Stimuli‐Responsive, Shape‐Transforming Nanostructured Particles

Abstract

Development of particles that change shape in response to external stimuli has been a long-thought goal for producing bioinspired, smart materials. Herein, the temperature-driven transformation of the shape and morphology of polymer particles composed of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers (BCPs) and temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) surfactants is reported. PNIPAM acts as a temperature-responsive surfactant with two important roles. First, PNIPAM stabilizes oil-in-water droplets as a P4VP-selective surfactant, creating a nearly neutral interface between the PS and P4VP domains together with cetyltrimethylammonium bromide, a PS-selective surfactant, to form anisotropic PS-b-P4VP particles (i.e., convex lenses and ellipsoids). More importantly, the temperature-directed positioning of PNIPAM depending on its solubility determines the overall particle shape. Ellipsoidal particles are produced above the critical temperature, whereas convex lens-shaped particles are obtained below the critical temperature. Interestingly, given that the temperature at which particle shape change occurs depends solely on the lower critical solution temperature (LCST) of the polymer surfactants, facile tuning of the transition temperature is realized by employing other PNIPAM derivatives with different LCSTs. Furthermore, reversible transformations between different shapes of PS-b-P4VP particles are successfully demonstrated using a solvent-adsorption annealing with chloroform, suggesting great promise of these particles for sensing, smart coating, and drug delivery applications.

Switchable Full-Color Reflective Photonic Ellipsoidal Particles

“…Surfactants play a critical role in the emulsification of BCPs as the nature of the surfactant determines which block is exposed at the outer surface of the particle. [39][40][41][42][43][44] To promote favorable interactions to each block of den-BBCP, we synthesized cetyltrimethylammonium bromide (CTAB)derived complementary surfactants having AW (S AW ) or BnW (S BnW ) groups. (Figure 1b, See the Supporting Information for synthetic details.)…”

Two-step deswelling in the Volume Phase Transition of thermoresponsive microgels

“…Through DLS, we measured the autocorrelation function of the scattered intensity at a fixed value of q = q DLS . At high dilution, this can be put in relation with the square of the self intermediate scattering function Fs( q, t) 2 , which for simply diffusive systems has the functional shape of a convolution of exponential decays, taking into account the effects of polydispersity. The analysis of Fs( q, t) 2 has been performed by cumulant analysis, up to the second central moment of the distribution of decay rates:…”

Transformable Colloidal Polymer Particles with Ordered Internal Structures

“…[32] Besides, a switchable transformation between pupa-like and faveolated particles by changing the location of pH and/or temperature responsive additives were reported. [33,36] The addition or removal of additives can vary the volume fraction, thereby inducing the transformations in the internal structure of the particles. [37] Since the volume fraction of BCP is dependent on their chain stretching, we expect that a variation of solvent selectivity can be applied to drive morphological transformations of the BCP particles without employing any additives.…”