Abstract
Suspensions of anisometric particles are known to self-assemble into various liquid crystal (LC) phases, namely, the nematic, smectic (A or B or both), and in some cases, columnar phases, due to the effects of excluded volume. For some applications, LC phases with higher degrees of order are desired, but due to the fact that these phases generally exist at larger volume fractions, they can be difficult to handle experimentally. Here, we explore the effect of a weak attractive interaction localized at the tips of rod-like particles on the phase behavior of these suspensions. We perform large-scale molecular dynamics simulations of rigid rod-like particles with both monodispersed and polydispersed lengths and a variety of aspect ratios. The rods are composed of rigidly connected beads, and the inter-rod bead interactions are modeled with a combination of Weeks–Chandler–Anderson and Lennard-Jones potentials. By increasing rod-tip attraction, we observe a favoring of the higher order smectic phase over the lower order nematic phase at lower volume fractions. With sufficiently strong rod-tip attraction, the nematic phase is removed from the phase diagram. Furthermore, we show how polydispersity influences this competition between LC phases.
Highlights
The liquid crystallinity exhibited by some anisometric particles, such as cellulose nanocrystals (CNCs), filamentous viruses, metallic nanorods, and other colloidal particles, is an on-going area of interest
We explore the nature of colloidal rod-like particles with localized attractive interactions at the rod tips, using deterministic Langevin Dynamics (LD) simulations
To aid in the understanding of the phase behavior of the rod particles and to determine the critical φ where phase transitions begin and end, we calculated the equation of state throughout time
Summary
The liquid crystallinity exhibited by some anisometric particles, such as cellulose nanocrystals (CNCs), filamentous viruses, metallic nanorods, and other colloidal particles, is an on-going area of interest. For lyotropic liquid crystals (LCs), the positional, orientational, and/or rotational orders of the particle suspensions depend on several factors including the aspect ratio (and overall shape), the volume fraction, and particle–particle interactions. Observations of the selfassembly of colloidal particles due to this entropy-driven behavior have been reported many times by experimentalists throughout the years.. The rodlike particles exhibiting purely hard-core repulsion can transition between the two phases predominantly due to the changes in density (entropy driven). Similar to many experimental studies, Onsager’s model estimates that the phase transition occurs at a volume fraction that decreases with the increase in the particle aspect ratio. Extensions and refinements to Onsager’s theory have been made to understand the behavior of particle systems with other properties beyond simple monodispersity and hard-core repulsion.
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