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Hou J, Sampson W, Dumanli AG. Macromolecular crowding in chiral assembly of ellipsoidal nanoparticles. J Chem Phys 2024; 160:054905. [PMID: 38341709 DOI: 10.1063/5.0160172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Accepted: 01/09/2024] [Indexed: 02/13/2024] Open
Abstract
Anisotropic colloidal particles have the ability to self-assemble into cholesteric structures. We used molecular dynamics to simulate the self-assembly of ellipsoidal particles with the objective to establish a general framework to reveal the primary factors driving chiral interactions. To characterize these interactions, we introduce a characteristic parameter following the crowding factor (CF) theory. Our simulations and statistical analysis showed good agreement with the CF theory; at the early stages of the assembly process, the ellipsoidal particles go through a critical aggregation point followed by further clustering toward nematic order. Furthermore, we demonstrate that under high CF conditions, small initial clusters may induce a chiral twist, which subsequently forms a cholesteric structure with no directional preference in higher organization states.
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Affiliation(s)
- Jiaxin Hou
- Department of Materials, The University of Manchester, Oxford Rd., Manchester M13 9PL, United Kingdom
- Henry Royce Institute, The University of Manchester, Oxford Rd., Manchester M13 9PL, United Kingdom
| | - William Sampson
- Department of Materials, The University of Manchester, Oxford Rd., Manchester M13 9PL, United Kingdom
- Henry Royce Institute, The University of Manchester, Oxford Rd., Manchester M13 9PL, United Kingdom
| | - Ahu Gümrah Dumanli
- Department of Materials, The University of Manchester, Oxford Rd., Manchester M13 9PL, United Kingdom
- Henry Royce Institute, The University of Manchester, Oxford Rd., Manchester M13 9PL, United Kingdom
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Molecular Dynamics Simulations on the Flow Behavior of 5CB Liquid Crystal Sandwiched Between Iron Walls. ADVANCED THEORY AND SIMULATIONS 2022. [DOI: 10.1002/adts.202200346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Shim YH, Ahn H, Lee S, Kim SO, Kim SY. Universal Alignment of Graphene Oxide in Suspensions and Fibers. ACS NANO 2021; 15:13453-13462. [PMID: 34324294 DOI: 10.1021/acsnano.1c03954] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Graphene oxide (GO) has become a key component for high-performance carbon-based films or fibers based on its dispersibility and liquid crystallinity in an aqueous suspension. While the superior performance of GO-based fiber relies on their alignment at the submicrometer level, fine control of the microstructure is often hampered, in particular, under dynamic nature of GO-processing involving shear. Here, we systemically studied the structural variation of GO suspensions under shear conditions via in situ rheo-scattering and shear-polarized optical microscope analysis. The evolution of GO alignment under shear is indeed complex. However, we found that the shear-dependent structural equilibrium exists. GO showed a nonlinear structural transition with shear, yet there is a "universal" shear threshold for the best alignment, resulting in graphene fiber achieved an improvement in mechanical properties by ∼54% without any chemical modification. This finding challenges the conventional concept that high shear stress is required for the good alignment of particles and their best performance.
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Affiliation(s)
- Yul Hui Shim
- School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea
- School of Chemical and Biological Engineering, Seoul National University (SNU), Seoul 08826, Republic of Korea
| | - Hyungju Ahn
- Pohang Accelerator Lab, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Sangsul Lee
- Pohang Accelerator Lab, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Sang Ouk Kim
- National Creative Research Initiative Center for Multi-Dimensional Directed Nanoscale Assembly, Department of Materials Science & Engineering, KAIST, Daejeon 34141, Republic of Korea
| | - So Youn Kim
- School of Chemical and Biological Engineering, Seoul National University (SNU), Seoul 08826, Republic of Korea
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Liu M, Shiba H, Liu H, Peng H. Molecular-dynamics simulations on the mesophase transition induced by oscillatory shear in imidazolium-based ionic liquid crystals. Phys Chem Chem Phys 2021; 23:6496-6508. [PMID: 33688864 DOI: 10.1039/d0cp05677d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular dynamics simulations were performed on a 1-dodecyl-3-methylimidazolium hexafluorophosphate ([C12mim][PF6]) ionic liquid crystal (ILC) with the application of an oscillatory shear. We found that the oscillatory shear can both accelerate and suppress mesophase formation depending on shear amplitude. A small amplitude shear can speed up the mesophase transition dynamics and result in a more ordered mesomorphic structure than that without shear, i.e., an effect of accelerated aging. The mesophase is destabilized when the shear amplitude is large enough, resulting in a smectic A (SmA) to liquid or a smectic B (SmB) to SmA transition, with the mesophase behaviour summarized in an out-of-equilibrium phase diagram. Inside the layer plane a medium-range hexatic order was observed, with the correlation length extending to several nanometres in the shear-induced SmA phase. We rationalize the nonequilibrium mesophase behaviour from the rheology of isotropic liquids, finding a temperature-independent critical relaxation time for the mesophase transition in the translational or rotational dynamics. This finding can be used to predict the mesophase behaviour in the sheared ILCs from the rheology of isotropic liquids.
