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Shen Z, Carrillo JMY, Sumpter BG, Wang Y. Mesoscopic two-point collective dynamics of glass-forming liquids. J Chem Phys 2023; 159:114501. [PMID: 37712790 DOI: 10.1063/5.0161866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 08/24/2023] [Indexed: 09/16/2023] Open
Abstract
The collective density-density and hydrostatic pressure-pressure correlations of glass-forming liquids are spatiotemporally mapped out using molecular dynamics simulations. It is shown that the sharp rise of structural relaxation time below the Arrhenius temperature coincides with the emergence of slow, nonhydrodynamic collective dynamics on mesoscopic scales. The observed long-range, nonhydrodynamic mode is independent of wave numbers and closely coupled to the local structural dynamics. Below the Arrhenius temperature, it dominates the slow collective dynamics on length scales immediately beyond the first structural peak in contrast to the well-known behavior at high temperatures. These results highlight a key connection between the qualitative change in mesoscopic two-point collective dynamics and the dynamic crossover phenomenon.
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Affiliation(s)
- Zhiqiang Shen
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Jan-Michael Y Carrillo
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Bobby G Sumpter
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Yangyang Wang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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2
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Gałązka M, Jasiurkowska-Delaporte M, Ermelinda S. Eusébio M, T. S. Rosado M, Juszyńska-Gałązka E, Dryzek E. Study on molecular dynamics and phase transitions in 1,2-cyclohexanediol and 1,3-cyclohexanediol isomers by calorimetric and dielectric spectroscopy. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.120874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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3
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Ojovan MI, Tournier RF. On Structural Rearrangements Near the Glass Transition Temperature in Amorphous Silica. MATERIALS 2021; 14:ma14185235. [PMID: 34576458 PMCID: PMC8466242 DOI: 10.3390/ma14185235] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 09/04/2021] [Accepted: 09/08/2021] [Indexed: 12/29/2022]
Abstract
The formation of clusters was analyzed in a topologically disordered network of bonds of amorphous silica (SiO2) based on the Angell model of broken bonds termed configurons. It was shown that a fractal-dimensional configuron phase was formed in the amorphous silica above the glass transition temperature Tg. The glass transition was described in terms of the concepts of configuron percolation theory (CPT) using the Kantor-Webman theorem, which states that the rigidity threshold of an elastic percolating network is identical to the percolation threshold. The account of configuron phase formation above Tg showed that (i) the glass transition was similar in nature to the second-order phase transformations within the Ehrenfest classification and that (ii) although being reversible, it occurred differently when heating through the glass–liquid transition to that when cooling down in the liquid phase via vitrification. In contrast to typical second-order transformations, such as the formation of ferromagnetic or superconducting phases when the more ordered phase is located below the transition threshold, the configuron phase was located above it.
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Affiliation(s)
- Michael I. Ojovan
- Department of Materials, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK
- Department of Radiochemistry, Moscow State University Named after M.V. Lomonosov, Leninskie Gory 1, Bd.3, 119991 Moscow, Russia
- Correspondence: ; Tel.: +44-747-828-9098
| | - Robert F. Tournier
- Laboratoire National des Champs Magnétiques Intenses, European Magnetic Field Laboratory, UPR 3228 Centre National de la Recherche Scientifique, Université Grenoble Alpes, Institut National des Sciences Appliquées de Toulouse, F-31400 Toulouse, France;
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4
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Olguín-Arias V, Davis S, Gutiérrez G. Extended correlations in the critical superheated solid. J Chem Phys 2019. [DOI: 10.1063/1.5111527] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Vivianne Olguín-Arias
- Departamento de Física, Facultad de Ciencias Exactas, Universidad Andres Bello, Sazié 2212, piso 7, Santiago, 8370136, Chile
| | - Sergio Davis
- Departamento de Física, Facultad de Ciencias Exactas, Universidad Andres Bello, Sazié 2212, piso 7, Santiago, 8370136, Chile
- Comisión Chilena de Energía Nuclear, Casilla 188-D, Santiago, Chile
| | - Gonzalo Gutiérrez
- Grupo de Nanomateriales, Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile
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Bakai O, Bratchenko M, Dyuldya S. Three-state mesoscopic model of a heterophase fluid in application to the gas-liquid and dielectric-semiconductor-metal transformations in expanded mercury. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2018.03.068] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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6
