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Liquid repellent layers can be fabricated by coating a fractal-like layer of candle soot particles with a silicon oxide layer, combusting the soot at 600 °C and subsequently silanizing with perfluoroalkylsilanes. Drops of different liquids deposited on these so called “superamphiphobic” layers easily roll off thanks to the low liquid-solid adhesion. The lower value of the surface tension of liquids that can be repelled depends on details of the processing. Here, we analyze the influence of the soot deposition duration and height with respect to the flame on the structure and wetting properties of the superamphiphobic layer. The mean diameter of the soot particles depends on the distance from the wick. Close to the wick, the average diameter of the particles varies between 30 and 50 nm as demonstrated by scanning electron microscopy (SEM). Close to the top of the flame, the particles size decreases to 10–20 nm. By measuring the mass of superamphiphobic layers and their thickness by laser scanning confocal microscopy (LSCM) in reflection mode, we could determine that the average porosity is 0.91. The height-dependent structural differences affect the apparent contact and roll-off angles. Lowest contact angles are measured when soot is deposited close to the wick due to wax that is not completely burnt, smearing out the required overhanging structures. The small particle size close to the top of the flame also reduces contact angles, again due to decreasing size of overhangs. Sooting in the middle of the flame led to optimal liquid repellency. Furthermore, for sooting times longer than 45 s the properties of the layer did not change with sooting time, verifying the self-similarity of the layer.

We report the use of Y3+-substituted TiO2 (0.5% Y-TiO2) in solid-state mesoscopic solar cells, consisting of CH3NH3PbI3 as the light harvester and spiro-OMeTAD as the hole transport material. A power conversion efficiency of 11.2% under simulated AM 1.5 full sun illumination was measured. A 15% improvement in the short-circuit current density was obtained compared with pure TiO2, due to the effect of Y3+ on the dimensions of perovskite nanoparticles formed on the semiconductor surface, showing that the surface modification of the semiconductor is an effective way to improve the light harvesters' morphology and electron transfer properties in the solid-state mesoscopic solar cells.

The Bjerrum length is approached in a low polarity solvent by encapsulating, both, a borate anion and a phosphonium cation in a rigid lipophilic dendrimer shell. In addition the cation size is varied by 34-fold. We thus obtain superweak ions with potential applications in catalytic processes.

One way of measuring adhesion forces in fine powders is to place the particles on a surface, retract the surface with a high acceleration, and observe their detachment due to their inertia. To induce detachment of micrometer-sized particles, an acceleration in the order of 500,000g is required. We developed a device in which such high acceleration is provided by a Hopkinson bar and measured via laser vibrometry. Using a Hopkinson bar, the fundamental limit of mechanically possible accelerations is reached, since higher values cause material failure. Particle detachment is detected by optical video microscopy. With subsequent automated data evaluation a statistical distribution of adhesion forces is obtained. To validate the method, adhesion forces for ensembles of single polystyrene and silica particles on a polystyrene coated steel surface were measured under ambient conditions. We were able to investigate more than 150 individual particles in one experiment and obtained adhesion values of particles in a diameter range of 3-13 μm. Measured adhesion forces of small particles agreed with values from colloidal probe measurements and theoretical predictions. However, we observe a stronger increase of adhesion for particles with a diameter larger than roughly 7-10 μm. We suggest that this discrepancy is caused by surface roughness and heterogeneity. Large particles adjust and find a stable position on the surface due to their inertia while small particles tend to remain at the position of first contact. The new device will be applicable to study a broad variety of different particle-surface combinations on a routine basis, including strongly cohesive powders like pharmaceutical drugs for treatment of lung diseases.

The motion of dilute and concentrated dispersions of colloids by external electric or magnetic fields is discussed. Electrokinetics is studied for colloids in confinement, where the confining walls can be flat or rough. As an example for a rough wall superhydrophobic surfaces are chosen. It is shown that the reduced friction at the water-air interface is insufficient to enhance electro-osmosis. Magnetic particles are pulled through a crystalline matrix formed by nonmagnetic colloids to investigate local melting and recrystallization of a crystalline matrix. The average strain field is calculated and the reorganization processes are compared to those induced by shear fields. Using single domain, magnetically blocked particles of different shape and surface characteristics, the interplay between particles, their environment and an external field is investigated.

A combination of energy filtered transmission electron microscopy (EFTEM) and thermally stimulated current (TSC) was used in order to investigate the effect of thermal annealing on the performance of an organic solar cell based on P3HT and PCBM as a well-studied reference system. By probing specific elements, EFTEM allowed spectroscopic imaging with enhanced resolution compared to standard TEM techniques. Here, we applied EFTEM to cross-sections of pristine and thermally annealed organic solar cells to probe the sulfur concentration as a measure for the P3HT distribution within the photoactive layer. Thermal annealing for 10 min at 130 °C resulted in a reordering of P3HT and PCBM into better defined domains. The effect of the morphological changes on the presence of trap states was studied by TSC measurements. The TSC spectra recorded for the pristine and the thermally annealed solar cells showed three contributions, respectively, that could be assigned to the neat materials P3HT and PCBM as well as the b...

