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The purpose of this research paper is to investigate the changes in free volume by adding acrylate modified nanodiamond particles. In this study, a cross-linked thiol-ene (T) network was obtained under ultraviole light. The changes in free volume were analyzed when acrylate-modified nanodiamond (M-ND) particles were added to the nanocomposites obtained. Positron annihilation lifetime spectroscopy (PALS), a well-established method, was used for this analysis. In addition, the effect of nanocomposites containing different ratios of acrylate M-ND particles (1, 2, 3 and 5 Wt. %) on the surface and the thermal properties were also examined.

The impact of different quantities of acrylate M-ND on the free volume and surface morphological properties of thiol-ene polymer networks were studied by using scanning electron microscopy, differential scanning calorimetry, attenuated total reflection, Fourier transform infrared spectroscopy, PALS and thermogravimetric analysis measurements.

The thermal properties of T/M-ND were found to depend on the weight percentages of the M-ND content. For increasing weight percentages of M-ND added to thio-lene polymer networks, the glass transition temperature (T_g) increased from 103°C to 154°C. The ortho-positronium (o-Ps) lifetime (free volume) and free volume fraction characterization of T/M-ND nanocomposites were investigated using PALS. Increasing temperature caused both the o-Ps lifetime (free volume) to change with increasing saturation and to linearly increase the intensity; however, an increasing weight percentage of M-ND caused no change at all for the o-Ps lifetime (free volume) and the free volume fraction.

According to published literature, and to the best of the authors’ knowledge, this is the first time a study examining the free volume properties in a thiol-ene system has been carried out.

Porous silica has been used as support for catalysts used to convert renewable and fossil resources into useful energy sources. Understanding the pore structure of these materials is crucial for the design and synthesis of supported metal catalysts. Positron annihilation lifetime spectroscopy (PALS) can be used to characterize the nanoscale pore structure of these materials. Silica powders with two different porous structures were subjected to compressive pressure deformation using a hydraulic press. SEM images at 100K magnification show that the more-porous silica has larger granules compared to low-porous silica. A decrease in granular size due to deformation is clearly observed for more-porous silica and almost unchanged for low-porous silica. The positron third lifetime component in the more-porous silica showed 6.6 ns lifetime (pore size of ~ 11 Å) with 3.4% intensity, while these values after 20 kPSI pressure deformation were 2.9 ns (pore size of ~ 6.8 Å) with 12.4% intensity. This shows that the larger-pores collapse to form 3-4 times more smaller-pores and consistent with the almost same values observed for the fractional free volume in the uncompressed and deformed samples. The effect of deformation on the low-porous silica is negligible at the applied pressure. The third lifetime for this sample is 1.8 ns (pore size of ~ 5.2 Å) with intensity of 4.3% for both as-made and deformed samples.

Polyimide nanocomposites were prepared with 0 and 1 wt% single wall-and double wall- CNTs (functionalized and non-functionalized) from BPADA and BAPP by refluxing in NMP. These nanocomposites were characterized using FT-IR, TGA, DSC, tensile strength, and Positron annihilation lifetime spectroscopy (PALS). The FT-IR spectra for all the samples showed the characteristic peaks of polyimide. TGA curves showed weight loss with temperature in two stages. The first stage 180-300 °C showed a weight loss of ~ 15% that may be associated with the release of trapped NMP. The second stage 500-750 °C with a drastic weight loss is associated with decomposition. The residual weight is ~ 40% at 750 °C for both pure polyimide and polyimide nano composites made with functionalized single or double wall CNTs. The non-functionalized CNT dispersed polyimide showed similar two-step behavior, but the weight loss is remarkably less and about 80% weight remained at 750 °C. DSC curves of all polyimide samples showed two distinguishable endothermic peaks at around 90 °C (the onset of NMP release) and 200 °C (structural change). PALS was used to study the nano-porosity. Positron lifetime has a correlation with tensile strength showing a decrease in tensile strength with increasing pore size in CNT-polyimide composites.

A large number of new analytical techniques have proved themselves at least potentially useful in coatings research. One of these, investigated by Jilek [Progress in Organic Coatings, 5, 2 (1977) p. 97], is described as ortho‐positronium annihilation. The positronium atom results from the combination of an electron with a positron whose energy level has been diminished through successive collisions. The positronium atom can be thought of as a hydrogen isotope where the nucleus has been replaced by the positron. The positronium atom will eventually annihilate with an electron and, in so doing, it will release energy in the form of gamma rays. Thus, one possibility for use of the positronium ion is to determine crosslink density of a polymer. If in fact it can be used for this it will be an extremely valuable tool, for the degree of crosslink density is not easily determined by known techniques, and work that has been done is largely empirical. The author proposes that positronium annihilation could provide a means for studying comparative crosslink densities and polymers.

Over the past decades, intense efforts have been devoted to design and synthesize efficient photocatalysts which are active under sunlight for environmental and energy applications. Titanium dioxide (TiO₂) has attracted much attention over many years for organic contaminant degradation in air or water due to its strong optical absorptivity, chemical stability and low cost. However, TiO₂ has a very low photo quantum yield which prompts the easy recombination of photogeneration electron/hole pairs. In addition, bandgap of 3.2 eV restrains application of this photocatalyst mainly to the UV range.

Vertically oriented one-dimensional TiO₂ nanostructures remarkably improve electron transport by creating a direct conduction pathway, decreasing intercrystalline contacts and stretching grown structure with the specified directionality. In this research, to enhance the visible light absorbance of TiO₂, prearranged hydrogenated titanium dioxide nanorods (H-TNRs) in the presence of H₂/N₂ gas flow are hydrothermally synthesized.

The X-ray diffraction patterns illustrated the characteristic peaks of tetragonal rutile TiO₂ and confirmed that there is no phase change after hydrogenation. Trivalent titanium ions surface defects and oxygen vacancies were considered as major reasons for redshift of absorption edge toward visible region and subsequently narrowing the bandgap to 2.27 eV. The optimized photocatalysts exhibited high visible-light-driven photocatalytic activity for degradation of methylene blue in water within 210. The synthesized H-TNRs established themselves as promising photocatalysts for organic compounds degradation in the aqueous solution.

To the best of the authors’ knowledge, this work is original and has not been published elsewhere nor is it currently under consideration for publication elsewhere.