In situ study of the effect of endogenous and exogenous agents on color stability, hardness, and surface roughness of an elastomer for facial prostheses.

PURPOSE: To evaluate in situ the influence of sweat, oil, sunscreen, and disinfectant solution on the color stability, hardness, and roughness of elastomer for facial prostheses. MATERIALS AND METHODS: Standardized and intrinsically pigmented specimens remained in contact with human skin from the same person for 30 days, considering exposures (n = 36 per group), absent of exposition (Control, C); sweat and oiliness contact (SO); sweat and oiliness associated with sunscreen (SOS); 0.12% chlorhexidine digluconate immersion (CD0.12%); and all agents exposed (SOSCD). The main variables were color change (CIELab and National Standard Bureau system, NBS), Shore A hardness, and surface roughness, measured at baseline and 30 days. Qualitative analyses were performed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The data were analyzed by Kruskal-Wallis tests (color) and two-way ANOVA (hardness and roughness) with Sidak post-test (α = 0.05). RESULTS: CD0.12% (1.54 ± 0.49) and SOSCD (2.10 ± 1.03) had similar effects and caused the smallest color changes, considered mild and noticeable (NBS), respectively. SOS promoted the greatest color change (6.99 ± 1.43, NBS: large) and hardness (17.97 ± 0.56); SOS promoted intermediate roughness (3.48 ± 1.05) between SOSCD (2.25 ± 0.53), and two similar groups: C (4.46 ± 0.95), and CD0.12% (4.39 ± 1.26). The qualitative analysis showed an irregular, dense, dry, and whitish layer on the surface of the specimens exposed to sunscreen, which was reduced when in contact with 0.12% chlorhexidine digluconate. CONCLUSIONS: Endogenous and exogenous factors are capable of altering elastomer properties. The 0.12% chlorhexidine digluconate minimized the changes caused by sweat, oil, and sunscreen.

Ethylene scavenging properties from hydroxypropyl methylcellulose-TiO2 and gelatin-TiO2 nanocomposites on polyethylene supports for fruit application.

Several technologies have been proposed to preserve fruits and to avoid postharvest losses. The degradation of ethylene produced by the fruits using TiO2 photocatalysis has shown to be a good option to delay the ripening of fruits. This paper proposed a new application of biopolymers-TiO2 nanocomposites developed to extend the shelf-life of fruits. Photocatalytic coatings were applied on the expanded polyethylene foam nets to degrade ethylene. Gelatin and hydroxypropyl methylcellulose (HMPC) were tested as hydrophobic and hydrophilic matrices for the TiO2 incorporation. First, nanocomposite films prepared by casting were evaluated with regards to their photocatalytic properties. Both matrices, which were loaded with 1 wt% TiO2, degraded 40% of the ethylene injected in a batch reactor. By Langmuir-Hinshelwood model, ethylene degradation using gelatin-TiO2 films (kapp = 0.186 ± 0.021 min-1) was faster than the HPMC-TiO2 films (kapp = 0.034 ± 0.003 min-1). Then, gelatin-TiO2 dispersion was applied as a coating on the foam nets by dip coating. The gelatin-TiO2 bilayer exhibited higher concentration of ethylene degraded per photocatalytic area and photocatalyst mass unit (13.297 ± 0.178 ppmv m2 [Formula: see text] ) than its film form (18.212 ± 1.157 ppmv m2 [Formula: see text] ), which makes gelatin-TiO2/foam nets a promising composite design for fruit postharvest application.

Hydroxypropyl methylcellulose-TiO2 and gelatin-TiO2 nanocomposite films: Physicochemical and structural properties.

Photocatalytic properties of titanium dioxide (TiO2) have been widely studied. However, its tendency to aggregation in biopolymer-based nanocomposites limits its application for food packaging and has been few studied. The aim of this work was to study the dispersion of TiO2 (0-2 wt%) incorporated in the hydroxypropyl methylcellulose (HPMC-TiO2) and gelatin (gelatin-TiO2) film forming solutions. Particle size and zeta potential of TiO2 nanoparticles were investigated. Nanocomposite films were characterized as to the thickness, moisture content, solubility, color, absorption to the light, relative opacity, morphology, chemical composition, crystallinity, thermal and mechanical properties and water vapor permeability (WVP). TiO2 nanoparticles showed better dispersion in acid medium than water. Moisture content, water solubility and WVP of the gelatin-TiO2 films were influenced by the incorporation of TiO2, while HPMC-TiO2 films were not. The increase of relative opacity of the films as TiO2 was more attenuated for the gelatin-TiO2 films due to lower TiO2 aggregation in gelatin. Morphology, chemical composition, crystallinity and thermal properties of the films evidenced that TiO2 was better dispersed in both matrices at 1 wt%. It was also concluded that TiO2 aggregation generated more biphasic regions in HPMC than generated in gelatin, which caused a microstructural reorganization in the matrices.

High rectification in organic diodes based on liquid crystalline phthalocyanines.

The optical and electrical properties of mesogenic metal-free and metalated phthalocyanines (PCs) with a moderately sized and regioregular alkyl periphery were investigated. In solution, the individualized molecules show fluorescence lifetimes of 4-6 ns in THF. When deposited as solid thin films the materials exhibit significantly shorter fluorescence lifetimes with bi-exponential decay (1.4-1.8 ns; 0.2-0.4 ns) that testify to the formation of aggregates viaπ-π intermolecular interactions. In diode structures, their pronounced columnar order outbalances the unfavorable planar alignment and leads to excellent rectification behavior. Field-dependent charge carrier mobilities are obtained from the J-V curves in the trap-limited space-charge-limited current regime and demonstrate that the metalated PCs display an improved electrical response with respect to the metal-free homologue. The excited-state lifetime characterization suggest that the π-π intermolecular interactions are stronger for the metal-free PC, confirming that the metallic centre plays an important role in the charge transport inside these materials.