Light-Active, Reversibly Shape-Shifting Block Copolymer Particles Using Photo-switchable Au Nanoparticle Surfactants

Abstract

Dynamic particles with switchable shapes in response to light have attracted great interest to develop programmable smart materials with superior spatial and temporal resolution. Herein, a facile strategy for light-responsive, shape-changing block copolymer (BCP) particles is developed. Key to this strategy is the design of azobenzene-grafted Au nanoparticles (Au@Azo NPs) as photoswitchable surfactants through photoisomerization of Azo ligands. Under visible light, onion-like polystyrene-block-poly­(2-vinylpyridine) (PS-b-P2VP) BCP particles with PS outer layer form due to the nonpolar nature of trans-Azo ligands, whereas the isomerization to polar cis-Azo surfactants with UV irradiation transforms these spheres into ellipsoids with both PS and P2VP exposed on their surfaces. This light-driven shape change is robust and reversible over multiple irradiation cycles. The reversible shape evolution between spherical and ellipsoidal BCP particles induced by photoactive Au@Azo NP surfactants is elucidated using a cryogenic electron microscope. Furthermore, light-dependent fluorescence and shape of the BCP particles are successfully demonstrated, enabling the visualization of particle shape into an optical signal.

Effect of Molecular Structure of Photoswitchable Surfactant on Light-Responsive Shape Transition of Block Copolymer Particles

“…Similar to the PS-b-P4VP system, the Δ(PS − P2VP) value was critical to transition between spheres and ellipsoids (i.e., for sphere, above 1.94 mN m −1 ; for ellipsoid, below 0.51 mN m −1 ) (Figure S17 and Table S4), suggesting that Δ(PS − P2VP) depending on the SP-XTAB spacer length is important to achieve shape-transforming PS-b-P2VP particles in response to light. 16…”

Poly(vinylpyridine)-containing block copolymers for smart, multicompartment particles

“…For designing temperature-responsive PVP-containing particles, various N -substituted polyacrylamides 126,130,178 serve as candidates for temperature-responsive surfactants for the facile tuning of the shape-transition temperature of the PVP-containing microparticles. Recently, growing interest in applying photoresponsive surfactants for shape-tuning PVP-containing particles afforded the development of various photoresponsive surfactants that contain nitrobenzyl ester, 95 azobenzene, 127,133 and spiropyran groups. 128 We envision that it will be important to develop other photoresponsive surfactants that can expand the range of accessible wavelengths to induce reversible photoresponsiveness.…”

“…Consequently, the particle shape transformed from onions with PS-outermost layers to prolate ellipsoids with a neutral interface, and finally reverse onions with P2VP-outermost layers upon UV irradiation. To overcome the irreversibility of photocleavage chemistry, surfactants that can isomerize depending on the wavelength of the irradiated light, such as azobenzene 127,133 (Fig. 8b) and spiropyran 128 (Fig.…”

Shaping Block Copolymer Microparticles by Positively Charged Polymeric Nanoparticles

“…Shape‐transforming block copolymer (BCP) microparticles, whose morphologies and functionalities can be regulated in response to environmental stimuli (e.g., ionic strength, light, pH, and others), [ 1–5 ] have many applications in nanotechnology, biomedicine, interfacial science, and other fields. [ 6–10 ] Recently, the 3D confined assembly in volatile emulsion droplets has proven to be a powerful strategy for preparing shape‐transforming BCP particles, as it provides a soft boundary and a deformable confining space.…”