Fabrication of robust wettability gradients on soft surfaces through physicochemical modulations

Abstract

The creation of robust surface gradients on soft materials is an emerging area of research in materials chemistry. Polydimethylsiloxane (PDMS), an elastomeric soft material, is widely employed in diverse research fields due to its exceptional properties including ease of processability, newlinebiocompatibility, and transparency. These properties make it an ideal choice for applications in microfluidics, soft robotics, and biomedical devices. Creating surface gradients on soft surfaces can be challenging, requiring expensive chemicals, sophisticated instrumentation, time, and complex experimental setups. This study presents simple and cost-effective methods newlinefor creating chemical (wettability) and physical (morphological) gradients on newlinePDMS surfaces. The methods we developed to create wettability gradients involves (i) newlinecreation of a gradient of crosslinking density on the PDMS surface by using newlinea differential curing method and (ii) selective inhibition of normal curing newlineusing an inhibitor. Contact angle measurements confirm the successful newlinecreation of both radial and linear gradient of surface wettability using both these methods with regions of higher crosslinking density exhibiting higher hydrophobicity. We have also devised an innovative technique for fabricating morphological gradients on soft surfaces. The method makes use of newlinedifferential curing and buckling instability to create hierarchical wrinkled patterns on the PDMS surface. Optical microscopy and profilometry confirm the uniformity, reproducibility, and controlled optical properties of the wrinkled surface patterns. newlineGradients we prepared demonstrated excellent performance in various applications, including water collection, cell adhesion, and triboelectric charge generation. They can be utilized in microfluidics, sensors, and newlinebiomedical devices due to their structural consistency, controllable physical newlineresponses, and reproducibility of the performances.