Solvent-Free High-Temperature Capillary Stamping of Stimuli-Responsive Polymers: Wettability Management by Orthogonal Substrate Functionalization

The wettability of surfaces determines their antifouling, antifogging, anti-icing, and self-cleaning properties as well as their usability for sensing, oil-water separation, water collection, and water purification. Solvent-free high-temperature capillary stamping of stimuli-responsive polymers yielding arrays of stimuli-responsive polymer microdots on differently modified substrates enables the flexible generation of switchable surfaces with different water contact angles (WCAs). Potential problems associated with the deposition of polymer solutions, such as the handling of volatile organic solvents, phase separation induced by solvent evaporation, and capillarity-driven flow processes, are circumvented. We used composite stamps with topographically patterned contact surfaces consisting of metallic nickel cores and porous MnO2 coatings taking up the stimuli-responsive polymers. The short transport paths from the MnO2 contact layers to the counterpart substrates enabled the stamping of polymer melts containing components impeding flow, such as carbon nanotubes (CNTs). Thus-obtained arrays of polymer-CNT hybrid microdots prevent problems associated with continuous coatings including delamination and crack propagation. Moreover, the range within which the properties of the stamped stimuli-responsive polymer microdots are switchable can be tuned by orthogonal substrate modification. As an example, we stamped hybrid microdots consisting of poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate) (PFcMA) and CNTs onto indium tin oxide (ITO) substrates. Coating the ITO substrates with a poly(ethylene oxide)-terminated silane shifted the WCAs obtained by switching the PFcMA between its oxidized and reduced states by nearly 50{\deg}

Reactive additive capillary stamping with double network hydrogel-derived aerogel stamps under solvothermal conditions

Integration of solvothermal reaction products into complex thin-layer architectures is frequently achieved by combinations of layer transfer and subtractive lithography, whereas direct additive substrate patterning with solvothermal reaction products has remained challenging. We report reactive additive capillary stamping under solvothermal conditions as a parallel contact-lithographic access to patterns of solvothermal reaction products in thin-layer configurations. To this end, corresponding precursor inks are infiltrated into mechanically robust mesoporous aerogel stamps derived from double-network hydrogels (DNHGs). The stamp is then brought into contact with a substrate to be patterned under solvothermal reaction conditions inside an autoclave. The precursor ink forms liquid bridges between the topographic surface pattern of the stamp and the substrate. Evaporation-driven enrichment of the precursors in these liquid bridges along with their liquid-bridge-guided conversion into the solvothermal reaction products yields large-area submicron patterns of the solvothermal reaction products replicating the stamp topography. As example, we prepared thin hybrid films, which contained ordered monolayers of superparamagnetic submicron nickel ferrite dots prepared by solvothermal capillary stamping surrounded by nickel electrodeposited in a second, orthogonal substrate functionalization step. The submicron nickel ferrite dots acted as magnetic hardener halving the remanence of the ferromagnetic nickel layer. In this way, thin-layer electromechanical systems, transformers and positioning systems may be customized

Orthogonal substrate functionalization using additive contact lithography

This work focuses on the orthogonal substrate functionalization by using parallel, additive contact lithography. Orthogonal functionalization of substrates patterned by capillary stamping may yield functional hybrid layers, in which the properties of the stamped pattern and the second component can be coupled. The coupling of functional films can lead to both additive and synergistic effects, allowing the properties of the hybrid film to be targeted for specific applications. Three different examples were investigated for this purpose. Lithiumniobate (LiNbO3), nickel ferrite (Ni2Fe4O4), and poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate) (PFcMA) were each stamped and orthogonally functionalized with various components. While the stamping of LiNbO3 on previously developed stamping techniques, the other two examples involve new developed stamping techniques such as solvothermal stamping and stamping from polymer melts. Microstructured LiNbO3 holey films were generated by direct stamping with a polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) stamp an aqueous solution of lithium acetate (C2H3LiO2) and niobium oxalate hydrate (C10H5NbO2 • 6 (H2O)). Calcination of the stamped precursor film on ITO resulted in pure LiNbO3 without any impurities. Orthogonal modification of the LiNbO3-film with gold nanoparticles via electrodeposition at the positions of the macropores increased the intensity of the second harmonic output by a factor of 5.4. Capillary imprinting with DNHG-derived aerogel stamps combined with a solvothermal synthesis based on ethanol solutions of iron(III) acetylacetonate (Fe(C5H7O2)3) and nickel(II) acetylacetonate (C10H14NiO4) yielded submicron arrays of nickel ferrite dots on indium tin oxide (ITO) substrates. Then, the ITO substrates functionalized with ordered monolayers of submicron nickel ferrite dots were further orthogonally functionalized with metallic nickel by electrodeposition. The submicron nickel ferrite dots reduced the remanence of the ferromagnetic nickel film by half, while the saturation value of the magnetic moment per area remained largely constant. Furthermore, hybrid stamps made of Ni/MnO2 were generated for capillary microstamping of the stimuli-responsive ferrocene-containing polymer (PFcMA) blended with multiwalled carbon nanotubes (CNTs) from the melt. Electrochemical WCA switching reversibly transformed the PFcMA-CNT hybrid microdots from a high-WCA state, in which the PFcMA is reduced, to a low-WCA state, in which the PFcMA is oxidized (the ferrocene units are positively charged), and vice versa. Orthogonal substrate functionalization of the areas around the PFcMA-CNT hybrid microdots shifted the WCA switching range by nearly 50°

