Micro- and nano-thermal analysis applied to multi-layered biaxially-oriented polypropylene films

In this paper we compare Wollaston and silicon probes for localized thermal analysis measurements (LTA) on biaxially oriented polypropylene (BOPP) films. Up till now, no real comparison was reported in literature between the different transition temperatures measured using Wollaston and silicon probes. Using different types of probes for studying the same material proves to be very interesting. Using the Wollaston probe, the thermal properties and thickness of a 1 μm thick skin layer can be determined by through-thickness local thermal analysis measurements. The improved resolution of the silicon probes, enables the measurement of thermal properties of individual layers in a cross-sectioned film, even for layers of only 1 μm thickness. Based on the results, the silicon probes seem to be more sensitive toward the start of the melting process, since the silicon probe already penetrates at lower temperature, as compared to the Wollaston probes. This sensitivity can be exploited for studying the effect of variations in thermal history between or within samples.     

Optical gain from the open form of a photochromic molecule in the solid state

This work presents evidence for line-narrowing from the UV photoexcited open form of the photochromic molecule, indolinospiropyran (1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro [2H-1-benzopyran-2,2'-(2H)-indole]) in the solid state. The line-narrowing is attributable to amplified spontaneous emission induced by optical gain and assisted by the waveguiding within the organic film. Optical gain throughout a band as large as 28 nm, with a maximum gain coefficient of 5.6 cm(-1), is observed in the merocyanine emission region (660-730 nm). These results open the way to the realization of hybrid devices based on the coupling between photochromic behavior and stimulated emission from conjugated molecules, such as lasing optical memories, and lasers gated by optical molecular switches.     

Tetrabromo hydrogenated cardanol: Efficient and renewable brominating agent

2,4,4,6-Tetrabromo-3-n-pentadecyl-2,5-cyclohexadienone (TBPCO) has been synthesized and used as a new efficient, convenient, and environmentally friendly brominating agent.     

Study of optical properties of electrospun light-emitting polymer fibers

We realize light-emitting polymer fibers based on both optically inert polymers doped by molecules exhibiting optical gain and optically active conjugated polymers. Waveguiding properties of the produced polymer structures are demonstrated, with a loss coefficient of around 10³ cm⁻¹. We also find that single polymer fibers doped with gain molecules form Fabry–Pérot cavities, showing photoluminescence spectra with modes equally spaced by 1.7 nm. Coherent emission is demonstrated from fibers made upon increasing the excitation fluence above threshold values of the order of a few tens of μJ/cm².     

Combination of microstructuring and laser-light irradiation for the reversible wettability of photosensitised polymer surfaces

The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. In particular, UV laser pulses at 308 nm are responsible for the enhancement of the hydrophilicity of the surfaces, since the embedded non-polar spiropyran molecules convert to their polar merocyanine isomers upon UV absorption. The process is reversed upon irradiation with green laser pulses at 532 nm. When the photochromic-polymeric surfaces are micropatterned using soft lithography or photo-polymerisation techniques, they can change their wettability towards a more hydrophobic or more hydrophilic behaviour depending on the dimensions of the patterned features and on the hydrophilicity-hydrophobicity of the flat surface. Furthermore, the light-induced wettability variations on these structured surfaces are greatly enhanced compared to the flat surfaces. This significant increase to the wettability changes is attributed to the combination of the photochromic interconversions upon laser irradiation together with the photoinduced reversible volume changes of the patterned features. PACS 61.82.Pv; 68.08.Bc; 81.16.Nd; 82.35.-x; 42.60.-v; 68.47.Mn     

The trapping of j,x-biradicals,photochemically produced,with 4-cyanopyridine in neutral and acidic medium

4-Cyanopyridine is able to trap 1,x-biradicals produced by direct photochemical excitation of some ketones, showing in some cases that unaspected species are formed and pyridine producs which are not explainable on the basis of actual knowledge.     

Gel-sol evolution of cyclodextrin-based nanosponges: role of the macrocycle size

The effect of the macrocycle size on the gel-to-sol evolution of cyclodextrin-based hydrogel is here investigated by using Fourier transform infrared absorption in attenuated total reflectance geometry (FTIR-ATR). Different types of nanosponges obtained by polymerization of α- and β-cyclodextrin (CDNS) with an activated derivative of ethylenediaminetetraacetic acid have been progressively hydrated in order to follow the evolution of these systems from a gel state to a liquid suspension. The in deep analysis of the high-frequency vibrational dynamics of the hydrogel during its gel-sol evolution revealed that the microscopic origin of this phenomenon is strictly connected to different hydrogen bond environments in which water molecules confined in the pores of nanosponges can arrange. By following a well consolidated approach, the OH stretching band of water, clearly observed in the high-frequency range of the vibrational spectra of nanosponges hydrogel, has been decomposed into sub-bands assigned to different arrangements of water molecules at various degrees of cooperativity. A comparison of the diagrams obtained for homologous CDNS prepared from α- and β-CD shows how the size of cyclodextrin macrocycle allows to efficiently modulate the gelation points at constant cyclodextrin/crosslinker molar ratio n.     

Interfacial interaction in EVA‐carbon nanotube and EVA‐clay nanocomposites

Proper filler‐matrix compatibility is a key factor in view of obtaining nanocomposites with well‐dispersed nanofillers displaying enhanced properties. In this respect, polymer‐filler interaction can be improved by a proper combination of matrix and nanofiller polarities. This is explored for matrices ranging from nonpolar high density poly(ethylene) to ethylene‐vinyl acetate (EVA) copolymers with varying vinyl acetate contents, in combination with several types of organoclay or carbon nanotubes. A novel in situ characterization methodology using modulated temperature differential scanning calorimetry is presented to evaluate the matrix‐filler interaction. During quasi‐isothermal crystallization of the matrix, an “excess” contribution is observed in the recorded heat capacity signal because of reversible melting and crystallization. Its magnitude considerably decreases upon addition of nanofiller in case of strong interfacial interaction, whereas the influence is moderate in case of a less interacting matrix‐filler combination. It is suggested that the “excess heat capacity” can be used to quantify the segmental mobility of polymer chains in the vicinity of the nanofiller. Hence it provides valuable information on the strength of interaction, governed by the physical and chemical nature of matrix and filler. Heating experiments subsequent to quasi‐isothermal crystallization point at a certain degree of molecular ordering, responsible for crystal nucleation in EVA copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1291–1302, 2007     

Synthesis and reactions of nitro derivatives of hydrogenated cardanol

3-n-Pentadecylphenol (hydrogenated cardanol) and its derivative 5-n-pentadecyl-2-tert-butylphenol can be nitrated using nitric acid in acetonitrile or methanol to give mono, di or trinitro products. 5-n-Pentadecyl-2-nitrophenol undergoes reductive carbonylation to give a benzoxazole-2-one derivative. An efficient catalytic oxidation reaction in the presence of MeReO₃ has also been studied.