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Affiliation(s)
- Min Liu
- School of Materials Science and Engineering, Central South University, Changsha 410083, China.
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Sarman S, Laaksonen A. Microscopic shear flow simulations of a biaxial smectic A liquid crystal based on the soft ellipsoid string-fluid. Phys Chem Chem Phys 2021; 23:15183-15195. [PMID: 34227627 DOI: 10.1039/d1cp00957e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have studied the behaviour of a biaxial smectic A liquid crystal based on the soft ellipsoid string-fluid in shear flow by molecular dynamics simulation using the SLLOD equation of motion. This is facilitated by the fact that the biaxial symmetry allows linear relations between the pressure and the velocity gradient. This means that linear irreversible thermodynamics can be applied independently of the simulations to obtain the torques determining the orientations of the system and that the predictions of this theory can be cross-checked by the simulations. It turns out that there is a torque turning the smectic layers to the orientation parallel to the vorticity plane if the simulation is started in another orientation. In the orientation parallel to the vorticity plane where the director formed by the long axes of the molecules, nw, is perpendicular to the vorticity plane there is another torque keeping the director formed by the normals of the broadsides of the molecules, nu, parallel to this plane at a constant alignment angle, ψ relative to the streamlines independently of the strain rate. Moreover, this alignment angle seems to be the one where the irreversible energy dissipation rate, , is minimal. This is in agreement with a recently proven theorem according to which is minimal in the linear regime of a nonequilibrium steady state. Finally, we studied the orientation of nu when the smectic layers are parallel to the shear plane. In a simulation this orientation is stabilised by the periodic boundary conditions. Then we found that there was a nonlinear torque turning nu to the orientation perpendicular to the streamlines thus minimising the value of even though this value is larger than the value of in the orientation parallel to the vorticity plane. This means that is minimized given the external boundary conditions.
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Affiliation(s)
- Sten Sarman
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
| | - Aatto Laaksonen
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden. and State Key Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing, 210009, P. R. China and Centre of Advanced Research in Bionanoconjugates and Biopolymers, Petru Poni Institute of Macromolecular Chemistry Aleea, Grigore Ghica-Voda, 41A 700487 Iasi, Romania and Department of Engineering Sciences and Mathematics, Division of Energy Science Luleå, University of Technology, SE-97187 Luleå, Sweden
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Huang Z, Zhu G, Chen P, Hou C, Yan LT. Plastic Crystal-to-Crystal Transition of Janus Particles under Shear. PHYSICAL REVIEW LETTERS 2019; 122:198002. [PMID: 31144934 DOI: 10.1103/physrevlett.122.198002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Indexed: 05/26/2023]
Abstract
Colloidal Janus spheres in the bulk typically spontaneously assemble into plastic crystalline phases, while particle orientations exhibit glasslike dynamics without long-range order. Through Brownian dynamics simulations, we demonstrate that shear can trigger a phase transition from an isotropic crystal with orientational disorder to an orientationally ordered crystal with lamellae along the shear direction. This nonequilibrium transition is accompanied with the orientational ordering following a nucleation and growth mechanism. By performing a phenomenological extension of free energy analysis, we reveal that the nucleation originates from the orientation fluctuations induced by shear. The growth of the orientationally crystalline cluster is examined to be disklike, captured by developing a lattice model with memoryless state functions. These findings bring new insights into the mechanisms for the ordering transition of anisotropic particles at nonequilibrium states.
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Affiliation(s)
- Zihan Huang
- State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
| | - Guolong Zhu
- State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
| | - Pengyu Chen
- State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
| | - Cuiling Hou
- State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
| | - Li-Tang Yan
- State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
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