Electroreductive Coupling Layer-by-Layer Assembly

Pillararene-containing polymers with tunable fluorescence properties based on host-guest interactions

Linear polymers containing pillar[5]arenes as the pendant groups were designed and synthesized via a ring-opening metathesis polymerization. Such polymers could form supramolecular brush polymers and exhibited tunable fluorescence properties based on the host-guest interactions.

Hierarchical Core-Shell Fe₃O₄@mSiO₂@Chitosan Nanoparticles for pH-Responsive Drug Delivery

Hierarchical nanoparticles are of great interest because they possess unique physicochemical properties and multiple functionalities, providing a wealth of possibilities for various applications. In this work, we have developed a well-designed method to prepare hierarchical magnetic nanoparticles Fe₃O₄@mSiO₂@CS by integrating a solvothermal method for synthesizing the Fe₃O₄ core, a dualtemplating micelle system for preparing a layer of mesoporous silica (mSiO₂) shell, and a silane coupling method via γ-glycidoxypropyltrimethoxysilane for binding a chitosan (CS) layer on the silica surface. The porous hierarchical nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering nanoparticle size analyzer, and specific surface area and pore size analyzer. The loading capacity and the release behavior of the as-prepared nanoparticles for doxorubicin hydrochloride were studied, and it was found that the drug release rate was faster at pH 6.0 than at pH 7.4, revealing the pH-responsive property of the nanoparticles.

The Future of Layer-by-Layer Assembly: A Tribute to ACS Nano Associate Editor Helmuth Möhwald

Layer-by-layer (LbL) assembly is a widely used tool for engineering materials and coatings. In this Perspective, dedicated to the memory of ACS Nano associate editor Prof. Dr. Helmuth Möhwald, we discuss the developments and applications that are to come in LbL assembly, focusing on coatings, bulk materials, membranes, nanocomposites, and delivery vehicles.

Interlock or Chemical Bond: Investigation on the Interface of Graphene Oxide and Styrenic Block Copolymers as Layer-by-Layer Films

In the paper, graphene oxide (GO) and two kinds of styrenic resins, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) and maleic anhydride (MA) grafted SEBS (MA-g-SEBS), were utilized to explore the interfacial interaction of carbon-based materials and block copolymers as layer-by-layer (LBL) assembly films. The details of the interlayer interaction of the two kinds of composite films were investigated through the analysis of the mechanical properties and internal structure of the composites. For the SEBS/GO composite film, the "interlock" structure tended to form between the GO sheets and SEBS resin, and the physical "interlocking effect" could make full use of the excellent mechanical properties of GO nanosheets. As a result, both failure strength and elongation at break of the SEBS/GO composite film were enhanced by 50 and 25%, respectively. On the other hand, some different structures were found in the MA-g-SEBS/GO composite film, where the GO sheets stacked onto the resin closely because of the chemical interaction between them and no obvious "interlocks" was found within the interface, and the chemical interface interaction was strong enough to prevent the slide of GO nanosheets under tension after the graphene sheets were highly oxidized, so the mechanical properties of the MA-g-SEBS/GO composite film could be also enhanced. Based on an overall consideration of the research results of these LBL assembled composites, choosing more perfect materials and structures is needed, which should use physical and chemical interfacial interactions more efficiently, to obtain better mechanical properties of inorganic carbon-organic resin composites.

Stabilization of a Cyclometalated Ruthenium Sensitizer on Nanocrystalline TiO2 by an Electrodeposited Covalent Layer

A cyclometalated ruthenium sensitizer 3 containing a triphenylamine unit was synthesized and immobilized on a nanocrystalline TiO₂ surface. By using oxidative electrochemical deposition, a covalent layer of a related cyclometalated ruthenium complex 2 was coupled to the top of dye 3. Electrochemical studies suggested that complex 2 was immobilized on the TiO₂/3 film surface by a tetraphenylbenzidine linker to form a dimer-like structure. The immobilization of 3 and 2 was further supported by absorption spectral analysis. The resulting electrodeposited TiO₂/(3+2) film displays significantly enhanced sensitizer stabilization toward basic aqueous NaOH solution with respect to the original TiO₂/3 film. The dye-sensitized solar cells with the TiO₂/(3+2) photoanode display a power conversion efficiency of 4.4%, which is slightly inferior to that with the TiO₂/3 film (5.1%) under the same measurement conditions.

Nanocrystalline Sb-doped SnO2 films modified with cyclometalated ruthenium complexes for two-step electrochromism

Sb-Doped nanocrystalline SnO2 (SnO2:Sb) thin films functionalized with cyclometalated ruthenium complexes 1 or 2 on FTO conductive glasses have been prepared and characterized. These complexes contain a redox-active amine unit separated from the ruthenium ion by a phenyl or biphenyl linker, respectively, to modify the absorption wavelengths at different redox states. Near-infrared electrochromism of both films has been examined by oxidative spectroelectrochemical measurements and double-potential-step chronoamperometry. A contrast ratio (ΔT%) of 33% at 1070 nm and 63% at 696 nm has been achieved for the SnO2:Sb/1 film in two stepwise oxidation processes, respectively. The other film with complex 2 shows two-step electrochromism at 1310 and 806 nm with ΔT% of 36% and 76%, respectively. The response time of electrochromic switching is around a few seconds. Taking advantage of the good contrast ratio, the rapid response, and the long retention time of each oxidation state, these films have been successfully used to demonstrate surface-confined flip-flop memory functions with a high ON/OFF ratio.

Tuning Optical Limiting of Heterosized AuNPs and Fullerene by Countable Electrochemical Assembly

Tuning optical limiting was achieved based on the nanostructural and synergistic effects of heterosized gold nanoparticles and fullerene on electrochemical assembly. In particular, with thicknesses of 200, 1, and 10 nm, heterosized AuNP multilayers with periodical pairs of layers present a superior threshold of 0.59 J cm^-2 to monosized AuNP films with the values of 0.89-2.55 J cm^-2, which was further significantly enhanced by the introduction of C₇₀ with a significant threshold drop from 0.43 to 0.13 J cm^-2, indicating that the reverse saturable absorption of C₇₀ had a key contribution compared to the free carrier absorption of AuNPs. This paper not only demonstrates that the hybrid engineering of heterosized AuNPs into an identical film is an effective way to enhance the optical limiting but also indicates that the reverse saturable absorption of C₇₀ is superior to free carrier absorption of AuNPs in optical limiting in AuNPs and C₇₀ hybrid films.