Xueyi Chang

Spiropyran-Decorated SiO2–Pt Janus Micromotor: Preparation and Light-Induced Dynamic Self-Assembly and Disassembly

The controlled self-assembly of self-propelled Janus micromotors may give the micromotors some potential applications in many fields. In this work, we design a kind of SiO2-Pt Janus catalytic micromotor functionalized by spiropyran (SP) moieties on the surface of the SiO2 hemisphere. The spiropyran-modified SiO2-Pt Janus micromotor exhibits autonomous self-propulsion in the presence of hydrogen peroxide fuel in N,N-dimethylformamide (DMF)/H2O (1:1 in volume) mixture. We demonstrate that the self-propelled Janus micromotors can dynamically assemble into multiple motors because of the electrostatic attractions and π-π stacking between MC molecules induced by UV light irradiation (λ = 365 nm) and also quickly disassemble into mono motors when the light is switched to green light (λ = 520 nm) for the first time. Furthermore, the assembled Janus motors can move together automatically with different motion patterns propelled by the hydrogen peroxide fuels upon UV irradiation. The work provides a new approach not only to the development of the potential application of Janus motors but also to the fundamental science of reversible self-assembly and disassembly of Janus micromotors.

Novel ferrocenyl-terminated linear-dendritic amphiphilic block copolymers: synthesis, redox-controlled reversible self-assembly, and oxidation-controlled release.

Novel linear-dendritic amphiphilic block copolymers with hydrophilic poly(ethylene glycol) (PEG) block and hydrophobic Percec-type dendrons containing ferrocenyl terminals were synthesized by the esterification reaction of poly(ethylene glycol) methyl ether with ferrocenyl-terminated alkyl-substituted benzoic acid dendrons. On the basis of the results that the critical aggregation concentration (CACox) of the oxidation state polymer is much higher than CACred of the corresponding reduction state, these polymers can reversibly self-assemble into various aggregates, such as spherical, wormlike micelles, and vesicles, and also disassemble into irregular fragments in aqueous solution by redox reaction when changing the polymer concentrations. Copolymer PEG45-b-Fc3 (3) with 3,4,5-tris(11-ferrocenylundecyloxy) benzoic acid (2) can self-assemble into nanoscale wormlike micelles when the polymer concentration in aqueous solution is above its CACox. These wormlike micelles can be transformed into nanosized vesicles by Fe2(SO4)3 and regained by vitamin C. Interestingly, copolymer PEG45-b-Fc2 (5) with 3,5-bis(11-ferrocenylundecyloxy) benzoic acid (4) can reversibly self-assemble into spherical micelles with two different sizes by redox reaction above the CACox, indicating that the terminal hydrophobic tail number of dendrons plays a key role in determining the self-assembled structures. Furthermore, rhodamine 6G (R6G)-loaded polymer aggregates have been successfully used for the oxidation-controlled release of loaded molecules, and the release rate can be mediated by the concentrations of oxidant and copolymers. The results provide an effective approach to the reversible self-assembly of linear-dendritic amphiphilic block copolymers and also promise the potential of these novel redox-responsive amphiphilic block copolymers in drug delivery systems, catalyst supports, and other research fields.

Synthesis and characterization of a novel ferrocenyl-terminated percec-type dendron and application for redox batteries

A novel ferrocenyl-terminated percec-type dendron 3,4,5-tris (11-ferrocenylundecyloxy) benzoic acid (Fc3CO2H) was synthesized for the first time through nucleophilic substitution reaction between 11-bromoundecyl ferrocene and methyl 3,4,5-trihydroxybenzoate, followed by a hydrolysis process. The structural characteristics of the resultant dendron Fc3CO2H were confirmed through NMR, Fourier transform infrared (FT-IR), and elemental analysis. Furthermore, its stacking structures and physical properties were detected by X-ray diffraction (XRD), thermogravimetry (TG) analysis, differential scanning calorimetry (DSC), and polarized optical microscope (POM). Both cyclic voltammograms (CV) and galvanostatic charge/discharge measurements indicate the as-synthesized dendron has high electrochemical stability and redox reversibility, which makes it a promising candidate for redox batteries.

Controlled Self-Assembly of Multiple-Responsive Superamphiphilc Polymers Based on Host-Guest Inclusions of a Modified PEG with β-Cyclodextrin

Superamphiphilic polymers (SAPs) constructed by host-guest inclusion can self-assemble into various nanostructures in solution, which can find applications in many fields such as nanodevices, drug delivery, and template synthesis. Herein, we report the controlled self-assembly of multiple-responsive SAP based on a selective host-guest inclusion of β-cyclodextrin (β-CD) with a modified poly(ethylene glycol) (PEG) (FcC11AzoPEG) consisting of a ferrocene (Fc) end group, a C11 alkyl chain, an azobenzene (Azo) block, and a poly(ethylene glycol)methyl ether (PEG) chain. These SAPs can self-assemble into interesting nanostructures in water upon exposure to different stimuli because β-CD can be selectively included with different guests, such as Fc, Azo, and C11 alkyl chain, under different stimuli. The inclusion complex of Fc with β-CD (Fc@β-CD SAP) can form nanowire micelles in aqueous solution. The nanowire micelles can be transformed into spindle micelles with the addition of oxidant because the majority of β-CDs dissociated from the complex Fc@β-CD SAP due to a conversion of Fc to Fc+ and will preferentially include with Azo group to form another dominant inclusion complex (Azo@β-CD SAP). After UV irradiation, the spindle micelles can be further transformed into spherical micelles because most of β-CDs are excluded from the complex Azo@β-CD SAP due to a trans- to cis-Azo conversion and then form a dominant inclusion complex with C11 alkyl chains (C11@β-CD SAP). This work not only demonstrates the selective host-guest inclusion of stimuli-responsive groups modified PEG with β-CD but also provides a useful approach for construction of diverse morphologies.

Rheology of a spiropyran functionalized hydrophobically modified ethoxylated urethane in aqueous solution

Hydrophobically modified ethoxylated urethanes (HEURs) have been widely used as effective thickeners for improving the solution rheological properties in a variety of applications for over 40 years. We designed and prepared a novel photosensitive spiropyran-functionalized HEUR polymer (SP-HEUR), which was used to investigate the influence of hydrophobicity change of hydrophobes induced by photoisomerization of spiropyran (SP) group on the solution aggregation and rheological properties. The concentrated SP-HEUR solutions show an interesting photoresponsive rheological behavior upon alternative exposure to ultraviolet and visible light due to a reversible SP- to merocyanine-form conversion and back. A reversible rearrangement of micellar junctions through loop-bridge or bridge-loop transitions is proposed to interpret the influence of photoisomerozation of spiropyran groups on the associative structure and rheological properties of the polymer solution. This work will not only provide new insights into the...