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This Feature Article evaluates ongoing efforts to adapt adhesives toward the goal of zero-waste living and suggests the most promising future directions. Adhesives are not always considered in zero-waste manufacturing because they represent only a small fraction of a product and offer no additional functionality. However, their presence restricts the reintegration of constituent parts into a circular economy, so a new generation of adhesives is required. Furthermore, their production often leads to harmful pollutants. Here, two main approaches toward addressing these problems are considered: first, the use of natural materials that replace petroleum-based polymers from which conventional adhesives are made and second, the production of dismantlable adhesives capable of debonding on demand with the application of an external stimulus. These approaches, either individually or combined, offer a new paradigm in zero-waste industrial production and consumer applications.

I review experimental developments in the growth and application of surface-grafted weak polyelectrolytes (brushes), concentrating on their surface, tribological, and adhesive and bioadhesive properties, and their role as actuators.

Attachment assays of a Pseudomonas isolate to fused silica slides showed that treatment with DNaseI significantly inhibited cellular adsorption, which was restored upon DNA treatment. These assays confirmed the important role of extracellular DNA (eDNA) adsorption to a surface. To investigate the eDNA adsorption mechanism, single-molecule force spectroscopy (SMFS) was used to measure the adsorption of eDNA to silicon surfaces in the presence of different concentrations of sodium and calcium ions. SMFS reveals that the work of adhesion required to remove calcium-bound eDNA from the silicon oxide surface is substantially greater than that for sodium. Molecular dynamics simulations were also performed, and here, it was shown that the energy gain in eDNA adsorption to a silicon oxide surface in the presence of calcium ions is small and much less than that in the presence of sodium. The simulations show that the length scales involved in eDNA adsorption are less in the presence of sodium ions than those in the presence of calcium. In the presence of calcium, eDNA is pushed above the surface cations, whereas in the presence of sodium ions, short-range interactions with the surface dominate. Moreover, SMFS data show that increasing [Ca2+] from 1 to 10 mM increases the adsorption of the cations to the silicon oxide surface and consequently enhances the Stern layer, which in turn increases the length scale associated with eDNA adsorption.

Neutron specular reflectometry (SR) and off-specular scattering (OSS) are nondestructive techniques which, through deuteration, give a high contrast even among chemically identical species and are therefore highly suitable for investigations of soft-matter thin films. Through a combination of these two techniques, the former yielding a density profile in the direction normal to the sample surface and the latter yielding a depth-resolved in-plane lateral structure, one can obtain quite detailed information on buried morphology on length scales ranging from the order of ångströms to ∼10 µm. This is illustrated via quantitative evaluation of data on SR and OSS collected in time-of-flight (ToF) measurements of a set of films composed of immiscible polymer layers, protonated poly(methyl methacrylate) and deuterated polystyrene, undergoing a decomposition process upon annealing. Joint SR and OSS data analysis was performed by the use of a quick and robust originally developed algorithm including a common absolute-scale normalization of both types of scattering, which are intricately linked, constraining the model to a high degree. This, particularly, makes it possible to distinguish readily between different dewetting scenarios driven either by the nucleation and growth of defects (holes, protrusionsetc.) or by thermal fluctuations in the buried interface between layers. Finally, the 2D OSS maps of particular cases are presented in different spaces and qualitative differences are explained, allowing also the qualitative differentiation of the in-plane structure of long-range order, the correlated roughness and bulk defects by a simple inspection of the scattering maps prior to quantitative fits.

Sustainable management activities focus on creating value for organizations. This is particularly relevant in service organizations as they are under increasing pressure to capture and process information efficiently. We advocate that the amount of information and the way teams process this information have a substantial impact on an organization’s ability to sustain a competitive advantage. This study addresses a gap in the literature by examining the impact of the level of information intensity on performance in the service industry. It also contributes to the debate about whether team structure facilitates performance in a service-based organization. A longitudinal design was employed to determine whether information-intensive processes influence performance, and if so, whether the impact differs between team designs. To do this, data were collected from 24,925 motor insurance claims over two distinct time periods. While our findings confirm that information intensity has a direct impact on the performance of claims processing, they also challenge traditional beliefs about self-managed work teams’ dominance. By adopting a more nuanced and context-specific perspective, we discovered that in certain situations the production line approach to team design was more productive than self-directed work teams in respect to critical operational tasks. This research sheds light on a relatively unexplored aspect of the service industry, has implications for sustainable management practices relating to team design, and provides a rich vein for future research studies.

