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The development of nanoscale composites with hierarchical architecture and complex anisotropies enables the fabrication of new classes of devices. Stretchable strain sensors have been developed in the past for applications in various fields such as wearable electronics and soft robotics, yet the sensing capacities of most of these sensors are independent of the direction of deformation. In the present work, we report on the preparation of a direction-sensitive strain sensor using the anisotropic optical properties of a monolayer of oriented plasmonic 1D nano-objects. Grazing incidence spraying (GIS) is used for depositing a monolayer of in-plane aligned silver nanowires with a controlled density on a deformable and transparent substrate. Using the selective excitation of transverse and longitudinal localized plasmon resonance modes of silver nanowires by polarized UV-visible-NIR spectroscopy, we show that the macroscopic anisotropic properties of the monolayer upon stretching are highly dependent on the stretching direction and light polarization. Measuring the polarized optical properties of the anisotropic thin films upon stretching thus allow for retrieving both the local strain and the direction of the deformation using a simple model.

Gold nanoparticles decorated with analyte recognition units can form the basis of colorimetric (bio)sensors. The presentation of those recognition units may play a critical role in determining sensor sensitivity. Herein, we use a model system to investigate the effect of the architecture of a polymeric linker that connects gold nanoparticles with the recognition units. Our results show that the number of the latter that can be adsorbed during the assembly of the colorimetric sensors depends on the linker topology. We also show that this may lead to substantial differences in colorimetric sensor performance, particularly in situations in which the interactions with the analyte are comparably weak. Finally, we discuss design principles for efficient colorimetric sensor materials based on our findings.

Polymer brushes, consisting of densely end-tethered polymers to a surface, can exhibit rapid and sharp conformational transitions due to specific stimuli, which offer intriguing possibilities for surface-based sensing of the stimuli. The key toward unlocking these possibilities is the development of methods to readily transduce signals from polymer conformational changes. Herein, we report on single-fluorophore integrated ultrathin (40 nm) polymer brush surfaces that exhibit changing fluorescence properties based on polymer conformation. The basis of our methods is the change in occupied volume as the polymer brush undergoes a collapse transition, which enhances the effective concentration and aggregation of the integrated fluorophores, leading to a self-quenching of the fluorophores' fluorescence and thereby reduced fluorescence lifetimes. By using fluorescence lifetime imaging microscopy, we reveal spatial details on polymer brush conformational transitions across complex interfaces, including at the air-water-solid interface and at the interface of immiscible liquids that solvate the surface. Furthermore, our method identifies the swelling of polymer brushes from outside of a direct droplet (

Functional elastomers with incredible toughness and stretchability are indispensable for applications in soft robotics and wearable electronics. Furthermore, coupled with excellent electrical and thermal properties, these materials are at the forefront of recent efforts toward widespread use in cutting-edge electronics and devices. Herein, we introduce a highly deformable eutectic-GaIn liquid metal alloy-embedded natural rubber (NR) architecture employing, for the first time, industrially viable solid-state mixing and vulcanization. Standard methods of rubber processing and vulcanization allow us to fragment and disperse liquid metals into submicron-sized droplets in cross-linked NR without compromising the elastic properties of the base matrix. In addition to substantial boosts in mechanical (strain at failure of up to ∼650%) and elastic (negligible hysteresis loss) performances, the tearing energy of the composite was enhanced up to 6 times, and a fourfold reduction in the crack growth rate was achieved over a control vulcanizate. Moreover, we demonstrate improved thermal conductivity and dielectric properties for the resulting composites. Therefore, this work provides a facile and scalable pathway to develop liquid metal-embedded soft elastomeric composites that could be instrumental toward potential applications in soft-matter engineering.

We report on the surprising observation of a unique perforated lamellar (PL) morphology in a mixture of an asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer and CdSe–Cd...

Electrofluorochromic (EFC) materials have gained extensive attention owing to their interesting modulations of fluorescence by an electric stimulus. However, the limited performances, especially th...

A scalable method for the assembly of oriented bacterial cellulose (BC) films is presented based on using wrinkled thin silicone substrates of meter-square size as templates during biotechnological...

