Boundary- and Screening-Induced Bubbly Phases in Autophoretic Active Matter

Abstract: Spatial confinement and chemical screening fundamentally reshape the non-equilibrium phase behavior of autophoretic active particles. Here, we present a systematic study mapping the collective dynamics of self-propelled particles governed by chemo-attractive translational forces ($μ_t &lt; 0$) and chemo-repulsive rotational torques ($μ_r &gt; 0$) across varying screening parameters $κ$, torque magnitudes $μ_r$, and boundary condition coefficients $Λ<sup>c$. Beyond standard chemotactic macro-phase separation and dynamic clustering, we report the emergence of novel boundary- and screening-induced bubbly phases, classified into boiling and bursting bubbles. Using a metric triad of steady-state cluster fraction $\langle S \rangle$, temporal fluctuation magnitude $σ_S$, and coordination number $\langle Q \rangle$, we draw phase diagrams to demarcate phases for no-flux boundaries ($Λ^c = 1$) and chemically permeable interfaces ($Λ^c = 0$) . Increasing chemical screening ($κ$) systematically suppresses long-range attraction, driving sequential phase transitions from macro-scale collapse toward bubbly states, dynamic micro-clusters, and homogeneous gas phases, while simultaneously inducing aggregate shape anisotropy. These findings provide predictive design rules for controlling active assembly and transport in microfluidic environments.