Reactive walls enhance and prolong diffusiophoretic transport into dead-end channels

Nonequilibrium colloidal transport mechanisms such as diffusiophoresis and Marangoni transport enable rapid and targeted delivery of colloids by exploiting in-situ or externally imposed chemical gradients, particularly in systems like dead-end pores where pressure-driven flow is ineffective. However, the duration of such transport is limited by how long the driving gradient persists. Here, we present a general strategy to prolong gradient-driven colloidal transport in dead-end channels using channel walls that preferentially adsorb the driving solute. Solute partitioning reduces the effective diffusivity of the cross-sectionally averaged solute field, slowing the evolution of the solute field without reducing particle diffusiophoresis. We demonstrate this concept in a controlled microfluidic system, where polystyrene particles migrate diffusiophoretically down sodium dodecyl sulfate gradients whose evolution can be controlled by coating channel walls with polyethylene diacrylate hydrogel layers. Absorbing walls are shown to enhance particle delivery into dead-end pores, with particle velocity fields and increases in particle deliveries that agree qualitatively and quantitatively with theoretical predictions. This approach offers a general framework to control and direct microscale transport in complex geometries, with potential applications in enhanced oil recovery, drug delivery, and consumer product design.