Colloidal rods in optical potential energy landscapes

Abstract

We study the static and dynamic behaviour of colloidal rods in an optical potential energy landscape. We explore the stable states of a colloidal rod in a single optical trap close to a flat wall. Here, two metastable states are observed, horizontal and vertical, both of which experience a parabolic potential energy landscape. Next we place a colloidal rod into a onedimensional sinusoidal optical potential energy landscape and introduce a constant driving velocity. When driven below the critical velocity, the particle is confined to a single potential energy minimum of the optical landscape and the equilibrium position of a particle is investigated. The equilibrium position of a rod is found to vary substantially from that of a sphere, due to the drag coefficient of a rod being highly dependent on its proximity to an optical trap. The driving velocity is increased to enable the particle to traverse the periodic landscape and above the critical velocity, the average particle velocity increases as the square root of the driving velocity. When introducing oscillations to the driving velocity we observe dynamic mode locking and characterise the nature of synchronised motion of the rodlike particles.

Effect of sample height and particle elongation in the sedimentation of colloidal rods

“…These include spherocylinders with dipolar, [40][41][42][43][44] Coulombic 45,46 and patchy [47][48][49] interactions, active spherocylinders, [50][51][52][53] as well as spherocylinders coated with soft layers. 54,55 Moreover, the hard spherocylinder model can be a reasonable approximation to the shape and the interaction of real colloidal particles such as natural clay rods, 56 fd virus, 57 rod-like boehmite particles, 58 polystyrene ellipsoids, 59 silica rods, [60][61][62] as well as PMMA rods 63,64 and ellipsoids. 65,66 Sedimentation experiments, in which a colloidal suspension is equilibrated under the influence of a gravitational field, are one of the basic tools to investigate phase behaviour in colloidal science.…”

“…These include spherocylinders with dipolar, 40–44 Coulombic 45,46 and patchy 47–49 interactions, active spherocylinders, 50–53 as well as spherocylinders coated with soft layers. 54,55 Moreover, the hard spherocylinder model can be a reasonable approximation to the shape and the interaction of real colloidal particles such as natural clay rods, 56 fd virus, 57 rod-like boehmite particles, 58 polystyrene ellipsoids, 59 silica rods, 60–62 as well as PMMA rods 63,64 and ellipsoids. 65,66…”

Diffusion of Anisotropic Particles in Random Energy Landscapes—An Experimental Study

“…In addition to optical tweezers, extended light fields can be used to expose particles to external potential energy landscapes [30]. Different light fields can be created to produce random, periodic or other potential energy landscapes [31][32][33][34][35][36]. Typically, energy modulations of the order of the thermal energy, k B T, are applied.…”

“…Recently light fields have also been imposed on anisotropic particles [36,42,43]. Dilute suspensions of ellipsoids or multimers consisting of spherical particles, particularly dimers and trimers, have been subjected to a periodic light field.…”

Transport of a colloidal particle driven across a temporally oscillating optical potential energy landscape

“…Exact particle motion has been shown to heavily rely on the form of the landscape and can give rise to freely diffusive as well as trapped particles [16,21]. Further to this, the study of colloidal particle transport across periodic potential energy surfaces has led to many interesting observations such as subdiffusion [22,23], superdiffusion [23][24][25][26], ballistic motion [26,27] and synchronisation [28][29][30]. Structured surfaces have also been created to achieve precise particle sorting [31,32] or directed transport [33,34].…”