Vehicle routing problems with alternative paths: An application to on-demand transportation

20 pagesInternational audienceThe class of vehicle routing problems involves the optimization of freight or passenger transportation activities. These problems are generally treated via the representation of the road network as a weighted complete graph. Each arc of the graph represents the shortest route for a possible origin-destination connection. Several attributes can be dened for one arc (travel time, travel cost . . . ), but the shortest route modelled by this arc is computed according to one single criterion, generally travel time. Consequently, some alternative routes proposing a dierent compromise between the attributes of the arcs are discarded from the solution space. In this work, we propose to represent the road network with a multigraph, so that these alternative routes are considered, and to evaluate how it impacts on solution algorithms and solution values. A simple insertion algorithm is proposed and illustrated in the context of a on-demand transportation system developed in a French area. Computational experiments on academic and realistic data underline the potential cost savings brought by the multigraph model

Plaque Biology, Realizing the Clinical Potential

EU renewable energy support policy: Faith or facts?

The growth response of Alternanthera philoxeroides in a simulated post-combustion emission with ultrahigh [CO2] and acidic pollutants

Although post-combustion emissions from power plants are a major source of air pollution, they contain excess CO2 that could be used to fertilize commercial greenhouses and stimulate plant growth. We addressed the combined effects of ultrahigh [CO2] and acidic pollutants in flue gas on the growth of Alternanthera philoxeroides. When acidic pollutants were excluded, the biomass yield of A. philoxeroides saturated near 2000 micromol mol(-1) [CO2] with doubled biomass accumulation relative to the ambient control. The growth enhancement was maintained at 5000 micromol mol(-1) [CO2], but declined when [CO2] rose above 1%, in association with a strong photosynthetic inhibition. Although acidic components (SO2 and NO2) significantly offset the CO2 enhancement, the aboveground yield increased considerably when the concentration of pollutants was moderate (200 times dilution). Our results indicate that using excess CO2 from the power plant emissions to optimize growth in commercial green house could be viable.

Static and fatigue failure of quasi-brittle materials at a V-notch using a Dugdale model

International audienceThe prediction of crack nucleation at stress concentration points in brittle and quasi-brittle materials may generally rely on either an Irwin-like criterion, involving a critical value of the generalized stress intensity factor of the singularity associated to the stress concentration, or on cohesive zone models. Leguillon's criterion enters the first category and combines an energy condition and a stress one. Thanks to matched asymptotics procedures, the associated numerical values at crack initiation under quasi-static monotonic loadings are shown to be comparable to those obtained using the Dugdale cohesive zone model. Both approaches are therefore adapted to the description of brittle and quasi-brittle fracture. A macroscopic Paris-like propagation law is derived from the Dugdale model through a relevant cumulating law at the microscopic scale of the process zone. Comparisons with experimental results are performed and display good agreement. The important matter of nucleation and growth of a fatigue crack at the root of a V-notch is finally addressed. A general Paris law featuring the elastic singularity exponent and then dependent on the V-notch angle can be expressed for small cyclic loadings in the early growth stage

Control of morphology orientation in thin films of PS-b-PEO diblock copolymers and PS-b-PEO/resorcinol molecular complexes

