Emergent tetratic order in crowded systems of rotationally asymmetric hard kite particles

Abstract

Considering multi-body systems of monodisperse hard Brownian particles, it remains challenging to predict the forms of order that can emerge in their dense assembled structures. Surprisingly, here, using Monte Carlo simulations, we show that tetratic-ordered phases emerge in a dense two-dimensional system of hard kites that are rotationally asymmetric and have opposite 72° and α ≈ 90° internal angles. We observe a new tetragonal rectangular crystal (TRX) phase possessing (quasi-)long-range fourfold molecular-orientational order. We propose a method based on local polymorphic configurations of neighboring particle pairs (LPC-NPPs) to understand this emergent tetratic order and show that LPC-NPPs can be useful for predicting orientational order in such systems. To examine the dependence of the tetratic order on α, we apply LPC-NPP analysis to other hard kites for 54° ≤ α ≤ 144°. Our work provides insight into the creation of novel ordered materials by rationally designing particle shape based on anticipated LPC-NPPs.

Orientational ordering in a fluid of hard kites: A density-functional-theory study

“…The new proposal (13) was numerically implemented to calculate two different phase diagrams with the aim to comparing both theories. Also we wanted to confront the new theory with recent MC simulations for hard kites 37 .…”

“…We concentrate only on the de- Open circles and triangles show transitions from I to liquid-crystalline uniform phases and from uniform to non-uniform phases, respectively, as obtained from the MC simulations of Ref. 37 . Different regions, from R1 to R4, correspond to the division of the interval [54 • , 144 • ] introduced by the authors of Ref.…”

“…Different regions, from R1 to R4, correspond to the division of the interval [54 • , 144 • ] introduced by the authors of Ref. 37 ; from left to right, these regions indicate the stability intervals for H mo phase (see the text for its definition), an asymmetric tetratic phase T2, and the usual symmetric T1 phase. In region R5 (not calculated in Ref.…”

“…In recent experiments the phase diagram of kites with one of its unequal interior angles, α 1 , fixed to 72 • with the other, α 2 being variable, was elucidated 37 . Interestingly, kites with a shape departing from the square geometry also form a T phase for some values of α 2 37 . Fig.…”

“…This study allowed our new DFT theory to be contrasted with the recent Monte Carlo (MC) simulations of Ref. 37 . We showed that, by varying α 1 in the interval [54 • , 180 • ], both phases, T and TR, are stable, with the former having the largest stability region.…”