A series of phenyl-capped cyclohexa[c]thiophene derivatives (nCHT-TEG, n = 2, 4, or 6) have been synthesized. nCHT-TEG are well-soluble in common organic solvents. The absorption spectra of neutral nCHT-TEG oligomers indicated a shorter effective conjugation length than conventional oligothiophenes based on the non-coplanarity of the thiophene rings. nCHT-TEG can be oxidized/reduced reversibly. The results of cyclic voltammetry and UV–Vis–NIR spectroscopy of the oxidized nCHT-TEG revealed that the effective conjugation length increases at the higher oxidation state. Density functional theory (DFT) calculations indicate that the quinoidal structure of the oxidized nCHT contributes to the improved effective conjugation length. nCHT-TEG radical cations and dications were characterized by electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopies, respectively. NMR results of nCHT-TEG dication revealed that 2CHT-TEG2+ have closed-shell bipolaron structure, while 4CHT-TEG2+ and 6CHT-TEG2+ are the mixture of closed-shell bipolaron and open-shell two-polaron structures.

A supramolecular organogel was prepared by mixing the glycidyl triazole polymers (GTP) functionalized with crown ether and secondary ammoniumion at the side groups. The polymers form an organogel above a concentration of 3 wt % via physical cross-links of the inclusion complex. The organogel responds to multiple stimuli, e.g., temperature, acid/base, and chemical species. The number of the effective cross-links estimated from the storage modulus and the affine network model suggests that some part of the binding sites could not work as the physical cross-links. Rheological measurement under large deformation showed that the storage modulus was constant up to 250% strain and larger than the loss modulus up to 600% strain. The high elasticity of the gel is attributable to the material design based on the high-molecular-weight flexible glycidyl polymers with many binding sites in the single polymer chain. The organogel also showed nice self-healing behavior. The molecular diffusion in the gel network was cha...

The mechanism of particle formation from submicrometer emulsion droplets by solvent evaporation is revisited. A combination of dynamic light scattering, fluorescence resonance energy transfer, zeta potential measurements, and fluorescence cross-correlation spectroscopy is used to analyze the colloids during the evaporation process. It is shown that a combination of different methods yields reliable and quantitative data for describing the fate of the droplets during the process. The results indicate that coalescence plays a minor role during the process; the relatively large size distribution of the obtained polymer colloids can be explained by the droplet distribution after their formation.

Nanomolar suspensions of Au nanorods were analyzed by photon correlation spectroscopy (PCS) complemented by optical absorption spectroscopy. We observed a wavelength-dependent enhancement of the anisotropic scattering as a consequence of the excitation of a longitudinal plasmon mode. The strong scattering intensity near the longitudinal surface plasmon resonance (LSPR) frequency for rods oriented parallel to the excitation optical field allowed the resolution of the translational anisotropy in an isotropic medium. Estimations of lengths and thicknesses of the Au nanorods from both translational and rotational diffusion coefficients were in qualitative agreement with values from transmission electron microscopy images. This wavelength-dependent anisotropic light scattering opens up new applications such as probing dynamics in complex environments at a single-particle level by depolarized PCS and sorting plasmonic nanoparticles according to their size/shape by polarized microscopy.

The contact between liquid drops and hot solid surfaces is of practical importance for industrial processes, such as thermal spraying and spray cooling. The contact and bouncing of solid spheres is also an important event encountered in ball milling, powder processing, and everyday activities, such as ball sports. Using high speed video microscopy, we demonstrate that hydrogel drops, initially at rest on a surface, spontaneously jump upon rapid heating and continue to bounce with increasing amplitudes. Jumping is governed by the surface wettability, surface temperature, hydrogel elasticity, and adhesion. A combination of low-adhesion impact behavior and fast water vapor formation supports continuous bouncing and trampolining. Our results illustrate how the interplay between solid and liquid characteristics of hydrogels results in intriguing dynamics, as reflected by spontaneous jumping, bouncing, trampolining, and extremely short contact times., Drops of liquid on a hot surface can exhibit fascinating behaviour such as the Leidenfrost effect in which drops hover on a vapour layer. Here Pham et al. show that when hydrogel drops are placed on a rapidly heated plate they bounce to increasing heights even if they were initially at rest.

