Additive Effect on the Structure of PEDOT:PSS Dispersions and Its Correlation with the Structure and Morphology of Thin Films.

We reported on the interaction between poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and high-boiling-point additives in PEDOT:PSS aqueous dispersions and in the final polymer films with the aim of stablishing correlations between the structure of both inks and solid thin films. By Small-Angle X-ray Scattering (SAXS) using synchrotron radiation, it was found that the structural changes of dispersions of PEDOT:PSS with high-boiling-point additives can be explained as a two-step mechanism depending on the additive concentration. A compaction of PEDOT:PSS grains was observed at low concentrations while a swelling of the grains together with a phase segregation between PEDOT and PSS segments was evidenced at larger concentrations. Thin films' morphology and structure were investigated by atomic force microscopy (AFM) and synchrotron Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) respectively. Our two-step model provides an explanation for the small and sharp domains of PEDOT:PSS thin films observed for low-additive concentrations (first step) and larger domains and roughness found for higher-additive concentrations (second step). A reduction of the ratio of PSS in PEDOT:PSS thin films upon the presence of additives was also observed. This can be related to a thinning of the PSS shells of PEDOT:PSS grains in the dispersion. The results discussed in this work provide the basis for a controlled tuning of PEDOT:PSS thin films structure and the subsequent electrical properties.

Synergistic Effect of Fullerenes on the Laser-Induced Periodic Surface Structuring of Poly(3-Hexyl Thiophene).

Ordered and homogeneous laser-induced periodic surface structures (LIPSS) could be fabricated in poly(3-hexyl thiophene):[6,6]-phenyl C71-butyric acid methyl ester (P3HT:PC71BM) blends by using wavelengths in the ultraviolet (UV) range (266 nm). The absorption coefficient of PC71BM, which is maximum in its UV⁻Visible absorption spectrum around 266 nm, enhanced the overall absorption of the blend. In addition, PC71BM itself was capable of developing homogeneous LIPSS by laser irradiation at λlaser = 266 nm. Therefore, we proposed that the synergistic effect of PC71BM on the LIPSS formation in P3HT:PC71BM (1:1) was due to a templating effect for the LIPSS formation of the PC71BM itself, which added to the overall increment of the absorption of the blend. LIPSS formation at ambient conditions in this wavelength range led to chemical modification of both P3HT and PC71BM, which rendered to non-conducting samples. Irradiation in vacuum significantly reduced radiation damage, rendering to the characteristic electrical conductivity pattern observed in P3HT LIPSS samples irradiated in the visible range. This effect could be of potential interest in order to obtain LIPSS in low absorbing polymers.

Patterning Conjugated Polymers by Laser: Synergy of Nanostructure Formation in the All-Polymer Heterojunction P3HT/PCDTBT.

In this work we report a broad scenario for the patterning of semiconducting polymers by laser-induced periodic surface structures (LIPSS). Based on the LIPSS formation in the semicrystalline poly(3-hexylthiophene) (P3HT), we have extended the LIPSS fabrication to an essentially amorphous semiconducting polymer like poly[N-90-heptadecanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT). This polymer shows a good quality and well-ordered nanostructures not only at the 532 nm laser wavelength, as in the case of P3HT, but also at 266 nm providing gratings with smaller pitch. In addition, we have proven the feasibility of fabricating LIPSS in the P3HT/PCDTBT (1:1) blend, which can be considered as a model bulk-heterojunction for all-polymer solar cells. In spite of the heterogeneous roughness, due to phase separation in the blend, both P3HT and PCDTBT domains present well-defined LIPSS as well as a synergy for both components in the blend when irradiating at wavelengths of 532 and 266 nm. Both, P3HT and PCDTBT in the blend require lower fluence and less pulses in order to optimize LIPSS morphology than in the case of irradiating the homopolymers separately. Near edge X-ray absorption fine structure and Raman spectroscopy reveal a good chemical stability of both components in the blend thin films during LIPSS formation. In addition, scanning transmission X-ray spectro-microscopy shows that the mechanisms of LIPSS formation do not induce a further phase segregation neither a mixture of the components. Conducting atomic force microscopy reveals a heterogeneous electrical conductivity for the irradiated homopolymer and for the blend thin films, showing higher electrical conduction in the trenches than in the ridge regions of the LIPSS.