The design of colloidal nanostructures as surface-enhanced Raman scattering (SERS) substrates requires control over both structural and optical characteristics. A widespread expectation is that the SERS efficiency depends crucially on whether the plasmonic excitation matches the exciting laser wavelength. However, also the balance between radiative (scattering) and non-radiative (absorbing) properties plays a major role, regarding both the efficiency of near field enhancement and the experimentally observed signal intensity. We present a study of the influence of mode-excitation matching and extinction characteristics for core/satellite superstructures, comprising gold nanotriangles decorated with small gold nanospheres. The variation of the core size and aspect ratio allowed tuning the main coupled mode between 700 and 800 nm, from off-resonant through resonant at 785 nm, as well as tuning extinction contributions, from dominantly absorbing to dominantly scattering. We observed additional gains of 1-2 orders of magnitude in signal enhancement, which were correlated to core size and diffuse optical properties. Our findings indicate a competition between SERS enhancement and increased scattering losses in larger assemblies. Thus, a balance of optical parameters is required for efficient SERS and the development of assemblies as advanced sensing devices.

Cononsolvency occurs if a mixture of two good solvents causes the collapse or demixing of polymers into a polymer-rich phase in a certain range of compositions of these two solvents. The better sol...

Because of its multiresponsive behavior upon variation of pH value, temperature, and ionic strength, poly­(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) is an attractive candidate for adaptive surface coatings, especially in the field of biomedical sensors. In the presented article, PDMAEMA Guiselin brushes (5–12 nm, dry thickness) were prepared by the grafting-to approach, and the thermoresponsive UCST-type (upper critical solution temperature) behavior of the generated films, induced by [Fe­(CN)6]3–, was demonstrated for the first time. To clarify the specific mechanism of the temperature responsiveness, the molecular interactions between polymer chains and complex ions were studied by in situ infrared spectroscopy and in situ ellipsometry, showing wavenumber shifts of the ν­(CN) band due to ion pairing as well as changes of the ν­(OH) band intensity due to swelling. Conclusively, experimental data suggest that the electrostatic interaction between the two components plays a significant role in the thermoresponsive behavior of PDMAEMA films. Using this knowledge, the UCST of the PDMAEMA Guiselin brushes could be adjusted between 34.0 ± 1.2 °C at pH 8 and 40.7 ± 2.0 °C at pH 5.

We investigated the temperature-dependent optical response of ordered lattices of noninteracting gold-core/poly(N-isopropylacrylamide)-shell nanoparticles (NPs), a system with proven photothermal a...

β-Sheets in natural spider dragline silk proteins are typically formed by polyalanine (An) as well as alanine-glycine (AG) and GGA sequences flanking these An regions. The hydrophobic β-sheet-rich ...

Noble metal hydro- and aerogels exhibit a variety of unique properties, including large surface areas, ultralow densities, and high porosities. While their potential use in various applications ran...

Co-nonsolvency occurs if a mixture of two good solvents causes the collapse or demixing of polymers into a polymer-rich phase in a certain range of compositions of these two solvents. In this work, we systematically study the co-nonsolvency behavior of poly(N-isopropylacrylamide) brushes of different grafting densities in a series of alcohol–water binary mixtures with increasing hydrophobic parts ranging from methanol to 1-butanol by using ellipsometry. We report a strong collapse transition by increasing the alcohol concentration in the water-rich phase, which is enhanced for longer-chain alcohols. The analysis of the thermodynamic properties of the alcohol–water series displays that an increasing demixing tendency between alcohol and water is correlated with an enhancement of the collapse transition of the brush. The increase of grafting density weakens the transition behavior but does not shift the solvent composition point of maximum brush collapse, which is in agreement with the predictions of a rece...

A novel wet-chemical protocol is reported for the synthesis of “temperature-programmable” catalytic colloids consisting of bimetallic core@shell AuAg nanoparticles encapsulated into poly(N-isopropy...