One of the main limits in the use of block copolymers for nanotechnological applications lies in the poor control over the alignment of the nanoscopic domains. The self-assembling behavior of polystyrene- block -poly(ethylene oxide) (PS- b -PEO) has been modified by stoichiometric complexation of the ethylene oxide units with resorcinol and a simple procedure to prepare nanostructured films with normally oriented cylinders is reported. By direct spin coating of a series of complexated PS- b -PEO samples with different molecular weight and composition, films with the same morphology and orientation (i.e., normally oriented packed cylinders) have been obtained, also when different nanostructures and alignments were expected on the basis of the volume fraction composition and self-assembling behavior of pure copolymers. Tuning of the cylinder diameters in the range from 20 to 50 nm was possible by varying the length of the PEO block. The effects of resorcinol complexation have been studied by differential scanning calorimetry and X-ray diffraction and the morphologies of PS- b -PEO and PS- b -PEO/resorcinol films have been monitored by atomic force microscopy and electron microscopies. DSC and XRD analyses demonstrate that resorcinol significantly influences the crystallization behavior of the PEO block. The varied interfacial and surface energies of the PEO domains and the overall reduction of the crystalline phase in PS- b -PEO/resorcinol films appear to be strictly related to the morphological changes occurring by complexation. Keywords Block copolymers Orientation Self-assembly Supramolecular interactions 1 Introduction In the last decade block copolymers have received an ever increasing attention in the nanoscience and nanotechnology research [1–4] . The main reasons that have made block copolymers promising and efficient candidates for the preparation of a wide range of periodic structures in the nanoscopic length scale are: (a) the dimension of the domains, which is in the range of tens of nanometers; (b) the self-assembling capability of block copolymers, that is related to the thermodynamic incompatibility of the blocks and that drives them to segregate in different domains, e.g., lamellar, gyroid, hexagonal and body-centered cubic for diblock copolymers; and (c) the convenient size and shape tunability of these nanodomains, provided by simply changing their molecular weights and compositions, the chain architecture and the chemical interactions existing between the blocks [5] . In many advanced applications (functional membranes and coatings, optoelectronic devices, etc.) polymers are used in the form of thin films. It is under this form that block copolymer systems are exploited with the aim of obtaining controlled morphological patterns well extended in surface and with the desired orientation. It is well known that structural behavior of thin layers compared with bulk materials is often much more complicated. Due to the prevalence of surface and interface forces, thin films of block copolymers may undergo both surface relaxations and reconstruction, thus showing unexpected structural shapes [6,7] . In general, structural order over large extension can be created in self-organizing materials through several molecular interactions including hydrophilic and hydrophobic effects, hydrogen bonding, columbic interactions and van der Waals forces [8–11] . Different techniques have been used to increase the level of order in block copolymer films [12] , such as application of electric fields [13,14] , chemically patterned substrates [15,16] , shear forces [17,18] , controlled interfacial interactions [19] and temperature gradient [20] . Also thermal and solvent annealing have a great influence on the morphology of thin films formed by deep casting or spin coating [21–24] . Both the rate of solvent evaporation and solvent annealing have been invoked for interpreting strong effects of ordering and orientation on the nanostructured morphologies of block copolymers [25] . In particular, solvent annealing may improve the ordering in copolymer thin films, removing the defects of domain organization and achieving a long range lateral order [26–28] . The effects of solvent vapor treatments appear to be time-dependent, showing high initial rates in the ordering behavior or differences in the nanostructures with treatment times [7,29] . A supramolecular approach to block copolymer self-assembly, based on attractive hydrogen bonding interactions between different block copolymers [30] or between one of the blocks and small molecules bearing hydroxyl and/or carboxylic groups [31] , has been also proposed. This approach appears to provide a simple and powerful technique for fine tuning of the block copolymer morphologies, and has been successfully applied in bulk and in thin films. Interesting results have been obtained by complexation of polystyrene- block -poly(4-vinyl pyridine) (PS- b -P4VP) copolymers with different small molecules like, for example, 1,5-dihydroxynapthalene [32] , 3- n -pentadecylphenol [33,34] and 2-(4′-hydroxybenzeneazo)benzoic acid [35] . In all such cases the small molecules contain hydroxyl groups which selectively interact with the pyridine nitrogen of PS- b -P4VP via hydrogen bonding, driving the block copolymer complex to the formation of ordered nanostructured films with specific domain orientations depending on the applied experimental conditions of solvent annealing. Most of the studies on the supramolecular approach to nanoscale structures have been so far performed with PS- b -P4VP copolymers, however the same strategy may be positively adopted with other block copolymers as long as one of the blocks may interact specifically with some probe molecules. In particular polystyrene- block -poly(ethylene oxide) (PS- b -PEO) diblock copolymers appear to be a natural choice as they are already known to form thin films with nanostructured patterns whose extent and orientation is affected by solvent treatments [19,28] . In this work we present the most significant results of a basic and comprehensive study carried out on self-assembled PS- b -PEO thin films with the final aim to propose a methodology of wider applicability for the fabrication of well-oriented block copolymer