Laser-Induced Periodic Surface Structures on P3HT and on Its Photovoltaic Blend with PC71BM.

We describe the conditions for optimal formation of laser-induced periodic surface structures (LIPSS) over poly(3-hexylthiophene) (P3HT) spin-coated films. Optimal LIPSS on P3HT are observed within a particular range of thicknesses and laser fluences. These conditions can be translated to the photovoltaic blend formed by the 1:1 mixture of P3HT and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) when deposited on an indium tin oxide (ITO) electrode coated with (poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). Solar cells formed by using either a bilayer of P3HT structured by LIPSS covered by PC71BM or a bulk heterojunction with a P3HT:PC71BM blend structured by LIPSS exhibit generation of electrical photocurrent under light illumination. These results suggest that LIPSS could be a compatible technology with organic photovoltaic devices.

Laser Fabrication of Polymer Ferroelectric Nanostructures for Nonvolatile Organic Memory Devices.

Polymer ferroelectric laser-induced periodic surface structures (LIPSS) have been prepared on ferroelectric thin films of a poly(vinylidene fluoride-trifluoroethylene) copolymer. Although this copolymer does not absorb light at the laser wavelength, LIPSS on the copolymer can be obtained by forming a bilayer with other light-absorbing polymers. The ferroelectric nature of the structured bilayer was proven by piezoresponse force microscopy measurements. Ferroelectric hysteresis was found on both the bilayer and the laser-structured bilayer. We show that it is possible to write ferroelectric information at the nanoscale. The laser-structured ferroelectric bilayer showed an increase in the information storage density of an order of magnitude, in comparison to the original bilayer.

Coadministration of a 9-Valent Human Papillomavirus Vaccine With Meningococcal and Tdap Vaccines.

BACKGROUND: This study in 11- to 15-year-old boys and girls compared the immunogenicity and safety of GARDASIL 9 (9-valent human papillomavirus [9vHPV] vaccine) administered either concomitantly or nonconcomitantly with 2 vaccines routinely administered in this age group (Menactra [MCV4; Neisseria meningitidis serotypes A/C/Y/W-135] or Adacel [Tdap; diphtheria/tetanus/acellular pertussis]). METHODS: Participants received 9vHPV vaccine at day 1 and months 2 and 6; the concomitant group (n = 621) received MCV4/Tdap concomitantly with 9vHPV vaccine at day 1; the nonconcomitant group (n = 620) received MCV4/Tdap at month 1. Antibodies to HPV-, MCV4-, and Tdap-relevant antigens were determined. Injection-site and systemic adverse events (AEs) were monitored for 15 days after any vaccination; serious AEs were monitored throughout the study. RESULTS: The geometric mean titers for all HPV types in 9vHPV vaccine 4 weeks after dose 3, proportion of subjects with a fourfold rise or greater in titers for 4 N meningitidis serotypes 4 weeks after injection with MCV4, proportion of subjects with antibody titers to diphtheria and tetanus ≥0.1 IU/mL, and geometric mean titers for pertussis antigens 4 weeks after injection with Tdap were all noninferior in the concomitant group compared with the nonconcomitant group. Injection-site swelling occurred more frequently in the concomitant group. There were no vaccine-related serious AEs. CONCLUSIONS: Concomitant administration of 9vHPV vaccine with MCV4/Tdap was generally well tolerated and did not interfere with the antibody response to any of these vaccines. This strategy would minimize the number of visits required to deliver each vaccine individually.

In situ monitoring of laser-induced periodic surface structures formation on polymer films by grazing incidence small-angle X-ray scattering.

