A Facile Synthesis of Dynamic, Shape‐Changing Polymer Particles

Abstract

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles exhibiting a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric PS-b-P2VP in dispersed droplets. In a second step, the dynamic shape change is realized by crosslinking the P2VP domains, hereby connecting glassy PS discs with pHsensitive hydrogel actuators.© Wiley-VCH Verlag GmbH &co. KGaA, Weinheim Supporting information for this article is available on the WWWunder http://dx.doi.org/10.1002/anie.201xxxxxx. The ability of nature to precisely control the shape and functionality of nanoparticles in a range of biological systems has long motivated researchers to strive for similar control in synthetic nanomaterials. [1] This challenge has been partially fulfilled in inorganic systems where the ability to tailor shape and size in order to tune properties has been extensively studied. [2] In direct contrast, the toolbox for controlling the shape and functionality of polymer-based nanoparticles is still in its infancy [3] with future success being critical to the preparation of bio-inspired materials with applications ranging from drug-delivery systems to artificial camouflage. [1c] In addressing this need, the development of dynamic, shape-changing polymer particles requires three main structural features to be incorporated into a single system: shape anisotropy, spatial control over internal morphology and the introduction of stimuliresponsiveness to the nanoparticles. Unfortunately, current examples address each aspect separately with multifunctional, dynamic systems not being realized. [3] Anisotropic particles, for instance, have been prepared by a multistep procedure which relies on the stretching of spherical particles. [3a, 4] Even though such elongated particles show interesting properties [5] only a few examples combine shape anisotropy with either well-defined internal morphologies [6] or stimuli-responsive properties. [7] For example, we have recently reported the use of tailored Au nanoparticles as surface active agents for the preparation of shape anisotropic particles with an internally structured morphology. [8] While the potential of block copolymer self-assembly in colloidal systems is promising, [9] the use of Au nanoparticles represents a significant synthetic limitation and did not lead to a dynamic, stimuli-responsive material. As a result, the facile formation of multifunctional nanoparticles that combine all three mentioned features (shape anisotropy, internal morphology, and stimuli-responsiveness) remains a major challenge. NIH Public AccessHerein, we report the development of a facile and powerful new strategy for the preparation of functional particles that serves as a broad platform for nanoscale materials. Key to the success of this strategy is the use of functional surfactant mixtures to control the phase separat...

Self‐Assembly of Multiblock Copolymers

“…With further CTAB addition, also the bottom half changed to axially‐stacked lamellae resulting in entirely elliptic microparticles, where PS, PI, and P2VP all share an interface with surfactant/water. This morphology preferably forms when the interfacial energies are comparable for all blocks as previously studied in detail for AB diblock copolymers . From here one, an increase of the CTAB content inverts the block arrangement to first bud‐like, and finally to onion‐like particles with PS facing CTAB/water.…”

“…Using one surfactant, usually one block shows a preference to the surfactant/water interface leading to microparticles with concentric onion‐like lamella (assuming equal‐sized blocks). However, using two surfactants that match both blocks, the morphology alters its orientation from spherical onion‐like particles to elliptic “tulip‐bulb” particles with an axially stacked lamella morphology . The evaporation rate of the solvent is a kinetic set screw to control the particle shape, but also affects the arrangement of BCPs at the particle interface.…”

Three-Dimensional Visualization and Characterization of Polymeric Self-Assemblies by Transmission Electron Microtomography

“…55 The morphological transformation between an axially stacked lamellar and onionlike structure was observed under spherical 3D confinement. 54 Figure 6 shows the morphological transformation of lamellaforming SI BCP in nanoparticles dispersed in water (i.e., a poor solvent for SI) by applying thermal annealing.…”

Reversible Shape‐Morphing and Fluorescence‐Switching in Supramolecular Nanomaterials Consisting of Amphiphilic Cyanostilbene and Cucurbit[7]uril

“…Shape‐morphing nanomaterials are drawing great interest in many fields, because the reversible and stimuli‐responsive shape change renders specific switching of various physical properties including viscosity, color, and fluorescence for example . Among many shape‐morphing nanomaterials, one showing high‐contrast fluorescence switching and good water‐compatibility is considered as a key nanomaterial in developing a reliable biosensor .…”