Dynamic single molecule force spectroscopy was performed to monitor the unbinding of fibronectin with the proteoglycans syndecan-4 and decorin, and to compare this with the unbinding characteristics of α5β1-integrin. A single energy barrier was sufficient to describe the unbinding of both syndecan-4 and decorin from fibronectin, while two barriers were observed for the dissociation of α5β1-integrin from fibronectin. The outer (high affinity) barrier in the interactions of fibronectin with α5β1-integrin and syndecan-4 are characterized by larger barrier heights and widths, and slower dissociation rates than those of the inner (low affinity) barrier in the interactions of fibronectin with α5β1-integrin and decorin. These results indicate that syndecan-4 and (ultimately) α5β1-integrin have the ability to withstand deformation in their interactions with fibronectin, while the decorin-fibronectin interaction is considerably more brittle.

Force spectroscopy was used to show that extracellular DNA (eDNA) has a pre-eminent structural role in a biofilm. The adhesive behavior of extracellular polymeric substances to poly(ethylene terephthalate), a model hydrophobic surface, was measured in response to their degradation by hydrolytic enzymes known for their biofilm dispersion potential: DNaseI, protease, cellulase, and mannanase. Only treatment with DNaseI significantly decreased the adhesive force of the model bacterium Micrococcus luteus with the surface, and furthermore this treatment almost completely eliminated any components of the biofilm maintaining the adhesion, establishing a key structural role for eDNA.

Specular and off-specular neutron reflectometry have been used in a combined approach to study thin polymer films. Our goal in this work is to illustrate the power of the off-specular scattering technique to probe the properties of the buried interface of immiscible polymer bilayers of deuterated polystyrene and protonated poly(methyl methacrylate) (h-PMMA). The diffuse scattering stemming from these systems is discussed in relation to thermal fluctuations at the polymer/polymer interface, providing a means to extract in-plane correlation lengths from buried interfaces. In addition the onset of hole formation in the top layer is evidenced by the diffuse scattering, not easily detectable by specular reflection alone.

Polyelectrolyte adhesives, either poly[2-(dimethylamino)ethyl methacrylate] or poly(methacrylic acid), functionalized with a surface-active calix[4]resorcinarene were grafted onto silicon wafers. Adhesion studies on these grafted-to brushes using polyelectrolyte hydrogels of opposite charge showed that it is the calix[4]resorcinarene, rather than adsorption of polyelectrolyte monomers, that adheres the brush to the silicon substrate. The adhesion measured was similar to that measured using polymers grafted from the surface, and was stronger than a control layer of poly(vinyl acetate) under the same test conditions. The limiting factor was determined to be adhesive failure at the hydrogel-brush interface, rather than the brush-silicon interface. Therefore, the adhesion has not been adversely affected by changing from a grafted-from to a grafted-to brush, demonstrating the possibility of a one-pot approach to creating switchable adhesives.

Direct glycan-glycan interactions are increasingly implicated in survival and pathogenicity of bacteria. Here, we show that they can be exploited by protozoan parasites in their insect hosts. Force spectroscopy revealed that Leishmania promastigotes display a high-affinity biomolecular interaction between their lipophosphoglycan glycocalyx and mimics of N-acetyl-D-galactosamine, commonly expressed on the midguts of a wide range of sand fly vector species. This enabled gut-adhesive nectomonad promastigotes of Leishmania mexicana to efficiently bind to membrane-bound mucin-like, O-linked glycoproteins of the sand fly Lutzomyia longipalpis, an event crucial for parasite survival, and accounts for a permissive mode of binding. Thus, direct interaction between parasite and sand fly midgut glycans are key to permitting vector competence for all forms of leishmaniasis worldwide. In addition, these studies demonstrate the feasibility of interfering with these interactions as transmission-blocking vaccines.

A model system for the investigation of diffusional transport in compartmentalized nanosystems is described. Arrays of "corrals" enclosed within poly[oligo(ethylene glycol)methyl ether methacrylate] (POEGMA) "walls" were fabricated using double-exposure interferometric lithography to deprotect aminosilane films protected by a nitrophenyl group. In exposed regions, removal of the nitrophenyl group enabled attachment of an initiator for the atom-transfer radical polymerization of end-grafted POEGMA (brushes). Diffusion coefficients for poly(ethylene glycol) in these corrals were obtained by fluorescence correlation spectroscopy. Two modes of surface diffusion were observed: one which is similar to diffusion on the unpatterned surface and a very slow mode of surface diffusion that becomes increasingly important as confinement increases. Diffusion within the POEGMA brushes does not significantly contribute to the results.

