Casimir self-assembly: A platform for measuring nanoscale surface interactions in liquids

Area of Science:

• Colloidal science
• Nanotechnology
• Biophysics

Background:

• Self-assembly (SA) is crucial for nanotechnology and bioinspired systems, but current investigation methods are limited to planar interfaces in liquids.
• Existing techniques often analyze collective particle behavior, failing to probe individual particle interactions crucial for understanding dynamics.

Purpose of the Study:

• Introduce Casimir self-assembly (CaSA) as a novel platform for studying long-range interactions and stability in planar self-assembly systems.
• Enable direct, in situ investigation of Casimir-Lifshitz electrostatic interactions in liquid environments.
• Develop a method to map colloidal material stability regimes and measure single-particle surface charge density.

Main Methods:

• Integrate colloidal science, nanophotonics, and fluctuational electrodynamics.
• Utilize thermal fluctuations as a probe and visible-range Fabry-Pérot resonances for optical readout.
• Vary ionic strength to analyze suspension stability and aggregation limits.

Main Results:

• Demonstrate in situ study of Casimir-Lifshitz electrostatic interactions.
• Successfully map stability regimes of colloidal materials.
• Achieve precise measurement of surface charge density on individual colloidal objects down to fractions of an electron charge per square nanometer.

Conclusions:

• CaSA overcomes limitations of current methods, offering an experimental tool for exploring SA dynamics in situ.
• Expands understanding of suspension stability in liquids at the single-particle level.
• CaSA is scalable for interfacial force studies and adaptable for multivalent electrolytes and biosensing.