Orientation control and nonlinear trajectory tracking of colloidal particles using microfluidics

Abstract

Suspensions of anisotropic Brownian particles are commonly encountered in a wide array of applications such as drug delivery and manufacturing of fiber-reinforced composites. Technological applications and fundamental studies of small anisotropic particles critically require precise control of particle orientation over defined trajectories and paths. In this work, we demonstrate robust control over the two-dimensional (2D) center-of-mass position and orientation of anisotropic Brownian particles using only fluid flow. We implement a path-following model predictive control scheme to manipulate colloidal particles over defined trajectories in position space, where the speed of movement along the path is a degree of freedom in the controller design. We further explore how the external flow field affects the orientation dynamics of anisotropic particles in steady and transient extensional flow using a combination of experiments and analytical modeling. Overall, this technique offers new avenues for fundamental studies of anisotropic colloidal particles using only fluid flow, without the need for external electric or optical fields. arXiv:1907.08567v1 [cond-mat.soft]

Conformational dynamics and phase behavior of lipid vesicles in a precisely controlled extensional flow

“…The MPC feedback controller determines the necessary flow rates required to achieve trapping at a specific point while maintaining a nearly constant strain rate in extensional flow and is achieved using computer-controlled pressure regulators. In this way, the Stokes trap can be used to confine vesicles under zero-flow conditions (with no external or net flow) or under non-zero net flow conditions [47,48], and the latter method was used to study non-equilibrium flow dynamics in the work.…”

“…In this paper, we present a detailed flow-phase diagram of non-equilibrium vesicle shape transitions in extensional flow using a Stokes trap [47][48][49], which enables precise control over the center-of-mass position of single or multiple particles in flow. In this way, we directly observe vesicle shape transitions over long observation times across a wide range of parameters including reduced volume ν and capillary number Ca.…”

Flow Topology During Multiplexed Particle Manipulation Using a Stokes Trap

“…The flow model and the model predictive control (MPC) scheme for multiplexed particle manipulation have been previously described [16,17]. The following section summarizes the salient features of these models for understanding flow topology during trapping.…”

“…, where x i,0 indicates the i th particle's initial position and x i,F indicates the target final position. A model predictive control (MPC) scheme is used to achieve precise manipulation of multiple particles [16,17,30]. Using MPC, the flow rates required for particle manipulation are obtained by minimizing an objective function that determines an optimal balance between: (1) trajectories that move particles along the shortest path between the initial and final positions and (2) trajectories that require minimal flow rates but may require complicated paths.…”

“…Particle trapping has been used for diverse applications including parallel manipulation of single particles [1], determination of DNA physical properties [2], and direct observation of viral DNA packaging by a molecular motor [3]. Trapping methods rely on a variety of physical mechanisms and fundamental forces for manipulating particles, including optical fields [4,5], magnetic fields [6,7], electrical fields [8,9], acoustic forces [10,11], and fluidic forces [12][13][14][15][16][17].…”