Stimulus-Responsive Heteroaggregation of Colloidal Dispersions: Reversible Systems and Composite Materials

Abstract

Abstract:Heteroaggregation is the aggregation of mixed particle systems where the colloidal particles may differ in charge, size and chemical composition. The phenomenon of heteroaggregation is of great relevance in industrial processes and the natural environment. This review will focus on binary heteroaggregation where at least one of the particles is a stimulus-responsive smart particle. Aggregation under various conditions of pH, temperature, light and relative concentration can be induced by the careful manipulation of any one or more of these environmental conditions during the heteroaggregation of smart particles. Stimulus response provides the potential for reversibility from an aggregated to a stable system and exceptional control over inter-particle interactions. The significant fundamental and applied studies that have made an impact in this area will be discussed.

Controlled heteroaggregation of two types of nanoparticles in an aqueous suspension

“…However, when the process is too fast, nonhomogeneous, disordered, colloidal structures are formed. Only by slowing down the kinetics of heteroaggregation with controlling the inter-particle interactions in the mixed systems, well-ordered hetero-aggregated structures can be obtained [83]. In our case, the slower heteroaggregation due to chemical interactions resulted in a much greater and much more homogeneous coverage of the larger aSNPs with the smaller cMNPs compared to the faster heteroaggregation caused by the attractive electrostatic interactions.…”

Influence of microgel packing on raspberry-like heteroaggregate assembly

“…[14] Heteroaggregates are caused by the aggregation of particles with different compositions and/or sizes in colloidal dispersions and have been investigated for use in manufacturing coatings, separations techniques, as well as pharmaceutical devices and biotechnology. [15] Previous methods to produce core-shell heteroaggregates have often relied on ion-pairing to drive heteroaggregation or require covalent grafting of a shell onto a core particle. [16][17][18][19] Such methods result in a construct where the core particle is surrounded by a nanoparticle shell, which resembles a raspberry and is often termed a raspberry-like particle (RLP).…”

“…As an example of such soft/hard heteroaggregates, poly(N-isopropylacrylamide) (pNIPAm) microgels have been employed due to interest in their thermosensitivity. [15] PNIPAm exhibits a volume phase transition temperature (VPTT) at ~32 °C where it transitions from a swollen gel to a collapsed globular state. [26] PNIPAm microgels have been assembled atop SiO 2 core particles in a number of studies to produce RLPs.…”

Mechanistic Heteroaggregation of Gold Nanoparticles in a Wide Range of Solution Chemistry

“…10,13,15−17 In a more complex natural or biological setting, aggregation occurs in presence of other dissimilar particles − in terms of chemical composition, electrical charge, size, or shape − and is termed as heteroaggregation. 18−22 Heteroaggregation of ENMs is identified as an important phenomenon not only in biological and natural systems but also in engineered processes; for example, separation technology, 23 coating processes, 24 food and biotechnological processes, 12,18 ceramic industries, 25 and composites or core−shell materials. 24 Nanomaterial interaction in such heterosystems is also likely to be influenced by physicochemical properties and background chemical conditions.…”