Magnetic Nanorods Confined in a Lamellar Lyotropic Phase

TL;DR

This study investigates how magnetic nanorods interact with and influence the structure of a lamellar phase, revealing shape-dependent aggregation and controllable orientation transitions under magnetic fields.

Contribution

It demonstrates the effect of nanorod shape on their interactions within a lamellar phase and shows how magnetic fields can induce reorientation of nanorods and phase texture changes.

Findings

Nanorods align with magnetic field, changing lamellar texture.

Attractive interactions lead to aggregation in concentrated phases.

Shape influences particle behavior, unlike spherical counterparts.

Abstract

The dilute lamellar phase of the nonionic surfactant C$_{12}$EO$_5$ was doped with goethite (iron oxide) nanorods up to a fraction of 5 vol. %. The interaction between the inclusions and the host phase was studied by polarized optical microscopy (with or without an applied magnetic field) and by small-angle X-ray scattering. We find that, when the orientation of the nanorods is modified using the magnetic field, the texture of the lamellar phase changes accordingly; one can thus induce a homeotropic-planar reorientation transition. On the other hand, the lamellar phase induces an attractive interaction between the nanorods. In more concentrated lamellar phases (under stronger confinement) the particles form aggregates. This behavior is not encountered for a similar system doped with spherical particles, emphasizing the role of particle shape in the interaction between doping particles and the host phase.