We introduce a novel concept for mechanosensitive hydrogel microparticles, which translate deformation into changes in fluorescence and can thus function as mechanical probes. The hydrogel particles with controlled polymer network are produced via droplet microfluidics from poly(ethylene glycol) (PEG) precursors. Förster resonance energy transfer donors and acceptors are coupled to the PEG hydrogel network for reporting local deformations as fluorescence shifts. We show that global network deformations, which occur upon drying/rehydration, can be detected via a characteristic fluorescence shift. Combined characterization with confocal laser scanning microscopy and atomic force microscopy (AFM) shows that also local deformation of the particles can be detected. Using AFM, the mechanical properties of the particles can be quantified, which allows linking strain with stress and thus force sensing in a three-dimensional environment. Microfluidic material design allows for precisely varying the size of our hydrogel microparticles as well as their mechanical properties and polymer network structure with regard to the choice of the macromolecular precursors and their functionalization with fluorophores. Thus, concomitant changes in mechanical properties and mechanosensitivity qualify these hydrogel microparticles as an adjustable material platform for force sensing in structural mechanics or cell culturing.

Azobenzene-containing polymers (azopolymers) can serve as building blocks for an emerging class of soft photonics. Using their photoresponses for the micro/nanofabrication of smart surface is a key but still a challenging step. Here, we report a simple visible-light-illumination strategy to trigger diverse configurations of surface wrinkling on azopolymer-based film/substrate systems, which can be switched between flat and wrinkled states by controlling the intensity of the incident light. Different photoresponsive characteristics of azobenzene are involved in driving the wrinkling/dewrinkling switch. For the first time, we achieve the controlled wrinkling with an unexpected high aspect ratio and surprisingly polarization-independent ordered orientation by exploiting the unique photosoftening effect of azobenzene. Theoretical analysis reveals that an in situ photoinduced reversible soft/hard-contrast boundary determines the wrinkling orientation, which is used to fabricate diverse on-demand hierarchical wrinkles. These photoresponsive systems find broad photonic applications that are not easily accessible to other systems, e.g., optically reversible smart display, information security, and well-regulated optical devices.

We investigate the formation of chains of few plasmonic nanoparticles-so-called plasmonic oligomers-by strain-induced fragmentation of linear particle assemblies. Detailed investigations of the fragmentation process are conducted by in situ atomic force microscopy and UV-vis-NIR spectroscopy. Based on these experimental results and mechanical simulations computed by the lattice spring model, we propose a formation mechanism that explains the observed decrease of chain polydispersity upon increasing strain and provides experimental guidelines for tailoring chain length distribution. By evaluation of the strain-dependent optical properties, we find a reversible, nonlinear shift of the dominant plasmonic resonance. We could quantitatively explain this feature based on simulations using generalized multiparticle Mie theory (GMMT). Both optical and morphological characterization show that the unstrained sample is dominated by chains with a length above the so-called infinite chain limit-above which optical properties show no dependency on chain length-while during deformation, the average chain length decrease below this limit and chain length distribution becomes more narrow. Since the formation mechanism results in a well-defined, parallel orientation of the oligomers on macroscopic areas, the effect of finite chain length can be studied even using conventional UV-vis-NIR spectroscopy. The scalable fabrication of oriented, linear plasmonic oligomers opens up additional opportunities for strain-dependent optical devices and mechanoplasmonic sensing.

Cellulose nanocrystals (CNCs) are a particularly appealing format of the natural biopolymer due to their exceptional strength, nanoscale dimensions, and needle-like shape anisotropy. However, CNCs are hydrophilic and hence their wettability makes them impractical for many coating applications, with various approaches using chemical functionalization to overcome this. Here we show that CNC-coated surfaces can be rendered hydrophobic by alignment of the native CNCs using a wrinkled template-mediated printing process. We present a novel and simple method allowing full release of the CNCs from the template and their permanent adsorption into fine patterns onto the surface, thus preventing CNC repositioning during wetting. The aligned CNCs induce strong pinning effects that capture and retain water droplets with high contact angle and large roll-off angles, without becoming susceptible to oil contamination. The fabrication process for these coatings could be achieved by large-scale printing, making them a practical and cost-effective solution to hydrophobic coatings from raw cellulosic materials.

International audience; We investigate a morphological transition of surface-immobilized triblock terpolymer micelles: the splitting into well-defined clusters of satellite micelles upon pH changes. The multicompartment micelles are formed in aqueous solution of ABC triblock terpolymers consisting of a hydrophobic polybutadiene block, a weak polyanionic poly(methacrylic acid) block, and a weak polycationic poly(2-(dimethylamino)ethyl methacrylate) block. They are subsequently immobilized on silicon wafer surfaces by dip-coating. The splitting process is triggered by a pH change to strongly basic pH, which goes along with a charge reversal of the micelles. We find that the aggregation number of the submicelles is well-defined and that larger micelles have a tendency to split into a larger number of submicelles. Furthermore, there is a clear preference for clusters consisting of doublets and triplets of submicelles. The morphology of surface-immobilized clusters can be "quenched" by returning to the original pH. Thus, such well-defined micellar clusters can be stabilized and are available as colloidal building blocks for the formation of hierarchical surface structures. We discuss the underlying physicochemical principles of the splitting process considering changes in charge and total free energy of the micelles upon pH change. © 2016 American Chemical Society.

