Abstract
.The design of artificial microswimmers has generated significant research interest in recent years, for promise in applications such as nanomotors and targeted drug-delivery. However, many current designs suffer from a common problem, namely the swimmers remain in the fluid indefinitely, posing risks of clogging and damage. Inspired by recently proposed experimental designs, we investigate mathematically the dynamics of degradable active particles. We develop and compare two distinct chemical models for the decay of a swimmer, taking into account the material composition and nature of the chemical or enzymatic reaction at its surface. These include a model for dissolution without a reaction, as well as models for a reacting swimmer studied in the limit of large and small Damköhler number. A new dimensionless parameter emerges that allows the classification of colloids into ballistic and diffusive type. Using this parameter, we perform an asymptotic analysis to derive expressions for colloid lifetimes and their total mean squared displacement from release and validate these by numerical Monte Carlo simulations of the associated Langevin dynamics. Supported by general scaling relationships, our theoretical results provide new insight into the experimental applicability of a wide range of designs for degradable active colloids.Graphical abstract
Highlights
In recent years, scientists from a wide variety of different fields have given considerable attention to the subject of synthetic microswimmers
The change in the dynamics of colloidal particles arises through the time dependence of the translational diffusion coefficient, which is given by the Stokes-Einstein relation [36]
We compare them with Monte Carlo simulations of the associated Langevin dynamics to assert its validity, and subsequently with our analytical predictions for the asymptotic behaviour
Summary
Scientists from a wide variety of different fields have given considerable attention to the subject of synthetic microswimmers. We begin by presenting two theoretical models for the dissolution process, one suitable for designs in which the dissolution process is not driven by a reaction with a fuel in the solvent (such as dissolution by hydrogen bonding), and one for swimmers whose matrix is decomposed by means of a reaction (chemical or enzymatic) For further analysis the latter case is considered in the two limits of slow and fast reaction, the former corresponding to a fixed material flux boundary condition. In all these models we find expressions for the time dependence of the swimmer size, as well as their total lifetime in terms of the essential physical parameters.
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