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Polycrystalline thin films and single crystals of hybrid perovskites – a material group successfully used for photovoltaic and optoelectronic applications – reportedly display heterogeneous charge carrier dynamics often attributed to grain boundaries or crystalline strain. Here, we locally resolved the carrier diffusion in large, isolated methylammonium lead iodide (MAPbI3) grains via spatial- and time-resolved photoluminescence microscopy. We found that the anisotropic carrier dynamics directly correlate with the arrangement of ferroelastic twin domains. Comparing diffusion constants parallel and perpendicular to the domains showed carriers diffuse around 50–60% faster along the parallel direction. Extensive piezoresponse force microscopy experiments on the nature of the domain pattern suggest that the diffusion anisotropy most likely originates from structural and electrical anomalies at ferroelastic domain walls. We believe that the domain walls act as shallow energetic barriers, which delay the transversal diffusion of carriers. Furthermore, we demonstrate a rearrangement of the domains via heat treatment above the cubic-tetragnal phase transition. Together with the previously reported strain engineering via external stress, our findings promise additional routes to tailor the directionality of the charge carrier diffusion in MAPbI3-based photovoltaics and optoelectronics as well as other ferroelastic materials for optoelectronic applications.

In applications superhydrophobic surfaces are often irregular and nanostructured. On such a surface, it has been found that only a part of the surface is homogeneously wetted, i.e. wetting and slippage corresponding to that of a regularly structured surface. On the remaining part, large air inclusions occurred that possess a comparatively large slip length. In order to measure the velocity profile at distances below 1\textmu{}m close to the surface, an enhanced evaluation method for fluorescence correlation spectroscopy is developed in this work.

The removal of hydrophobic polymer coatings from artistic surfaces is a ubiquitous challenge in art restoration. Over the years, nanostructured fluids (NSFs), aqueous surfactant solutions containing a good solvent for the polymer, have been successfully applied in polymer removal interventions; however, the precise role of the surfactant in promoting polymer film dewetting is not fully understood. This contribution addresses the interaction of a NSF of water/propylene carbonate containing a nonionic surfactant with an acrylic polymer film commonly used in art conservation. Combining confocal microscopy and fluorescence correlation spectroscopy, we monitored the penetration of the fluid into the polymer film, defining its compositional changes and following the polymer swelling. The ensemble of results highlights that the surfactant role is twofold: (i) at the polymer-support interface, it promotes the detachment of the polymer film from the underlying support; (ii) inside the polymer film, it accelerates polymer swelling by increasing the chains' mobility.

Giant unilamellar vesicles (GUVs) are model membrane systems consisting of a single lipid bilayer separating an inner lumen from the outer solution, with dimensions comparable to that of eukaryotic cells. The importance of these biomimetic systems has recently grown with the development of easy and safe methods to assemble GUVs from complex biorelevant compositions. However, size and position control is still a key challenge for GUV formation and manipulation. Here, a gel-assisted formation method is introduced, able to produce arrays of giant unilamellar anchored vesicles (GUAVs) with a predetermined narrow size distribution. The approach based on micropatterned gel substrates of cross-linked poly(N-isopropylacrylamide) allows performing parallel measurements on thousands of immobile unilamellar vesicles. Such power and flexibility will respond to the growing need for developing platforms of biomimetic constructs from cell-sized single bilayers.

In this work, we present a method to pattern liquid crystal elastomers (LCEs) in the micrometer range without using any mechanical processing steps to prepare micron sized LCE actuators compatible with microelectromechanical system (MEMS) technology. Multi-layer spin-coating processes are developed to synthesise and structure 300–3500 nm thick LCE films. A water soluble sacrificial layer, a photoalignment layer and a LCE formulation, which is polymerised and crosslinked in its liquid crystal phase, are spin-coated successively onto a substrate. A fluorinated photoresist layer is used to structure LCE films with thicknesses up to 700 nm in a photolithographic and etching process. For thicker LCE films a hard mask process, using hydrogen silsesquioxane (HSQ) as hard mask, is used. Film thicknesses and homogeneities are analysed with profilometry. Actuation motions of LCE layers are investigated before and after patterning and LCE patterns are investigated via (polarised optical) microscopy (POM), scanning electron microscopy (SEM) and profilometry. A resolution of 1.5–2.0 microns is achieved with the described techniques, which make deformable micron sized LCE actuators of variable shape and director orientation accessible. The presented results demonstrate the potential of LCEs in MEMS devices.

