Multiscale computational modeling of photoacoustic generation from micrometer-size polymeric bead suspensions in liquid media

Photoacoustic sensing has emerged as a promising technique for detecting polymeric particles suspended in liquids through the conversion of absorbed optical energy into acoustic signals. Here, we present a multiscale computational study of the photoacoustic response of polystyrene (PS) beads suspended in water under pulsed optical excitation. The framework combines particle-resolved simulations of individual beads with point-particle descriptions of randomly distributed multi-particle suspensions. The results reveal a rapid acoustic transient followed by a residual pressure field persisting in the liquid. As particle concentration increases, the residual pressure level progressively rises and exhibits an approximately square-root dependence on the number of photoacoustic sources. The point-particle study further shows that the pressure response is closely related to the effective number of irradiated particles rather than to the nominal suspension concentration, while the induced particle motion remains negligible. Overall, the present results provide a physically grounded basis for interpreting photoacoustic signals from PS bead suspensions in water and support future developments of photoacoustic sensing strategies for applications ranging from microplastic detection in aqueous media to polymer-bead-based microfluidic and bioanalytical platforms.