Open AccessShape Matters in Magnetic-Field-Assisted Assembly of Prolate Colloids
Author(s) -
Antara Pal,
Carlo Andrea De Filippo,
Thiago Heiji Ito,
Md. Arif Kamal,
Andrei V. Petukhov,
Cristiano De Michele,
Peter Schurtenberger
Publication year - 2022
Publication title -
acs nano
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.554
H-Index - 382
eISSN - 1936-086X
pISSN - 1936-0851
DOI - 10.1021/acsnano.1c09208
Subject(s) - materials science , ellipsoid , prolate spheroid , anisotropy , colloid , liquid crystal , particle (ecology) , phase (matter) , soft matter , chemical physics , self assembly , field (mathematics) , condensed matter physics , aspect ratio (aeronautics) , nanotechnology , optics , physics , classical mechanics , chemistry , composite material , oceanography , optoelectronics , quantum mechanics , astronomy , mathematics , pure mathematics , geology
An anisotropic colloidal shape in combination with an externally tunable interaction potential results in a plethora of self-assembled structures with potential applications toward the fabrication of smart materials. Here we present our investigation on the influence of an external magnetic field on the self-assembly of hematite-silica core-shell prolate colloids for two aspect ratios ρ = 2.9 and 3.69. Our study shows a rather counterintuitive but interesting phenomenon, where prolate colloids self-assemble into oblate liquid crystalline (LC) phases. With increasing concentration, particles with smaller ρ reveal a sequence of LC phases involving para-nematic, nematic, smectic, and oriented glass phases. The occurrence of a smectic phase for colloidal ellipsoids has been neither predicted nor reported before. Quantitative shape analysis of the particles together with extensive computer simulations indicate that in addition to ρ, a subtle deviation from the ideal ellipsoidal shape dictates the formation of this unusual sequence of field-induced structures. Particles with ρ = 2.9 exhibit a hybrid shape containing features from both spherocylinders and ellipsoids, which make their self-assembly behavior richer than that observed for either of the "pure" shapes. The shape of the particles with higher ρ matches closely with the ideal ellipsoids, as a result their phase behavior follows the one expected for a "pure" ellipsoidal shape. Using anisotropic building blocks and external fields, our study demonstrates the ramifications of the subtle changes in the particle shape on the field-directed self-assembled structures with externally tunable properties.