Stacked polydopamine nanomembranes for light-controlled soft actuators

• Multilayered polydopamine nanomembranes fabricated via electropolymerization. • Stacking protocol overcomes PDA film thickness limits in membrane growth. • Thickness-independent mechanical, optical, and thermal performance shown. • Photoactuation enabled by reversible water sorption and light absorption. • Robust, scalable PDA membranes for soft robotics and responsive coatings. Soft actuators capable of reversible, remotely triggered motion are central to sensing technologies and bioinspired robotics. Here, we introduce a transfer-and-stacking strategy for electropolymerized polydopamine (PDA) that overcomes the thickness limit of single-step electropolymerization and yields robust, freestanding membranes with user-defined thickness. X-ray reflectivity shows that thickness is not strictly additive, consistent with interlayer compression and strong coupling during assembly. Despite this, stacked membranes behave as an effectively homogeneous material: within uncertainty, key intensive properties – Young modulus, the complex refractive index at 660 nm, and the in-plane/cross-plane thermal conductivities – remain invariant with thickness. This decouples material properties from geometry, making thickness a reliable design knob for scaling flexural rigidity, thermal resistance, absorbed power, and actuation amplitude. Using complementary characterization, we provide design inputs (elastic modulus, complex refractive index, thermal conductivity, and a water transport coefficient) and quantify millisecond-scale photoactuation dynamics governed by reversible water sorption. These results establish stacked electropolymerized PDA nanomembranes as a thickness-engineerable, photothermally addressable platform for light-controlled soft actuation and related functional thin-film systems.