Shape of picoliter droplets on chemically striped patterned substrates

Area of Science:

• Surface science and nanotechnology
• Fluid dynamics and soft matter physics

Background:

• Understanding droplet behavior on patterned surfaces is crucial for applications like microfluidics and coatings.
• Previous studies focused on droplets significantly smaller or larger than the pattern's characteristic length scale.

Purpose of the Study:

• To investigate the shape of water droplets whose dimensions are comparable to the stripe period on a chemically patterned substrate.
• To bridge the knowledge gap between droplets on single stripes and those covering numerous stripes.

Main Methods:

• Experimental deposition of water droplets using an inkjet nozzle onto a substrate with alternating hydrophobic and hydrophilic stripes.
• Utilizing the lattice Boltzmann model for simulations to analyze droplet free energies and volume dependence.
• Comparing experimental results with simulation data for validation.

Main Results:

• Droplet shape is significantly influenced by the deposition position, differing when centered on a hydrophobic versus a hydrophilic stripe.
• The study successfully bridges the gap between small (single stripe) and large (many stripes) droplet regimes.
• Simulations revealed unexplored scaling properties of droplet shape parameters relative to the stripe pattern's period.

Conclusions:

• Droplet shape on chemically striped surfaces is highly sensitive to the precise deposition location.
• New scaling relationships for droplet shape parameters were identified for intermediate droplet sizes.
• The findings provide a more comprehensive understanding of droplet behavior on patterned substrates.