Unravelling soft interfaces: Visualization of gel ridges.

Area of Science:

• Soft Matter Physics
• Materials Science
• Interface Science

Background:

• Investigating soft gel contact systems is challenging due to their complex dual-phase nature (polymer and free liquid).
• Dual Wavelength-Reflection Interference Confocal Microscopy (DW-RICM) struggles with gels due to similar refractive indices of polymer networks and free liquids.
• Limited research exists on the hidden contact zones within purely soft gel systems.

Purpose of the Study:

• To enhance the visualization of contact zones in soft gel systems using nanoparticles.
• To investigate the configuration of phase-separated free oil within gel-on-gel contact systems.
• To improve understanding of adhesive contacts and interface phenomena in soft materials.

Main Methods:

• Fabrication of gel-on-gel contact systems using immiscible organogels and hydrogels.
• Introduction of titanium dioxide (TiO2) nanoparticles into organogels to modulate refractive indices.
• Utilized DW-RICM, side-view imaging, and inverted optical microscopy for observation and validation.

Main Results:

• Minimal TiO2 nanoparticle addition effectively delineated the direct contact radius between organogel and hydrogel surfaces.
• TiO2 addition did not negatively impact the gels' mechanical or surface properties.
• Significant enhancement in visualizing gel contact deformation was observed, providing crucial interface information.

Conclusions:

• Nanoparticle-modified soft gels offer improved visualization of hidden contact zones.
• This technique advances the study of adhesive contacts in gel systems.
• Findings have implications for understanding interfaces in biological soft tissues and cells.