Uniform onion micelles formed from up to ten nano-structured polymer layers were produced by the aqueous self-assembly of highly-branched copolymers. Highly-branched poly(alkyl methacrylate)s were chain extended with poly(acrylic acid) in a two-step reversible addition–fragmentation chain transfer-self-condensing vinyl polymerization (RAFT-SCVP) in solution. The resulting polymers were dispersed into water from oxolane (THF) using a self-organized precipitation-like method and the self-assembled particles were studied by phase-analysis light scattering, small-angle neutron scattering, and electron microscopy techniques. The relative hydrophobicity of the blocks was varied by changing the alkyl methacrylate (methyl, butyl, or lauryl) and this was found to affect the morphology of the particles. Only the poly(butyl methacrylate)-containing macromolecule formed an onion micelle structure. The formation of this morphology was observed to depend on: the evaporation of the good solvent (THF) during the self-assembly process causing kinetic trapping of structures; the pH of the aqueous phase; and also on the ratio of hydrophobic to hydrophilic segments within the copolymer. The lamellar structure could be removed by annealing the dispersion above the glass transition temperature of the poly(butyl methacrylate). To exemplify how these onion micelles can be used to encapsulate and release an active compound, a dye, rhodamine B (Rh B), was encapsulated and released. The release behaviour was dependent on the morphology of the particles. Particles formed containing the poly(methyl methacrylate) or poly(lauryl methacrylate) core did not form onions and although these materials absorbed Rh B, it was continuously released at room temperature. On the other hand, the lamellar structure formed from branch-poly(butyl methacrylate)-[poly(butyl methacrylate)-block-poly(acrylic acid)] allowed for encapsulation of approximately 45% of the dye, without release, until heating disrupted the lamellar structure.

Fluorescence correlation spectroscopy was used to show that the temperature-dependent diffusion coefficient of poly(ethylene oxide) (PEO) adsorbed on polystyrene and different poly(alkyl methacrylate) (PAMA) films in aqueous solution exhibited a maximum close to (but below) the surface glass transition temperature, Tgs, of the film. This elevated diffusion was observed over a small range of temperatures below Tgs for these surfaces, and at other temperatures, the diffusion was similar to that on silicon, although the diffusion coefficient for PEO on polystyrene at temperatures above Tgs did not completely decrease to that on silicon, in contrast to the PAMA surfaces. It is concluded that the enhanced surface mobility of the films near the surface glass transition temperature induces conformational changes in the adsorbed PEO. The origin of this narrow and dramatic increase in diffusion coefficient is not clear, but it is proposed that it is caused by a coupling of a dominant capillary mode in the liquid surface layer with the polymer. Friction force microscopy experiments also demonstrate an unexpected increase in friction at the same temperature as the increase in diffusion coefficient.

The diffusion of a polyzwitterion, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), in aqueous solution containing different alkali halides was studied by fluorescence correlation spectroscopy at single molecule level. It was found that the halide anion has a greater effect on the radius of zwitterionic PMPC molecules than alkali cations, which is due to the mechanism by which PMPC molecules interact with the surrounding hydrogen bond network of water molecules and adsorbed ions. With the addition of salt, the size of PMPC remains constant while its diffusion coefficient is reduced slightly, although larger cations (e.g. K+) result in slightly increased diffusion coefficient for 1 M potassium chloride-based solutions. This enhanced diffusion coefficient is attributed to the decrease in the viscosity of the aqueous solution on the addition of salt. When the counter-ion was varied in potassium-based salts, different effects were observed for different anions, resulting a reduction in the diffusion coefficient as a function of salt concentration. This reduction was modest for KBr, but significant for KI. Overall, no discernible changes were observed as the size of the PMPC coil was varied, except in case of KI for which a significant increase was observed at higher ionic strength. Divalent cations (Ca2+ and Mg2+), produced similar effects to those found for monovalent cations. These effects are explained by the interaction of PMPC with the hydrogen bond network of water molecules and with the adsorbed ions.

Spin coating, typically used to achieve nanometre thick films, is the established method for depositing perovskite precursors at lab scale for use in solar cells. This study investigates the dynamics of spin coating perovskite. By combining experimental measurement with a semi-empirical model the evaporation rate of the dimethylformamide solvent during the spin coating of a mixed lead halide precursor is determined to be 1.2 × 10 –8 m/s. When K-bar coating the same precursor the solvent does not significantly evaporate during the deposition process and when this film is crystallised on a hot plate a rough film results which gives a power conversion efficiency (PCE) of less than 2%. By increasing the airflow of the K-bar coated perovskite film during crystallisation to 2.7 × 10 –4 m/s the PCE increases significantly to 8.5% through an improvement in short-circuit current and fill factor.

International audience; The photophysics of water and propan-1-ol suspensions of poly[N-9”-heptadecanyl-2,7-carbazole-alt−5,5-(4,7-di-2-thienyl-2′,1′,3′- benzothiadiazole)] (PCDTBT) nanoparticles and mesoparticles has been studied by ultrafast spectroscopy. High molar mass polymer (HMM > 20 kg/mol) forms nanoparticles with around 50 nm diameter via mini-emulsion post-polymerization, while low molar mass (LMM < 5 kg/mol) polymer prepared by dispersion polymerization results in particles with a diameter of almost one order of magnitude larger (450 ± 50 nm). In this study, the presence of excited-states and charge separated species was identified through UV pump and visible/near-infrared probe femtosecond transient absorption spectroscopy. A different behavior for the HMM nanoparticles has been identified compared to the LMM mesoparticles. The nanoparticles exhibit typical features of an energetically disordered conjugated polymer with a broad density of states, allowing for delayed spectral relaxation of excited states, while the mesoparticles show a J-aggregate-like behavior where interchain interactions are less efficient. Stimulated emission in the red-near infrared region has been found in the mesoparticles which indicates that theypresent a more energetically ordered system.