Cultivation of adherently growing cells in artificial environments is of utmost importance in medicine and biotechnology to accomplish in vitro drug screening or to investigate disease mechanisms. Precise cell manipulation, like localized control over adhesion, is required to expand cells, to establish cell models for novel therapies and to perform noninvasive cell experiments. To this end, we developed a method of gentle, local lift-off of mammalian cells using polymer surfaces, which are reversibly and repeatedly switchable between a cell-attractive and a cell-repellent state. This property was introduced through micropatterned thermoresponsive polymer coatings formed from colloidal microgels. Patterning was obtained through automated nanodispensing or microcontact printing, making use of unspecific electrostatic interactions between microgels and substrates. This process is much more robust against ambient conditions than covalent coupling, thus lending itself to up-scaling. As an example, wound healing assays were accomplished at 37 °C with highly increased precision in microfluidic environments.

In this work, we investigate the ligand exchange of cetyltrimethylammonium bromide (CTAB) with bovine serum albumin for gold nanorods. We demonstrate by surface-enhanced Raman scattering measurements that CTAB, which is used as a shape-directing agent in the particle synthesis, is completely removed from solution and particle surface. Thus, the protein-coated nanorods are suitable for bioapplications, where cationic surfactants must be avoided. At the same time, the colloidal stability of the system is significantly increased, as evidenced by spectroscopic investigation of the particle longitudinal surface plasmon resonance, which is sensitive to aggregation. Particles are stable at very high concentrations (cAu 20 mg/mL) in biological media such as phosphate buffer saline or Dulbecco’s Modified Eagle’s Medium and over a large pH range (2–12). Particles can even be freeze-dried (lyophilized) and redispersed. The protocol was applied to gold nanoparticles with a large range of aspect ratios and sizes with main absorption frequencies covering the visible and the near-IR spectral range from 600 to 1100 nm. Thus, these colloidally stable and surfactant-free protein-coated nanoparticles are of great interest for various plasmonic and biomedical applications., ACS Applied Materials & Interfaces, 7 (10), ISSN:1944-8244, ISSN:1944-8252

The selective cross-linking of individual domains in block copolymer bulk morphologies represents an elegant strategy to generate nanostructured materials of tunable size and geometry. We demonstrate the preparation of highly periodic nanoporous sheets and core–shell cylinders from a stimuli-responsive triblock terpolymer, polybutadiene-block-poly(tert-butyl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate) (PB-b-PtBMA-b-PDMAEMA). By blending the terpolymer with different types and amounts of homopolymers, a variety of bulk morphologies is accessible, including rarely found examples such as tetragonally perforated lamellae and double gyroid networks. Selective cross-linking of the PB domains of the generated morphologies followed by sonication-assisted dispersion allows the preparation of well-defined nanostructures in nonselective solvents. Because of the PDMAEMA corona, the cross-linked structures are soluble in aqueous media. The high regularity of the pore diameter in combination with a tu...

We present a versatile approach to produce macroscopic, substrate-supported arrays of plasmonic nanoparticles with well-defined interparticle spacing and a continuous particle size gradient. The arrays thus present a "plasmonic library" of locally noncoupling plasmonic particles of different sizes, which can serve as a platform for future combinatorial screening of size effects. The structures were prepared by substrate assembly of gold-core/poly(N-isopropylacrylamide)-shell particles and subsequent post-modification. Coupling of the localized surface plasmon resonance (LSPR) could be avoided since the polymer shell separates the encapsulated gold cores. To produce a particle array with a broad range of well-defined but laterally distinguishable particle sizes, the substrate was dip-coated in a growth solution, which resulted in an overgrowth of the gold cores controlled by the local exposure time. The kinetics was quantitatively analyzed and found to be diffusion rate controlled, allowing for precise tuning of particle size by adjusting the withdrawal speed. We determined the kinetics of the overgrowth process, investigated the LSPRs along the gradient by UV-vis extinction spectroscopy, and compared the spectroscopic results to the predictions from Mie theory, indicating the absence of local interparticle coupling. We finally discuss potential applications of these substrate-supported plasmonic particle libraries and perspectives toward extending the concept from size to composition variation and screening of plasmonic coupling effects.