Motivated by the development of lubricant-infused slippery surfaces, we study a sessile drop of a nonvolatile (ionic) liquid which is embedded in a slowly evaporating lubricant film (n-decane) on a horizontal, planar solid substrate. Using laser scanning confocal microscopy we imaged the evolution of the shape of the liquid/liquid and liquid/air interfaces, including the angles between them. Results are compared to solutions of the generalized Laplace equations describing the drop profile and the annular wetting ridge. For all film thicknesses, experimental results agree quantitatively with the calculated drop and film shapes. With the verified theory we can predict height and volume of the wetting ridge. Two regimes can be distinguished: for macroscopically thick films (excess lubrication) the meniscus size is insensitive to changes in film thickness. Once the film is thin enough that surface forces between the lubricant/air and solid/lubricant interfaces become significant the meniscus changes significantly with varying film thickness (starved lubrication). The size of the meniscus is particularly relevant because it affects sliding angles of drops on lubricant-infused surfaces. published

Nanoadhesion on a self-assembled monolayer of 4-methyl-4'-mercaptobiphenyl is measured using a modified atomic force microscope. The dependence of the adhesion force on the loading rate is analyzed with the Dudko-Hummer-Szabo model, and the kinetic and interaction potential parameters for a single terminal group are extracted. The energy and location of the activation barrier suggest that the adhesion is dominated by van der Waals dispersion forces. The humidity effect on the nanoadhesion is also studied. The results are compared with previously measured values for methyl-terminated alkane thiols and the influence of the thiol rigidity on the adhesion force is discussed.

International audience; To predict the properties of superamphiphobic layers we analyzed the wetting of a square and a hexagonal array of vertical pillars composed of spheres (radius R) partially sintered together. Apparent contact angles above 150 degrees are obtained by pinning of a non-polar liquid surface at the underside of the top sphere resulting in a Fakir or Cassie state. Analytical equations are derived for the impalement pressure in the limiting case A(0) >> R-2, where A(0) is the area of the regular unit cell containing a single pillar. The case of close pillars is investigated numerically. By balancing forces at the rim of a drop, we calculate the apparent receding contact angle. To describe drag reduction of a flowing liquid we calculate the apparent slip length. When considering pressure-induced flow through cylindrical capillaries of radius r(c), significant drag reduction occurs only for thin capillaries. The mechanical stability with respect to normal forces and shear is analyzed. Nanoscopic silica glass pillars would be able to sustain the normal and shear stresses caused by capillary and drag forces. For a high impalement pressure and good mechanical stability A(0) should be small and R (respectively the neck diameter) should be large, whereas a large A(0) and a small R imply low contact angle hysteresis and high slip length.

A water drop moving on a superhydrophobic surface or an oil drop moving on a superoleophobic surface dissipates energy by pinning/depinning at nano- and micro-protrusions. Here, we calculate the work required to form, extend, and rupture capillary bridges between the protrusions and the drop. The energy dissipated at one protrusion Ws is derived from the observable apparent receding contact angle Theta(app)(r) and the density of protrusions n by W-s = gamma(cos Theta(app)(r) + 1)/n, where gamma is the surface tension of the liquid. To derive an expression for W-s that links the microscopic structure of the surface to apparent contact angles, two models are considered: A superhydrophobic array of cylindrical micropillars and a superoleophobic array of stacks of microspheres. For a radius of a protrusion R and a receding materials contact angle Theta(r), we calculate the energy dissipated per protrusion as W-s = pi gamma R-2[A - ln(R/K)]f(Theta(r)). Here, A = 0.60 for cylindrical micropillars and 2.9 for stacks of spheres. xis the capillary length. f(Or) is a function which depends on Theta(r) and the specific geometry, f ranges from approximate to 0.25 to 0.96. Combining both equations above, we can correlate the macroscopically observed apparent receding contact angle with the microscopic structure of the surface and its material properties. Refereed/Peer-reviewed

We synthesized a novel green-light-responsive tetra-ortho-isopropoxy-substituted azobenzene (ipAzo). Cis-ipAzo forms a strong host-guest complex with γ-cyclo dextrin (γ-CD) whereas trans-ipAzo binds weakly. This new photoresponsive host-guest interaction is reverse to the well-known azobenzene (Azo)/α-cyclodextrin (α-CD) complex, which is strong only between trans-Azo and α-CD. By combining the UV-light-responsive Azo/α-CD and green-light-responsive ipAzo/γ-CD host-guest complexes, a photoresponsive orthogonal supramolecular system is developed.

Applications of superoleophobic surfaces depend on the stability of the air cushion formed under liquid drops. To analyze the longevity of air cushions we used reflection-interference contrast microscopy (RICM) for drops on a porous fractal-like structure of sintered nanoparticles. RICM permits us to monitor the height of the air cushion with nanometer resolution. Whereas the air cushion under all investigated liquids was stable on a time scale of a few seconds to minutes and liquids rolled off, liquids with low surface tension penetrated the coating on the time scale of hours and longer. The penetration speed showed a power law dependence on time, dz/dt∼t^{p}, the exponent p varying from -0.5 to -1.2. Thus, penetration is qualitatively different from the Lucas-Washburn law that governs spontaneous capillary filling of porous structures.

Superomniphobic membranes for post-combustion CO

The field enhancement of individual cross-shaped nanoantennas for normal incident light has been measured by the relative photoemission yield using a photoemission electron microscope. We not only measured the electron yield in dependence on the intensity of infrared light (800 nm, 100 fs), but also the polarization dependence. In the normal incidence geometry, the electrical field vector of the illuminating light lies in the surface plane of the sample, independent of the polarization state. Strong yield variations due to an out-of-plane field component as well as changes in the polarization state described by the Fresnel laws are avoided. The electron yield is related to the near-field enhancement as a function of the polarization state of the incident light. The polarization dependence is well explained by numerical simulations.