Nanocomposites of polystyrene-block-polyisoprene-block-polystyrene triblock copolymer (SIS) and various types of neat and polystyrene-modified carbon nanotubes (CNT-PS) were prepared and distribution of the CNT-PS throughout the polymer matrix was evaluated using confocal laser scanning microscopy (CLSM). The Nanoamor MWCNT-PS with highest thickness of 25–60 nm were readily visualized using both reflection mode without necessity of fluorescent labelling and fluorescent mode after addition of free dye to the nanocomposite. Visualization of Nanocyl MWCNT-PS with thickness of 8–18 nm and SWCNT-PS was achieved after covalent labelling of the CNT-PS with benzothioxanthene fluorescent dye. The CLSM can serve as a non-invasive method for evaluation of quality of dispersion of nanofillers on quite large area and at various depth of polymer film.

The size control of nanomedicines for tumor diagnosis and therapy is of high importance, since it enables or disables deep and sufficient tumor penetration. Amphiphilic star-shaped block copolypept(o)ides offer substantial promise to precisely adjust the hydrophobic core and the hydrophilic corona, independent of each other, and therefore simultaneously control the size dimension in the interesting size range from 10 to 30 nm. To gain access to core-shell structures of such sizes, 3-arm and 6-arm PeptoStars, based on poly(gamma-tert-butyloxycarbonyl-L-glutamate)-b-polysarcosine (pGlu(OtBu)-b-pSar), were prepared via controlled living ring-opening polymerization (ROP) of the corresponding N-carboxyanhydrides. Moreover, size exclusion chromatography (SEC) proves the presence of well-defined star shaped polymers with molecular weights from 38 to 88 kg/mol with low polymer dispersities of 1.16 to 1.23. By varying the alpha-helical peptide core and maintain a constant polysarcosine corona, hydrodynamic size analyses revealed the importance of using a sufficiently large and dense hydrophilic shielding corona to prevent aggregation of the hydrophobic core and obtain uniform-sized spherical-shaped particles with hydrodynamic diameters below 24 nm. Fluorescence correlation spectroscopy (FCS) additionally demonstrates the absence of protein adsorption in human plasma for 6-arm polypept(o)ide stars and thus confirms polysarcosine as stealthlike material.

Controlling the organization of particles at liquid–gas interfaces usually relies on multiphasic preparations and external applied forces. Here, we show that micromolar amounts of a conventional cationic surfactant induce, in a single step, both adsorption and crystallization of various types of nanometer- to micrometer-sized anionic particles at the air–water interface, without any additional phase involved or external forces other than gravity. Contrary to conventional surfactant-induced particle adsorption through neutralization and hydrophobization at a surfactant concentration close to the critical micellar concentration (CMC), we show that in our explored concentration regime (CMC/1000-CMC/100), particles adsorb with a low contact angle and maintain most of their charge, leading to the formation of two-dimensional assemblies with different structures, depending on surfactant (Cs) and particle (Cp) concentrations. At low Cs and Cp, particles are repulsive and form disordered assemblies. Increasing Cp...

Mesoporous silica coated upconverting nanoparticles are loaded with the anticancer drug doxorubicin and grafted with ruthenium complexes as photoactive molecular valves. Drug release was triggered by 974 nm light with 0.35 W cm(-2). Such low light intensity minimized overheating problems and prevented photodamage to biological samples.

International audience; It was recently suggested that the electrostatic double-layer force between colloidal particles might weaken at high hydrostatic pressure encountered, for example, in deep seas or during oil recovery. We have addressed this issue by means of a specially designed optical trapping setup that allowed us to explore the interaction of a micrometer-sized glass bead and a solid glass wall in water at hydrostatic pressures of up to 1 kbar. The setup allowed us to measure the distance between bead and wall with a subnanometer resolution. We have determined the Debye lengths in water for salt concentrations of 0.1 and 1 mM. We found that in the pressure range from 1 bar to 1 kbar the maximum variation of the Debye lengths was

