Methods for charge-titrating particle assembly, and structures produced therefrom
Methods to fabricate tightly packed arrays of nanoparticles are disclosed, without relying on organic ligands or a substrate. In some variations, a method of assembling particles into an array comprises dispersing particles in a liquid solution; introducing a triggerable pH-control substance capable of generating an acid or a base; and triggering the pH-control substance to generate an acid or a base within the liquid solution, thereby titrating the pH. During pH titration, the particle-surface charge magnitude is reduced, causing the particles to assemble into a particle array. Other variations provide a device for assembling particles into particle arrays, comprising a droplet-generating microfluidic region; a first-fluid inlet port; a second-fluid inlet port; a reaction microfluidic region, disposed in fluid communication with the droplet-generating microfluidic region; and a trigger source configured to trigger generation of an acid or a base from at least one pH-control substance contained within the reaction microfluidic region.
1. An array of particles produced by a process comprising:
dispersing a plurality of first particles in a volume of liquid solution, wherein said first particles are characterized by an average zeta potential, and wherein said liquid solution is characterized by a starting pH;
introducing to said liquid solution before, during, or after said first particles are dispersed in said liquid solution, a triggerable pH-control substance capable of generating an acid or a base when triggered; and
triggering said pH-control substance to generate an acid or a base within said volume of liquid solution, thereby adjusting solution pH from said starting pH to a titrated pH, wherein said average zeta potential is closer to zero at said titrated pH compared to said starting pH, causing said first particles to assemble into a particle array.
2. The array of particles of claim 1 , wherein said array of particles is derived from at least one hundred individual particles, and wherein said array of particles is characterized by a packing density of at least 50 vol %.
3. A structure containing an array of particles, wherein said array of particles contains at least one hundred individual particles that are assembled together with a packing density of at least 50 vol %, and wherein said particles are essentially free of organic molecules chemically bonded or physically adsorbed to surfaces of said particles.
4. The structure of claim 3 , wherein said particles are characterized by an average particle size from about 5 nanometers to about 1 micron.