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In this paper, a simple but detailed new theoretical model is developed for a thin loop heat pipe (LHP) to predict: the overall thermal resistance, the temperature distribution, the heat transfer rate, the heat leakage by conduction and the length of single and two-phase working fluid flows within the condenser. The theoretical results were confronted with experimental data of a mini flat LHP, manufactured using sintering and diffusion bonding processes. The working fluid used was water. A workbench, capable of simulating the actual operating conditions of a modern chip processor, with 1 cm2 of heat dissipating area, as found in smartphones and other electronic gadgets, was used to evaluate the LHP thermal performance. The tested LHP had dimensions of 76 x 60 x 1.6 mm3. The cold source was natural air convection to the surroundings. The device operated successfully in the orientations: horizontal, gravity-assisted, and against gravity. Tests were conducted until the evaporator reached 100°C, the limit temperature of electronics, resulting in overall thermal resistances of 0.37 °C/W, 0.47 °C/W and 0.44 °C/W, respectively. The model could successfully predict all steady-state operational parameters of the LHP with small deviations, proving to be suitable for designing new LHPs and other thin devices. The difference between predicted and measured resistances were within 5.64%, while between predicted and measured temperatures were within 3.30%. Lastly, the heat leak from the evaporator to the liquid line had a deviation of 16.62%. The LHP, although very thin, showed to be a good solution for cooling small electronic gadgets, such as mobile smartphones. [ABSTRACT FROM AUTHOR]

Three photoactive compounds with π-extended conjugation based on the 2,1,3-benzothiadiazole unit were synthesized and characterized. The compounds exhibited absorption in the violet-blue region with molar absorptivity coefficients and radiative rate constants arising from spin and symmetry allowed 1 ππ* electronic transitions. An emission located in the green region with a large Stokes shift was observed, which was most likely due to a charge-transfer mechanism in the excited state. In spin-coated films a dependence on the fluorescence emission intensity with the size of the alkoxy chain could be observed, where an effective non-radiactive channel seems to be present to deactivate the excited state. The thermal properties were analyzed by differential scanning calorimetry (DSC), and all final compounds exhibited a similar behavior with a crystal-isotropic liquid transition during the heating scan and isotropic liquid-crystal transition during the cooling process. Thermogravimetric analysis indicated a main thermal event with an initial decomposition temperature that was higher than 340 °C. The electrochemical characterization indicate that the compounds exhibited a reversible peak at −1.48 V and an irreversible oxidation process at 0.94 V versus Ag/Ag + . The electrochemical band gap was calculated to be approximately 2.30 eV versus NHE. The spectroelectrochemical measurements demonstrated changes in the absorption spectra due to changes in the electronic structure of the conjugated molecules under oxidative and reductive potentials. [ABSTRACT FROM AUTHOR]

This work presents the synthesis and characterization of compounds based on the heterocycle tris-[1,2,4]-triazolo-[1,3,5]-triazine (TTT) obtained by a new building block that can be applied to afford different discotic materials in one step. The thermal properties were evaluated by TGA and DSC and indicate very thermal stable compounds. The compounds exhibited absorption in the UV-B region (∼280 nm) with molar absorptivity coefficients and radiative rate constants arising from spin and symmetry allowed π–π* electronic transitions. An emission located in the UV-A region (∼363 nm) was observed, which was most likely due to a normal emission because no evidence of a charge-transfer mechanism in the excited state was observed. Spin-coated films indicate the presence of π-stacking in compounds presenting lower alkyl chains. Cyclic voltammetry measurements showed reduction and oxidation processes. The HOMO energy was obtained from the oxidation potential corresponding and the LUMO energy was found by subtracting its optical band gap from the HOMO value. In addition, in situ UV-Vis measurements were employed to evaluate the changes in the absorption spectra due to the changes in the electronic structure of the conjugated molecules under oxidative and reductive potentials. [ABSTRACT FROM AUTHOR]