The diffusion of rhodamine-labeled poly(ethylene glycol) (r-PEG) within surface-grafted poly(ethylene glycol) (s-PEG) layers in aqueous solution at 18 °C was measured by fluorescence correlation spectroscopy. The diffusion coefficient of r-PEG within s-PEG was controlled by the grafting density, σ, and scaled as σ–1.42±0.09. It is proposed that a characteristic blob size associated with the grafted (brush) layer defines the region through which the r-PEG diffusion occurs. The diffusion coefficients for r-PEG in semidilute solution were found to be similar to those in the brushes.

The temperature and pH-dependent diffusion of poly(glycerol monomethacrylate)-block-poly(2-hydroxypropyl methacrylate) nanoparticles prepared via polymerization-induced self-assembly in water is characterized using fluorescence correlation spectroscopy (FCS). Lowering the solution temperature or raising the solution pH induces a worm-to-sphere transition and hence an increase in diffusion coefficient by a factor of between four and eight. FCS enables morphological transitions to be monitored at relatively high copolymer concentrations (10% w/w) compared to those required for dynamic light scattering (0.1% w/w). This is important because such transitions are reversible at the former concentration, whereas they are irreversible at the latter. Furthermore, the FCS data suggest that the thermal transition takes place over a very narrow temperature range (less than 2 °C). These results demonstrate the application of FCS to characterize order-order transitions, as opposed to order-disorder transitions. The temperature and pH-dependent diffusion of poly(glycerol monomethacrylate)-block-poly(2-hydroxypropylmethacrylate)- nanoparticles in water is characterized using fluorescence correlation spectroscopy. Lowering either the solution temperature or pH induces a worm-to-sphere transition and hence an increase in diffusion coefficient by a factor of between four and eight.

This review updates recent progress in the understanding of the behaviour of polymers at surfaces and interfaces, highlighting examples in the areas of wetting, dewetting, crystallization, and 'smart' materials. Recent developments in analysis tools have yielded a large increase in the study of biological systems, and some of these will also be discussed, focussing on areas where surfaces are important. These areas include molecular binding events and protein adsorption as well as the mapping of the surfaces of cells. Important techniques commonly used for the analysis of surfaces and interfaces are discussed separately to aid the understanding of their application.

International audience; Small-angle neutron scattering (SANS) and neutron spin-echo (NSE) have been used to investigate the temperature-dependent solution behaviour of highly-branched poly(N-isopropylacrylamide) (HB-PNIPAM). SANS experiments have shown that water is a good solvent for both HB-PNIPAM and a linear PNIPAM control at low temperatures where the small angle scattering is described by a single correlation length model. Increasing the temperature leads to a gradual collapse of HB-PNIPAM until above the lower critical solution temperature (LCST), at which point aggregation occurs, forming disperse spherical particles of up to 60 nm in diameter, independent of the degree of branching. However, SANS from linear PNIPAM above the LCST is described by a model that combines particulate structure and a contribution from solvated chains. NSE was used to study the internal and translational solution dynamics of HB-PNIPAM chains below the LCST. Internal HB-PNIPAM dynamics is described well by the Rouse model for non-entangled chains.

The nanoscopic adhesive and frictional behaviour of end-grafted poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with gold- or PDMAEMA-coated atomic force microscope tips in potassium halide solutions with different concentrations up to 300 mM is a strong function of salt concentration. The conformation of the polymers in the brush layer is sensitive to salt concentration, which leads to large changes in adhesive forces and the contact mechanics at the tip–sample contact, with swollen brushes (which occur at low salt concentrations) yielding large areas of contact and friction–load plots that fit JKR behaviour, while collapsed brushes (which occur at high salt concentrations) yield sliding dominated by ploughing, with conformations in between fitting DMT mechanics. The relative effect of the different anions follows the Hofmeister series, with I− collapsing the brushes more than Br− and Cl− for the same salt concentration.

The Flory-Huggins free energy of mixing is shown to be appropriate for the analysis of the temporal evolution of a ternary blend of polystyrene and poly (methyl methacrylate) during spin-coating from toluene using an in-situ light scattering technique. For the range of concentrations studied, both the onset of film instability and the observation of a scattering ring occur at the same toluene volume fraction. The success of Flory-Huggins theory indicates that polymer chains retain random walk characteristics during spin-coating. It is also concluded that the thermodynamics of phase separation during film formation is independent of the initial solvent concentration.

