Shape Matters in Magnetic-Field-Assisted Assembly of Prolate Colloids

Antara Pal, Carlo Andrea De Filippo, Thiago Ito, Md Arif Kamal, Andrei V. Petukhov, Cristiano De Michele, Peter Schurtenberger

Research output: Contribution to journalArticleAcademicpeer-review


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.

Original languageEnglish
Pages (from-to)2558–2568
Number of pages11
JournalACS Nano
Issue number2
Publication statusPublished - 22 Feb 2022


  • Monte Carlo (MC) simulation
  • directed self-assembly
  • liquid crystals
  • magnetic anisotropic colloids
  • particle shape-analysis
  • small-angle X-ray scattering (SAXS)


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