A computer simulation study of the anchoring transitions driven by rod–coil amphiphiles at aqueous–liquid crystal interfaces

Abstract

Dissipative particle dynamics simulations have been conducted to study the anchoring transitions of nematic liquid crystals in the presence of a rod-coil amphiphilic monolayer at the aqueous-liquid crystal interface. Instead of amphiphile interfacial coverage, the repulsion interaction parameter (a MR ) between the mesogens and rod blocks of the amphiphiles is used as a tunable and quantitative parameter to control the anchoring transition. Depending on a complicated interplay between the interfacial interactions and the packing effects, we have observed a novel anchoring transition sequence of planar-tilted-homeotropic-tilted-planar when continuously decreasing the value of a MR .

Mesoscopic simulations of temperature-dependent anchoring and wetting behavior at aqueous–liquid crystal interfaces in the presence of a rod–coil amphiphilic monolayer

“…The principle qualitatively drawn from these experiments is that, with increasing the amphiphile coverage, the amphiphile monolayer is packed more densely and orderly with the amphiphile tails stretching further, which allows the deeper penetration of LC molecules into the amphiphile monolayer and in turn induces homeotropic anchoring. Our simulation study 13 has further revealed that the tails of amphiphiles may act as an interfacial orientation eld in dictating the orientational ordering of LCs, which is in the same spirit as the conclusions of Bahr. 14,15 Moreover, recent work also suggests that the ordering of LCs also has a signicant effect on the interfacial assembly of amphiphiles.…”

“…For more details about the choice of bead number for each individual molecule we also refer to ref. 13. Note that three types of beads (M, R and C) are considered in our simulation systems.…”

“…With this favorable interaction, it has been demonstrated that the ordered rod blocks tend to orient along the interface normal and in turn act as an interfacial orientation eld to align mesogens with a homeotropic anchoring at a given temperature T ¼ 0.50. 13 Both the mesogens and amphiphiles are modelled as beadspring chains, wherein the spring potential is dened as U bond ¼ 0.5k bond (r À r eq ) 2 with k bond ¼ 100 and r eq ¼ 2/3, Two additional potentials are applied for the mesogen and the rod block of the amphiphile to keep their rod-like structures: 23 an extra bond potential between the rst and last bead, U bond ex ¼ 0.5k bond [r À (n À 1)r eq ] 2 with k ex ¼ 500 and a bond bending potential,…”

“…As a computationally efficient method for probing the large-scale cooperative behavior in particularly complex systems, dissipative particle dynamics (DPD) simulation technique in combination with generic coarse-grained models are employed in this paper to investigate the basic mechanism of how the temperature affects the anchoring behavior of LCs at the aqueous-LC interfaces laden with rod-coil amphiphiles. Actually, our previous work 13 has already demonstrated the rationality and efficiency of this model system in studying the anchoring behavior, i.e., a rich anchoring transition sequence is successfully reproduced by tuning an individual interaction parameter for the repulsion between the mesogens and the rod blocks of amphiphiles, which is essentially playing a role of changing the chemical constitution of amphiphilic molecules or mesogens. As an succeeding application of our coarsegrained models for this interfacial system, 13 by xing the above repulsion parameter and the amphiphile interfacial coverage, here we mainly explore the temperature dependent anchoring behavior.…”

Manipulating molecular order in nematic liquid crystal capillary bridgesviasurfactant adsorption: guiding principles from dissipative particle dynamics simulations

“…LCs' aggregates such as spherical droplets, [13][14][15][16][17][18][19][20] flat surfaces 9,12,[21][22][23][24][25] or cylindrical formations (capillaries and bridges) [26][27][28][29][30] have been investigated. Kim et al quantified the optical, structural and topological features of tetrapodes assembled in flat layers, round capillaries and spherical droplets; the results for round capillaries revealed different textures depending on the inner diameter and system temperature.…”