Non-invasive pH-responsive colloidal gate for tunable porosity and permeability in adaptive porous media

We introduce a multilayered poly(acrylic acid)-grafted silica colloid paste that functions as an adaptive, pH-responsive non-invasive colloidal gate, allowing precise modulation of liquid flow. Through iterative carbodiimide-mediated grafting, up to five stratified PAA layers are precisely engineered onto micron-scale silica colloids, amplifying polymer density and interfacial interactions. Our system uniquely expands its interconnected particulate network under basic conditions, enabling tunable porosity (up to 0.82) and permeability (up to 1 . 5 × 1 0 − 12 m 2 ) for programmable fluid transport. The paste exhibits a permeability range, from complete occlusion at low pH to a flow rate of 0.32 mL/min at high pH. We show that the porosity of the colloid paste, governed by PAA self-assembly, plays a central role in this behavior: when the particulate network collapses under acidic conditions, the system becomes nearly non-porous, while under alkaline conditions, swelling increases void volume and interparticle connectivity. Quantitative analysis using Darcy’s law and the Kozeny–Carman equation confirms that permeability scales directly with porosity and surface chemistry, underscoring the structural control offered by multilayer design. These adaptive characteristics establish the colloidal paste as an effective non-invasive “colloidal gate” for tunable flow control. The system achieved complete removal (100%) of aniline blue dye at pH 3 with 3–5 layer pastes, while maintaining high water permeability at pH 7–9. This pH-triggered modulation of both porosity/permeability and contaminant retention offers a versatile platform for adaptive size-selective filtration and dynamic water purification systems.