Unidirectional Droplet Propulsion onto Gradient Brushes without External Energy Supply.

Area of Science:

• Soft Matter Physics
• Nanotechnology
• Polymer Science

Background:

• Understanding self-propelled motion is crucial for nanoscale applications.
• Polymer brushes offer tunable surfaces for controlling droplet behavior.

Purpose of the Study:

• To investigate the possibility of sustained unidirectional droplet motion (durotaxis) on polymer brush substrates with stiffness gradients.
• To identify key parameters governing durotaxis efficiency without external energy supply.

Main Methods:

• Extensive molecular dynamics simulations using a coarse-grained model.
• Analysis of droplet-substrate interactions and energy landscapes.

Main Results:

• Demonstrated sustained unidirectional motion (durotaxis) of droplets on stiffness-gradient polymer brushes.
• Identified grafting density and droplet adhesion as critical parameters for durotaxis efficiency.
• Showed that interfacial energy increase drives motion, with force declining with brush roughness.

Conclusions:

• Achieved energy-free nanoscale droplet motion via durotaxis on specifically designed polymer brushes.
• Findings highlight the importance of brush grafting density and droplet adhesion for controlling motion.
• Opens new avenues for designing systems with autonomous nanoscale transport.