and octadecanol solvent were investigated to analyse how different molar ratios of developer influences the structural, optical and thermal properties. Increasing the amount of developer gives stronger absorption in the visible region and larger colour contrast between coloured and discoloured states. The colour clearing temperature of all studied composites is well below their melting point and the phase transitions are influenced only little by the content of the developer. The crystalline structure is fully controlled by the solvent; it changes from the g phase to the liquid at heating and returns through the rotator phase into the »gama« phase at cooling. Crystallinity of the composites diminishes with the content of the developer, causing increased scattering of light. The dye: developer molar ratio equal to 1:3 was determined to be large enough to open lactone ring in all dye molecules. Colour hysteresis of such composites shrinks to practically single sigmoidal curve whereas the colour contrast still increases with higher amount of the developer. This effect could be attributed to developer e solvent interactions in a composite with lower crystallinity.
COBISS.SI-ID: 5594394
The aim of the paper was to find a direct connection between dynamic colour changes, phase changes and chemical interactions in model three-component leuco dye based thermochromic systems. The model systems, containing crystal violet lactone as a colour former, bisphenol A as a developer and 1-tetradecanol as a co-solvent, were analysed by DSC and FTIR spectroscopy and the results were related to the characteristics of the dynamic colour change. The ternary thermochromic systems were also compared with binary mixtures of the co-solvent with the developer and colour former, respectively. The temperatures characterizing the dynamic colour change at decolouration limits were directly related to the solid-liquid transition on heating and liquid-solid transition on cooling, regardless the concentration of bisphenol A. In ternary thermochromic systems, an indistinctive phase transition at the temperatures below the solid-solid (crystal-rotator) transition was observed. The straight connection between the phase transitions and temperatures characterizing the dynamic colour change at colouration limits was not proved. The colour contrast of thermochromic systems was found to be directly related to the ratio of integrated intensity of lactone ring opened (solid) and lactone ring closed (liquid) carbonyl vibration characterized by infrared spectroscopy.
COBISS.SI-ID: 5983514
Double-printing of dielectric layers is commonly used to prevent electrical shorts in parallel-plate capacitors, but this increases the thickness of the dielectric layer and diminishes the corresponding capacitance. Doubleprinting also complicates the production process and increases production costs. In this paper, it is demonstrated that capacitors with single-printed dielectric layers are without shorts if the layer is completely polymerized. Therefore, electrical shorts could also be related to the state of polymerization in a defectfree dielectric layer. To demonstrate this, the electrical functionality of capacitors with single-printed dielectric layers was studied in terms of intrinsic properties of the ultraviolet (UV) curable dielectric layer, which were varied according to the curing energy. The chemical structure of the cured layer was analyzed with infrared spectroscopy to obtain the appearance of polymerizable groups and crosslinks within the polymer structure. Differential scanning calorimetry was used to measure the glass transition temperature of the dielectric material. It increases rapidly with UV curing until the polymerization is completed, whereas a small increase with further curing confirms dielectric layer in the presence of electrical shorts between electrodes is discussed. This research confirms that a completely polymerized layer forms a barrier to leakage and helps to prevent the formation of conductive paths between electrodes. Therefore, a connection between the structure of polymerized layer and its electrical properti es is highly reasonable.
COBISS.SI-ID: 5689370
Microcapsules consisting of paraffin wax cores with a melting point of approximately 42◦C and a melamine-formaldehyde resin shell were synthesized using in situ polymerization. These microcapsules have a uniform distribution with a spherical shape and an average diameter of approximately 15 μm. The thickness of the shell was approximately 1.5 _m. Shape-stabilized phase change materials (PCM)based on high-density polyethylene (HDPE) mixed with micro-encapsulated paraffin wax were prepared and investigated for application in thermal energy storage. The distribution of the capsules within the HDPE matrix was uniform without any tendency toward agglomeration. The microencapsulated paraffin wax acts as a high-latent-heat material, whereas the HDPE matrix ensures the compact shape, structural compactness and mechanical strength of the final PCM. The periodic temperature method was used to determine the thermal conductivity and thermal diffusivity of the phase change materials. A guarded hot plate unit was used to determine the latent heats of these phase-change materials. The thermal conductivity and diffusivity of the investigated PCMs decreased as the microcapsule content increased. In contrast, the latent, sensible and total heat of the PCMs increased with the paraffin content.
COBISS.SI-ID: 1573980
Colour changes of a thermochromic liquid crystal (TLC) ink printed on a black substrate are clearly observed by the naked eye, and therefore it is reasonable to expect that every approach recommended for colour measurements of samples with solid colour would be appropriate. In addition, the published spectroscopic analyses of TLC inks do not provide any guidance or limitations for the measurement geometry. On the other hand, our study demonstrates that spectroscopic measurements of such samples are not so straightforward. When using the most simple and commonly used measurement equipment with a directional illumination and viewing approach, the temperature-dependent spectral features resolve in a narrow spectral region that gives only a small part of the colour play effect. Detection of the entire effect requires the use of integrating spheres, which spatially integrate the radiant flux reflected on a sample in any direction; better results are obtained by spheres of larger diameter. The comparision of spectroscopic and colorimetric results obtained when different measurement geometries are applied on the same sample may demonstrate certain properties of the liquid crystal material inside microcapsules and help in understanding some details of the optical properties of the ink layer.
COBISS.SI-ID: 6071066