International audience; We have used neutron reflectivity to investigate the stratification of poly(3-hexylthiophene) (P3HT) and phenyl-C-61-butyric acid methyl ester (PCBM) blend films. Films were spun-cast on poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and titanium oxide (TiOx) layers to mimic the procedures followed for the fabrication of conventional and inverted organic photovoltaics respectively. The resultant scattering length density profiles reveal a PCBM-rich layer is formed in the vicinity of PEDOT: PSS or TiOx, while PCBM is depleted at the free surface of the film. PCBM segregation close to the substrate is further enhanced by annealing. This stratification is considered to be favorable only for inverted devices. (C) 2013 Elsevier B. V. All rights reserved.

We demonstrate the diffusion of single poly(ethylene glycol) molecules on surfaces which change from hydrophilic to hydrophobic over a few micrometers. These gradients in surface energy are shown to drive the molecular diffusion in the direction of the hydrophilic component. The polymer diffusion coefficients on these surfaces are measured by fluorescence correlation spectroscopy and are shown to be elevated by more than an order of magnitude compared to surfaces without the surface energy gradient. Along the gradient, the diffusion is asymmetric, with diffusion coefficients approximately 100 times greater in the direction of the gradient than orthogonal to it. This diffusion can be explained by a Stokes-Einstein treatment of the surface-adsorbed polymer.

We have used neutron reflectometry to characterize the swelling behaviour of brushes of poly[2-(diethyl amino)ethyl methacrylate], a polybase, as a function of pH. The brushes, synthesized by the "grafting from" method of atom transfer radical polymerization, were observed to approximately double their thickness in low pH solutions, although the pKa is shifted to a lower pH than in dilute solution. The composition-depth profile obtained from the reflectometry experiments for the swollen brushes reveals a region depleted in polymer between the substrate and the extended part of the brush. © The Royal Society of Chemistry.

For environmentally-switchable adhesive systems to be reused repeatedly, the adhesive strength must not deteriorate after each adhesion cycle. An important criterion to achieve this goal is that the integrity of the interface must be retained after each adhesion cycle. Furthermore, in order to have practical benefits, reversing the adhesion must be a relatively rapid process. Here, a double-network hydrogel of poly(methacrylic acid) and poly[oligo(ethylene glycol)methyl ether methacrylate] is shown to undergo adhesive failure during pH-switchable adhesion with a grafted (brush) layer of polycationic poly[2-(diethyl amino)ethyl methacrylate], and can be reused at least seven times. The surfaces are attached at pH 6 and detached at pH 1. A single-network hydrogel of poly(methacrylic acid), also exhibits pH-switchable adhesion with poly[2-(diethyl amino)ethyl methacrylate] but cohesive failure leads to an accumulation of the hydrogel on the brush surface and the hydrogel can only be reused at different parts of that surface. Even without an environmental stimulus (i.e. attaching and detaching at pH 6), the double-network hydrogel can be used up to three times at the same point on the brush surface. The single-network hydrogel cannot be reused under such circumstances. Finally, the time taken for the reuse of the double-network hydrogel is relatively rapid, taking no more than an hour to reverse the adhesion.

We describe an investigation of fluorescence correlation spectroscopy into the diffusion of fluorescein-tagged dextran (FDEX) in a poly(methacrylic acid) (PMAA) hydrogel. The temperature dependence of FDEX diffusion is shown to follow Zimm behavior in pure water, and the decrease in the diffusion coefficient when in the PMAA hydrogel has been modeled. The addition of acid and alkali (HCl and NaOH, respectively) not only control the swelling and collapse of the hydrogel but also reveal a strong pH dependence of the dextran diffusion coefficient, which shows a (nonmonatonic) increase with pH. The addition of NaCl and CaCl2 salts similarly showed evidence of network swelling, most notably at low salt concentration, but also that the diffusion coefficient within the gel at these low concentrations is larger than that in the equivalent solution without the hydrogel, indicating that the combination of hydrogel and salt works to increase the diffusion coefficient above that in pure water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

We consider the behaviour of single molecules on surfaces and, more generally, in confined environments. These are loosely split into three sections: single molecules in biology, the physics of single molecules on surfaces and controlled (directed) diffusion. With recent advances in single molecule detection techniques, the importance and mechanisms of single molecule processes such as localised enzyme production and intracellular diffusion across membranes has been highlighted, emphasising the extra information that cannot be obtained with techniques that present average behaviour. Progress has also been made in producing artificial systems that can control the rate and direction of diffusion, and because these are still in their infancy (especially in comparison to complex biological systems), we discuss the new physics revealed by these phenomena.