morphologies. We have investigated in some detail the self-assembling behavior of three different PS- b -PEO samples, taking into account the consequence of introducing supramolecular interactions in the block copolymer films. We showed for the first time that by spin coating PS- b -PEO solutions containing resorcinol is possible to obtain directly nanostructured films with relatively well ordered PEO/resorcinol packed cylinders oriented perpendicularly to the substrate, independently on the block copolymer molecular weight. This behavior is likely to depend on the changes introduced in the crystalline block: complexated PEO has a different crystallographic structure than pure PEO, interfacial and surface energies of PEO domains must be affected by complexation with resorcinol and the overall amount of crystalline phase in the complexated block copolymer films decreases with respect to the amorphous one. 2 Experimental 2.1 Materials PS 563 - b -PEO 705 ( M n = 58600- b -31000), PS 308 - b -PEO 250 ( M n = 32000- b -11000) and PS 183 - b -PEO 145 ( M n = 19000- b -6400) were purchased from Polymer Source Inc. (Dorval, Canada) and used without further purification in this study. The volume fraction of the PEO block ( Φ PEO ) is: Φ PEO = 0.36 for PS 563 - b -PEO 705 and Φ PEO = 0.24 for both PS 308 - b -PEO 250 and PS 183 - b -PEO 145 . Resorcinol and benzene were both purchased from Sigma–Aldrich. 2.2 Films preparation PS- b -PEO benzene solutions were prepared at a concentration of 5 wt%. PS- b -PEO and resorcinol mixtures with a molar ratio resorcinol:ethylene oxide (R:EO) of 1:2 were also dissolved in benzene. A few drops of each solution were spin-coated onto mica substrates, using a 8″ Desk-top Precision Spin Coating System, model P-6708D vs. 2.0. All the films were prepared following the same spin coating program in order to reproduce the film thickness and therefore avoid variations in the film nanostructure. After spin coating the films were dried in a hood at ambient temperature for at least 12 h in order to have a complete evaporation of the solvent. Post-evaporation solvent vapor treatments were performed under a saturated benzene atmosphere in a hermetic Pyrex flask preheated at 60 °C. 2.3 Characterization Atomic Force Microscopy (AFM) was used to obtain information on the block copolymer film morphologies. Analysis were performed in air at room temperature with a Park Systems instrument, model XE-100, operating in tapping mode. A silicon microcantilever with the reflective side coated with aluminum (force constant 20 N/m and resonance frequency of 265 kHz) and conical silicon tips (radius of curvature less than 10 nm, tip height 15–20 μm, full tip cone angle less than 30°) were used for the scanning. Scan rates were set between 1 and 2 Hz. Topographic (height-mode) and viscoelastic (phase-mode) data were recorded simultaneously. Transmission electron microscope (TEM) studies were performed on a Philips CM-12, working at an accelerating voltage of 100 kV or on a Zeiss Libra 120. In order to prepare cross-sectional specimens, films were embedded in a low viscosity modified Spurr epoxy resin, which was cured at 60 °C. After trimming to shape by a Leica EM TRIM, ultrathin sections (less than 100 nm) were cut at room temperature using a Leica Ultracut UCT microtome equipped with a diamond knife. At the end, ultrathin sections were collected in a trough filled with water and lifted onto Formvar coated copper grids. In order to prevent the diffusion of the epoxy resin into the polymer film, a thin layer of carbon was evaporated over the film surface. Top-view specimens were prepared by separating the thin films from the mica substrate, spun-coated as reported above, by floating it on water, due to the strong affinity of water for mica. Film fragments were then collected using Formvar coated copper grids. Scanning electron microscope (SEM) were performed with a Zeiss UltraPlus field emission SEM equipped with a Inlens detector. Fourier Transform Infrared Spectroscopy (FTIR) was used to investigate the hydrogen bond interactions between block copolymers and resorcinol. Samples were prepared by solvent casting from benzene onto silica wafers and transmission infrared spectra were collected with a Thermo-Nicolet FTIR Nexus instrument with a DTGS detector. The measurements were carried out in the spectral range of 4000–400 cm −1 , with a resolution of 4 cm −1 and 32 scans. Thermal analysis were carried out with a Q200 (TA Instruments) Differential Scanning Calorimeter equipped with a refrigerated cooling system in the temperature range from −100 to 150 °C, with a scanning rate of 20 °C/min and under nitrogen atmosphere. Sealed aluminum pans containing ∼5 mg of samples were used. X-ray diffraction (XRD) measurements of polymer films were carried out with a conventional rotating anode source (Siemens D5005). The drive axis was 2 θ for a scan range of 10–35° with a step of 0.02°. High intensity Cu Kα X-rays, obtained after passing through both a kβ filter and counter monochromator, were employed for the diffraction experiments. 3 Results and discussion Spun-cast thin films of PS- b -PEO copolymers with different composition in terms of block length and volume fraction have been prepared following the procedure described in the experimental section. PS- b -PEO melts and solutions are systems in a hard confinement regime, that is PEO is expected to crystallize confined in microdomains since crystallization occurs at temperatures below the glass transition of the PS matrix. According to their volume fraction composition, the block copolymer samples considered in this study predominantly self-segregate in cylindrical morphologies or in mixed cylinders and lamellae when the PEO composition is closed to the domain transition composition. The film surfaces shown in Fig. 1 a–c exhibit non-equilibrium morphologies obtained by spin coating PS- b -PEO solutions on mica sheets. Fig. 1 d–f show the improved and regular morphologies obtained by solvent annealing spun-cast films. On the basis of theoretical considerations PEO microdomains should be oriented parallel to the surface due to preferential interactions of the PEO blocks with either air or the mica substrate. On the contrary some of the resulting morphologies