The degree of curing of epoxy composites and coatings is one key parameter to control the reliability of manufacturing processes, particularly in printed circuit board (PCB) manufacturing where epoxy buildup composites are partially cured before processing. We show that the reaction of curing of an industrially relevant buildup composite (epoxy-phenol reinforced with silica fillers) can be monitored by diffuse reflectance infrared Fourier transform (DRIFT) in the near-infrared range. The accuracy of DRIFT measurements is confirmed by comparison with measurements in transmission mode on reference composite samples. DRIFT is demonstrated to offer an easy and reliable measurement of the epoxy degree of curing on PCB coupons.

A general method is proposed to produce oriented and highly crystalline conducting polymer layers. It combines the controlled orientation/crystallization of polymer films by high-temperature rubbing with a soft-doping method based on spin-coating a solution of dopants in an orthogonal solvent. Doping rubbed films of regioregular poly(3-alkylthiophene) s and poly(2,5-bis(3-dodecylthiophen- 2-yl) thieno[3,2-b] thiophene) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) yields highly oriented conducting polymer films that display polarized UV-visible-near-infrared (NIR) absorption, anisotropy in charge transport, and thermoelectric properties. Transmission electron microscopy and polarized UV-vis-NIR spectroscopy help understand and clarify the structure of the films and the doping mechanism. F(4)TCNQ(-) anions are incorporated into the layers of side chains and orient with their long molecular axis perpendicular to the polymer chains. The ordering of dopant molecules depends closely on the length and packing of the alkyl side chains. Increasing the dopant concentration results in a continuous variation of unit cell parameters of the doped phase. The high orientation results in anisotropic charge conductivity (sigma) and thermoelectric properties that are both enhanced in the direction of the polymer chains (sigma = 22 +/- 5 S cm(-1) and S = 60 +/- 2 mu V K-1 ). The method of fabrication of such highly oriented conducting polymer films is versatile and is applicable to a large palette of semiconducting polymers.

An organogelator based on a N,N′-substituted H-bonding perylenebisimide (PBI-C10) self-assembles to form either a green J-type (form I) or a red H-type (form II) aggregate structure. The molecular packing of both polymorphs was determined from a combination of Transmission Electron Microscopy (TEM) (low dose electron diffraction and high resolution), Grazing incidence X-ray diffraction and polarized infrared spectroscopy. To that aim, highly oriented films have been prepared by mechanical rubbing at controlled film temperature and DFT calculations were performed to identify representative vibrational IR bands and their associated polarizations. H-Bonding between amides generates either a rectangular columnar phase (form I) in the dried gel or a hexagonal packing of supramolecular 21/1 helices with a long period of 97 Å (form II) in annealed thin films. In aligned films of form I, polarized FTIR spectroscopy helps determine the orientation of both intermolecular H-bonds and the PBI core with respect to the substrate. In form II, PBI-C10 molecules assemble into pairs to form off-centered 21/1 helices whose helical axis is made of strongly H-bonded amides. TEM investigations show that three 21/1 helices are packed in a frustrated trigonal structure formed by H-bonding. The Form I → Form II transformation implies a redistribution of a single population of strong intra-columnar H-bonds between amides in form I to a mixture of strong and weak H-bonds in the supramolecular helices, the strong H-bonds forming the spine of the helices.

Conversion-type electrode materials show extremely interesting performance in terms of capacity, which is however usually associated with bad Coulombic efficiency. The latter is mainly the consequence of the relentless evolution of solid electrolyte interphase (SEI) formed and/or dissolved during conversion/back-conversion reactions on the continuously reshaping active material surface. The thorough comprehension of the dynamic processes occurring during cycling in a working electrochemical cell, such as solvation/desolvation of ionic species and formation/dissolution of the SEI at the electrode/electrolyte interface, is thus of utmost relevance in the study of electrochemical mechanism and performance of conversion-type electrode materials. Operando Fourier transform infrared (FTIR) spectroscopy, one of the methods of choice for the study of such phenomena, was applied to study the dynamic interfacial properties of NiSb2, a representative intermetallic conversion-type electrode material for Li batteries, during cycling in the presence of a commercial electrolyte based on LiPF6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). Using a specifically developed in situ ATR-IR electrochemical cell, it was possible to correlate the electrochemical processes to the ratio between solvent molecules associated with Li+ ions and free solvent molecules and thus to follow the dynamic evolution of the concentration of lithium in the electrolyte during cycling.

Binary c–T phase diagrams of organogelators in solvent are frequently simplified to two domains, gel and sol, even when the melting temperatures display two distinct regimes, an increase with T and a plateau. Herein, the c–T phase diagram of an organogelator in solvent is elucidated by rheology, DSC, optical microscopy, and transmitted light intensity measurements. We evidence a miscibility gap between the organogelator and the solvent above a threshold concentration, cL. In this domain the melting or the formation of the gel becomes a monotectic transformation, which explains why the corresponding temperatures are nonvariant above cL. As shown by further studies by variable temperature FTIR and NMR, different types of H-bonds drive both the liquid–liquid phase separation and the gelation.

