The interfacial origin of self-diffusiophoretic propulsion: Bridging theory and experiment in colloidal motors

Colloidal motors offer a versatile platform for exploring non-equilibrium transport and autonomous motion at small scales. Among various propulsion mechanisms, self-diffusiophoresis stands out for its ability to achieve sustained propulsion via self-generated concentration gradients without external fields. However, a persistent gap remains between theoretical predictions and experimental observations, particularly regarding performance degradation under high ionic strength and at reduced length scales. In this review, we demonstrate that these challenges share a common physical origin: the physicochemical processes occurring within the interfacial layer adjacent to the motor surface. By adopting an interfacial perspective, we show that self-diffusiophoretic propulsion is governed not by bulk transport, but by the transduction of solute gradients into hydrodynamic slip via local solute-interface interactions. We analyze how these interactions dictate propulsion direction, mobility, and stability, and identify where oversimplified models fail. Furthermore, we examine how ionic screening and size effects disrupt interfacial coupling and discuss how rational surface engineering can restore propulsion in complex environments. By centralizing the interfacial layer, this review provides a unified framework connecting chemical kinetics, hydrodynamics, and environmental response, offering critical design principles for next-generation adaptive colloidal motors and micro-/nanorobotics.