are normally oriented. As already mentioned in the introduction, a number of factors can interfere in the ordering and orientation of nanodomains during the drying of the swollen film, and the dynamics of solvent evaporation and post-evaporation treatments appear to be among the most important ones. Being a non-selective solvent for both PS and PEO, benzene is able to effectively dissolve either blocks and to reduce preferential interactions not only in polymer solutions but also after casting, when the solvent still swells the film, thus allowing thermodynamically unfavorable morphologies. The AFM phase images of Fig. 1 a–c demonstrate that by spin coating block copolymer solutions nanophase separation occurs, but the morphology obtained is far from the equilibrium one. Kinetic factors can direct nanophase separation as well. Solvent evaporation is a highly directional process and if it is sufficiently fast nanodomains may arrange in a vertical morphology, even if the in-plane one is more thermodynamically stable. On the other hand, low evaporation rate will produce a lower perpendicular orientation but higher lateral order because the chains have enough time to approach their thermodynamically stable equilibrium. Moreover, the solvent evaporation rate and the formation of a solvent evaporation gradient in the film depend on the solvent mobility, which is related to the domain size and shape, and to the copolymer chemical composition, molecular weight and, as it will be discussed further in this paper, to crystallinity. For the samples with Φ PEO = 0.24, molecular weight, or some other molecular weight depending parameter, is clearly the key parameter that determines the final orientation: under the same, fast drying conditions, the PS 308 - b -PEO 250 sample has PEO cylinders aligned in the plane of the film ( Fig. 1 b), while the lower molecular weight PS 183 - b -PEO 145 arranges preferentially in a vertical cylinder morphology ( Fig. 1 c). In both cases the degree of lateral order is low and spinning speeds faster than 1000 rpm, i.e., the speed applied in the last step of preparation of the reported films, did not seem to significantly affect the orientation of the resulting morphologies. A great improvement in the lateral ordering of nanodomains was achieved by placing the films under a benzene atmosphere for 24 h at 60 °C ( Fig. 1 d–f). Post-evaporation solvent annealing induces a transition from the disordered to the ordered state which results in the highly regular morphologies shown in Fig. 1 d–f. These findings confirm the reported studies by Russell et al. [28,36–38] on the possibility to obtain normally oriented cylindrical arrays from a PS- b -PEO copolymer with very similar composition (around 25,000 g/mol and Φ PEO of ca. 0.24) of the lowest molecular weight sample chosen for this study. Fig. 1 demonstrates that this possibility can be extended to PS- b -PEO copolymers with longer chains and different molar composition thus obtaining highly oriented vertical lamellae and in-plane parallel cylinders. Another important parameter affecting microdomain segregation in block copolymer films is the length of the annealing treatment. During solvent annealing of PS- b -PEO films under benzene vapor, which is a good solvent for both blocks, a number of morphological transitions have been observed. For example, after one hour of solvent annealing the unaligned PEO cylinders ( Fig. 1 b) obtained by spin coating PS 308 - b -PEO 250 , acquire a periodic vertical orientation. Continued annealing to 15 h causes another transition approaching the equilibrium morphology, that consists of long and extended cylinders oriented parallel to the substrate ( Fig. 1 d). This structure is maintained also at longer annealing time, but after 48 h the morphology appears altered due to the high mobility given by the solvent vapor to the block copolymer chains and to dewetting phenomena. These observations demonstrate that both thermodynamic and kinetic effects can be exploited to guide self-assembling, but at the same time the number of factors affecting nanophase segregation is such that at the present level of knowledge it is very difficult to gain a full control over ordering and orientation on block copolymer films. As for the majority of nanotechnological applications the desired morphology is that of hexagonal-packed cylinders perpendicularly oriented, the design of a simple and straightforward method to prepare nanostructured films with this morphology is of great interest. In this respect a supramolecular approach based on the addition of a small molecule that preferentially interacts with one of the block is very promising. Russell et al. showed that salt complexation of block copolymer films dramatically affects the orientation of cylindrical nanodomains producing normally orientated cylinder arrays with enhanced lateral order [39] . Here, we demonstrate that also the capability of resorcinol to complex EO units by hydrogen bonding can strongly affect the copolymer film morphology especially because of the modification either of surface and interface interactions and of the crystallization behavior of the PEO block. It is known that, compared with other molecules bearing hydroxyl groups, the hydrogen bond between resorcinol and PEO is relatively strong. The binary phase diagram for PEO/resorcinol blends exhibits two eutectic phase transitions at 40 and 80 °C, corresponding at resorcinol molar compositions of approximately 10% and 50%. In between the liquidus curve shows a maximum at 33 M % resorcinol, pointing to the formation of a stoichiometric complex. In particular, the 2:1 M ratio PEO/resorcinol complex may crystallize in two allotropic modifications, α and β. The α form consists in an orthorhombic unit cell containing eight EO monomer units and four resorcinol molecules and melts at approximately 90 °C [40] . As for the scope of this work the β form can be ignored because it is rather unstable and rapidly transforms into the more stable α form, as demonstrated by the presence of a single endotherm peak at approximately 90 °C in DSC analyses (the melting signal of the β form is expected around 70 °C). By spin coating the various copolymer/resorcinol solutions considered in this study, independently