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Bakai O. Mesoscopic equation of state of the heterophase fluid and its application to description of the liquid-gas asymmetry. J Mol Liq 2017. [DOI: 10.1016/j.molliq.2016.12.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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7
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Peng YJ, Cai CT, Zhang RC, Chen TH, Sun PC, Li BH, Wang XL, Xue G, Shi AC. Probing the two-stage transition upon crossing the glass transition of polystyrene by solid-state NMR. CHINESE JOURNAL OF POLYMER SCIENCE 2016. [DOI: 10.1007/s10118-016-1762-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Elamin K, Swenson J. Brownian motion of single glycerol molecules in an aqueous solution as studied by dynamic light scattering. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:032306. [PMID: 25871109 DOI: 10.1103/physreve.91.032306] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Indexed: 06/04/2023]
Abstract
Aqueous solutions of glycerol are investigated by dynamic light scattering (DLS) over the whole concentration range (10-98 wt.% water) and in the temperature range 283-303 K. The measurements reveal one slow relaxation process in the geometry of polarized light scattering. This process is present in the whole concentration range, although it is very weak at the highest and lowest water concentrations and is considerably slower than the structural α relaxation, which is too fast to be observed on the experimental time scale in the measured temperature range. The relaxation time of the observed process exhibits a 1/q2 dependence, proving that it is due to long-range translational diffusion. The Stokes-Einstein relation is used to estimate the hydrodynamic radius of the diffusing particles and from these calculations it is evident that the observed relaxation process is due to the Brownian motion of single or a few glycerol molecules. The fact that it is possible to study the self-diffusion of such small molecules may stimulate a broadening of the research field used to be covered by the DLS technique.
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Affiliation(s)
- Khalid Elamin
- Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
| | - Jan Swenson
- Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
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Elamin K, Cazzato S, Sjöström J, King SM, Swenson J. Long-Range Diffusion in Xylitol–Water Mixtures. J Phys Chem B 2013; 117:7363-9. [DOI: 10.1021/jp401633g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Khalid Elamin
- Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
| | - Stefano Cazzato
- Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
| | - Johan Sjöström
- SP Technical Research Institute of Sweden, SE-501 15 Borås, Sweden
| | - Stephen M. King
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX Oxfordshire,
United Kingdom
| | - Jan Swenson
- Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
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Angell CA, Zhao Z. Fluctuations, clusters, and phase transitions in liquids, solutions, and glasses: from metastable water to phase change memory materials. Faraday Discuss 2013; 167:625-41. [DOI: 10.1039/c3fd00111c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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Yuan H, Khatua S, Zijlstra P, Orrit M. Individual gold nanorods report on dynamical heterogeneity in supercooled glycerol. Faraday Discuss 2013; 167:515-27. [DOI: 10.1039/c3fd00091e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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12
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Kaminski K, Kaminska E, Wlodarczyk P, Adrjanowicz K, Wojnarowska Z, Grzybowska K, Paluch M. Dynamics of the slow mode in the family of six-carbon monosaccharides monitored by dielectric spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:365103. [PMID: 21386531 DOI: 10.1088/0953-8984/22/36/365103] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Broadband dielectric measurements performed on D-glucose, L-sorbose, D-fructose and D-galactose revealed that, except for the structural relaxation process, one can detect in the liquid phase of these carbohydrates a much slower relaxation mode. Recently we have demonstrated that in D-glucose this relaxation mode might be related to the long range correlation of density fluctuations (LRCDF), also called Fischer clusters (FC). Based on the dielectric data obtained for the four monosaccharides we were able to make a more general conclusion about the characteristic dielectric features of the slow mode in the whole family of carbohydrates. We found out that the timescale separation between structural and considered relaxation reaches up to six decades at the glass transition temperature and the dielectric strength decreases significantly with lowering temperature. Another very interesting feature of the slow process is that it can be described by an almost exponential response function. We have found out that the fragility of the slow process lies within the range m = 44-50. Finally, we have also shown that there is a close link between structural and slow relaxation.