Results of Pressure-Volume-Temperature measurement on Poly(methyl methacrylate) : Lead Titanate, PMMA : PbTiO3, composite system in the pressure and temperature range 0–200 MPa and 300–473 K, respectively, are presented. The thermal expansion coefficient in PMMA : PbTiO3 composite is expected to be quite complex because the polymer has positive thermal expansion coefficient, whereas the filler has a negative thermal expansion coefficient. In this present article, the effect of pressure on the volumetric thermal expansion coefficient in PMMA : PbTiO3 composite system is presented. It is shown that thermal expansion coefficient of the polymer can be tailored by adding filler which has negative thermal expansion coefficient. Theoretically, a simple additive rule is formulated which can predict the variation of expansion coefficient in the PMMA : PbTiO3 composite system. The limitation of the additive rule is also discussed. It is also shown that the glass transition temperature depends on filler concentration and also has strong pressure dependence. The reasons for large pressure dependence are discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Two cyanate ester monomers (CEMs) based on oligomeric aryl ether (OAE) derivatives of bisphenol AF and bisphenol A, with multiple reactive cyanate groups, were developed as technologically highly relevant thermosets. These CEMs are liquids processable at room temperature and can be crosslinked by cyclotrimerization of the cyanate groups to form extended polycyanurate (PC) networks at lower temperatures ( 2808C), with excellent thermal, mechanical, and dielectric properties. PC nanorods with diameters of 65 or 380 nm could be moulded in porous alumina templates from the OAE-CEMs. The high aspect ratio nanorods with a length in the order of 100 mm were hydrolytically stable upon extended exposure to boiling water.

Well-defined statistical, gradient and block copolymers consisting of isobornyl acrylate (IBA) and n-butyl acrylate (nBA) were synthesized via atom transfer radical polymerization (ATRP). To investigate structure–property correlation, copolymers were prepared with systematically varied molecular weights and compositions. Thermomechanical properties of synthesized materials were analyzed via differential scanning calorimetry (DSC), dynamic mechanical analyses (DMA) and small-angle X-ray scattering (SAXS). Glass transition temperature (Tg) of the resulting statistical poly(isobornyl acrylate-co-n-butyl acrylate) (P(IBA-co-nBA)) copolymers was tuned by changing the monomer feed. This way, it was possible to generate materials which can mimic thermal behavior of several homopolymers, such as poly(t-butyl acrylate) (PtBA), poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA) and poly(n-propyl acrylate) (PPA). Although statistical copolymers had the same thermal properties as their homopolymer equivalents, DMA measurements revealed that they are much softer materials. While statistical copolymers showed a single Tg, block copolymers showed two Tgs and DSC thermogram for the gradient copolymer indicated a single, but very broad, glass transition. The mechanical properties of block and gradient copolymers were compared to the statistical copolymers with the same IBA/nBA composition.

Large positive thermal expansion in polymers is one of the major drawbacks in using polymers in applications where the sample dimensions play an important role. In this paper, we report a method to vary the thermal expansion of PMMA-based polymer composites by blending with a negative thermal expansion material, PbTiO 3 . It is shown that the thermal expansion coefficient of the composite can be tailored by suitably adjusting the ratio of polymer and ceramic filler. The coefficient of thermal expansion has been measured using temperature-dependent step-height measurements via confocal microscopy. Using SEM, it is shown that the ceramic particles are homogeneously dispersed in the polymer matrix if the composite is obtained by the polymerization of the suspension of PbTiO 3 in the monomer MMA. Composite formation is confirmed using XRD and Raman spectroscopy. To estimate the technological viability of such composite films, preliminary results of stress-strain measurements are also presented.

This paper discusses static and dynamic mechanical properties of electron beam-cured mixtures made of the nematic liquid crystal (LC) E7 and either tripropyleneglycol diacrylate (TPGDA) or propoxylated glycerol triacrylate (GPTA) as monomers differing essentially by their functionnality. Dilution of the initial mixture with LC leads to a significant weakening of the film mechanical strength. Strong effects were found on Young modulus and rubbery state modulus. As the concentration of LC increases, these mechanical parameters drop significantly together with the glass transition temperature of the polymer showing a plasticizing effect. The results for the glass transition temperatures for the polymer and the LC were confirmed by thermograms obtained by differential scanning calorimetry.