We have studied the pH-dependent interaction between mycolic acid (MA) monolayers and hydrophobic and hydrophilic surfaces using molecular (colloidal probe) force spectroscopy. In both cases, hydrophobic and hydrophilic monolayers (prepared by Langmuir–Blodgett and Langmuir–Schaefer deposition on silicon or hydrophobized silicon substrates, respectively) were studied. The force spectroscopy data, fitted with classical DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory to examine the contribution of electrostatic and van der Waals forces, revealed that electrostatic forces are the dominant contribution to the repulsive force between the approaching colloidal probe and MA monolayers. The good agreement between data and the DLVO model suggest that beyond a few nm away from the surface, hydrophobic, hydration, and specific chemical bonding are unlikely to contribute to any significant extent to the interaction energy between the probe and the surface. The pH-dependent conformation of MA molecules in the monolayer at the solid-liquid interface was studied by ellipsometry, neutron reflectometry, and with a quartz crystal microbalance. Monolayers prepared by the Langmuir–Blodgett method demonstrated a distinct pH-responsive behaviour, while monolayers prepared by the Langmuir–Schaefer method were less sensitive to pH variation. It was found that the attachment of water molecules plays a vital role in determining the conformation of the MA monolayers.

Angle resolved XPS (ARXPS) and scanning force microscopy (SFM) are used to study polystyrene/poly(vinyl ethyl ether) 50/50 wt% blend thin films spin cast from toluene solution, as a function of polystyrene molecular weight and film thickness. ARXPS is used to investigate the composition depth profile (CDP) of the blend thin films and SFM to study their surface morphology and miscibility. The CDPs are modelled by an empirical hyperbolic tangent function with three floating parameters. These are determined by non-linear least squares regression, their uncertainties estimated and the curve fit residuals analysed to demonstrate that the hyperbolic tangent CDP is a satisfactory fit to the ARXPS data. Conclusions are drawn regarding the behaviour of the blend thin films as the thickness and polystyrene molecular weight are varied. Flory-Huggins interaction parameters (chi) for the mixtures are calculated based upon the segregation data, and suggest a value of chi = 0.05 to be appropriate for this system. (c) 2009 Elsevier B.V. All rights reserved.

Neutron reflectivity and photoluminescence measurements are reported on bilayers of polyfluorene-based conjugated polymers. By using a novel thermal processing procedure it is possible to control the width of the interface between poly(9,9-dioctylfluorene) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), and measure the impact of interfacial roughness on the resonant energy transfer of excitons at the interface (Forster transfer). It is found that increasing the root mean square (rms) roughness of the F8/F8BT interface over the range of ∼1 nm to ∼5 nm leads to a greatly enhanced Forster transfer from F8 to F8BT molecules. By comparing photoluminescence measurements with simple calculations it is concluded that the level of enhancement of the F8BT peak at rough interfaces can only be adequately explained if mixing of F8 and F8BT at a molecular level dominates over the interfacial roughness due to thermally excited capillary waves.

We suggest a link between film morphology and electrical properties of a crystalline organic semiconductor: polymer insulating blend. TIPS-Pentacene (6,13-bis(triisopropylsilylethynyl) pentacene) [J. Am. Chem. Soc. 123, 9482 (2001)] is formulated with various amorphous and semi-crystalline side chain aromatic low permittivity dielectric polymers. Film structure investigated by AFM microscopy and XPS gives invaluable information regarding film morphology and confirms potential intermolecular interaction. All these morphological observations were linked to the electrical characterisation of organic thin film transistors (OTFTs) and the determination of saturated hole mobility value. When an amorphous binder is used the more dilute the TIPS-pentacene the lower the saturated hole mobility value. When a semi-crystalline binder is used it is possible to massively dilute TIPS-pentacene within the polymer dielectric without loosing either the crystalline structure of the material or the electronic properties. Besides phase segregation, enrichment of the active interface in TIPS-Pentacene is demonstrated. [DOI: 10.1380/ejssnt.2009.455]

Electrolyte-gated organic field-effect transistors (EGOFETs), based on ultrathin pentacene films on quartz, were operated with electrolyte solutions whose pH was systematically changed. Transistor parameters exhibit nonmonotonic variation versus pH, which cannot be accounted for by capacitive coupling through the Debye–Helmholtz layer. The data were fitted with an analytical model of the accumulated charge in the EGOFET, where Langmuir adsorption was introduced to describe the pH-dependent charge buildup at the quartz surface. The model provides an excellent fit to the threshold voltage and transfer characteristics as a function of the pH, which demonstrates that quartz acts as a second gate controlled by pH and is mostly effective from neutral to alkaline pH. The effective capacitance of the device is always greater than the capacitance of the electrolyte, thus highlighting the role of the substrate as an important active element for amplification of the transistor response.