from the molecular weight and the composition of the PS- b -PEO copolymers, the PEO/resorcinol phase self-segregate in cylindrical domains with relatively good lateral order and perpendicular orientation, as clearly highlighted by TEM. Top-view and cross-sectional TEM images of unstained films from a PS- b -PEO/resorcinol solution (PS 563 - b -PEO 705 , molar ratio resorcinol:ethylene oxide 1:2) are shown in Fig. 2 a and b. In bright field images the PS matrix appears darker than the PEO domains possibly due to a greater electronic contrast, whereas the partial dishomogeneity of cylinder diameter in the top-view, apparently in contrast with the more homogeneous pattern visible in the AFM and SEM images ( Fig. 3 a and b), is ascribed to a partial swelling (i.e., water solubilization) during the procedure of specimen preparation. In particular, the most direct evidence of the presence of well-oriented nanodomains came from cross-section, where cylinders are seen to span perpendicularly across the entire film. The topography of the film surface ( Fig. 3 a) exhibits a regular assembly of nanosized depressions, approximately 7 nm deep, probably arising from shrinkage of the PEO/resorcinol domains during crystallization. The color contrast in AFM phase images proves that PEO/resorcinol cylinders are softer than the surrounding PS matrix. The result is a nanostructured polymer thin film with a medium surface roughness of few nanometers. Moreover, the AFM phase images in Fig. 4 show the capability, through the simple procedure of film preparation here described, of tuning the cylinder diameters by varying the length of the PEO block. The films investigated had cylindrical nanophases with average cylinder diameters ranging from 18 nm for the copolymer with the shorter PEO block ( M n = 6400 g/mol), to 26 nm for the medium one ( M n = 11000 g/mol) and 45 nm for the longer PEO block ( M n = 31000 g/mol). High dimensional homogeneity was observed within each film. Together these results indicate that complexation significantly modify the self-assembling behavior of PS- b -PEO copolymers. Assuming volumetric additivity of PEO and resorcinol, and ignoring any other effect directing the microdomain segregation, a lamellar structure should result from each of the three copolymer complexes. On the contrary the observed morphology is always normally oriented cylinders and this proves that the nanophase segregation process is governed by additional factors than the thermodynamic of self-assembling. To fully disclose the nature and number of forces that determine the final observed morphology further studies will be required, but it appears reasonable that the reduced difference between the glass transition temperature of PS (around 100 °C) and the melting point of the PEO/resorcinol complex (90 °C, also see the discussion of the DSC analyses reported below), with respect to the PEO one (between 50 and 60 °C), must have an effect on the crystallization forces acting almost at the same as the film formation. In these conditions the strong hydrogen bonds acting in the crystalline PEO phase, and in the amorphous one as well, allow to overcome the interfacial interactions governing the orientation of nanodomains in PS- b -PEO films. The formation of hydrogen bonding between resorcinol and ethylene oxide units of PS- b -PEO copolymers has been demonstrated by infrared spectroscopy and differential scanning calorimetry. Fig. 5 shows the infrared spectra of PS 563 - b -PEO 705 (a), resorcinol (b) and of the PS- b -PEO/resorcinol complex (c). According to Spěváček et al., that studied the formation of hydrogen bonding between PEO and different small molecules bearing polarized hydrogen atoms, the presence of a maximum in the hydroxyl absorption range at 3315 cm −1 is specific of the hydrogen bonding interaction between resorcinol and the oxygen atoms of the PEO block [41] . Another evidence is in the spectral range from 1200 to 1000 cm −1 , where some characteristic absorption peaks assigned to the C–O stretching of the ethylene oxide units (1114 and 1148 cm −1 ) and of resorcinol (1151 and 1167 cm −1 ) are slightly and regularly shifted indicating that in the presence of EO/resorcinol complexes the molecular environment is modified and characterized by a complex infrared absorption with maxima at 1087, 1110, 1147 and 1163 cm −1 . The formation of a complex between the PEO block and resorcinol is also proved by the shifting of the melting signal in the DSC curves [42] . Crystalline phases are strongly stabilized by hydrogen bonding and the strength of the hydrogen bond is reflected by the change in the melting transition. The PEO/resorcinol complex (curve c in Fig. 6 ), that is entirely in the α form, melts at a temperature approximately 30 °C higher than the corresponding pure block copolymer (curve b in Fig. 6 ). In curve c the absence of the melting signal of resorcinol confirms the complexation with EO. Moreover, the changes observed in the DSC curves of PS- b -PEO films and PS- b -PEO/resorcinol ones perfectly match with those expected for PEO and PEO/resorcinol complexes. This also confirms that the phase diagram of the PEO/resorcinol system is negligibly affected by polystyrene. The glass transition temperature of the PS block, and as a consequence its chains mobility, does not appear to be influenced by resorcinol, which is totally embedded in the PEO domains, either in the 2:1 EO/resorcinol complex crystalline phase and in the amorphous PEO phase. In addition to the weakened energy of the various interfaces the presence of resorcinol also influences the amount of crystalline phase in the copolymer films. An overview of the calorimetric data obtained from all the copolymer systems considered in this study is given in Table 1 . From these values it is possible to make some interesting considerations on the development of the crystallization degree of the PEO block by effect of resorcinol. In the PS- b -PEO copolymers the heat of fusion decreases with decreasing the chain length. In particular, the DSC curve of the lowest molecular weight copolymer does not show a definite endothermic melting signal preventing the calculation of the heat of fusion. The films prepared after complexation of the block copolymer