Condensation of water from the atmosphere on a solid surface is an ubiquitous phenomenon in nature and has diverse technological applications, e.g. in heat and mass transfer. We investigated the condensation kinetics of water drops on a lubricant-impregnated surface, i.e., a micropillar array impregnated with a non-volatile ionic liquid. Growing and coalescing drops were imaged in 3D using a laser scanning confocal microscope equipped with a temperature and humidity control. Different stages of condensation can be discriminated. On a lubricant-impregnated hydrophobic micropillar array these are: (1) Nucleation on the lubricant surface. (2) Regular alignment of water drops between micropillars and formation of a three-phase contact line on a bottom of the substrate. (3) Deformation and bridging by coalescence which eventually leads to a detachment of the drops from the bottom substrate. The drop-substrate contact does not result in breakdown of the slippery behaviour. Contrary, on a lubricant-impregnated hydrophilic micropillar array, the condensed water drops replace the lubricant. Consequently, the surface loses its slippery property. Our results demonstrate that a Wenzel-like to Cassie transition, required to maintain the facile removal of condensed water drops, can be induced by well-chosen surface hydrophobicity.

Superliquid repellency can be achieved by nano- and microstructuring surfaces in such a way that protrusions entrap air underneath the liquid. It is still not known how the three-phase contact line advances on such structured surfaces. In contrast to a smooth surface, where the contact line can advance continuously, on a superliquid-repellent surface, the contact line has to overcome an air gap between protrusions. Here, we apply laser scanning confocal microscopy to get the first microscopic videos of water drops advancing on a superhydrophobic array of micropillars. In contrast to common belief, the liquid surface gradually bends down until it touches the top face of the next micropillars. The apparent advancing contact angle is 180°. On the receding side, pinning to the top faces of the micropillars determines the apparent receding contact angle. Based on these observations, we propose that the apparent receding contact angle should be used for characterizing superliquid-repellent surfaces rather than the apparent advancing contact angle and hysteresis.

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

In the last two decades fluorescence correlation spectroscopy (FCS) has been increasingly applied to analyze systems and processes relevant to colloid and interface science. The method has become a routine tool to measure the hydrodynamic radii of small fluorescent molecules, macromolecules and nanoparticles, characterize their interactions and follow a possible aggregation. It was also used to study the diffusion of such species in inhomogeneous media like polymer melts, solutions, gels or porous structures. The formation kinetics and size of micelles of surfactants or block copolymers has been quantified. FCS has also been applied to characterize diffusion of tracers at fluid–liquid and solid–liquid interfaces and study the hydrodynamic boundary condition. The review is intended to summarize these applications and highlight perspectives but also limits of FCS in colloid and interface science.

The electrostatic and steric repulsion induced by different superplasticizers on ground granulated blast furnace slag in alkaline media have been studied. The superplasticizers were sulfonated naphthalene, sulfonated melamine, vinyl copolymer, and polycarboxylate- based admixtures. With these superplasticizers the slag suspensions had negative zeta potentials, ranging from -3 to -10 mV. For the first time the adsorbed layer thicknesses for superplasticizers on slag using colloidal probe atomic force microscopy has been measured. To model the interparticle force interactions an effective Hamaker constant was computed from dielectric properties measured on a dense slag sample produced by spark plasma sintering. The obtained results conclude that the dispersion mechanism for all the superplasticizers studied in the present work is mainly dominated by the steric repulsion. Results were then used in a yield stress model, YODEL, to predict the yield stress with and without the superplasticizers. Predictions of the yield stress agreed well with experimental results.

We measured the forces required to slide sessile drops over surfaces. The forces were measured by means of a vertical deflectable capillary stuck in the drop. The drop adhesion force instrument (DAFI) allowed the investigation of the dynamic lateral adhesion force of water drops of 0.1 to 2 μL volume at defined velocities. On flat PDMS surfaces, the dynamic lateral adhesion force increases linearly with the diameter of the contact area of the solid-liquid interface and linearly with the sliding velocity. The movement of the drop relative to the surfaces enabled us to resolve the pinning of the three-phase contact line to individual defects. We further investigated a 3D superhydrophobic pillar array. The depinning of the receding part of the rim of the drop occurred almost simultaneously from four to five pillars, giving rise to peaks in the lateral adhesion force.

To explore dynamical processes in granular matter, we use a combination of 3D imaging and mechanical testing. We analyze structural changes using confocal microscopy while applying a compression load simultaneously. Fluorescently labeled polydisperse silica particles were hydrophobized with long alkyl chains and dispersed in an index-matching liquid. The particles show a weak attraction. Photobleaching the central plane of individual particles generates an optical anisotropy without changing particle interaction. In a series of 3D images, we follow trajectories and rotation of single particles. We focus on particle translation and rotation in dependency of the local volume fraction. During compression, restructuring happens predominantly in regions of low packing density. We show that rotation plays an important role and is hence a key parameter for explaining dynamical processes in granular systems.