Resume. Nous presentons quelques exemples qui demontrent l’utilite et la puissance de la reflectometrie de neutrons pour l’etude des surfaces et des interfaces de polymeres. Ces exemples concernent l’interdiffusion entre deux polymeres miscibles, la penetration d’une chaine greffee dans un reseau du meme polymere, la cinetique de la formation d’une « brosse » de polymere et l’enrichissement d’un polymere a la surface d’un melange homogene de deux polymeres.

The molar mass and dispersity of a polycation, poly[2-(dimethyl amino)ethyl methacrylate)] (PDMAEMA) grafted from a poly(methyl methacrylate) (PMMA) backbone, was measured by single-molecule force spectroscopy (SMFS) and shown to be consistent with results from gel permeation chromatography for the same comb polymer in aqueous solution. Comparison was then made between the comb polymer and PDMAEMA brushes that were grown from the substrate, as a function of the pH and ionic strength of the surrounding medium, and the limits of reliable characterization of the polymers are determined. A large discrepancy was observed between the responses of the comb and brush layer at low pH when the PDMAEMA molecules are extended from the supporting substrate. Here it is believed that the atomic force microscope (AFM) tip can penetrate the comb layer and selectively desorb side-chains of the comb. In the case of the well solvated PDMAEMA brushes at high pH, the tip preferentially selects larger chains, resulting in an over-estimate of the brush molar mass. The addition of salt also influenced the molar mass obtained by this technique. It is believed that salted brushes did not adhere well to the AFM tip, with subsequent desorption resulting in an underestimate of the molar mass. However, SMFS was shown to be capable of demonstrating the effect of salt on brush conformation, with greater swelling after the addition of a small amount of NaCl, but a significant decrease when 100 mM is added.

Hydrogel brushes are materials composed of a water-swollen network, which contains polymer chains that are grafted with another polymer. Using a thermally responsive polymer, poly( N -isopropyl acrylamide) (polyNIPAM), as the graft component we are able to maintain the critical solution temperature ( T crit ), independent of the overall composition of the material, at approximately 32°C. The change in swelling at T crit is a function of the amount of polyNIPAM in the system. However, there is a much smaller change in the surface contact angles at T crit . PolyNIPAM-based materials have generated considerable interest, as ‘smart’ substrates for the culture of cells and here, we show the utility of hydrogel brushes in cell culture. Chondrocytes attached to the hydrogel brushes and yielded viable cell cultures. Moreover, the chondrocytes could be released from the hydrogel brushes without the use of proteases by reducing the temperature of the cultures to below T crit to induce a change in the conformation of the polyNIPAM chain at T crit . The importance of the crosslink hydrogel component is illustrated by significant changes in cell attachment/cell viability as the crosslink density is changed.

Specular neutron reflectivity and nuclear reaction analysis (NRA) are used to measure the interfacial width between poly(9,9-dioctylfluorene) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) in a 500 nm bilayer. Annealing at temperatures up to 280 °C allows us to vary this width over a large range, from ∼1 nm to greater than 30 nm. Approximate calculations using the predictions of self-consistent field theory (SCFT) for both Gaussian and semiflexible chains suggest that in the liquid−liquid regime the Gaussian results of SCFT are valid for this system. We also demonstrate the ability to control the interfacial width in 100 nm bilayers, on both silicon and indium tin oxide (ITO). The procedure of “preannealing” the F8 and F8BT layers, before bringing them together to make a bilayer, allows us to independently control the interfacial width and the properties of the bulk of these 100 nm films.

The mechanical properties of Rhodococcus RC291 were measured using force spectroscopy equipped with a bacterial cell probe. Rhodococcal cells in the late growth stage of development were found to have greater adhesion to a silicon oxide surface than those in the early growth stage. This is because there are more extracellular polymeric substances (EPS) that contain nonspecific binding sites available on the cells of late growth stage. It is found that EPS in the late exponential phase are less densely bound but consist of chains able to extend further into their local environment, while the denser EPS at the late stationary phase act more to sheath the cell. Contraction and extension of the EPS could change the density of the binding sites, and therefore affect the magnitude of the adhesion force between the EPS and the silicon oxide surface. By treating rhodococcal EPS as a surface-grafted polyelectrolyte layer and using scaling theory, the interaction between EPS and a solid substrate was modelled for the cell approaching the surface which revealed that EPS possess a large capacity to store charge. Changing the pH of the surrounding medium acts to change the conformation of EPS chains.

The reflectivity discontinuity arising from the concentration profile at critical adsorption at the liquid-vapour interface is interpreted in terms of the spectral properties of a potential well. When the well is soft enough at the top, the spectrum of bound states becomes continuous and reflectivity resonances caused by the potential well become a discontinuity. In order to apply this property to the true interaction potential between radiation and sample, we use a theorem of Abeles relating the reflectivity of a potential function to the reflectivity of a corresponding symmetric potential well.

