The Metallocene Battery: Ultrafast Electron Transfer Self Exchange Rate Accompanied by a Harmonic Height Breathing.

The first all-metallocene rechargeable battery consisting of poly-cobaltocenium/- and poly-ferrocene/reduced graphene oxide composites as anode and cathode was prepared. The intrinsically fast ET self-exchange rate of metallocenes was successfully combined with an efficient ion-percolation achieved by molecular self-assembly. The resulting battery materials show ideal Nernstian behavior, is thickness scalable up to >1.2 C cm-2 , and exhibit high coulombic efficiency at ultrafast rates (200 A g-1 ). Using aqueous LiClO4 , the charge is carried exclusively by the anion. The ClO4 - intercalation is accompanied by a reciprocal height change of the active layers. Principally, volume changes in organic battery materials during charging/discharging are not desirable and represent a major safety issue. However, here, the individual height changes-due to ion breathing-are reciprocal and thus prohibiting any internal pressure build-up in the closed-cell, leading to excellent cycling stability.

Functional Metalloblock Copolymers for the Preparation and In Situ Functionalization of Porous Silica Films.

Stimuli-responsive mesoporous silica films were prepared by evaporation-induced self-assembly through the physical entrapment of a functional metalloblock copolymer structuring agent, which simultaneously served to functionalize the mesopore. After end-functionalization with a silane group, the applied functional metalloblock copolymers were covalently integrated into the silica mesopore wall. In addition, they were partly degraded after the formation of the mesoporous film, which enabled the precise design of accessible mesopores. These polymer-silica hybrid materials exhibited remarkable and gating ionic permselectivity and offer the potential for highly precise pore filling design and combination with high-throughput printing techniques. This in situ functionalization strategy of mesoporous silica using responsive metalloblock copolymers has the potential to improve how we approach the design of complex architectures at the nanoscale for tailored transport. This functionalization strategy paves the way for a variety of technologies based on molecular transport in nanoscale pores, including separation, sensing, catalysis, and energy conversion.

Opposing Temperature Dependence of the Stretching Response of Single PEG and PNiPAM Polymers.

The response of switchable polymer blends and coatings to temperature variation is important for the development of high-performance materials. Although this has been well studied for bulk materials, a proper understanding at the molecular level, in particular for high stretching forces, is still lacking. Here we investigate the molecular details of the temperature-dependent elastic response of two widely used water-soluble polymers, namely, polyethylene glycol (PEG) and poly(N-isopropylacrylamide) (PNiPAM) with a combined approach using atomic force microscopy (AFM) based single molecule force spectroscopy (SMFS) experiments and molecular dynamics (MD) simulations. SMFS became possible by the covalent attachment of long and defined single polymers featuring a functional end group. Most interestingly, varying the temperature produces contrasting effects for PEG and PNiPAM. Surprising as these results might occur at first sight, they can be understood with the help of MD simulations in explicit water. We find that hydration is widely underestimated for the mechanics of macromolecules and that a polymer chain has competing energetic and entropic elastic components. We propose to use the temperature dependence to quantify the energetic behavior for high stretching forces. This fundamental understanding of temperature-dependent single polymer stretching response might lead to innovations like fast switchable polymer blends and coatings with polymer chains that act antagonistically.

Crossover from semi-dilute to densely packed thin polymer films at the air-water interface and structure formation at thin film breakup.

A series of poly(n-butyl acrylate) (PnBA, 5 to 32 kg mol-1) homopolymers and diblock copolymers with poly(ethylene glycol) (PEG, constant molecular weight of 0.3 kg mol-1) is synthesized for the purpose of the investigation of quasi-2D polymer films at the air-water interface. The presented compression isotherms show a transition from θ solvent behavior for PnBA homopolymers to good solvent conditions when the volume fraction of the PEG in the block copolymers is increased by decreasing the molecular weight of PnBA. A transition from a semi-dilute regime to a densely packed layer is observed in the pressure isotherms for all the polymers. In the densely packed films we found first evidence for thin film breakup of a thin polymer film directly at the air-water interface. Combination of results from Brewster-Angle-Microscopy and Surface X-ray scattering provide a consistent picture of the film breakup. Our results suggest a preferred length scale of 2.5 µm. This scenario is analogous to a spinodal mechanism driven by thermal fluctuations of the film height.