with resorcinol in stoichiometric proportion do not contain crystalline resorcinol phases and show a general reduction of the copolymer crystallization degree, especially for the higher molecular weight PEO block. The same trend of the crystalline phase was also confirmed by X-ray diffraction analysis. The X-ray diffraction pattern of the PS- b -PEO/resorcinol complexes ( Fig. 7 a–c, lower curves) differ from both pure copolymers ( Fig. 7 a–c, upper curves) and resorcinol ( Fig. 7 d) and this demonstrates that the complex has a different crystallographic structure, with smaller crystalline size. The structure is reasonably the same found for the 2:1 PEO/resorcinol system, even if SAXS should be performed to confirm this hypothesis [40] . In the complexated block copolymers of lower molecular weight the diffraction peaks of the PEO/resorcinol complex become proportionally less intense and the diffraction curve is dominated by the contribution of the amorphous phase, e.g., the introduction of the high crystalline resorcinol into PS 563 - b -PEO 705 and PS 183 - b -PEO 145 copolymers entailed a reduction of total crystallinity down to 9.2% (from 13%) and 2.5% (from 9.7%), respectively. The observations done on the changes occurring to the crystalline block and to the degree of crystallization, combined with the morphologies of the PS- b -PEO copolymers studied, demonstrate that these two aspects are related to each other. Going back to Fig. 1 , the only copolymer that was able to arrange in perpendicular cylinders was the low molecular weight one, which is also the less crystalline sample. At the beginning of this discussion we explained the perpendicular orientation of Fig. 1 c in terms of a solvent evaporation directional effect able to orientate mobile low molecular weight polymer chains. It may be expected that under the same experimental conditions of solvent evaporation, chain mobility increases with decreasing the chain length. It is also well known that the presence of crystalline domains reduces the overall mobility of polymer chains. Thus, the formation of PS- b -PEO/resorcinol complexes, reducing the crystallinity of the polymer film and enhancing the mobility of polymer chains during film formation, must be a significant factor ‘forcing’ the complexated copolymers to self-segregate by spin coating giving perpendicular oriented PEO/resorcinol cylinders. 4 Conclusions Self-assembling PS- b -PEO copolymers have been investigated for their capability of forming nanostructured thin films. Two different strategies have been followed to optimize and control order and alignment of the domains, namely solvent evaporation and selective supramolecular interaction of one of the blocks with an additional component. Solvent annealing of block copolymer films has proved to increase lateral order resulting in well aligned nanodomains over large surface extension, but it is through the supramolecular approach that it was possible to achieve a unique control on the self-assembling, obtaining the desired morphology and orientation of the domains directly by spin coating block copolymer solutions. Well-oriented cylinders perpendicular to the film substrate, with diameters from around 20–45 nm, were obtained by resorcinol complexation of block copolymers with total molecular weight from 25400 (PS 183 - b -PEO 145 , Φ PEO = 0.24) to 89600 g/mol (PS 563 - b -PEO 705 , Φ PEO = 0.36), respectively, thus emphasizing the simplicity and the general applicability of this procedure. Long range order is not always as good as in other works but no additional treatments to increase the domain periodicity were applied and the capability of producing films with the desired nanostructure and orientation is in itself an interesting result. In this study resorcinol molecules were used to hydrogen-bind the semicrystalline PEO blocks thus giving a PEO/resorcinol complex that is also able to crystallize, but at a minor extent than the original PEO block. The changed interfacial interactions due to the presence of resorcinol and the reduction in the crystalline phase appear to be related with the tendency of PS- b -PEO polymers and of their resorcinol complexes to self-assemble in perpendicular oriented PEO cylinders, also when different morphologies and alignments were expected. For example the PS 563 - b -PEO 705 ( Φ PEO = 0.36) sample, when annealed under benzene vapor, arranges in well ordered vertical lamellae and in principle its stoichiometric resorcinol complex should also have a lamellar morphology (being Φ PEO/Res equal to 0.51). By spin coating PS 308 - b -PEO 250 in benzene solution in-plane PEO cylinders are obtained, while following the same film deposition procedure the PEO/resorcinol domains arrange according to a perpendicular orientation. PS 183 - b -PEO 145 is the only sample that gives the same type of alignment both in the presence of resorcinol and in its absence. The very regular superstructures obtained, with controlled features on the nanometer scale, make them of great interest for a number of nanotechnological applications and especially as templates for the production of nanoporous membranes and for the ordering of metallic nanoparticles and oxides. Acknowledgments This work was realized with financial support by Regione Piemonte (regional project for applied scientific research 2004, D34) and by NIS (Nanostructured Interfaces and Surfaces) Centre of Excellence. M.L. acknowledges the Ministerio de Ciencia y Innovación for support through the program Ramon y Cajal. The authors also acknowledge the electron microscopy service of the University of Santiago de Compostela for experimental support with TEM and SEM measurements. References [1] M. Di Ventra S. Evoy J.R. Heflin Introduction to nanoscale science and technology 2004 Springer New York [2] M. Lazzari M.A. Lopez-Quintela Block copolymers as a tool for nanomaterial fabrication Adv Mater 15 2003 1583 1594 [3] A.V. Ruzette L. Leibler Block copolymers in tomorrow’s plastics Nat Mater 4 2005 19 31 [4] J.Y. Cheng C.A. Ross H.I. Smith E.L. Thomas Templated self-assembly of block copolymers: top-down helps bottom-up Adv Mater 18 2006 2505 2521 [5] I.W. Hamley The physics of block copolymers 1998 Oxford Oxford University Press [6] I. Tokarev R. Krenek