We systematically investigated the structure formation pathways and transient morphologies involved in the formation of mesoporous membranes by the self-assembly of block copolymers during nonsolvent-induced phase separation. Using AFM, SEM, and in situ synchrotron SAXS, we mapped the topological paths and characteristic transient structures into a ternary phase diagram. We focused on the stability region of an ordered pore phase which is relevant for the generation of integral asymmetric isoporous membranes. We could identify several characteristic morphologies, i.e., spinodal networks, sphere percolation networks, ordered pore structures, and disordered and ordered cylinder arrangements together with transient structures connecting their stability regions. With given evaporation rates for the pure solvents, we calculated the corresponding composition trajectories in the phase diagram to identify suitable experimental conditions in terms of initial polymer volume fraction, solvent composition, and immers...

Due to capillarity, sessile droplets of identical liquids will instantaneously fuse when they come in contact at their three-phase lines. However, with drops of different, completely miscible liquids, instantaneous coalescence can be suppressed. Instead, the drops remain in a state of noncoalescence for some time, with the two drop bodies connected only by a thin neck. The reason for this noncoalescence is the surface tension difference, Δγ, between the liquids. If Δγ is sufficiently large, then it induces a sufficiently strong Marangoni flow, which keeps the main drop bodies temporarily separated. Studies with spreading drops have revealed that the boundary between instantaneous coalescence and noncoalescence is sharp (Karpitschka, S.; Riegler, H. J. Fluid. Mech. 2014, 743, R1). The boundary is a function of two parameters only: Δγ and Θ(a), the arithmetic mean of the contact angles in the moment of drop-drop contact. It appears plausible that surface forces (the disjoining pressure) could also influence the coalescence behavior. However, in experiments with spreading drops, surface forces always promote coalescence and their influence might be obscured. Therefore, we present here coalescence experiments with partially wetting liquids and compare the results to the spreading case. We adjust different equilibrium contact angles (i.e., different surface forces) with different substrate surface coatings. As for spreading drops, we observe a sharp boundary between regimes of coalescence and noncoalescence. The boundary follows the same power law relation for both partially and completely wetting cases. Therefore, we conclude that surface forces have no significant, explicit influence on the coalescence behavior of sessile drops from different miscible liquids.

The self-assembly of block copolymers in the presence of additives represents an elegant strategy to adjust micellar morphologies in solution and to design complex structures that are not accessible otherwise. Herein, we use linear ABC triblock terpolymers comprising a polyamine block: polybutadiene-block-poly(tert-butyl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate) (PB-b-PtBMA-b-PDMAEMA) terpolymers coassembled with organic di- or triacids in mixtures of THF and water. The interactions between the organic multiacids and the hydrophilic PDMAEMA block can be adjusted via the chain architecture, amount, and functionality of added acid, the solvent quality, and the PDMAEMA block length. Consequently, these parameters allow a certain level of control over the resulting micellar morphology. Characterization by (cryogenic) transmission electron microscopy and atomic force microscopy revealed the formation of spherical, disk-shaped, and toroidal structures, alongside ribbons featuring enlarged en...

This work presents the modification of polyorganosiloxane microparticles by surface-initiated thiol-ene photochemistry. By this photocoating, we prepared different core/shell particles with a polymeric shell within narrow size distributions (PDI = 0.041-0.12). As core particle, we used highly monodisperse spherical polyorganosiloxane particles prepared from (3-mercaptopropyl)trimethoxysilane (MPTMS) with a radius of 0.49 μm. We utilize the high surface coverage of mercaptopropyl functions to generate surface-localized radicals upon irradiation with UVA-light without additional photoinitiator. The continuous generation of radicals was followed by a dye degradation experiment (UV/vis spectroscopy). Surface-localized radicals were used as copolymer anchoring sites ("grafting-onto" deposition of different PB-b-PS diblock copolymers) and polymerization initiators ("grafting-from" polymerization of PS). Photocoated particles were characterized for their morphology (SEM, TEM), size, and size distribution (DLS). For PS-coated particles, the polymer content (up to 24% in 24 h) was controlled by the polymerization time upon UVA exposure. The coating thickness was evaluated by thermogravimetric analysis (TGA) using a simple analytical core/shell model. Raman spectroscopy was applied to directly follow the time-dependent consumption of thiols by photoinitiation.