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Affiliation(s)
- K Kaminski
- Institute of Physics, Silesian University, ulica Uniwersytecka 4, 40-007 Katowice, Poland
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Kaminski K, Wlodarczyk P, Adrjanowicz K, Kaminska E, Wojnarowska Z, Paluch M. Origin of the Commonly Observed Secondary Relaxation Process in Saccharides. J Phys Chem B 2010; 114:11272-81. [DOI: 10.1021/jp1034773] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- K. Kaminski
- Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland
| | - P. Wlodarczyk
- Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland
| | - K. Adrjanowicz
- Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland
| | - E. Kaminska
- Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland
| | - Z. Wojnarowska
- Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland
| | - M. Paluch
- Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland
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15
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Bergman R, Jansson H, Swenson J. Slow Debye-type peak observed in the dielectric response of polyalcohols. J Chem Phys 2010; 132:044504. [DOI: 10.1063/1.3294703] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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16
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Kaminski K, Kaminska E, Adrjanowicz K, Wojnarowska Z, Wlodarczyk P, Grzybowska K, Dulski M, Wrzalik R, Paluch M. Observation of the dynamics of clusters in d-glucose with the use of dielectric spectroscopy. Phys Chem Chem Phys 2010; 12:723-30. [DOI: 10.1039/b916699h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Compressibility and thermal expansion coefficients of nanocomposites with amorphous and crystalline polymer matrix. Eur Polym J 2009. [DOI: 10.1016/j.eurpolymj.2009.04.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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18
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Zhou S, Solana JR. Progress in the Perturbation Approach in Fluid and Fluid-Related Theories. Chem Rev 2009; 109:2829-58. [DOI: 10.1021/cr900094p] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Shiqi Zhou
- State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083, China, and School of Physics Science and Technology, Central South University, Changsha, Hunan 410083, China
| | - J. R. Solana
- Applied Physics Department, University of Cantabria, 39005 Santander, Spain
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20
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Kuang Q, Zhang J, Wang Z. Revealing Long-Range Density Fluctuations in Dialkylimidazolium Chloride Ionic Liquids by Dynamic Light Scattering. J Phys Chem B 2007; 111:9858-63. [PMID: 17672491 DOI: 10.1021/jp071733+] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study, the structures and dynamics of ionic liquids of 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]) and 1-n-butyl-3-methylimidazolium chloride ([BMIM][Cl]) were studied by dynamic light scattering with polarized and depolarized geometries in the temperature range from 300 to 400 K. The temperature range covered supercooled and liquid states for [BMIM][Cl] and covered the liquid state for [AMIM][Cl]. The results show that for these ionic liquids at all chosen temperatures only one ultraslow relaxation is observed in the polarized component of dynamic light scattering, however, the ultraslow relaxation is not observed in the depolarized component. The ultraslow relaxation exhibited several typical features of the "cluster" mode generally found in glass-forming liquids and polymer melts, such as diffusive, strongly scattering-vector-dependent, and nearly exponential characters, which thus corresponded to long-range density fluctuations. The physical origin for long-range density fluctuations was the existence of heterogeneities with large characteristic length scales in these ionic liquids. It was further considered that molecules of these ionic liquids not only tended to aggregate to form dynamic clusters but also possibly formed dynamic networks in the supercooled state and the heterogeneities could exist even at temperatures higher than the melting points.