The hierarchical self-assembly and dynamics of poly(γ-benzyl-l-glutamate)-b-poly(l-proline) (PBLG-b-PLP) polypeptides are investigated with X-rays and solid state NMR. Both blocks possess helices stabilized solely either by hydrogen bonds (PBLG) or by steric hindrance (PLP) and are further packed in two different hexagonal cells. We report a trans/cis conformational change of PLP upon confinement that mimics the isomerization of isolated proline residues in proteins. These cis PLP conformations reside primarily at the PLP/PBLG interface, alleviate the packing frustration, and permit PBLG and PLP helices to pack with their bulk properties.

A series of novel polymers, glycidyl 4-functionalized 1,2,3-triazole polymers (functionalized GTP) were synthesized by click functionalization of glycidyl azide polymer (GAP). Quantitative functionalization of the glycidyl polymer side groups was achieved due to the high reactivity of the azide–alkyne Huisgen cycloaddition under mild conditions. The polymers were characterized by 1H NMR, 13C NMR, IR, GPC, DLS, DSC, and TGA. We confirmed that the solubility, glass transition temperature, and decomposition temperature were controllable by changing the functional group attached at 4-position of 1,2,3-triazole group. Functionalized GTP expands not only the application field of GAP toward non-explosive materials, but also the variety of poly(ethylene glycol) derivatives with different side groups.

Biphasic fluorocarbon/hydrocarbon amphiphiles tethered to cores at distances commensurate with their packing requirement can provide thermodynamic pathways toward equilibrium. This contrasts with the analogous semifluorinated alkanes. The dynamics of a fluorous biphasic hexa(3,5-substituted-phenyl)benzene (HPB) is studied with dielectric spectroscopy as a function of temperature and pressure in comparison to the parent biphasic diphenylacetylene (DPA). Dielectric spectroscopy is a sensitive probe of the fluorocarbon environment through the end C-F dipole. Four dielectrically active processes were observed that associate with the CF(3) environment within the different phases (isotropic, liquid-like lamellar, solid lamellar, glassy state). Pressure facilitates the construction of the equilibrium phase diagram. The kinetic pathways to fluorocarbon organization are explored by pressure-jump experiments. A highly cooperative process was found that is atypical of a nucleation and growth process expected for first-order transitions.

Elastic, microstructured surfaces (hydrophobic and hydrophilic) mimicking the surface structure of tree-frog toe-pads are fabricated. Their adhesion and friction behaviour in the presence of a liquid layer is evaluated and compared to flat controls. Tree-frog-like patterns are beneficial for wet adhesion only if the liquid does not wet the surface. The situation is different in friction, where the surface structure lead to significantly higher friction forces only if the liquid does wet the surface. Taking into account that tree-frog attachment pads are hydrophilic and that their secretion wets all kind of surfaces, our results indicate that the surface structure in tree-frog toe-pads has been developed for climbing, when shear (friction) forces are involved. These results evidence the benefits and limitations of the surface design (microstructure and hydrophilicity) for adhesion and friction under wet conditions.

Heated micromechanical cantilevers were used to probe the thermal properties of nanogram samples in two ways: (i) as a micromechanical thermogravimetric balance and (ii) as a local nano-heater for heating individual objects. For micromechanical thermogravimetry, 6ng of polyurethane nanocapsules containing silverazide were freeze dried and attached to the micromechanical cantilever apex. The resonant frequency of the micromechanical cantilever upon heating was recorded. After heating to 250^oC, 25% mass was found remaining on the micromechanical cantilever. In order to image structural changes, the tip of the heatable micromechanical cantilever was positioned on individual nanocapsules weighing less than 6fg, and the capsule was imaged using a scanning force microscope. Then the cantilever was heated and temperature-deflection curves were recorded. Both methods revealed a decomposition temperature of 180^oC for silverazide encapsulated in a polyurethane nanocapsule. Topographic images of individual capsules after decomposition showed a rupture of the shell at one position.

Reversibly responsive, thin or ultrathin polymer fi lms, often referred to as “smart surfaces”, can alter their properties upon application of external stimuli. [ 1 , 2 ] One particular application fi eld represents the engineering of nanostructured fi lms mimicking cell membranes. [ 3 , 4 ] Such materials offer application potential for sensors, textiles, construction materials, and smart coatings due to a rapid change in surface energy and morphology. [ 5–7 ] The surface response can be triggered by various external stimuli such as light, temperature, electrical potential, mechanical force, magnetic fi eld, pH change, or selective solvent treatment. [ 1 , 8–12 ] A variety of different thin polymer fi lms has been designed for this purpose. End-tethered polymers (e.g., (multiarm) block and homopolymers), layer-by-layer structures, cross-linked thin polymer fi lms as well as hybrid systems with inorganic particles are established, complex structures to generate responsive surface coatings. [ 13–20 ]

The self-organization and dynamics of bottlebrush polymers consisting of poly(2-bromoisobutyryloxyethyl methacrylate) (PBiBEM) backbone and grafted n-butyl acrylate (PBA) chains are studied as a function of the side-chain length by X-ray scattering, dielectric spectroscopy, and rheology in relation to the respective homopolymers. All short-range correlations are dominated by the PBA side chains, whereas long-range correlations reflect the screening of the backbones by the side chains. Such correlations show up also in the segmental dynamics. The PBA segmental dynamics are slowed-down, whereas the backbone dynamics are plasticized by the side chains. Overall the bottle-brush architecture imparts dynamic homogeneity to the backbone and side-chain dynamics.