The formation of laser-induced periodic surface structures (LIPSS) on model spin-coated polymer films has been followed in situ by grazing incidence small-angle X-ray scattering (GISAXS) using synchrotron radiation. The samples were irradiated at different repetition rates ranging from 1 up to 10 Hz by using the fourth harmonic of a Nd:YAG laser (266 nm) with pulses of 8 ns. Simultaneously, GISAXS patterns were acquired during laser irradiation. The variation of both the GISAXS signal with the number of pulses and the LIPSS period with laser irradiation time is revealing key kinetic aspects of the nanostructure formation process. By considering LIPSS as one-dimensional paracrystalline lattice and using a correlation found between the paracrystalline disorder parameter, g, and the number of reflections observed in the GISAXS patterns, the variation of the structural order of LIPSS can be assessed. The role of the laser repetition rate in the nanostructure formation has been clarified. For high pulse repetition rates (i.e., 10 Hz), LIPSS evolve in time to reach the expected period matching the wavelength of the irradiating laser. For lower pulse repetition rates LIPSS formation is less effective, and the period of the ripples never reaches the wavelength value. Results support and provide information on the existence of a feedback mechanism for LIPSS formation in polymer films.

Diameter selection of carbon nanotubes in polymer/SWCNT nanowire arrays fabricated by template wetting.

Arrays of polymer/SWCNT (single-wall carbon nanotube) nanowires supported on a residual nanocomposite film are prepared by melt wetting using porous anodic aluminum oxide (AAO) as a template. The aggregation parameter of SWCNTs extracted from the analysis of their Raman radial breathing modes gives the highest value for native SWCNTs, indicating that they tend to organize into bundles giving rise to a high degree of aggregation. However, the lowest value achieved at the interface between the nanocomposite film and the nanoarray is explained considering that the forces acting during infiltration are able to disrupt the SWCNT bundles inducing nanotube dispersion. In addition, scanning the nanoarrays along the nanowires length by Raman microscopy has shown a diameter selection of SWCNTs by the AAO membrane. The results reported in this work reveal that it is possible to fabricate arrays of nanowires with homogeneous SWCNT distribution along tens of microns, optimizing nanotube dispersion.

Crystallization under one-dimensional confinement in alumina nanopores of poly(trimethylene terephthalate) and its composites with single wall carbon nanotubes.

We report the preparation of semicrystalline polymer nanorods of PTT and of its nanocomposites with SWCNTs by infiltration of the molten polymer into disordered anodic alumina membranes. An accurate study of the crystalline orientation of these systems has been accomplished by means of X-ray microdiffraction. While polymer residual film exhibits isotropic character, edge-on lamellae are formed upon approaching the polymer/membrane interface. This effect might be due to the elongational flow that takes place in the molten state as polymer chains infiltrate the AAO membrane. At the interface, edge-on and flat-on crystalline lamellae coexist as a consequence of the strong interaction between the polymer and the AAO surface. Inside the nanopores, the confined environment induces a kinetic selection of polymer crystals which only allows the growth of crystalline lamellae with its a-axis parallel to that of the pore. In the case of PTT/SWCNT nanocomposites, this effect, in conjunction with the strong interaction between polymer and AAO surface, seems to prevail over the templating effect of the carbon nanotubes and a similar orientation to that of the neat PTT case is observed.

Understanding crystallization features of P(VDF-TrFE) copolymers under confinement to optimize ferroelectricity in nanostructures.

The successful development of ferroelectric polymer devices depends on the effective fabrication of polar ferroelectric crystalline nanostructures. We demonstrate, by scanning X-ray microdiffraction using synchrotron light, the heterogeneous character of high aspect ratio one-dimensional nanoarrays of poly(vinylidene fluoride-co-trifluoroethylene) copolymers supported by a residual polymer film. They were prepared by melt and solution template wetting, using porous anodic aluminum oxide as a template. The spatial evolution of different polymorphs from the mixture of paraelectric and ferroelectric crystal forms (residual film) to the pure ferroelectric form (nanoarray) is evidenced for the samples prepared by solution wetting. However, for samples prepared by melt wetting the ferroelectric phase is exclusively obtained in both the residual film and nanoarray. The crystal nuclei formed in the polymer film connected to the nanoarray play a key role in determining the formation of a crystallinity distribution gradient, where the crystallinity decreases along the first 5-10 microns in the nanorods reaching a steady value afterwards. The minimum decrease in crystallinity is revealed for samples prepared by melt wetting. The results reported in this work endeavour to enhance the understanding of crystallization under confinement for ferroelectric copolymers and reveal the parameters for improving the ferroelectric character of polymer nanostructures.

Correlation lengths, porosity and water adsorption in TiO2 thin films prepared by glancing angle deposition.

