Controllable Wetting Transitions on Photoswitchable Physical Gels

Area of Science:

• Materials Science
• Soft Matter Physics
• Surface Science

Background:

• Softness significantly influences droplet deformation at the three-phase contact line, leading to wetting ridges via elastocapillarity.
• Existing materials like swollen gels lack on-demand softness tunability, hindering controlled studies of wetting phenomena.
• Adjustable surfaces with tunable softness are crucial for achieving reversible transitions between wetting states on soft substrates.

Purpose of the Study:

• To introduce a novel photorheological physical soft gel with adjustable stiffness.
• To demonstrate the formation of wetting ridges upon droplet deposition on these switchable gels.
• To investigate the impact of tunable softness on wetting ridge characteristics and droplet behavior.

Main Methods:

• Development of a photorheological soft gel utilizing a spiropyran photoswitch for stiffness modulation.
• Fabrication of reversibly switchable softness patterns using UV light.
• Analysis of gels with varying stiffness to observe changes in wetting ridge height.
• Visualization of wetting ridges using confocal microscopy before and after photoswitching.

Main Results:

• The photorheological gel exhibits tunable softness controlled by UV light-induced spiropyran switching.
• Droplet deposition on the gel leads to the formation of observable wetting ridges.
• A decrease in wetting ridge height was observed with increasing gel stiffness.
• Confocal microscopy confirmed a transition in wetting properties from soft wetting to liquid/liquid wetting after photoswitching.

Conclusions:

• The developed photoswitchable gel offers a platform for on-demand control over surface softness and wetting properties.
• This technology enables the study of elastocapillarity and wetting phenomena with precise control over substrate mechanics.
• The findings pave the way for designing advanced soft materials with tunable interfacial properties for various applications.