Intercalation-free, fast switching of mesoporous antimony doped tin oxide with cathodically coloring electrochromic dyes

Mesoporous nanoparticle layers of transparent conductive oxides (TCOs) with anchored organic dyes are of great interest for electrochromic applications. Herein, we prepared mesoporous layers of antimony doped tin oxide (ATO) consisting of only 5 nm large particles with a low Sb concentration (2% antimony). The particles were prepared via a modified synthesis procedure based on hexahydroxostannate and pure Sb(V) hexahydroxoantimonate(V). We show that the ATO layers benefit from using a non-intercalating electrolyte such as tetrabutylammonium perchlorate (TBAP) compared to lithium perchlorate. Especially in the negative potential range, negative side effects, such as degradation due to lithium intercalation, are reduced. Furthermore, comparing the behavior of particles with varying antimony doping concentrations showed that the particles doped with 2% Sb are most suitable with respect to their conductivity and transparency. When modified with an electrochromic dye (viologen), the hybrid electrodes allow fully reversible (de)coloration with the non-intercalating electrolyte. Similar viologen/TiO2 electrodes on the other hand show severely restricted performance with the non-intercalating electrolyte as the oxidation of the dye is partially inhibited. Finally, we built a full electrochromic device composed of two ATO electrodes, each bearing a different electrochromic dye with TBAP as the electrolyte. Despite the dense morphology of the layers due to the small particle size as well as the large size of the electrolyte cation, the device displays remarkable switching times below 0.5 s

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO3(001)

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich CoxFe3−xO4 films with different stoichiometry (x=1.1 and x=1.4) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/Fe3O4 bilayers deposited before on Nb-doped SrTiO3(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of Co3+ cations in the low-spin state on octahedral sites for the Co1.4Fe1.6O4 film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO3(001)

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich CoxFe3−xO4 films with different stoichiometry (x=1.1 and x=1.4) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/Fe3O4 bilayers deposited before on Nb-doped SrTiO3(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of Co3+ cations in the low-spin state on octahedral sites for the Co1.4Fe1.6O4 film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO3_{3}(001)

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich Co$_x$Fe$_{3−x}$O$_4$ films with different stoichiometry (x=1.1 and x=1.4) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/Fe$_3$O$_4$ bilayers deposited before on Nb-doped SrTiO$_3$(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of Co$^{3+}$ cations in the low-spin state on octahedral sites for the Co$_{1.4}$Fe$_{1.6}$O$_4$ film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements

Reactive Additive Capillary Stamping with Double Network Hydrogel-Derived Aerogel Stamps under Solvothermal Conditions

Integration of solvothermal reaction products into complex thin-layer architectures is frequently achieved by combinations of layer transfer and subtractive lithography, whereas direct additive substrate patterning with solvothermal reaction products has remained challenging. We report reactive additive capillary stamping under solvothermal conditions as a parallel contact-lithographic access to patterns of solvothermal reaction products in thin-layer configurations. To this end, corresponding precursor inks are infiltrated into mechanically robust mesoporous aerogel stamps derived from double-network hydrogels. The stamp is then brought into contact with a substrate to be patterned under solvothermal reaction conditions inside an autoclave. The precursor ink forms liquid bridges between the topographic surface pattern of the stamp and the substrate. Evaporation-driven enrichment of the precursors in these liquid bridges, along with their liquid-bridge-guided conversion into the solvothermal reaction products, yields large-area submicron patterns of the solvothermal reaction products replicating the stamp topography. For example, we prepared thin hybrid films, which contained ordered monolayers of superparamagnetic submicron nickel ferrite dots prepared by solvothermal capillary stamping surrounded by nickel electrodeposited in a second orthogonal substrate functionalization step. The submicron nickel ferrite dots acted as a magnetic hardener, halving the remanence of the ferromagnetic nickel layer. In this way, thin-layer electromechanical systems, transformers, and positioning systems may be customized