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Affiliation(s)
- Qinglin Kuang
- CAS Key Laboratory of Engineering Plastics, Joint Laboratory of Polymer Science and Materials, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080 P. R. China
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21
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Bakai AS. On the role of frustration on the glass transition and polyamorphism of mesoscopically heterophase liquids. J Chem Phys 2006; 125:64503. [PMID: 16942294 DOI: 10.1063/1.2238858] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The model of heterophase fluctuations is developed accounting frustration of the mesoscopic solidlike fluctuons. Within the framework of this model, the glass transition and polyamorphous transformations are considered. It is shown that the frustration increases the temperature range in which the heterophase liquid state exists. the upper and lower boundaries of this temperature range are determined. These boundaries separate different phase states-amorphous solid, heterophase liquid, and fluid phases. Polyamorphous liquid-liquid transitions in the liquid are investigated. Frustration can call forth continuous fluid-solid phase transformation avoiding the first- or second-order phase transition. Conditions under which the first-order phase transition fraction takes place are formulated. Two scenarios of the first-order liquid-liquid polyamorphous transformation are described. As an example the glacial phase formation and the first-order liquid-liquid phase transition in triphenyl phosphate are considered and discussed. Impact of frustration on the liquid crystallization and crystallinity of the glassy state is studied.
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Affiliation(s)
- A S Bakai
- National Scientific Center, "Kharkiv Institute of Physics and Technology," Akademichna Street 1, 61108 Kharkiv, Ukraine.
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Takenaka M, Shimizu H, Nishitsuji S, Hasegawa H. Concentration Fluctuations Induced by Orientation Fluctuations in Polymer−Liquid Crystal Mixture. Macromolecules 2006. [DOI: 10.1021/ma061427e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mikihito Takenaka
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Hirofumi Shimizu
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Shotaro Nishitsuji
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Hirokazu Hasegawa
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
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Collin D, Martinoty P. Commentary on "Solid-like rheological response of non-entangled polymers in the molten state" by H. Mendil et al. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2006; 19:87-98; discussion 99-100. [PMID: 16416250 DOI: 10.1140/epje/e2006-00005-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Indexed: 05/06/2023]
Abstract
We discuss the rheology experiments on classical and liquid crystal polymer melts by Mendil et al., in the light of the old and new piezorheometry experiments we have carried out on both types of melt. The mechanical behavior we have observed in the linear and non-linear regimes are independent of the melt studied (classical or liquid crystal), and of their nature (siloxane-type, acrylate-type and styrene-type). In the linear regime, the mechanical behavior of the melts presents two components: the first one is the conventional contribution. It is due to polymer chains, and is independent of sample thickness. The second one, which can be observed only when a strong interaction between the compound and the substrate exists, is associated with the glass transition. This component displays an elastic response depending on the sample thickness, and disappears at high temperature. It can be explained by assuming the presence of long-range density fluctuations, which are associated with the glass transition, and frozen at the frequencies used in the experiments. The experiments as a function of the applied strain show that the value of the elastic component decreases when the applied strain increases. This slipping transition occurs progressively, which highlights the heterogeneous nature of the anchoring. The results on the classical polymer by Mendil et al. can be considered to be consistent with ours. In contrast, their results on the liquid crystal polymer differ markedly from ours, showing that the elastic response of this sample has not the same origin.
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Affiliation(s)
- D Collin
- Institut de Mécanique des Fluides et des Solides, UMR 7507 CNRS-ULP, 67000, Strasbourg, France
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Sills S, Gray T, Overney RM. Molecular dissipation phenomena of nanoscopic friction in the heterogeneous relaxation regime of a glass former. J Chem Phys 2005; 123:134902. [PMID: 16223326 DOI: 10.1063/1.2038907] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Nanoscale sliding friction involving a polystyrene melt near its glass transition temperature Tg (373 K) exhibited dissipation phenomena that provide insight into the underlying molecular relaxation processes. A dissipative length scale that shows significant parallelism with the size of cooperatively rearranging regions (CRRs) could be experimentally deduced from friction-velocity isotherms, combined with dielectric loss analysis. Upon cooling to approximately 10 K above Tg, the dissipation length Xd grew from a segmental scale of approximately 3 A to 2.1 nm, following a power-law relationship with the reduced temperature Xd approximately TR-phi. The resulting phi=1.89+/-0.08 is consistent with growth predictions for the length scale of CRRs in the heterogeneous regime of fragile glass formers. Deviations from the power-law behavior closer to Tg suggest that long-range processes, e.g., the normal mode or ultraslow Fischer modes, may couple with the alpha relaxation, leading to energy dissipation in domains of tens of nanometers.