Photoresponsive polymer brushes constitute an attractive platform for tuning surface properties and functionality. Since the degree of photoconversion can be controlled by the light dose, functional states with intermediate properties between those of the nonexposed and fully exposed brushes are accessible. Here we investigate the light-modulated interfacial, adhesion, and frictional properties of photosensitive polymer brushes with a methacrylate backbone and ionizable -COOH side groups modified with the photoremovable group 6-nitroveratryloxycarbonyl (NVOC). The original brush (PNVOCMA) gradually changes into a charged poly(methacrylic acid) (PMAA) brush upon exposure to ultraviolet light due to the photoremoval of the chromophore and generation of free COOH groups. We show how the physical properties of the brush can be gradually tuned with the exposure dose using condensation microscopy, atomic force microscopy (AFM), force mapping, and friction force spectroscopy.

While soft hydrogel nano- and microstructures hold great potential for therapeutic treatments and in vivo applications, their nanomechanical characterization remains a challenge. In this paper, soft, single-component, supported hydrogel films were fabricated using pendant-thiol-modified poly(methacrylic acid) (PMASH). The influence of hydrogel architecture on deformation properties was studied by fabricating films on particle supports and producing free-standing capsules. The influence of the degree of thiol-based cross-linking on the mechanical properties of the soft hydrogel systems (core-shell and capsules) was studied using a colloidal-probe (CP) AFM technique. It was found that film mechanical properties, stability, and capsule swelling could be finely tuned by controlling the extent of poly(methacrylic acid) thiol modification. Furthermore, switching the pH from 7.4 to 4.0 led to film densification due to increased hydrogen bonding. Hydrogel capsule systems were found to have stiffness values ranging from 0.9 to 16.9 mN m(-1) over a thiol modification range of 5 to 20 mol %. These values are significantly greater than those for previously reported PMASH planar films of 0.7-5.7 mN m(-1) over the same thiol modification range (Best et al., Soft Matter 2013, 9, 4580-4584). Films on particle substrates had comparable mechanical properties to planar films, demonstrating that while substrate geometry has a negligible effect, membrane and tension effects may play an important role in capsule force resistance. Further, when transitioning from solid-supported films to free-standing capsules, simple predictions of shell stiffness based on modulus changes found for supported films are not valid. Rather, additional effects like diameter increases (geometrical changes) as well as tension buildup need to be taken into account. These results are important for research related to the characterization of soft hydrogel materials and control over their mechanical properties.

Knowledge of the mechanical properties of singular clay lamellae is of crucial importance for the optimization of clay-polymer nanocomposites. On the basis of controlled stress release, singular 2:1 clay lamellae show regular wrinkles on a deformable substrate. A subsequent two-dimensional Fourier transformation gives an in-plane modulus of the clay lamella of approximately 150 GPa. Only readily-available topographical atomic force microscopy is required for analysis rendering that fast and facile procedure generally applicable for nanoplatelet characterization.

Transparency, flexibility, and especially ultralow oxygen (OTR) and water vapor (WVTR) transmission rates are the key issues to be addressed for packaging of flexible organic photovoltaics and organic light-emitting diodes. Concomitant optimization of all essential features is still a big challenge. Here we present a thin (1.5 μm), highly transparent, and at the same time flexible nanocomposite coating with an exceptionally low OTR and WVTR (1.0 × 10(-2) cm(3) m(-2) day(-1) bar(-1) and0.05 g m(-2) day(-1) at 50% RH, respectively). A commercially available polyurethane (Desmodur N 3600 and Desmophen 670 BA, Bayer MaterialScience AG) was filled with a delaminated synthetic layered silicate exhibiting huge aspect ratios of about 25,000. Functional films were prepared by simple doctor-blading a suspension of the matrix and the organophilized clay. This preparation procedure is technically benign, is easy to scale up, and may readily be applied for encapsulation of sensitive flexible electronics.

