departamento de Física de Materiales, Universidad del País Vasco (UPV/EHU), Apartado 1072, 20080 San Sebastián, Spain
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Morris C, Taylor AJ, Farhat IA, MacNaughtan W. Modelling of physical ageing in starch using the TNM equation. Carbohydr Res 2011; 346:1122-8. [PMID: 21531394 DOI: 10.1016/j.carres.2011.04.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 02/21/2011] [Accepted: 04/05/2011] [Indexed: 10/18/2022]
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Alcoutlabi M, Banda L, Kollengodu-Subramanian S, Zhao J, McKenna GB. Environmental Effects on the Structural Recovery Responses of an Epoxy Resin after Carbon Dioxide Pressure Jumps: Intrinsic Isopiestics, Asymmetry of Approach, and Memory Effect. Macromolecules 2011. [DOI: 10.1021/ma1027577] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Mataz Alcoutlabi
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409, United States
| | - Lameck Banda
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409, United States
| | | | - Jing Zhao
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409, United States
| | - Gregory B. McKenna
- Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409, United States
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Bansal SS, Kaushal AM, Bansal AK. Enthalpy relaxation studies of two structurally related amorphous drugs and their binary dispersions. Drug Dev Ind Pharm 2011; 36:1271-80. [PMID: 20815794 DOI: 10.3109/03639041003753847] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE The purpose of the current study was to evaluate the enthalpy relaxation behavior of valdecoxib (VLB) and etoricoxib (ETB) and their binary dispersions to derive relaxation constants and to understand their molecular mobilities. METHODS Solid dispersions of VLB and ETB were prepared with 1%, 2%, 5%, 10%, 15%, and 20% (w/w) concentrations of polyvinylpyrrolidone (PVP) in situ using differential scanning calorimetry (DSC). Enthalpy relaxation studies were carried out with isothermal storage periods of 1, 2, 4, 6, 16, and 24 hours at 40°C and 0% relative humidity (RH). RESULTS PVP increased the glass transition temperature (T(g)) and decreased the enthalpy relaxation. Significant differences between two drugs were observed with respect to their relaxation behavior which may be due to differences in intermolecular interactions as predicted by Couchman-Karasz equation and molecular mobility. Kohlrausch-Williams-Watts equation was found to be inadequate in describing complex molecular relaxations in binary dispersions. The enthalpy relaxation behavior of VLB and ETB was found to be significantly different. PVP stabilized VLB significantly; however, its effect on ETB was negligible. The extent of enthalpy relaxation was found to correlate with hydrogen bonding tendency of the drug molecules. CONCLUSION The outcome can help in rational designing of amorphous systems with optimal performance.
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Affiliation(s)
- Shyam Sunder Bansal
- Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research, Mohali, Punjab, India
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Flory AL, Ramanathan T, Brinson LC. Physical Aging of Single Wall Carbon Nanotube Polymer Nanocomposites: Effect of Functionalization of the Nanotube on the Enthalpy Relaxation. Macromolecules 2010. [DOI: 10.1021/ma901670m] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Anny L. Flory
- Department of Materials Science and Engineering, Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, 60208
| | - T. Ramanathan
- Department of Materials Science and Engineering, Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, 60208
| | - L. Catherine Brinson
- Department of Materials Science and Engineering, Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, 60208
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Shieh YT, Lin YS, Twu YK, Tsai HB, Lin RH. Effect of crystallinity on enthalpy recovery peaks and cold-crystallization peaks in PET via TMDSC and DMA studies. J Appl Polym Sci 2009. [DOI: 10.1002/app.31570] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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25
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Aou K, Hsu SL, Kleiner LW, Tang FW. Roles of Conformational and Configurational Defects on the Physical Aging of Amorphous Poly(lactic acid). J Phys Chem B 2007. [DOI: 10.1021/jp074509t] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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26
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Théneau C, Salmerón Sánchez M, Rodríguez Hernández JC, Monleón Pradas M, Saiter JM, Gómez Ribelles JL. The kinetics of the structural relaxation process in PHEMA-silica nanocomposites based on an equation for the configurational entropy. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2007; 24:69-77. [PMID: 17876514 DOI: 10.1140/epje/i2007-10214-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2007] [Accepted: 08/02/2007] [Indexed: 05/17/2023]
Abstract
The enthalpy relaxation of polymer-silica nanocomposites prepared by simultaneous polymerization of poly(2-hydroxyethyl methacrylate) (PHEMA) and tetraethyloxysilane, TEOS, a silica precursor, is investigated. Both the glass transition temperature, Tg, and the temperature interval of the glass transition, DeltaTg , increase as the silica content in the sample does. Structural relaxation experiments show that the temperature interval in which conformational motions take place broadens as the silica content in the hybrid increases. A phenomenological model based on the evolution of the configurational entropy during the structural relaxation process, the SC model, has been used for determining the temperature dependence of the relaxation times during the process. The results show an increase of the fragility of the polymer as the silica content increases, a feature that can be related to the broadening of the distribution of relaxation times characterized by the beta parameter of the stretched exponential distribution. On another hand the silica content increase produces a significant change of the relaxation times in the glassy state.
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Affiliation(s)
- C Théneau
- Center for Biomaterials, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022, Valencia, Spain
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Badrinarayanan P, Simon SL. Origin of the divergence of the timescales for volume and enthalpy recovery. POLYMER 2007. [DOI: 10.1016/j.polymer.2007.01.064] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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28
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Meng Y, Simon SL. Pressure relaxation of polystyrene and its comparison to the shear response. ACTA ACUST UNITED AC 2007. [DOI: 10.1002/polb.21320] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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