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06 Jun 07:19

Stimuli-Responsive, Shape-Transforming Nanostructured Particles

by Junhyuk Lee, Kang Hee Ku, Mingoo Kim, Jae Man Shin, Junghun Han, Chan Ho Park, Gi-Ra Yi, Se Gyu Jang, Bumjoon J. Kim

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.

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Dynamic, temperature-driven transformation of the shape and morphology of polymer particles is demonstrated using polystyrene-b-poly(4-vinylpyridine) block copolymers (BCPs) and temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) surfactants. The temperature-directed positioning of PNIPAM depending on its solubility determines both the shape and morphology of the BCP particles, suggesting great promise of these particles for use in sensing, smart coatings, and drug delivery applications.

11 Feb 01:04

Geogrid-Inspired Nanostructure to Reinforce a CuxZnySnzS Nanowall Electrode for High-Stability Electrochemical Energy Conversion Devices

by Jian-Ming Chiu, E-Ming Chen, Chuan-Pei Lee, Indrajit Shown, Venkatesh Tunuguntla, Jui-Sheng Chou, Li-Chyong Chen, Kuei-Hsien Chen, Yian Tai

Inspired by geogrids commonly applied in construction engineering to reinforce side slopes and retaining walls, the use of a “nano-geogrid” to reinforce a CuxZnySnzS (CZTS) nanowall electrode for application in electrochemical reactions is demonstrated. The CZTS nanowall electrode reinforced by the nano-geogrid (denoted as NWD) shows not only remarkable mechanical and electrochemical stability but also considerable electrochemical performances. The NWD demonstrated as a counter electrode in a dye-sensitized solar cell shows a power conversion efficiency of 7.44 ± 0.04%, comparable with the device using Pt as electrode, and also significantly improves device stability as compared with that afforded by an electrode comprising a CZTS nanowall without the nano-geogrid (denoted as NOD). In addition, applying the NWD electrode as a cathode in photo-electrochemical hydrogen evolution reactions (HERs) yields a photocurrent density of −10 mA cm−2 at −0.162 V (vs RHE) under AM 1.5 illumination. Moreover, when HERs are conducted under extreme conditions, the NWD electrode remains intact, whereas the NOD electrode is completely peeled off after 10 min of reaction. Therefore, the concept of using a mimetic rational nanostructure could pave the way for the possibility of improving the performance and stability of various devices.

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Inspired by geogrids commonly applied in construction engineering to reinforce side slopes and retaining walls, the use of a “nano-geogrid” to reinforce a CuxZnySnzS nanowall electrode for high stable electrochemical applications is demonstrated.