Competition between shape anisotropy and deformation in the ordering and close packing properties of quasi-one-dimensional hard superellipse fluids.

We investigate the orientational ordering and close-packing behavior of a quasi-one-dimensional (q1D) system of hard superellipses, where the centers of the particles are confined to a line, but they can rotate freely within a two-dimensional plane. The particle shape is tuned between an ellipse and a rectangle by varying the deformation parameter (n). The elongation of the particle is changed using the aspect ratio (k). The pressure ratio between freely rotating and parallel hard superellipses, which displays a single peak, serves as an effective marker for the continuous structural change from quasi-isotropic to nematic ordering. Our findings reveal a competition between the parameters k and n, with k promoting nematic alignment and n favoring tetratic ordering. Notably, in the close-packing regime, the packing properties become independent of k, as the relevant exponents depend solely on n. Furthermore, certain combinations of these exponents exhibit universality, remaining invariant with respect to particle shape.