We have used neutron reflectometry to study the kinetics of the formation of a surface-enriched layer of deuterated polystyrene from a film of a blend with normal (hydrogenated) polystyrene. Three blends are considered: one using a completely miscible blend and two approaching the coexistence curve from the one-phase region. A simple theory based upon the assumption that the surface-enriched layer is in local equilibrium with a depletion layer provides qualitative agreement with the data. The formation of a wetting layer "depinned" from the surface layer is not observed in the times studied in the experiment.

The curvilinear velocity (VCL) of boar spermatozoa between standard microscopy glassware decreases when the slides are coated with the hydrophobic polymer polystyrene (PS) compared with the less hydrophobic poly(methyl methacrylate) (PMMA) coating. Sperm from three boars were observed and analyzed using particle tracking software. The VCL did not differ significantly between coatings of different thickness, indicating no penetration of the sperm into the coating and that only the surface layer of the polymer film interacts with the sperm and buffer medium. The VCL of sperm between PS-coated surfaces was significantly reduced compared with PMMA surfaces (P < 0.0001), and this was attributed to a stronger hydrophobic effect between PS and water. The size of this effect varied between different boars, perhaps as a consequence of variations in hydrophobicity of sperm from different boars or different ejaculates. The modification of surface properties in this way may improve our understanding of sperm behavior and may provide improvements to assisted conception techniques as animal or human sperm used in assisted conception are frequently manipulated in laboratory plastics as part of diagnostic procedures (e.g., semen analysis) or before injection into an oocyte or during the co-incubation with the oocyte in IVF. Controlling the velocity of sperm using the interaction properties of inert polymer coatings could lead to new sperm selection procedures for clinical use or the development of model systems to better understand sperm-surface interactions.

International audience; We report the increased crystallization of poly(3-hexylthiophene) (P3HT) in the donor-acceptor mixture of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) with P3HT by the addition of a block copolymer, P3HT-b-PI, where PI refers to polyisoprene. The photovoltaic performance of devices created using this blend is markedly improved by the addition of the diblock copolymer. We have characterized the structure of thin films of the P3HT-b-PI containing mixtures using optical microscopy, scanning force microscopy, UV-vis absorption spectroscopy, neutron reflectometry, and grazing incidence X-ray diffraction (GIXD). The GIXD data provide the information on the crystallinity of the films, the absorption data were used to confirm that the addition of the diblock was responsible for the increase in crystallization, neutron reflectometry data reveal a PCBM-rich region near the hole injection layer, and the two microscopy techniques revealed the structural effect of the crystallization at the surface of the films.

Following the recent determinations of the fractional abundances of H30+ and H20 in dense interstellar clouds, the production and loss processes for these species have been investigated in the laboratory. The major processes involved are dissociative electron recombination of H30+ and proton transfer to and from H20. The complete product distribution for the H30+ recombination has now been determined and leads to the product channels OH + H2(0.36), OH+2H(0.29) and 0+ H + H2(0.30) with the channel H + H20 (0.05) being much smaller than previously assumed. It has been shown that loss of H30+ by proton transfer to a series of sulphur-containing species with larger proton affinities is very efficient and also non-dissociative, further establishing the trend for proton transfer reactions involving this ion. These data have been used in a limited model to predict the fractional abundance of H20 and the relative abundances of H20 and H30+ in Sgr B2. Predictions are also made for other dense interstellar clouds.

Interfaces between a poly(3-hexylthiophene) [P3HT] and an end-grafted (brush) layer of poly(methyl methacrylate) [PMMA] are shown using neutron reflectometry to be dependent on heat treatment. Annealing the samples allows part of the brush layer to cross into the P3HT layer creating a very asymmetric interface. We suggest that the P3HT rearrangement occurs, creating space for movement of the brush into the film. This interpenetration was observed with two different molecular weight (17.5 and 28 kg mol−1) P3HT films. Output characteristics of devices made from P3HT layers on PMMA brushes show that different amounts of heat treatment do not significantly change the device performance. Saturated hole mobilities are dependent on heat treatment, with devices made from a smaller molecular weight P3HT (22 kg mol−1) demonstrating larger mobilities than devices created using 48 kg mol−1 P3HT, but only after heat treatment.

We have fully characterized the three-dimensional morphology of thin films of mixtures of polystyrene and polybutadiene cast from a toluene solution, using nuclear reaction analysis, neutron reflectometry and transmission electron microscopy. Polystyrene-rich phases wet both the air and substrate interfaces and are separated by a polybutadiene-rich phase; these layers are very well defined and the interfaces between them are sharp (down to A ). Within the polybutadiene-rich central layer, lateral phase separation is also evident, with polystyrene-rich domains of oblate spheroidal shape. Under certain circumstances thin polystyrene-rich layers exist within the polybutadiene-rich phase. We discuss possible mechanisms for this unusual morphology in terms of surface effects on the mechanism of phase separation in the ternary polymer-solvent system from which the films are cast.