Y. Burkov D. Schmeisser A. Sidorenko S. Minko Microphase separation in thin films of poly(styrene-block-4-vinylpyridine) copolymer-2-(4′-hydroxybenzeneazo)benzoic acid assembly Macromolecules 38 2005 507 516 [7] P. Černoch P. Štěpánek J. Pleštil M. Šlouf A. Sidorenko M. Stamm Surface patterns of block copolymers in thin layers after vapor treatment Eur Polym J 43 2007 1144 1153 [8] M. Lazzari C. Rodríguez-Abreu J. Rivas M.A. Lopez-Quintela Self-assembly: a minimalist route to the fabrication of nanomaterials J Nanosci Nanotechnol 6 2006 892 905 [9] C. Liang K. Hong G.A. Guiochon J.W. Mays S. Dai Synthesis of a large-scale highly ordered porous carbon film by self-assembly of block copolymers Angew Chem 43 2004 5785 5789 [10] G. ten Brinke O. Ikkala Smart materials based on self-assembled hydrogen-bonded comb-shaped supramolecules Chem Rec 4 2004 219 230 [11] P. Zhang J. Gao B. Li Y. Han Surface morphology evolution of a thin polymeric supramolecular film by tuning interactions Macromol Rapid Commun 27 2006 295 301 [12] M. Lazzari C. De Rosa Methods for the alignment and the large-scale ordering of block copolymer morphologies M. Lazzari G.J. Liu S. Lecommandoux Block Copolymers in Nanoscience 2006 Wiley-VCH Weinheim 191 231 [13] T.L. Morkved M. Lu A.M. Urbas E.E. Ehrichs H.M. Jaeger P. Mansky Local control of microdomain orientation in diblock copolymer thin films with electric field Science 273 1996 931 933 [14] T. Thurn-Albrecht J. Schotter G.A. Kästle N. Emley T. Shibauchi L. Krusin-Elbaum Ultrahigh-density nanowire arrays grown in self-assembled diblock copolymer templates Science 290 2000 2126 2129 [15] L. Rockford S.G.J. Mochrie T.P. Russell Propagation of nanopatterned substrate templated ordering of block copolymers in thick films Macromolecules 34 2001 1487 1492 [16] S.O. Kim H.H. Solak M.P. Stoykovich H.J. Ferrier J.J. de Pablo P.F. Nealey Epitaxial self-assembly of block copolymers on lithographically defined nanopatterned substrates Nature 424 2003 411 414 [17] M.A. Villar D.R. Rueda F. Ania E.L. Thomas Study of oriented block copolymers films obtained by roll[hyphen]casting Polymer 43 2002 5139 5145 [18] R.J. Albalak E.L. Thomas Roll-casting of block copolymers and of block copolymer–homopolymer blend J Polym Sci Polym Phys 32 1994 341 350 [19] T. Hashimoto J. Bodycomb Y. Funaki K. Kimishima The effect of temperature gradient on the microdomain orientation of diblock copolymers undergoing an order–disorder transition Macromolecules 32 1999 952 954 [20] E. Huang L. Rockford T.P. Russell C.J. Hawker Nanodomain control in copolymer thin films Nature 395 1998 757 758 [21] H.C. Kim T.P. Russell Ordering in thin films of asymmetric diblock copolymers J Polym Sci B Polym Phys 39 2001 663 668 [22] G. Krausch R. Magerle Nanostructured thin films via self-assembly of block copolymers Adv Mater 14 2002 1579 1583 [23] J. Peng Y. Han W. Knoll D.H. Kim Development of nanodomain and fractal morphologies in solvent annealed block copolymer thin films Macromol Rapid Commun 28 2007 1422 1428 [24] J. Zhao S. Jiang X. Ji L. An B. Jiang Study of the time evolution of the surface morphology of thin asymmetric diblock copolymer films under solvent vapor Polymer 46 2005 6513 6521 [25] G. Kim M. Libera Morphological development in solvent-cast polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer thin films Macromolecules 31 1998 2569 2577 [26] K. Fukunaga T. Hashimoto H. Elbs G. Krausch Self-assembly of a lamellar ABC triblock copolymer thin film Macromolecules 35 2002 4406 4413 [27] H. Elbs C. Drummer V. Abetz G. Krausch Thin film morphologies of ABC triblock copolymers prepared from solution Macromolecules 35 2002 5570 5577 [28] S.H. Kim M.J. Misner T. Xu M. Kimura T.P. Russell Highly oriented and ordered arrays from block copolymers via solvent evaporation Adv Mater 16 2004 226 231 [29] Y. Xuan J. Peng L. Cui H. Wang B. Li Y. Han Morphology development of ultrathin symmetric diblock copolymer film via solvent vapor treatment Macromolecules 37 2004 7301 7307 [30] S. Jiang A. Göpfert V. Abetz Novel morphologies of block copolymer blends via hydrogen bonding Macromolecules 36 2003 6171 6177 [31] G. ten Brinke J. Ruokolainen O. Ikkala Supramolecular materials based on hydrogen-bonded polymers Adv Polym Sci 207 2007 113 177 [32] A. Laforgue C.G. Bazuin R.E. Prud’homme A study of the supramolecular approach in controlling diblock copolymer nanopatterning and nanoporosity on surfaces Macromolecules 39 2006 6473 6482 [33] J. Ruokolainen M. Saariaho O. Ikkala G. ten Brinke E.L. Thomas M. Torkkeli Supramolecular routes to hierarchical structures: comb-coil diblock copolymers organized with two length scales Macromolecules 32 1999 1152 1158 [34] R. Mäki-Ontto K. de Moel W. de Odorico J. Ruokolainen M. Stamm G. ten Brinke Hairy tubes: mesoporous materials containing hollow self-organized cylinders with polymer brushes at the walls Adv Mater 13 2001 117 121 [35] A. Sidorenko I. Tokarev S. Minko M. Stamm Ordered reactive nanomembranes/nanotemplates from thin films of block copolymer supramolecular assembly J Am Chem Soc 125 2003 12211 12216 [36] M. Zhang L. Yang S. Yurt M.J. Misner J.T. Chen E.B. Coughlin Highly ordered nanoporous thin films from cleavable polystyrene-block-poly(ethylene oxide) Adv Mater 19 2007 1571 1576 [37] Z. Lin D.H. Kim X. Wu L. Boosahda D. Stone L. LaRose A rapid route to arrays of nanostructures in thin films Adv Mater 14 2002 1373 1376 [38] S.H. Kim M.J. Misner T.P. Russell Solvent-induced ordering in thin film diblock copolymer/homopolymer mixtures Adv Mater 16 2004 2119 2123 [39] S.H. Kim M.J. Misner L. Yang O. Gang B.M. Ocko T.P. Russell Salt complexation in block copolymer thin films Macromolecules 39 2006 8473 8479 [40] E. Delaite J.J. Point P. Damman M. Dosière Two allotropic forms for the poly(ethylene oxide)-resorcinol molecular complex Macromolecules 25 1992 4768 4778 [41] J. Spěváček L. Paternostre P. Damman A.C. Draye M. Dosière Solid state 13 C NMR study of molecular complexes of poly(ethylene oxide) and hydroxybenzenes Macromolecules 31 1998 3612 3616 [42] H. Schmalz V. Abetz A.J. Müller Thermal and self-nucleation behavior of molecular complexes formed by p -nitrophenol and the poly(ethylene oxide) end block within an ABC triblock copolymer Macromol Symp 183 2002 179 184