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Affiliation(s)
- Scott Sills
- Department of Chemical Engineering, University of Washington, Seattle, Washington 98195-1750, USA
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Kokshenev VB, Borges PD, Sullivan NS. Moderately and strongly supercooled liquids: A temperature-derivative study of the primary relaxation time scale. J Chem Phys 2005; 122:114510. [PMID: 15836232 DOI: 10.1063/1.1855877] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The primary relaxation time scale tau(T) derived from the glass forming supercooled liquids (SCLs) is discussed within ergodic-cluster Gaussian statistics, theoretically justified near and above the glass-transformation temperature T(g). An analysis is given for the temperature-derivative data by Stickel et al. on the steepness and the curvature of tau(T). Near the mode-coupling-theory (MCT) crossover T(c), these derivatives separate by a kink and a jump, respectively, the moderately and strongly SCL states. After accounting for the kink and the jump, the steepness remains a piecewise conitnuous function, a material-independent equation for the three fundamental characteristic temperatures, T(g), T(c), and the Vogel-Fulcher-Tamman (VFT) T(0), is found. Both states are described within the heterostructured model of solidlike clusters parametrized in a self-consistent manner by a minimum set of observable parameters: the fragility index, the MCT slowing-down exponent, and the chemical excess potential of Adam and Gibbs model (AGM). Below the Arrhenius temperature, the dynamically and thermodynamically stabilized clusters emerge with a size of around of seven to nine and two to three molecules above and close to T(g) and T(c), respectively. On cooling, the main transformation of the moderately into the strongly supercooled state is due to rebuilding of the cluster structure, and is attributed to its rigidity, introduced through the cluster compressibility. It is shown that the validity of the dynamic AGM (dynamically equivalent to the standard VFT form) is limited by the strongly supercooled state (T(g) < T < T(c)) where the superrigid cooperative rearranging regions are shown to be well-chosen parametrized solidlike clusters. Extension of the basic parameter set by the observable kinetic and diffusive exponents results in prediction of a subdiffusion relaxation regime in SCLs that is distinct from that established for amorphous polymers.
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Drozd-Rzoska A, Rzoska SJ, Paluch M, Pawlus S, Zioło J, Santangelo PG, Roland CM, Czupryński K, Dabrowski R. Mode coupling behavior in glass-forming liquid crystalline isopentylcyanobiphenyl. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 71:011508. [PMID: 15697609 DOI: 10.1103/physreve.71.011508] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2003] [Revised: 09/10/2004] [Indexed: 05/24/2023]
Abstract
Linear and nonlinear dielectric measurements of liquid crystalline chiral isopentylcyanobiphenyl (5*CB) and n -pentylcyanobiphenyl (5CB), combined with viscosity eta (T) data, are presented. The 5*CB compound glassifies on cooling in the cholesteric phase whereas 5CB crystallizes in the nematic phase. In both compounds the temperature evolution of dielectric relaxation times, the dc conductivity, and the viscosity are well described by the "critical-like" description from mode coupling theory (MCT). However, for 5*CB a unique coincidence of the MCT "critical" temperature and extrapolated temperature of the hypothetical continuous isotropic-cholesteric (T*) phase transition was found. The temperature dependence of the strong electric-field-induced changes of the dielectric permittivity exhibits a strong anomaly in the direction of negative values on approaching T* , not observed up to now. The anomaly is described by the susceptibility-related critical exponent gamma=1 . The divergence of the "nonlinear" dielectric relaxation follows a power dependence described by the exponent y=1 . This paper recalls the recent discussions on the glassy dynamics of a "hard-ellipsoid" liquid and the possible relationship between the glass transition, critical phenomena, and isotropic-nematic transition.
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