Confinement and shear effects on the rotational diffusion of a minimal virus-inspired colloidal particle

Abstract

The rotational diffusion of a rigid spherical body decorated with dimers in an explicit fluid environment is reported. This model acts as a simplified representation of an enveloped virus bearing peplomers immersed in a coarse-grained fluid. Using dissipative particle dynamics, we explicitly study the hydrodynamic effects on the rotational diffusion of this virus-inspired particle subjected to oscillatory shear flow and confined between two solid-like surfaces. Since the rotational response depends on the type of imposed flow, we first characterize the oscillatory shear, identifying distinct flow regimes in terms of the so-called P\'eclet number, $Pe$. Our findings indicate that, under confinement, the rotational diffusivity is strongly modulated by the oscillatory flow amplitude and only weakly affected by the number of peplomers, since their effect is mainly determined by their dimeric structure and associated effective size. For high $Pe$, the rotational diffusion coefficient, $D_{r}$, tends to decrease as the number of peplomers ($N_{s}$) increases, whereas at low $Pe$, rotational diffusion becomes weakly dependent on the number of peplomers. However, at intermediate values of $Pe$, the interplay between oscillatory forcing and thermal fluctuations prevents the emergence of a clear trend between $D_{r}$ and $N_{s}$. Our results provide a clear picture of how, in confined environments, the interplay between fluid flow and thermal fluctuations affects the rotational diffusion of spiked particles, thereby helping to explain how fluid conditions can modify the alignment of peplomers with their potential targets.