Thermochromic composites of benzofluoran dye, bisphenol A developer 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
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. Double-printing 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 crosslinking of the polymer. The influence of structuring effects within a 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