Recent Trends in Metallopolymer Design: Redox-Controlled Surfaces, Porous Membranes, and Switchable Optical Materials Using Ferrocene-Containing Polymers.

Metallopolymers with metal functionalities are a unique class of functional materials. Their redox-mediated optoelectronic and catalytic switching capabilities, their outstanding structure formation and separation capabilities have been reported recently. Within this Minireview, the scope and limitations of intriguing ferrocene-containing systems will be discussed. In the first section recent advances in metallopolymer design will be given leading to a plethora of novel metallopolymer architectures. Discussed synthetic pathways comprise controlled and living polymerization protocols as well as surface immobilization strategies. In the following sections, we focus on recent advances and new applications for side-chain and main-chain ferrocene-containing polymers as (i) remote-switchable materials, (ii) smart surfaces, (iii) redox-responsive membranes, and some recent trends in (iv) photonic structures and (v) other optical applications.

Metallopolymer-Based Block Copolymers for the Preparation of Porous and Redox-Responsive Materials.

Metallopolymers are a unique class of functional materials because of their redox-mediated optoelectronic and catalytic switching capabilities and, as recently shown, their outstanding structure formation and separation capabilities. Within the present study, (tri)block copolymers of poly(isoprene) (PI) and poly(ferrocenylmethyl methacrylate) having different block compositions and overall molar masses up to 328 kg mol-1 are synthesized by anionic polymerization. The composition and thermal properties of the metallopolymers are investigated by state-of-the-art polymer analytical methods comprising size exclusion chromatography, 1H NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. As a focus of this work, excellent microphase separation of the synthesized (tri)block copolymers is proven by transmission electron microscopy, scanning electron microcopy, energy-dispersive X-ray spectroscopy, small-angle X-ray scattering measurements showing spherical, cylindrical, and lamellae morphologies. As a highlight, the PI domains are subjected to ozonolysis for selective domain removal while maintaining the block copolymer morphology. In addition, the novel metalloblock copolymers can undergo microphase separation on cellulose-based substrates, again preserving the domain order after ozonolysis. The resulting nanoporous structures reveal an intriguing switching capability after oxidation, which is of interest for controlling the size and polarity of the nanoporous architecture.

Ferrocene-Modified Block Copolymers for the Preparation of Smart Porous Membranes.

The design of artificially generated channels featuring distinct remote-switchable functionalities is of critical importance for separation, transport control, and water filtration applications. Here, we focus on the preparation of block copolymers (BCPs) consisting of polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) having molar masses in the range of 91 to 124 kg mol-1 with a PHEMA content of 13 to 21 mol %. The BCPs can be conveniently functionalized with redox-active ferrocene moieties by a postmodification protocol for the hydrophilic PHEMA segments. Up to 66 mol % of the hydroxyl functionalities can be efficiently modified with the reversibly redox-responsive units. For the first time, the ferrocene-containing BCPs are shown to form nanoporous integral asymmetric membranes by self-assembly and application of the non-solvent-induced phase separation (SNIPS) process. Open porous structures are evidenced by scanning electron microscopy (SEM) and water flux measurements, while efficient redox-switching capabilities are investigated after chemical oxidation of the ferrocene moieties. As a result, the porous membranes reveal a tremendously increased polarity after oxidation as reflected by contact angle measurements. Additionally, the initial water flux of the ferrocene-containing membranes decreased after oxidizing the ferrocene moieties because of oxidation-induced pore swelling of the membrane.

Fluid Flow Programming in Paper-Derived Silica-Polymer Hybrids.

In paper-based devices, capillary fluid flow is based on length-scale selective functional control within a hierarchical porous system. The fluid flow can be tuned by altering the paper preparation process, which controls parameters such as the paper grammage. Interestingly, the fiber morphology and nanoporosity are often neglected. In this work, porous voids are incorporated into paper by the combination of dense or mesoporous ceramic silica coatings with hierarchically porous cotton linter paper. Varying the silica coating leads to significant changes in the fluid flow characteristics, up to the complete water exclusion without any further fiber surface hydrophobization, providing new approaches to control fluid flow. Additionally, functionalization with redox-responsive polymers leads to reversible, dynamic gating of fluid flow in these hybrid paper materials, demonstrating the potential of length scale specific, dynamic, and external transport control.