Symmetric Diblock Copolymers Form Versatile and Switchable Ultrasmall Nanoparticles.

Block copolymers (BCPs) can form nanoparticles having different morphologies that can be used as photonic nanocrystals and are a platform for drug delivery, sensors, and catalysis. In particular, BCP nanoparticles having disk-like shape have been recently discovered. Such nanodisks can be used as the next-generation antitumor drug delivery carriers; however, the applicability of the existing nanodisks is limited due to their poor or unknown ability to respond to external stimuli. In this work, we showed that the simplest symmetric diblock copolymers in equilibrium can form nanodisks that can be reversibly switched into a multitude of various nanoparticles potentially applicable in nanophotonics, biomedicine, and hierarchical self-assembly. These structures include patchy and onion-like nanoparticles, striped ellipsoids, mixed morphology nanocolloids, and spherical micelles. The transitions between nanodisks and the aforementioned nanoparticles are sharp, direct, and can be achieved by tuning the block-block and polymer-solvent incompatibility. We demonstrated that this versatility of nanoparticle morphologies can be achieved upon reducing the nanoparticle size to approximately two lamellar periods of the BCP. Upon aggregation of such small nanocolloids, a larger assembly can be formed. In turn, these bigger particles could form many other structures including a chain-like supramolecular aggregate of nanodisks and a multilayered disk-like nanoparticle. We obtained our results by performing self-consistent field theory calculations according to an algorithm designed to produce equilibrium nanoparticle morphology. This work demonstrates that nanodisks prepared from the simplest type of BCPs are extremely tunable; therefore, symmetric diblock copolymers can become a platform for producing the next-generation stimuli-responsive nanoparticles.