Foamed products are a popular class of food products. The mechanism of stabilization of the air bubbles is often only partially understood. The current study aims at better understanding the stabilization of air–water interfaces through the low molecular weight surfactant polyglycerol ester (PGE). We chose PGE films as an exemplary case for a non-equilibrium situation at an air–water interface – a situation that requires the development of new experimental techniques. Several different film preparation and transfer methods onto solid substrates have been tested. The films were then investigated by scanning force microscopy, and structural artifacts associated to the sample preparation were identified and discussed. In addition to the study of Langmuir monolayers and Gibbs adsorption layers, we have proposed a new approach to investigate the skins of foam bubbles. We thereby were able to determine that PGE indeed covers bubbles by a multilayer structure and that the pH plays a role in the structuring of the films. We show that a combination of different film preparation methods allows us to get an insight into the aggregation behavior of PGE at the air–water interface and thereby better understand the stabilization mechanism of this particular surfactant.

Nanomechanical cantilevers (NMC) were used for the characterization of the film formation process and the mechanical properties of colloidal monolayers made from polystyrene (PS). Closely packed hexagonal monolayers of colloids with diameters ranging from 400 to 800 nm were prepared at the air-water interface and then transferred in a controlled way on the surface of NMC. The film formation process upon annealing of the monolayer was investigated by measuring the resonance frequency of the NMC (≈12 kHz). Upon heating of non-cross-linked PS colloids, we could identify two transition temperatures. The first transition resulted from the merging of polymer colloids into a film. This transition temperature at 147 ± 3 °C as measured at ≈12 kHz remained constant for subsequent heating cycles. We attributed this transition temperature to the glass transition temperature T g of PS which was confirmed by dynamic mechanical thermal analysis (DMTA) and using the time temperature superposition principle. The second transition temperature (175 ± 3 °C) was associated with the end of the film formation process and was measured only for the first heating cycle. Furthermore, the transition of the colloidal monolayer into a homogeneous film preserved the mass loading on the NMC which allowed determination of the Young's modulus of PS (≈3 GPa) elegantly. © 2011 American Chemical Society.

To investigate the temperature profiles on laser heated polymer films, we track the thermal radiation with 1 μs time and 1 μm spatial resolution. The resulting two-dimensional temperature graphs are compared to finite element simulations in order to understand the heat conversion and flow. The temperature measurement setup consists of a NIR laser and an optical detection system, which includes high performance optics and a microsecond gated camera, equipped with several interference filters. In this way the thermal radiation is detected in the visible range with spectral resolution. Fitting the spectrum with Planck’s law, two-dimensional micrographs of the temperature distribution are obtained. For polystyrene surfaces we were able to analyze the heating and the ablation behavior. Good agreement was found between experimental results and finite element simulations, when ablation is limited to a few tens of nanometers of the film thickness. Ablation of polystyrene starts at 150°C, 50 K above the glass transition temperature. We suggest a photomechanical ablation mechanism at that threshold fluence. For ablation at higher fluence and peak temperature, experiments indicate a thermal decomposition reaction. The temperature range of spinodal decomposition is not reached and can in our case be ruled out as ablation mechanism.

We present a method to measure the absorption of water molecules from the liquid and the vapour phase into polymer nano-films and the diffusion inside these films. Film thickness can be down to 45 nm. To demonstrate the possibilities of this method we use polymer films that are deposited on the upper side of a silicon cantilever by plasma polymerization of norbornene. When a microdrop of water is deposited onto the initially straight cantilever, the drop causes the cantilever to bend while it evaporates. Evaporation of such small water drops usually takes less than a second. An upwards bending is due to capillary forces and a downwards bending is due to the diffusion of water into the polymer film – and the consequent volume expansion (swelling) of the film. The magnitude of the capillary forces and the extent of swelling continuously change during drop evaporation. When drop evaporation is over the cantilever returns to its initial straight position. We simulate the time dependent bending with a numerical model that qualitatively agrees with the experiment. From the time dependence of cantilever bending we are able to determine the diffusion coefficient of water in the thin polymer film.