High frequency stimulation can block axonal conduction

High frequency stimulation (HFS) is used to control abnormal neuronal activity associated with movement, seizure, and psychiatric disorders. Yet, the mechanisms of its therapeutic action are not known. Although experimental results have shown that HFS suppresses somatic activity, other data has suggested that HFS could generate excitation of axons. Moreover it is unclear what effect the stimulation has on tissue surrounding the stimulation electrode. Electrophysiological and computational modeling literature suggests that HFS can drive axons at the stimulus frequency. Therefore, we tested the hypothesis that unlike cell bodies, axons are driven by pulse train HFS. This hypothesis was tested in fibers of the hippocampus both in-vivo and in-vitro. Our results indicate that although electrical stimulation could activate and drive axons at low frequencies (0.5-25 Hz), as the stimulus frequency increased, electrical stimulation failed to continuously excite axonal activity. Fiber tracts were unable to follow extracellular pulse trains above 50 Hz in-vitro and above 125 Hz in-vivo. The number of cycles required for failure was frequency dependent but independent of stimulus amplitude. A novel in-vitro preparation was developed, in which, the alveus was isolated from the remainder of the hippocampus slice. The isolated fiber tract was unable to follow pulse trains above 75 Hz. Reversible conduction block occurred at much higher stimulus amplitudes, with pulse train HFS (>150 Hz) preventing propagation through the site of stimulation. This study shows that pulse train HFS affects axonal activity by: (1) disrupting HFS evoked excitation leading to partial conduction block of activity through the site of HFS; and (2) generating complete conduction block of secondary evoked activity, as HFS amplitude is increased. These results are relevant for the interpretation of the effects of HFS for the control of abnormal neural activity such as epilepsy and Parkinson's disease.

Structural basis for the phototoxicity of the fluorescent protein KillerRed

The red fluorescent protein KillerRed, engineered from the hydrozoan chromoprotein anm2CP, has been reported to induce strong cytotoxicity through the chromophore assisted light inactivation (CALI) effect. Here, we present the X‐ray structures of KillerRed in its native and bleached states. A long water‐filled channel is revealed, connecting the methylene bridge of the chromophore to the solvent. This channel facilitates the transit of oxygen and of reactive oxygen species (ROS) formed by reaction with the excited chromophore. The functional roles of key mutations used to produce KillerRed are discussed, strong chromophore distortions in the bleached state are revealed, and mechanisms for ROS production and self protection are proposed. The presence of a partially mature, photo‐resistant, green‐emitting state is characterized, which accounts for enhanced CALI by “pre‐bleached” KillerRed.

Chronic TNFα and cAMP pre‐treatment of human adipocytes alter HSL, ATGL and perilipin to regulate basal and stimulated lipolysis

We examined the effects of chronic TNFα and dibutyryl‐cAMP (Db‐cAMP) pre‐treatment on the lipolytic machinery of human hMADS adipocytes. TNFα decreased adipose triglyceride lipase (ATGL) and hormone‐sensitive lipase (HSL) protein content and triglycerides (TG)‐hydrolase activity but increased basal lipolysis due to a marked reduction in perilipin (PLIN) protein content. Conversely, Db‐cAMP increased ATGL and HSL protein content but prevented PLIN phosphorylation, the net result being accentuated basal lipolysis. In forskolin‐stimulated conditions, TNFα and Db‐cAMP pre‐treatment decreased stimulated TG‐hydrolase activity and impaired PLIN phosphorylation. Together, this resulted in a severely attenuated response to forskolin‐stimulated lipolysis.

Cancer and fecundity issues mandate a multidisciplinary approach

To review the existing options for preserving fecundity in young cancer patients, outlining the differences that exist in each individual cancer situation and how these affect our choice of fecundity-preserving measures.