Intrinsic and Water-Triggered Hydrophilicity in Tween 20-PDMS Composites for Dynamic and Long-Term Wettability...

Achieving stable and tunable hydrophilicity in soft elastomers such as polydimethylsiloxane (PDMS) remains a long-standing challenge due to hydrophobic recovery and surface reorientation. Here, we report a one-step bulk integration of the non-ionic surfactant Tween 20 into the PDMS matrix to create intrinsically and water-triggered hydrophilic composites with long-term stability. First, density functional theory (DFT) analysis demonstrates that the oligo(ethylene glycol) (OEG) chains of Tween 20 could physically coordinate with the siloxane backbone, establishing intrinsic surface polarity. Experiments confirm the intrinsic hydrophilicity and further found a time-dependent wetting transition, which may arise from unbound or semi-bound Tween 20 molecules at the interface that reorient upon water contact, exposing additional hydrophilic groups and forming hydrogen-bond networks. Meantime, the Tween 20-PDMS composites exhibit concentration-dependent wetting dynamics, maintaining hydrophilicity for over 100 days, preserving surface functionality under mechanical stretching. Finally, versatile applications were developed based on Tween 20-PDMS, including (i) self-driven unidirectional liquid transport; (ii) oil-in-water (O/W) droplet generation; (iii) and spatially selective cell culture. The present work demonstrates a simple, quick and stable way to make hydrophilic PDMS by bulk modification with Tween 20, offering a universal strategy for adaptive, energy-free, and biocompatible microfluidic systems.