Nonreciprocal Mixtures in Suspension: The Role of Hydrodynamic Interactions
Physical Review Letters American Physical Society (APS) 135:10 (2025) 108301
Abstract:
The collective chasing dynamics of nonreciprocally coupled densities leads to stable traveling waves which can be mapped to a model for emergent flocking. In this Letter, we couple the nonreciprocal Cahn-Hilliard model to a fluid to minimally describe scalar active mixtures in a suspension, with the aim to explore the stability of the waves, i.e., the emergent flock in the presence of self-generated fluid flows. We show that the emergent polarity is linearly unstable to perturbations for a specific sign of the active stress recalling instabilities of orientational order in a fluid. Using numerical simulations, we find, however, that nonreciprocity stabilizes the waves against the linear instability in a large region of the phase space.Continuous-time multifarious systems. I. Equilibrium multifarious self-assembly.
The Journal of chemical physics 163:12 (2025) 124904
Abstract:
Multifarious assembly models consider multiple structures assembled from a shared set of components, reflecting the efficient usage of components in biological self-assembly. These models are subject to a high-dimensional parameter space, with only a finite region of parameter space giving reliable self-assembly. Here, we use a continuous-time Gillespie simulation method to study multifarious self-assembly and find that the region of parameter space in which reliable self-assembly can be achieved is smaller than what was obtained previously using a discrete-time Monte Carlo simulation method. We explain this discrepancy through a detailed analysis of the stability of assembled structures against chimera formation. We find that our continuous-time simulations of multifarious self-assembly can expose this instability in large systems even at moderate simulation times. In contrast, discrete-time simulations are slow to show this instability, particularly for large system sizes. For the remaining state space, we find good agreement between the predictions of continuous- and discrete-time simulations. We present physical arguments that can help us predict the state boundaries in the parameter space and gain a deeper understanding of multifarious self-assembly.Continuous-time multifarious systems. II. Non-reciprocal multifarious self-organization.
The Journal of chemical physics 163:12 (2025) 124905
Abstract:
In the context of self-assembly, where complex structures can be assembled from smaller units, it is desirable to devise strategies toward disassembly and reassembly processes that reuse the constituent parts. A non-reciprocal multifarious self-organization strategy has been recently introduced and shown to have the capacity to exhibit this complex property. In this work, we study the model using continuous-time Gillespie simulations and compare the results against discrete-time Monte Carlo simulations investigated previously. Furthermore, using the continuous-time simulations, we explore important features in our system, namely, the nucleation time and interface growth velocity, which comprise the timescale of shape-shifting. We develop analytical calculations for the associated timescales and compare the results to those measured in simulations, allowing us to pin down the key mechanisms behind the observed timescales at different parameter values.Effervescence in a binary mixture with nonlinear non-reciprocal interactions
Nature Communications Nature Research 16:1 (2025) 7310
Abstract:
Non-reciprocal interactions between scalar fields that represent the concentrations of two active species are known to break the parity and time-reversal (PT) symmetries of the equilibrium state, as manifested in the emergence of travelling waves. We explore the notion of nonlinear non-reciprocity and consider a model in which the non-reciprocal interactions can depend on the local values of the scalar fields in such a way that the non-reciprocity can change sign. For generic cases where such couplings exist, we observe the emergence of spatiotemporal chaos in the steady-state. We associate this chaotic behaviour with a local restoration of PT symmetry in fluctuating spatial domains, which leads to the coexistence of oscillating densities and phase-separated droplets that are spontaneously created and annihilated. We uncover that this phenomenon, which we denote as effervescence, can exist as a dynamical steady-state in large parts of the parameter space in two different incarnations, as characterised by the presence or absence of an accompanying travelling wave.A roadmap for next-generation nanomotors
Nature Nanotechnology (2025) 1-11