We report on the role of surface wettability during the printing transfer of nanoparticles from wrinkled surfaces onto flat substrates. As we demonstrate, this parameter dominates the transfer process. This effect can further be utilized to transfer colloidal particles in a structured fashion, if the substrates are patterned in wettability. The resulting colloidal arrangements are highly regular over macroscopic surface areas and display distinct pattern features in both the micrometer and nanoscale regime. We study the obtained structures and discuss the potential of this approach for creating hierarchical particle assemblies of high complexity. Our findings not only contribute to a better understanding of technologically relevant colloidal assembly processes, but also open new avenues for the realization of novel materials consisting of nanoparticles. In this regard, the presented structuring method is especially interesting for the design of optically functional surface coatings.

Crystal architectures delimited by sinuous boundaries and exhibiting complex hierarchical structures are a common product of natural biomineralization. However, related forms can also be generated in purely inorganic environments, as exemplified by the existence of so-called “silica-carbonate biomorphs”. These peculiar objects form upon coprecipitation of barium carbonate with silica and self-assemble into aggregates of highly oriented, uniform nanocrystals, displaying intricate noncrystallographic morphologies such as flat sheets and helicoidal filaments. While the driving force steering ordered mineralization on the nanoscale has recently been identified, the factors governing the development of curved forms on global scales are still inadequately understood. In the present work, we have investigated the circumstances that lead to the expression of smooth curvature in these systems and propose a scenario that may explain the observed morphologies. Detailed studies of the growth behavior show that morpho...

This work aims at establishing a link between process conditions and resulting micromechanical properties for aminoplast core/shell microcapsules. The investigated capsules were produced by the in situ polymerization of melamine formaldehyde resins, which represents a widely used and industrially relevant approach in the field of microencapsulation. Within our study, we present a quantitative morphological analysis of the capsules' size and shell thickness. The diameter of the investigated capsules ranged from 10 to 50 μm and the shell thickness was found in a range between 50 and 200 nm. As key parameter for the control of the shell thickness, we identified the amount of amino resin per total surface area of the dispersed phase. Mechanical properties were investigated using small deformations on the order of the shell thickness by atomic force microscopy with a colloidal probe setup. The obtained capsule stiffness increased with an increasing shell thickness from 2 to 30 N/m and thus showed the same trend on the process parameters as the shell thickness. A simple analytical model was adopted to explain the relation between capsules' geometry and mechanics and to estimate the elastic modulus of the shell about 1.7 GPa. Thus, this work provides strategies for a rational design of microcapsule mechanics.

Iodide ions have been used as an additive to fabricate homogeneous gold spheres with a la carte dimensions, ranging from the nano- (50 nm) to the microscale (ca. 1 μm). Due to the high uniformity and surface functionalization of the produced materials, they undergo spontaneous assembly into organized superlattices upon solvent drying. Thus, optical properties of the particles including localized surface plasmon resonances and surface enhanced Raman scattering (SERS) response, both in solution and organized into superlattices, are also reported. © 2012 American Chemical Society., This work was funded by the Spanish Ministerio de Ciencia e Innovacion (CTQ2011-23167) and by the German science foundation within SFB 840, TP B5.

In this paper, we report on the mechanical characterization of polyelectrolytes multilayer (PEM) films prepared from poly(glutamic acid)–poly(styrenesulfonate) (PGA–PSS) blends, deposited in alternated spray deposition with poly(allylamine hydrochloride) (PAH). The polyanion composition of the blended film was first investigated by Fourier transformed infrared spectroscopy in the attenuated total reflection mode. The monomer molar fraction of PGA in the film increases almost linearly with x, i.e., the monomer molar fraction of PGA in the sprayed polyanion solution. The mechanical properties of the blended (PAH/PGAx-PSS1-x)n film were measured using two methods: (i) the wrinkling metrology method and (ii) by colloidal probe atomic force microscopy. We demonstrate that Young's modulus of the PAH/PGAx-PSS1-x multilayer films can be systematically controlled by the chemical composition of these films, depending on x. Measurements indicate that increasing the monomer molar fraction of PGA in the blended film r...

