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Lin S, Zhao L, Liu S, Wang Y, Fu G. Modeling the viscoelastic relaxation dynamics of soft particles via molecular dynamics simulation-informed multi-dimensional transition-state theory. SOFT MATTER 2023; 19:502-511. [PMID: 36541141 DOI: 10.1039/d2sm00848c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Viscoelastic soft colloidal particles have been widely explored in mechanical, chemical, pharmaceutical and other engineering applications due to their unique combination of viscosity and elasticity. The characteristic viscoelastic relaxation time shows an Arrhenius-type (or super-Arrhenius due to temperature-dependent transition attempts) thermally-activated behavior, but a holistic explanation from the relevant transition-state theory remains elusive. In this paper, the viscoelastic relaxation times of Lennard-Jones soft colloidal particle systems, including a single particle type system and a binary particle mixture based on the Kob-Andersen model, are determined using molecular dynamics (MD) simulations as the benchmark. First, the particle systems show a non-Maxwellian behavior after comparing the MD-predicted viscoelastic relaxation time and dynamic moduli (storage and loss modulus) to the classic Maxwell viscoelastic model and the recent particle local connectivity theory. Surprisingly, neither the Maxwell relaxation time τMaxwell (obtained from the static shear viscosity η and the high-frequency shear modulus G∞) nor the particle local connectivity lifetime τLC can capture the super-Arrhenius temperature-dependent behavior in the MD-predicted relaxation time τMD. Then, the particle dissociation and association transition kinetics, fractal dimensions of the particle systems, and neighbor particle structure (obtained from the radial distribution functions) are shown to collectively determine the viscoelastic relaxation time. These factors are embedded into a new multi-dimensional transition kinetics model to directly estimate the viscoelastic relaxation time τModel, which is found to agree with the MD-predicted τMD remarkably well. This work highlights the microscopic origin of viscoelastic relaxation dynamics of soft colloidal particles, and theoretically connects rheological dynamics and transition kinetics in soft matters.
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Affiliation(s)
- Shangchao Lin
- Institute of Engineering Thermophysics, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China.
| | - Lingling Zhao
- Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy & Environment, Southeast University, Nanjing, Jiangsu, 210096, China
- Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, China
| | - Shuai Liu
- Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy & Environment, Southeast University, Nanjing, Jiangsu, 210096, China
| | - Yang Wang
- Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy & Environment, Southeast University, Nanjing, Jiangsu, 210096, China
| | - Ge Fu
- Institute of Engineering Thermophysics, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China.
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Popli P, Kayal S, Sollich P, Sengupta S. Exploring the link between crystal defects and nonaffine displacement fluctuations. Phys Rev E 2019; 100:033002. [PMID: 31639940 DOI: 10.1103/physreve.100.033002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Indexed: 11/07/2022]
Abstract
We generalize and then use a recently introduced formalism to study thermal fluctuations of atomic displacements in several two- and three-dimensional crystals. We study both close-packed and open crystals with multiatom bases. Atomic displacement fluctuations in a solid, once coarse grained over some neighborhood, may be decomposed into two mutually orthogonal components. In any dimension d there are always d^{2} affine displacements representing local strains and rotations of the ideal reference configuration. In addition, there exist a number of nonaffine localized displacement modes that cannot be represented as strains or rotations. The number of these modes depends on d and the size of the coarse-graining region. All thermodynamic averages and correlation functions concerning the affine and nonaffine displacements may be computed within harmonic theory. We show that for compact crystals, such as the square and triangular crystals in d=2 and the simple body-centered-cubic and face-centered-cubic crystals in d=3, a single set of d-fold degenerate modes always dominates the nonaffine subspace and is separated from the rest by a large gap. These modes may be identified with specific precursor configurations that lead to lattice defects. In open crystals, such as the honeycomb and kagome lattices, there is no prominent gap, although soft nonaffine modes continue to be associated with known floppy modes representing localized defects. Higher-order coupling between affine and nonaffine components of the displacements quantifies the tendency of the lattice to be destroyed by large homogeneous strains. We show that this coupling is larger by almost an order of magnitude for open lattices as compared to compact ones. Deformation mechanisms such as lattice slips and stacking faults in close-packed crystals can also be understood within this framework. The qualitative features of these conclusions are expected to be independent of the details of the atomic interactions.
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Affiliation(s)
- Pankaj Popli
- Tata Institute for Fundamental Research, Centre for Interdisciplinary Sciences, 36/P Gopanapally, Hyderabad 500107, India
| | - Sayantani Kayal
- Tata Institute for Fundamental Research, Centre for Interdisciplinary Sciences, 36/P Gopanapally, Hyderabad 500107, India
| | - Peter Sollich
- Department of Mathematics, King's College London, London WC2R 2LS, United Kingdom.,Institute for Theoretical Physics, University of Göttingen, 37077 Göttingen, Germany
| | - Surajit Sengupta
- Tata Institute for Fundamental Research, Centre for Interdisciplinary Sciences, 36/P Gopanapally, Hyderabad 500107, India
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