This paper reports a study of static and dynamic mechanical properties of electron beam (EB) cured polymer dispersed liquid crystals. These systems consist of micron-sized droplets dispersed in a solid polymer matrix. They are prepared according to the polymerization induced phase separation process initiated by exposure to electron radiation. A difunctional monomer Tripropylene Glycol Diacrylate in short TPGDA is used with the eutectic liquid crystal mixture E7 having a nematic to isotropic transition temperature at 60°C. Strong effects are found on Young modulus and rubbery state modulus in terms of the EB dose and the liquid crystal concentration. As the concentration of small molecules increases, these mechanical parameters drop significantly together with the glass transition temperature Tg of the polymer showing a plasticizing effect. The results for Tg are confirmed by DSC thermograms in terms of liquid crystal concentration and EB dose.

A static light scattering study of monomeric (uncured) and Electron Beam (EB) cured Tripropyleneglycoldiacrylate (TPGDA) and E7 (a nematic Liquid Crystal) systems is reported. This study includes a detailed investigation of the structural properties in terms of temperature, composition and scattering angle. Knowledge of the phase diagrams helps us to achieve a better understanding of the scattering curves and rationalize data in terms of the LC configuration inside droplets. The depolarized component of the scattered intensity measured under cross polarizers exhibits patterns reminiscent of anisotropic objects. The results can be correlated to the electro-optical responses of the investigated systems relevant to applications in display technology and smart windows.

The phase separation of the polymer blend polystyrene/poly(methyl phenyl siloxane) (PS/PMPS) is studied in situ by laser scanning confocal microscopy (LSCM) and by fluorescence correlation spectroscopy (FCS) at macroscopic and microscopic length scales, respectively. It is shown for the first time that FCS when combined with LSCM can provide independent information on the local concentration within the phase-separated domains as well as the interfacial width.

We present a new method for three-dimensional imaging of the inversed ferroelectric domains hidden inside nonlinear photonic structures. The method is based on Cerenkov-type second harmonic generation laser scanning microscopy and offers sub-micrometer resolution.

Sessile liquid drops are predicted to deform an elastic surface onto which they are placed because of the combined action of the liquid surface tension at the periphery of the drop and the capillary pressure inside the drop. Here, we show for the first time the in situ experimental confirmation of the effect of capillary pressure on this deformation. We demonstrate micrometer-scale deformations made possible by using a low Young's modulus material as an elastic surface. The experimental profiles of the deformed surfaces fit well the theoretical predictions for surfaces with a Young's modulus between 25 and 340 kPa.

We report the results of direct measurements of velocity profiles in a microchannel with hydrophobic and hydrophilic walls, using a new high-precision method of double-focus spatial fluorescence cross correlation under a confocal microscope. In the vicinity of both walls the measured velocity profiles do not go to zero by supplying a plateau of constant velocity. This apparent slip is proven to be due to a Taylor dispersion, an augmentation by shear diffusion of nanotracers in the direction of flow. Comparing the velocity profiles near the hydrophobic and hydrophilic walls for various conditions shows that there is a true slip length due to hydrophobicity. This length, of the order of several tens of nanometers, is independent of the electrolyte concentration and shear rate.

The dynamics of the amphiphilic semifluorinated F(CF2)(12)(CH2)(12)H (F12H12) alkane that undergoes two condensed phase transitions have been investigated by Brillouin light spectroscopy, shear rheometry, small(SAXS) and wide-angle (WAXS) X-ray scattering, and thermodynamic PVT measurements. The solid (I)-solid (II) transition (T,) is marked by a stronger temperature dependence of the sound velocity in phase II and by a 2 orders of magnitude drop of the shear modulus. Between the T, and the melting transition (T-m), the presence of two phonons implies a coexistence of solid (II) and amorphous (liquid) regions in the submicrometer range at thermal equilibrium as revealed by the SAXS pattern of a single reflection superimposed on a very broad amorphous halo. This intriguing finding of a transient, very slow (over 10 h) solid/liquid coexistence within phase II is rationalized by a two-stage mechanism for melting of the smectic phase (II) of F12H12. A refinement of the known packing motifs for the two solid-state structures is proposed. Journal of Physical Chemistry B

An apparatus for dynamical mechanic measurements was modified in order to allow broadband dielectric spectroscopy measurements (10 mHz to 10 MHz) on systems under shear stress. Shear oscillatory deformation was applied to different systems under conditions of controlled deformation amplitude, choosing different shear frequencies and amplitudes, including the range of the non-linear viscoelastic response. The plate-plate geometry was used, with the two metallic sample holders serving both as mechanical tools and as electrodes of a capacitor. The rheo-dielectric technique was used to study the effect of oscillatory shear on two classes of systems: nematic liquid crystals and polymeric melts. (c) 2007 Published by Elsevier B.V.

