To aggregate, or not to aggregate? considerations in the design and application of polymeric thermally-responsive nanoparticles

Abstract

The aim of this review is to highlight some of the challenges in designing thermally responsive nanoparticles, where the responsivity is endowed by a responsive polymeric corona. A review of the literature reveals many contradictory observations upon heating these particles through their transition temperature. Indeed, both an increase in size due to aggregation and particle shrinkage have been reported for apparently similar materials. Furthermore, careful review of the literature shows that responsive nanoparticles do not have the same transition temperature or properties as their constituent polymers. These observations raise serious questions as to how to achieve the rational design of a responsive particle with a predictable and reproducible response. Here we highlight specific cases where conflicting results have been observed for spherical particles and put these results into the context of flat-surface grafted polymer brushes to explain the behaviour in terms of grafting density, curvature, chain end effects and the role of the underlying substrate. A better understanding of these observations should lead to the improved design of nanoparticles with real function and applications.

Multi-responsive fluorescence of amphiphilic diblock copolymer containing carboxylate azobenzene and N-isopropylacrylamide

“…With the temperaturesensitivity and good biocompatibility, PNIPAm-containing materials have been widely utilized in drug delivery systems and temperature-targeted therapy materials [35,38e40]. Recently, researchers have employed PNIPAm to adjust the fluorescence of some fluorophores by thermally-induced aggregations [35,38,39] and micro-environmental changes [41e43]. Wang et al prepared tetraphenylethene-based PNIPAm, which assembled into organic nanoparticles in water, showing aggregation-induced emission (AIE), and the fluorescent intensity decreased with increasing temperature [41].…”

Nanohybrids of Gold Particles

“…[35] They are indeed ideal candidates, as they are very cheap and can introduce special properties to the nanoparticles, such as thermoresponsivity or just solubility in certain solvents. While citrate AuNPs seem to be toxic, [36][37][38][39] coverage with polymers reduces the nanoparticles' toxicity, [40,41] enabling medical applications.…”

Self‐Storage: A Novel Family of Stimuli‐Responsive Polymer Materials for Optical and Electrochemical Switching

“…[ 1 ] Booming development of polymer science allows these materials to be designed with abundant types and also versatile functions. [ 2 ] There are quite a few families in this fi eld, for instance, gels, [ 3 ] micelles, [ 4 ] colloids, [ 5 ] polymer brushes, [ 6 ] and the like. Some applications, such as delivering drugs, [ 7 ] tissue engineering, [ 8 ] diagnosis, [ 9 ] sensing, [ 10 ] and self-healing, [ 11 ] always regard SRPMs as ideal candidates.…”