This paper reports a thorough microstructural characterization of glancing angle deposited (GLAD) TiO(2) thin films. Atomic force microscopy (afm), grazing-incidence small-angle x-ray scattering (GISAXS) and water adsorption isotherms have been used to determine the evolution of porosity and the existence of some correlation distances between the nanocolumns constituting the basic elements of the film's nanostructure. It is found that the deposition angle and, to a lesser extent, the film thickness are the most important parameters controlling properties of the thin film. The importance of porosity and some critical dimensions encountered in the investigated GLAD thin films is highlighted in relation to the analysis of their optical properties when utilized as antireflective coatings or as hosts and templates for the development of new composite materials.

Structure of glancing incidence deposited TiO(2) thin films as revealed by grazing incidence small-angle X-ray scattering.

For the first time, grazing incidence small-angle X-ray scattering (GISAXS) analysis is used to characterize the morphology of TiO(2) thin films grown by glancing angle physical vapor deposition (GLAD). According to cross-section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO(2) columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the tilted geometry of the TiO(2) columns. The patterns also show the existence of two populations of columns in these GLAD-TiO(2) films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.

Confinement-induced one-dimensional ferroelectric polymer arrays.

This work demonstrates the use of wetting nanoporous alumina template with polymer solution to produce arrays of isolated poly(vinylidene fluoride) (PVDF) ferroelectric gamma-type nanorods supported within a nonpolar alpha-structure film. The method is based upon a crystal phase transition which occurs due to PVDF confinement within alumina nanoporous. The system was studied using scanning X-ray microdiffraction (micro-XRD) that allows the solid-solid phase transition from the alpha-nonpolar crystal form (bulk) to the gamma polar ferroelectric form (nanorod array) to be spatially resolved, as well as providing crystallinity and orientation information. The results reveal that the interaction between polymer chains and the porous membrane's walls imposes a flat-on lamella growth along the nanorrods long axis, while improving crystal orientation.

Stacking of main chain-crown ether polymers in thin films.

Thin films (9-70 nm) of a series of polymers containing in the main chain dibenzo-18-crown-6 ether unit (DB18C6) linked to an aliphatic spacer of different length (10C and 14C) and nature have been prepared, from chloroform solutions, by spin coating on a silicon substrate. The quality and homogeneity of the polymer coatings was revealed by their reflectivity spectra and atomic force microscopy (AFM). The grazing incidence small-angle X-ray scattering (GISAXS) patterns show an out-of-plane structure correlation (interference maximum near the horizon) of scale size related to the polymer repeating unit length. Above this Bragg reflection, the shape of the scattering observed, in the GISAXS pattern, reveals an orientation of the stacked molecular columns in the coated polymer. A thermal treatment of the samples improves the nanostructure by increasing the lamellar coherence size (in y-direction) as well as the vertical orientation of the molecular columns.

Dendritic morphology in homeotropically aligned discotic films.

A hexa-alkylether-substituted hexa-peri-hexabenzocoronene, as a discotic liquid crystal, spontaneously homeotropically self-orients when cooled from the isotropic phase. During this process, a dendritic morphology is formed in which a significant optical difference is observed between the dendritic shapes and their periphery. However, local structural analysis using microfocus synchrotron radiation experiments demonstrate that there is an identical supramolecular order in both areas. Three-dimensional confocal surface measurements reveal that these dendritic structures result from a dewetting process, which occurs during solidification. Thereby, the contact area between the organic material and the surface is reduced. These results are important for the design of organic electronics, since the reduction of the contact area in an electronic device might inhibit the charge transport between the discotic semiconductor and the electrode.

From macro- to nanoscopic templating with nanographenes.

A hexa-peri-hexabenzocoronene carrying six long, branched alkyl chains has been processed in nano- and macroscopic pore templates. An extraordinary self-organization of this material was observed within macroscopically large glass capillaries after cooling from the isotropic phase. Thereby, the columnar structures were long-range aligned along the capillary axis over several centimeters. This behavior was explained by the pronounced directional self-assembly of the molecules, whereby the curvature effect of the capillary was negligible. The processing in nanoscopic pores of an inorganic membrane yielded an improved supramolecular organization. It was possible to remove the inorganic template and to obtain bundles and single nanorods. The templating over different dimensions opens a variety of potential applications.