The phase behavior, structure, and dynamics of rodlike mesogens with various flexibility using dissipative particle dynamics simulation

Abstract

We present a systematic dissipative particle dynamics (DPD) study on the phase behavior, structure, and dynamics of rodlike mesogens. In addition to a rigid fused-bead-chain model with RATTLE constraint method, we also construct a semirigid model in which the flexibility is controlled by the bending constant of k(φ). Using this notation, the rigid model has an infinite bending constant of k(φ)=∞. Within the parameter space studied, both two kinds of models exhibit the nematic and smectic-A phases in addition to the isotropic and solid phases. All of the phase transitions are accompanied by the discontinuities in the thermodynamical, structural, and dynamical quantities and the hysteresis around the transition points, and are therefore first order. Note that the obtained solid state exhibits an in-layer tetragonal packing due to the high density. For the rigid model, the simulations show that the liquid crystal phases can be observed for mesogens with at least five beads and the nematic phase is the first one to appear. More importantly, the phase diagram of seven-bead-chain models is obtained as a function of k(φ) and temperature. It is found that decreasing the value of k(φ) reduces the anisotropy of molecular shape and the orientational ordering, and thereby shifts the liquid crystal phases to the lower temperature end of the phase diagram. Due to the different k(φ) dependence of phase transition temperatures, the nematic phase range exhibits a more marked narrowing than the smectic-A phase as k(φ) is reduced, implying that the flexibility has a destabilizing effect on the nematic and smectic-A phases. We also have investigated the anisotropic translational diffusion in liquid crystal phases and its temperature and flexibility dependence. In our study, we find that the phases formed, their statical and dynamic properties, as well as the transition properties are in close accord with those observations in real thermotropic liquid crystals. It is clear that both the rigid and semirigid models we used are valuable models with which to study the behavior of thermotropic liquid crystals using DPD algorithm.

Ordering of anisotropic nanoparticles in diblock copolymer lamellae: Simulations with dissipative particle dynamics and a molecular theory

“…It is worth noting that semi-rigid mesogens can be also simulated with DPD using an additional spring force between their first and last particles 58 or by introducing angle potentials. 59 For the sake of comparison we perform some simulations by replacing nanorods with flexible chains consisting of N R = 5 particles of R type.…”

Structure and electronic absorption spectra of nematogenic alkoxycinnamic acids – a comparative study based on semiempirical and DFT methods

“…The design and synthesis of new organic compounds, which exhibit a nematic phase with a specific spectrum of properties, have essential contributions in establishing and expanding the multibillion dollar LCD industry. The need to develop new liquid crystalline (LC) compounds, for desired applications and technology provides a new motivation to develop a deeper understanding in molecular electronic structure and bonding [2,3]. Even though advances in synthesis and characterization explore many achievements [4] regarding nematic materials, it is often desirable; to have a sense of material behavior prior to synthesis [5].…”

Effect of Non-Mesogenic Solvent on Molecular Conformations and Interactions of a Nematogen: A Probabilistic Approach

“…These are responsible for packing, intermolecular distances, and alignment of molecules to form mesophases [10]. The structure of the nematic phase near the transition can, therefore, be approximated as a calculable perturbation of the structure of the coexisting isotropic liquid.…”