Surface anchoring behavior of 5CB liquid crystal confined between iron surfaces: A molecular dynamics study

Chen, Hui; Xu, Chonghai; Xiao, Guangchun; Chen, Zhaoqiang; Yi, Mingdong; Zhang, Jingjie

doi:10.1016/j.apsusc.2020.145284

Cited by 10 publications

(9 citation statements)

References 42 publications

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“…The difference between the velocity distribution of sg-5CB and that of sf-5CB is somewhat related to the diffusion behavior of 5CB under confinement between iron walls without shear, which we demonstrated in our previous study. [21] For the 5CB between grooved walls, the diffusion coefficient along the x-direction (i.e., the shear direction in this study) near the walls is significantly smaller than that for 5CB between flat walls, and hence the mobility of 5CB in the former case is lower, leading to a larger solid-like region.…”

Section: Boundary Conditions Of Sheared 5cbmentioning

confidence: 55%

“…The force field used for 5CB combines the pairwise, angular and torsional angle interactions developed by Zhang et al [19] and bond interactions developed by Tiberio et al [20] ; these parameters have been verified as valid in our prior simulations. [21] The iron surfaces were described by the Lennard-Jones potential, [22] and the Lennard-Jones parameters between different types of atoms were mixed using the standard Lorentz-Berthelot rules, i.e., 𝜀 ij = (𝜀 i 𝜀 j ) 1∕2 and…”

Section: Model and Simulationmentioning

confidence: 99%

“…The anchoring behaviors of 5CB on flat and grooved iron walls were investigated in our previous simulations. [21] As illustrated in Figure 2, the atoms in the bottom layer of the lower iron walls were fixed. Various pressures (P = 26, 260, and 1000 MPa) and velocities (v = 1, 10, and 100 m s −1 ) were applied to the outermost layer of the upper iron wall in order to study the influence of these parameters on 5CB LC.…”

Section: Model and Simulationmentioning

confidence: 99%

“…In order to reduce velocity fluctuations caused by the thermodynamic motion of atoms, the velocities were time-averaged over the final 8 ns of the simulations. Same as the analysis method of P 2l , the 5CB molecules were split into 60 For clarity, the molecular orientation of the 5CB molecule is represented by the N-C3 vector (as defined in Figure 1) using a red stick, as in our previous simulation [21] and others. [19,20] blocks across the film thickness direction, and the atomic mass density of each block was calculated.…”

Section: Boundary Conditions Of Sheared 5cbmentioning

confidence: 99%

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Molecular Dynamics Simulations on the Flow Behavior of 5CB Liquid Crystal Sandwiched Between Iron Walls

Chen

Sun

Xiao

et al. 2022

Advcd Theory and Sims

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The 4-n-pentyl-4′-cyano biphenyl (5CB) liquid crystal (LC) sandwiched and sheared between atomically flat and grooved iron walls, respectively, is simulated using molecular dynamics, and the flow behavior of the system under confinement, pressure, and shear is investigated. The order parameter P 2 , velocity, and density of 5CB are profiled as a function of distance from the walls using a block analysis method. The flow-alignment phenomenon is reproduced, and alignment angles ranging from 11.3°to 13.9°are observed. The competition between the elastic effect of the surface and viscous effect of the flow on the orientation of the 5CB molecules is investigated. The P 2 of 5CB located in the vicinity of the grooved walls is higher than that of the flat walls, while this difference is negligible in the case of 5CB distanced from the walls. Instead of boundary slip or Couette flow, the velocity profiles reveal a boundary condition (BC) of central localization, which is very different from the assumed Couette flow BC in most analytical models of LC flow. This work enhances the current molecular-scale understanding of the flow behavior of confined liquid crystals and provides additional insights into the phenomenon.

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Section: Boundary Conditions Of Sheared 5cbmentioning

confidence: 55%

Section: Model and Simulationmentioning

confidence: 99%

Section: Model and Simulationmentioning

confidence: 99%

Section: Boundary Conditions Of Sheared 5cbmentioning

confidence: 99%

See 2 more Smart Citations

Molecular Dynamics Simulations on the Flow Behavior of 5CB Liquid Crystal Sandwiched Between Iron Walls

Chen

Sun

Xiao

et al. 2022

Advcd Theory and Sims

Self Cite

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“…For ease of use, the majority of rheology measurements were performed between sand-blasted steel surfaces of a 40 mm parallel-plate geometry at a gap of h=500±1 µm on a strain-controlled rheometer, ARES G-2 (TA Instruments). Molecular dynamics simulations indicate that 5CB prefers random planar alignment on atomically-smooth iron surfaces [40]. Random alignment will generate discontinuities between regions of uniform alignment, some of which will nucleate s = − 1 2 disclinations.…”

Section: B Methodsmentioning

confidence: 99%

The yielding of defect-entangled dispersions in a nematic solvent

Katyan

Schofield

Wood

2021

Journal of Rheology

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Oscillatory rheology, at both small (SAOS) and large (LAOS) amplitude, was performed to measure the dynamic response of a soft-solid, formed on dispersing colloids into a thermotropic nematic liquid crystal at volume fractions φ > 18%. Due to weak homeotropic anchoring of nematogens at colloid surfaces, a Saturn-ring defect-line, known as a 'disclination', encircles each particle and entangles with neighbouring Saturn-ring disclinations [1]. We present the first experimental investigation of the yielding behaviour of the resulting gel to reveal the underpinning physics. Results reveal the frequency response of the composite is independent of the volume fraction φ ; an indication that the dispersed phase simply increases the density of disclinations spanning the composite without further effect. Beyond the linear viscoelastic regime (LVR), LAOS experiments indicate the composite is an elastoplastic fluid exhibiting both strain-hardening and shear-thinning behaviour, with Chebyshev coefficients e 3 > 0 and ν 3 < 0 respectively. We deduce that the disclination density n is constant until the strain amplitude is sufficient to break disclinations leading to shear-thinning behaviour beyond the LVR. A simple theory is introduced revealing that the Ericksen number E r determines the onset of flow, when E r > 1, generating a strain-hardening response since the Frank elasticity resists reorientation of molecular alignment within confined nematic domains. Above a critical frequency ω c the loss modulus G increases slowly due to enhanced viscosity within confined nematic domains, G ∝ ω 1/2 [2]. Observation of this behaviour in a small-molecule nematic solvent provides insights into the physics of flow behaviour in other, more complex, defect-mediated liquid crystalline structures exhibiting similar properties [3][4][5].

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Alignment control of thermotropic liquid crystals by topography and chemical functionality of a surface: A review

Xin

Chen

Song³

et al. 2023

Materials Today Communications

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Surface anchoring behavior of 5CB liquid crystal confined between iron surfaces: A molecular dynamics study

Cited by 10 publications

References 42 publications

Molecular Dynamics Simulations on the Flow Behavior of 5CB Liquid Crystal Sandwiched Between Iron Walls

Molecular Dynamics Simulations on the Flow Behavior of 5CB Liquid Crystal Sandwiched Between Iron Walls

The yielding of defect-entangled dispersions in a nematic solvent

Alignment control of thermotropic liquid crystals by topography and chemical functionality of a surface: A review

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