The dynamics of the herringbone structure formation have been studied in a monobromo hexa-peri-hexabenzocoronene derivative by infrared spectroscopy and complementary techniques. Selective probing of the vibration modes corresponding to the aromatic core and the alkyl chains, allowed investigation of their role in the phase transformation dynamics over an extraordinarily broad time-window (1-10(5) s). Identical kinetics were found suggesting that both the core and the alkyl chains simultaneously drive the system from the undercooled liquid crystalline to the crystalline phase with the herringbone structure. Journal of Physical Chemistry B

The diffusion of nanoparticles at a water-alkane interface is studied using fluorescence correlation spectroscopy. Hydrophilic and hydrophobic quantum dots of 5, 8, and 11 nm radius are used. A slow-down of nanoparticle diffusion at the liquid-liquid interface is observed. The effect is most evident when the viscosities of both liquid phases are similar, here, at the water-decane interface. In this case, the interfacial diffusion coefficients of the hydrophilic particles are 1.5 times and those of the hydrophobic particles 2 times lower than the corresponding bulk values.

We investigated the photoinduced changes in the surface potential and conductivity for locally degraded active layers of organic solar cell materials using electrical modes of scanning force microscopy. Samples were degraded under different partial pressures of oxygen and humidity in the presence of light. Degraded and nondegraded areas were investigated by Kelvin Probe Force Microscopy (KPFM) and conductive scanning force microscopy (cSFM). The analysis allowed us to quantify the extent of degradation and compensate the contribution of the probe tip. Two typical blends used for organic solar cell, i.e., P3HT:PCBM and PCPDTBT:PCBM, were investigated. We observed that P3HT:PCBM photodegraded significantly more than PCPDTBT:PCBM for an environment containing oxygen. For short photodegradation times (1 h), we verified that changes in the surface potential and conductivity of P3HT:PCBM films were fully reversible after annealing. For individual layers of P3HT and PCBM, we found that only P3HT degrades. Howeve...

a b s t r a c t We investigated the reinforcement of blends made from poly(ethyl methacrylate) (PEMA) and PEMA- grafted nanoparticles at a nanometer length scale. The reinforcement was probed by nanowear experiments based on scanning force microscopy (SFM). In addition to imaging, the SFM is applied to wear the surface of samples at the length scale of nanoparticles. Blends with different miscibility of nanoparticles were prepared by varying the molecular weights of polymer grafted from the nanoparti- cles (N) and polymer forming the matrix (P). We were able to associate a critical force for the onset of nanowear by analyzing the nanowear patterns resulting from different normal loads during the nanowear experiment. The definition of this critical force allows quantitative comparison of nanoparticle-polymer systems of different composition. Nanowear tests indicated that only mixtures where N/P > 1 reinforced the composite material compared to the pure homopolymer. Under these conditions the grafted polymers were swollen and the nanoparticles acted as additional anchor sites. As reference experiments we used a blend made from PEMA homopolymer and unmodified particles. Non-grafted nanoparticles clearly did not account for any reinforcement.

The initial stages of spontaneous spreading of a solvent drop (toluene) on the surface of a soluble polymer (polystyrene) have been studied with a high-speed camera. For drops of 1–4 μL volume, the increase in contact radius r can be described by a power law \( r \propto {t^{\alpha }} \), with the spreading exponent α = 0.50 and for the first ≈8 ms. Thereafter, the three-phase contact line was pinned leading to a macroscopic static contact angle of Θ0 = 12–15°. The insoluble liquids ethanol (α = 0.47, Θ0 = 0) and water (α = 0.35, Θ0 = 90°) showed a slower spreading. We attribute the fast spreading of toluene to the strong interaction with the polymer, like in reactive wetting. The finite macroscopic contact angle indicates the formation of a ridge by softening of polystyrene due to permeated toluene and the subsequent plastic deformation by the surface tension of the liquid. This interpretation is supported by experiments on polymers grafted from a silicon wafer. Toluene completely wets polymer brush surfaces. Transport of toluene through the vapor phase plays a significant role.

The properties of a monolayer of the non-ionic Pluronic F127 at the air/water interface and the effect of an anionic surfactant (sodium dodecyl sulphate, SDS) were characterized using a Langmuir film balance and the Monolayer Particle Interaction Apparatus; Pluronic F127 is a triblock copolymer of poly(ethylene oxide) (PEO groups)–poly(propylene oxide) (PO groups)–poly(ethylene oxide) (PEO groups). The surface pressure–area ( Π – A ) isotherms and the forces between a silica particle and the monolayer in the water phase were measured in the absence and presence of SDS molecules. The isotherm of the monolayer showed the characteristics of a pancake-to-brush transition upon compression of the monolayer. An adhesion was measured between the particle and the F127 monolayer. We attribute it to hydrogen bonds between the PEO groups and the silanol groups of the particle. The adhesion increased upon compression of the monolayer, due to the resulting increase in the number of hydrophilic PEO groups in the water phase. The adhesion decreased upon the addition of SDS, interpreted by an adsorption of SDS to the air/water interface. The presence of SDS at the interface results in an electrostatic repulsion between the negatively charged SDS headgroups and the negatively charged silica particle. The addition of SDS also decreased the stiffness of the monolayer. This increased flexibility can be explained by (1) the more fluid nature of the SDS molecules in comparison to the polymer molecules, (2) the electrostatic repulsion between the SDS groups in the monolayer, and/or (3) binding between the hydrophobic PO groups and the hydrophobic tails of the SDS molecules.