In this work, we develop the concept of evaporation-induced self-structuring as a novel approach forproducing organised films by exploiting cooperative physical and chemical interactions under far-fromequilibriumconditions (spin-coating), using sol–gel precursors with multiple functional groups. Thin filmsof self-structured silsesquioxane nanohybrids have been deposited by spin coating through the sol–gelhydrolysis and condensation of a bridged organosilane bearing self-assembling urea groups. The resultingnanostructure, investigated by FTIR, AFM and SEM, is shown to be highly dependent on the catalyst used(nucleophilic or acidic), and can be further modulated by varying the spinning rate. FTIR studies revealed thepresence of highly organised structures under acidic catalysis due to strong hydrogen bonding between ureagroups and hydrophobic interactions between long alkylene chains. The preferential orientation of the ureacross-links parallel to the substrate is shown using polarized FTIR experiments.

to reversible liquid-crystal like ordering. We can expect strong induced birefringence and dichroism depending on dielectric properties of the suspension [1]. In general, colloids are stabilized with ionic surfactants. Colloids alignment along the electric field thus occurs through the reorganization of ions at the particle/solvent interface. In the case of metallic particles, ordering will be achieved through the intrinsic conductivity of the particles. Among the metallic particles, plasmonic ones, like gold nanoparticles, exhibit a transverse localized surface plasmon mode and a longitudinal one, whose resonance red-shift depends on the aspect ratio (AR) of the nanoparticle. The larger the aspect ratio is, the stronger should be their optical anisotropy [2]. It is thus of interest to create reversible ordering of gold nanoparticles as their localized surface plasmon properties make them appealing for applications like bio-sensing or metamaterials.In this work, we study two kinds of particles: gold nanorods (GNRs) dispersed in water with an aspect ratio AR ≈10 (Φ=10nm) and new ultrathin gold nanowires (GNWs) dispersed in hexane with an AR up to 1000 (Φ=1.5nm) [3].With our recently developed electro-optic setup [1], we measure the birefringence induced in the sample by short pulses of high-frequency electric field. We study also the field-induced dichroism of the suspensions, using the same sample, sealed in a flat optical glass capillary, and the same experimental setup, mounted either on a polarizing microscope or on a UV-Vis spectrophotometer. In our experimental setup, the electrodes are placed outside the sample. In this configuration, they do not interact with the suspension avoiding electrophoretic effect.We observed alignment of both GNRs and GNWs along the applied electric field. Time responses of GNRs to the electric field are of the order of the millisecond and of more than 10 ms for GNWs. The saturated voltage is 4 times smaller in this last case compared to GNRs. Those results are in agreement with a change in the aspect ratio. In the visible range, birefringence appears negative as theoretically predicted [2]. More surprising, in both cases, a positive linear dichroism is revealed in the optical visible range. On the contrary, we expect a negative dichroism (ie extinction higher for polarization perpendicular to the electric field), while in this frequency range we are sensitive to the transverse mode of the plasmon band [4]. Spectroscopic measurements of the absorbance confirm this result but show in addition that the longitudinal mode is well polarized along the electric field: absorbance increases (decreasing) with the applied electric field for a polarization parallel (perpendicular) to this field. This suggests that the transverse mode is less sensitive to polarization than the longitudinal one (figure 1). This may arise from partial alignment causing light depolarization.Figure : 1. Absorbance spectra of Gold NanoRods suspension for light polarization perpendicular to the electric field. Reference spectrum has been recorded from the isotropic state. 2. Gold NanoWire fibers oriented at 45° between crossed polarizers.Concerning GNWs, similarly to carbon nanotubes, we observe their progressive assembly into fibers strictly oriented along the electric field due long range dipolar interaction. Those fibers appear highly birefringent between crossed polarizers (figure2.). Their properties and the way to control their growth are under investigation.Acknowledgement: This work is supported by the ANR (France) through the grant NASTAROD.[1] I. Dozov, et al., “Electric field induced perfect anti-nematic order in isotropic suspension of nautral clay”, J. Phys. Chem. B Vol. 115, 7751-7765 (2011).[2] NG. Klebhstov , “Anisotropic properties of plasmonic nanoparticles: birefringence, dicroism and depolarisation ratio.”, J. of Nanophot. Vol. 4, 041587-041604 (2010).[3] A. Loubat , et al., “Growth and self assembly of ultrathin gold nanowire into expanded hexagonal superlattice studied by in situ SAXS”, Lang. Vol. 115, 7751-7765 (2014).[4] BMI Van der Zande, JJM Koper, HNW. Lekkerkerker, “Alignement of rod shaped gold particles by electric fields”, J. Phys. Chem. B, Vol. 103, 5754-5760 (1999).