Letter abstract
Nature Physics 1, 103 - 106 (2005)
doi:10.1038/nphys124
Subject Categories: Polymer physics | Materials physics | Condensed-matter physics
Anomalous field-induced particle orientation in dilute mixtures of charged rod-like and spherical colloids
F. Mantegazza1, M. Caggioni2, M. L. Jiménez2 and T. Bellini2
Charged colloids in aqueous suspension often reconfigure counter-intuitively in the presence of an external electric field1, 2, 3, 4, 5, 6, 7. Despite decades of substantial theoretical effort, a clear understanding of such electrokinetic phenomena is only available for the electric polarization and migration of diluted spheres in low fields8. The interpretation of the electric response of charged rod-like particles is far less advanced. Here we report that diluted rod-like particles suspended in a sea of smaller spherical particles having similar charge align perpendicular to the external electric field. This 'anomalous' orientation, which contradicts the notion that charged rods in dilute suspensions always align parallel to external electric fields9, seems to be universal in dilute mixtures of charged rod-like and spherical colloids. The dependence of the perpendicular orientation on frequency and particle charge, size and concentration indicates the presence of field-induced asymmetric crowding of spherical particles around each rod, which gives rise to asymmetric electro-osmotic flows that induce a negative torque.
- DIMESAB, Università di Milano–Bicocca and CNR-INFM, via Cadore 48, 20052 Monza (MI), Italy
- Dipartimento di Chimica, Biochimica e Biotecnologie per la Medicina and CNR-INFM, Università di Milano, via Fratelli Cervi 93, 20090 Segrate (MI), Italy
Correspondence to: F. Mantegazza1 e-mail: francesco.mantegazza@unimib.it
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