We present an experimental approach to flow profiling within femtoliter sample volumes, which allows the high-precision measurements at the solid interface. The method is based on the spatial cross-correlation of the fluorescence response from labeled tracer particles (latex nanospheres or single dye molecules). Two excitation volumes, separated by a few micrometers, are created by two laser foci under a confocal microscope. The velocity of tracer particles is measured in a channel about 100 microm wide within a typical accuracy of 0.1%, and the positions of the walls are estimated independently of any hydrodynamic data. The underlying theory for the optical method is given for an arbitrary velocity profile, explicitly presenting the numerical convolutions necessary for a quantitative analysis. It is illustrated by using the Poiseuille flow of a Newtonian liquid with slip as an example. Our analysis yields a large apparent fluid velocity at the wall, which is mostly due to the impact of the colloidal (electrostatic) forces. This colloidal lift is crucially important in accelerating the transport processes of molecules and nanoparticles in microfluidic devices.

We use a multiwell micromechanical cantilever sensor (MCS) device to measure surface stress changes induced by specific adsorption of molecules. A multiplexed assay format facilitates the monitoring of the bending of 16 MCSs in parallel. The 16 MCSs are grouped within four separate wells. Each well can be addressed independently by different analyte liquids. This enables functionalization of MCS separately by flowing different solutions through each well. In addition, each well contains a fixed reference mirror which allows measuring the absolute bending of MCS. In addition, the mirror can be used to follow refractive index changes upon mixing of different solutions. The effect of the flow rate on the MCS bending change was found to be dependent on the absolute bending value of MCS. Experiments and finite element simulations of solution exchange in wells were performed. Both revealed that one solution can be exchanged by another one after 200 microl volume has flown through. Using this device, the adsorption of thiolated DNA molecules and 6-mercapto-1-hexanol on gold surfaces was performed to test the nanomechanical response of MCS.

In order to study the failure mechanism of micron sized particles, ruby (α‐Al2O3:Cr3+) spheres of R=75μm radius were compressed between two sapphire (α‐Al2O3) plates. A confocal microscope was used to measure the local spectral shifts of the luminescence lines in the ruby sphere while slowly increasing the load up to failure at 6–7N. From the spectral shifts the local stress was calculated. The results show a steplike decrease of stress starting at a load of 4.3–4.7N. We interpret this as the formation of microcracks, which lead to a relaxation of stress. In the vicinity of the contact area luminescence spectra with multiple distinct peaks were observed. This indicates the presence of regions of homogeneous stress, which are mechanically decoupled and which are even smaller than the observation volume of ≈(2μm)3.

We report of a method for fabricating two-dimensional, regular arrays of polymer microlenses with focal lengths variable between 0.2 and 4.5 mm. We first make concave microlenses by ink-jetting solvent on a polymer substrate with a commercial drop-on-demand device. Solvent evaporation restructures the surface by a series of combined effects, which are discussed. In the second step we obtain convex elastomeric microlenses by casting the template made in the first step. We demonstrate the good optical quality of the microlenses by characterising their surfaces with atomic force microscopy and white light interferometry, and by directly measuring their focal lengths with ad-hoc confocal laser scanning microscopy. (C) 2007 Optical Society of America.

We present a new method to study flow of liquids near solid surface: Total internal reflection fluorescence cross-correlation spectroscopy (TIR-FCCS). Fluorescent tracers flowing with the liquid are excited by evanescent light, produced by epi-illumination through the periphery of a high numerical aperture oil-immersion objective. The time-resolved fluorescence intensity signals from two laterally shifted observation volumes, created by two confocal pinholes are independently measured. The cross-correlation of these signals provides information of the tracers' velocities. By changing the evanescent wave penetration depth, flow profiling at distances less than 200 nm from the interface can be performed. Due to the high sensitivity of the method fluorescent species with different size, down to single dye molecules can be used as tracers. We applied this method to study the flow of aqueous electrolyte solutions near a smooth hydrophilic surface and explored the effect of several important parameters, e.g. tracer size, ionic strength, and distance between the observation volumes.