Acousto-optically generated potential energy landscapes: Potential mapping using colloids under flow

Abstract

Optical potential energy landscapes created using acousto-optical deflectors are characterized via solvent-driven colloidal particles. The full potential energy of both single optical traps and complex landscapes composed of multiple overlapping traps are determined using a simple force balance argument. The potential of a single trap is shown to be well described by a Gaussian trap with stiffness found to be consistent with those obtained by a thermal equilibrium method. We also obtain directly the depth of the well, which (as with stiffness) varies with laser power. Finally, various complex systems ranging from double-well potentials to random landscapes are generated from individually controlled optical traps. Predictions of these landscapes as a sum of single Gaussian wells are shown to be a good description of experimental results, offering the potential for fully controlled design of optical landscapes, constructed from single optical traps.

Colloidal dynamics over a tilted periodic potential: Nonequilibrium steady-state distributions

“…Here an external potential field is used to mimic the effect of an energy landscape, which is usually imposed by the surrounding molecules to a test particle. Similar attempts have also been made in the study of colloidal transport and diffusion in a 1D optical trap (optical tweezers) with either a periodic or random variation of the laser light intensity [21][22][23][24]. Understanding the effect of the external force on thermally activated kinetics is a concern of a common class of transport problem, such as particle separation by electrophoresis [25,26], electromigration of atoms on the surface of metals [27] and semiconductors [28], motion of a three-phase contact line under the influence of an unbalanced capillary force [29], control of crystal growth [30], and design of nanoscale machineries [31,32].…”

“…While the laser-generated potential is a useful system for the study of colloidal dynamics over different potentials [21][22][23][24], the colloidal platform has several advantages in the experimental implementation. (i) It is a pure potential field and does not have any nonconservative component, as the laser beam does [50,51].…”

Zigzag transitions and nonequilibrium pattern formation in colloidal chains

“…To interpret this difference, consider the nontrivial solution of equation U 0 (h * ) = 0 with U 0 given by Eq. (21). Close to the threshold, we obtain…”

“…21 Here, δr(l) = r(l) − R(l) and the additive constant is chosen such that the minimum corresponds to V T = 0. The parameters V 0 and k 0 specify, respectively, the depth of the well and the stiffness of the potential.…”

“…It is important to note that k 0 and V 0 can be changed in the experiment but that their ratio always remains virtually constant and therefore characterizes the optical trap. 21 Based on these basic ingredients, the repulsive, Eq. (1), and optical trap, Eq.…”