Directed assembly of nanoparticles into continuous microstructures by standing surface acoustic waves.

Area of Science:

• Materials Science
• Nanotechnology
• Acoustic Assembly

Background:

• Directed-assembly using standing surface acoustic waves (SSAWs) is attractive due to minimal system requirements.
• Previous SSAW applications primarily achieved reversible nanoparticle arrangements.
• Colloid surface chemistry critically impacts aggregation and sintering, influencing microstructure permanence.

Purpose of the Study:

• To develop a method for forming permanent, conductive silver microstructures using SSAWs.
• To control nanoparticle sintering by manipulating surface chemistry.
• To overcome limitations in microstructure length and achieve continuous assembly.

Main Methods:

• Utilizing SSAWs for directed-assembly of silver nanoparticles in a microfluidic channel.
• Manipulating nanoparticle surface chemistry by adding chloride ions to remove polyacrylic capping.
• Controlling the timing of ion addition relative to acoustic assembly.

Main Results:

• Addition of chloride ions triggered nanoparticle sintering, forming stable, conducting silver microstructures.
• Assembling destabilized nanoparticles resulted in significantly thinner microstructures.
• Continuous streaming of destabilized nanoparticles enabled the formation of microstructures unlimited in length.

Conclusions:

• Controlling colloid surface chemistry is key to achieving permanent nanoparticle microstructures via SSAWs.
• This method overcomes the challenge of balancing dispersant use with the need for particle contact.
• The developed technique allows for the scalable production of long, conductive silver microstructures.