A surface with stress, extensional elasticity, and bending stiffness.

Area of Science:

• Materials Science
• Surface Science
• Soft Matter Physics

Background:

• Soft solid surfaces, often assumed to have liquid-like constant surface stress, govern phenomena like wetting and contact.
• The constitutive response of soft solid surfaces beyond simple surface stress is an area of active scientific debate.

Purpose of the Study:

• To investigate the complex surface elasticity of soft solids, specifically polydimethylsiloxane (PDMS) treated with ultraviolet ozonolysis (UVO).
• To determine if UVO-treated PDMS surfaces exhibit elasticity beyond a simple liquid-like model.

Main Methods:

• Studied the deformation of surface-patterned materials: untreated PDMS, an organogel, and UVO-treated patterned PDMS.
• Characterized surface stress, extensional elasticity (Shuttleworth Effect), and surface bending elasticity.

Main Results:

• UVO-treated PDMS surfaces exhibit significant surface stress and considerable extensional elasticity.
• Demonstrated complex surface elasticity in UVO-treated PDMS, analogous to Gibbs elasticity in liquids with interfaces.
• Observed surface bending elasticity in the treated PDMS formulation.

Conclusions:

• The surface of UVO-treated PDMS displays complex elastic properties, challenging the assumption of liquid-like surface stress in soft solids.
• Surface behavior in soft solids can dominate bulk deformation, making these findings broadly applicable.
• This research provides new insights into the mechanical behavior of treated soft solid surfaces.