The adhesion behavior between modified polysaccharide layers capable of forming host-guest complexes has been determined by direct force measurements with the atomic force microscope (AFM). Polysaccharides bearing either host or guest moieties were obtained by derivatization of chitosan with pendant β-cyclodextrin (CD) and adamantane (AD) moieties, respectively. These modified polysaccharides were covalently immobilized either to flat surfaces or to AFM-probes. The number of interacting polymer segments has been reduced significantly by covalently immobilizing chitosan to an AFM-tip with small radius and measuring the forces between the protruding polymer segments and a chitosan layer immobilized to a flat surface. By this approach, it was possible to determine the interaction between polymer layers on the level of single polymer strands. To separate contributions to the adhesion due to the formation of host-guest complexes from unspecific interactions, we performed measurements between various combinations of chitosan derivatives. With the same polymer probe of adamantane-modified chitosan, the interaction against a number of different chitosan layers has been determined, including ones that are not able to form host-guest complexes, such as unmodified chitosan or β-cyclodextrin modified chitosan, which has been blocked previously by addition of adamantane. The resulting adhesion behavior has been analyzed in terms of the total work of adhesion, the number of rupture events, and the corresponding lengths of the polymer segments as well as rupture forces. A clear difference has been found for systems where the formation of host-guest complexes is possible in comparison to the absence of specific multivalent interaction between the polysaccharide layers. In particular, the work of adhesion is increasing up to an order of magnitude upon the formation of host-guest complexes between the chitosan layers.

Polyelectrolyte multilayers were prepared by the layer-by-layer (LbL) technique from polyanions bearing aldehyde and polycations with 4-methylpyridinium moieties. The aldol reaction of these complementary reactive groups can be followed by the formation of fluorescent merocyanine dyes, resulting in cross-linked, ultrathin polymer films. The efficient stabilization of the polymer films allows for their intact removal from high surface energy supports, such as glass or surface oxidized silicon wafers, by simple treatment with salt solutions, yielding free-standing membranes. Increasing separation of the reactive polycation and polyanion layers with layers of inert polycation and polyanion analogues only gradually prevents the coupling reaction. From this dependence, polyions assembled in consecutive adsorption layers seem to be able to penetrate into as far as three neighboring layers.

We studied the swelling of polyelectrolyte (PE) multilayers (PEM) in water (H2O) vapors. The PEM were made from polyanion poly(styrene sulfonate) (PSS) and polycation poly(diallyldimethylammonium chloride)-N-methyl-N-vinylacetamide (pDADMAC-NMVA). While PSS is a fully charged polyanion, pDADMAC-NMVA is a random copolymer made of charged pDADMAC and uncharged NMVA monomer units. Variation of the relative amount of these two units allows for controlling the charge density of pDADMAC-NMVA. The degree of swelling was studied as it function of the relative humidity in the experimental chamber (respectively water concentration in the gas phase) for PEM prepared from PSS and pDADMAC-NMVA with their different charge densities - 100%, 89% and 75%. The films were prepared by means of spraying technique and consisted of six PE couples-PSS/pDADMAC-NMVA. Neutron reflectometry was applied as main tool to observe the swelling process. The technique allows to obtain in a single experiment information about film thickness and amount of water in the film. The experiments were complemented with AFM measurements to obtain the thickness of the films. It was found that the Film thickness increases when the charge density of the polycation decreases. The swelling of the PEM increases with the relative humidity and it depends on the charge density of pDADMAC-NMVA. The swelling behavior is 2-fold, splitting up in a charge dependent mode with relatively little volume increase, and a second mode With high volume expansion, which is independent from charge density of PEM. The "swelling transition" occurs for all samples at a relative humidity about 60% and a volume increase of ca. 20%. The results were interpreted according to the Flory-Huggins theory which assumes a phase separation in PEM network at higher water contents.

We report on large-scale fabrication of wrinkled polyelectrolyte multilayers (PEMs) with well-defined surface relief structures by embossing. The embossed assembly films show hierarchical topography consisting of patterns on the micrometer scale defined by the stamp used for embossing that are decorated by stable and highly regular patterns on the submicrometer scale. The periodicities of the concentric wrinkles can be controlled well down to 250 nm. We propose that a new mechanism of combining inelastic deformation of the support and selective wetting by the PEM film to be responsible for the above wrinkling with high stability in the wet state and enhanced aspect ratio.