Multi-Conformational Luminescence and Phosphorescence of Few Phenazine 1,2,3-Triazole Molecules

Dropcast films produced from blends solutions of phenazine 1,2,3-triazole molecules in very low concentrations in a 1,3-Bis (N-carbazolyl) benzene (mCP) matrix were investigated at room temperature. The mCP acts as an optically inert matrix, having no influence on the emission properties of the guest molecules. Its conductive properties also ensure that blend films, within a completely organic character, are formed as truly active layers. The fluorescent and phosphorescent emission properties of the phenazine molecules, depending on their conformational states, allowed relatively intense emissions in blue, green, red and also in white, without the need to mix different materials. Although the results of absorption of the blended films have shown no characteristics of the guest molecules, due to their relatively low concentrations, the excitation of them occurs directly by the incident laser beam. The steady-state spectroscopy for the monomer and dimer singlet fluorescence states of respective blue and green emissions of the films were investigated. The analysis of their temporal decays were done using a different approach based on the Exponentially Modified Gaussian (EMG) function. The phosphorescent emissions of the triplet steady-states, occurring in the orange or in the red wavelength regions, were observed to be correlated, respectively, to the formation of guest monomers or to the guest dimers singlet states.

Physico-chemical properties of irradiated poly (vinyl alcohol)–Ethylene glycol blend films by γ-rays and ion beam

Poly (vinyl alcohol) is blended with ethylene glycol by casting method to form PVA-EG blend films. These films were irradiated by both N2 ion beam extracted from dc ion source at different ion fluences and γ-rays with various irradiation doses. The effects of ion beam and γ-rays irradiation on the thermal, micro-hardness, and gel fraction properties of PVA-EG blend films were investigated. The gel fraction % and micro-hardness increase with increasing the γ-rays doses up to 150 kGy and then decreased, where they increased at all fluences of ion beam irradiation. The improvement in the gel fraction percentage and micro-hardness suggest that PVA-EG blend films exhibited a crosslink density. The thermal behavior was examined by thermogravimetric analysis and it shows different thermal patterns depending on the type and dose of radiation. The thermal stability parameters of γ-rays- and ion beam-irradiated PVA-EG samples were evaluated using the Ti, Ts, T0.5, Tf temperatures, and activation energy (Ea) values. The thermal stability parameters were dependent on both the type and extent of irradiation dose and fluence. Finally, there is a good agreement between the obtained results from different measurement techniques.

Biobased Terpene Derivatives: Stiff and Biocompatible Compounds to Tune Biodegradability and Properties of Poly(butylene succinate)

Different copolymers incorporating terpene oxide units (e.g., limonene oxide) have been evaluated considering thermal properties, degradability, and biocompatibility. Thus, polycarbonates and polyesters derived from aromatic, monocyclic and bicyclic anhydrides have been considered. Furthermore, ring substitution with myrcene terpene has been evaluated. All polymers were amorphous when evaluated directly from synthesis. However, spherulites could be observed after the slow evaporation of diluted chloroform solutions of polylimonene carbonate, with all isopropene units possessing an R configuration. This feature was surprising considering the reported information that suggested only the racemic polymer was able to crystallize. All polymers were thermally stable and showed a dependence of the maximum degradation rate temperature (from 242 °C to 342 °C) with the type of terpene oxide. The graduation of glass transition temperatures (from 44 °C to 172 °C) was also observed, being higher than those corresponding to the unsubstituted polymers. The chain stiffness of the studied polymers hindered both hydrolytic and enzymatic degradation while a higher rate was detected when an oxidative medium was assayed (e.g., weight losses around 12% after 21 days of exposure). All samples were biocompatible according to the adhesion and proliferation tests performed with fibroblast cells. Hydrophobic and mechanically consistent films (i.e., contact angles between 90° and 110°) were obtained after the evaporation of chloroform from the solutions, having different ratios of the studied biobased polyterpenes and poly(butylene succinate) (PBS). The blend films were comparable in tensile modulus and tensile strength with the pure PBS (e.g., values of 330 MPa and 7 MPa were determined for samples incorporating 30 wt.% of poly(PA-LO), the copolyester derived from limonene oxide and phthalic anhydride. Blends were degradable, biocompatible and appropriate to produce oriented-pore and random-pore scaffolds via a thermally-induced phase separation (TIPS) method and using 1,4-dioxane as solvent. The best results were attained with the blend composed of 70 wt.% PBS and 30 wt.% poly(PA-LO). In summary, the studied biobased terpene derivatives showed promising properties to be used in a blended form for biomedical applications such as scaffolds for tissue engineering.

Synthesis and characterization of poly N-isopropylacrylamide-co-acrylic acid and their binary blend films properties

In past decades, the combination of polymers to obtain blends in film shapes has been a very effective strategy to meet the needs of the increasingly demanding market. In this sense, pH- and thermo-sensitive (PHT) polymers have recently drawn the attention of researchers for their countless applications. However, binary mixtures of typical PHTs like polyacrylic acid (p-AAc) and poly-N-isopropylacrylamide (p-NIPAm) were unable to form films. In this sense, it was hypothesized that NIPAm copolymerized with AAc monomers can yield blends with virtually the same functional group composition of binary mixtures of p-NIPAm and p-AAc homopolymers but with different properties of film formation. For this, a copolymeric radical synthesis and the subsequent analytical studies were complemented to get a broad description of these materials. P-NIPAm and p-AAc homopolymers and different proportions of copolymers p-NIPAm-co-AAc were obtained and thoroughly characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Size Exclusion Chromatography (SEC), acid-basic titration, and rotational rheology. Among the samples, the solutions of p-AAc with p-NIPAm and p-NIPAm-co-AAc copolymers with a higher proportion of NIPAm units (0.8 and 0.6 NIPAm/AAc) precipitated as interpolymer complexes. Since it was expected, the combination with p-NIPAm-co-AAc 40/60 copolymer, which has a higher proportion of AAc groups and pH sensitivity, allowed obtaining blends suitable for the preparation of films. Furthermore, despite the fact that the combinations of p-NIPAm-co-AAc 40/60 with p-NIPAm-co-AAc 80/20 or p-NIPAm were successful, the mechanical properties of the films are worse compared to the other blends, leaving this issue open for subsequent studies.