We present a scaling formula for size-dependent viscosity coefficients for proteins, polymers, and fluorescent dyes diffusing in complex liquids. The formula was used to analyze the mobilities of probes of different sizes in HeLa and Swiss 3T3 mammalian cells. This analysis unveils in the cytoplasm two length scales: (i) the correlation length ξ (approximately 5 nm in HeLa and 7 nm in Swiss 3T3 cells) and (ii) the limiting length scale that marks the crossover between nano- and macroscale viscosity (approximately 86 nm in HeLa and 30 nm in Swiss 3T3 cells). During motion, probes smaller than ξ experienced matrix viscosity: η(matrix) ≈ 2.0 mPa·s for HeLa and 0.88 mPa·s for Swiss 3T3 cells. Probes much larger than the limiting length scale experienced macroscopic viscosity, η(macro) ≈ 4.4 × 10(-2) and 2.4 × 10(-2) Pa·s for HeLa and Swiss 3T3 cells, respectively. Our results are persistent for the lengths scales from 0.14 nm to a few hundred nanometers.

The effect of dipole substitution on the self-assembly, thermodynamics, and dynamics has been studied in a series of hexa-peri-hexabenzocoronenes (HBCs). The HBCs bear the same number and type of aliphatic chains, but different dipoles directly attached to the cores ranging from similar to 0 to similar to 3.4 D. Dipole substitution alters the energetics and reduces the transition temperature favoring the columnar hexagonal liquid crystalline phase at the expense of the crystalline phase. The equation of state was obtained by independent pressure volume temperature measurements in both phases that resulted in the equilibrium phase diagram. According to the latter, increasing pressure imparts stability to the crystalline phase. The molecular and supramolecular dynamics investigated, respectively, by dielectric spectroscopy and rheology, identified a hierarchy of motions comprising a fast axial motion, a slower process that completely relaxes the dipole moment, and an even slower soliton-like relaxation of structural defects. Journal of Physical Chemistry B

Hollow silica nanoparticles (HSNP) with diameters comparable to visible wavelengths and with thin shells (

The adhesion force between a silicon nitride tip and a 1-dodecanethiol monolayer have been measured at different loading rates and different humidity. A way to extract the kinetic and interaction potential parameters for a single molecule interaction is demonstrated. The effect of the increase of van der Waals interaction strength per molecule with increasing humidity is explained by assuming a gradual adsorption of water into the tip surface hollows. The study should help in better understanding of the humidity effect on molecular level and in avoiding the underestimation of adhesion forces in micro- and nano-engineering in ambient conditions.

Semifluorinated alkanes (C(n)F(2n+1)C(m)H(2m+1)), short FnHm display local phase separation of mutually incompatible hydrocarbon and fluorocarbon chain moieties, which has been utilized as a structure-forming motif in supramolecular architectures. The packing of semifluorinated alkanes, nominally based on dodecyl subunits, such as perfluoro(dodecyl)dodecane (F12H12) and perfluoro(dodecyl)eicosane (F12H20), as well as a core extended analogue, 1,4-dibromo-2-((perfluoroundecyl)methoxy)-5-(dodecyloxy)benzene) (F11H1-core-H12), was studied at the air/water interface. Langmuir monolayers were investigated by means of neutron reflectivity directly at the air/water interface and scanning force microscopy after transfer to silicon wafers. Narrowly disperse surface micelles formed in all three cases; however, they were found to bear different morphologies with respect to molecular orientation and assembly dimensionality, which gives rise to different hierarchical aggregate topologies. For F12H12, micelles of ca. 30 nm in diameter, composed of several circular or "spherical cap" substructures, were observed and a monolayer model with the fluorocarbon block oriented toward air is proposed. F12H20 molecules formed larger (ca. 50 nm diameter) hexagonally shaped surface micelles that were hexagonally, densely packed, besides more elongated but tightly interlocked wormlike structures. Conversely, F11H1-core-H12 films organized into linear rows of elongated surface micelles with comparable width, but an average length of ca. 400 nm, apparently formed by antiparallel molecular packing.

The electropolymerization of 3,4-ethylenedioxythiophene (EDOT) to poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in the air and water-stable ionic liquids 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate [HMIm]FAP and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]TFSA. In situ scanning tunnelling microscopy (STM) results show that the electropolymerization of EDOT in the ionic liquid can be probed on the nanoscale. In contrast to present understanding, it was observed that the EDOT can be oxidised in ionic liquids well below its oxidation potential and the under potential growth of polymer was visualized by in situ STM. These results serve as the first study to confirm the under potential growth of conducting polymers in ionic liquids. Furthermore, ex situ microscopy measurements were performed. Quite a high current of 670 nA was observed on the nanoscale by conductive scanning force microscopy (CSFM).