Polymer-nanoparticle composite coatings: Formulation, characterization and evaluation

Part I: Radiative cooling by polymer-nanoparticle composite coatings. Thermal management is a major field of interest in academia and industry. As electronics become faster and smaller, heat dissipation is a problem of concern. Conventional techniques (heat sinks, mechanical fans) are bulky, consume external power and may not be suitable for these challenges. Use of coatings to enhance heat dissipation by radiative cooling is an attractive option, since they are almost space-less and independent of surroundings. In this work, nanodiamond powder (NDP), multi-wall carbon nanotube (MWCNT), and carbon black (CB) were dispersed in acrylate emulsion (AC) to form composite materials. These materials were coated on aluminum panels (alloy 3003) to give thin coatings, termed "molecular fan - MF". The order of lattice quantization, as investigated by Raman spectroscopy, is in the order of MWCNT > CB >> NDP. The enhanced surface emissivity of the MF coating (as observed by IR imaging) is well-correlated to lattice quantization resulting in better cooling performance by MWCNT-AC composite. MF coatings with different concentrations (0%, 0.4%, 0.7%, and 1%) of MWCNT were prepared. The equilibrium temperature lowering of the coated panel was observed with increased loading of carbon nanotubes and was measured as 17°C for 1% loading of MWCNT. This was attributed to increased density of active phonons in the MF coating.Part II: An instrument for evaluation of performance of heat dissipative coatings. An instrument is developed to evaluate the performance of heat dissipative coatings. The instrument has features to measure the apparent emissivity of a given surface under different input power settings. The emissivity of aluminum (Al Q-panel) and copper, as measured from 60-135°C, showed a value of 0.15+/-0.03 and 0.42+/-0.05 respectively, consistent with reported values in literature. The relative emissivity of a heat dissipative coating, called as molecular fan carbon nanotube 'MF-CNT', was found to be &sim 0.97. A simple mathematical model is built to evaluate the role of different heat transfer mechanisms (convection and radiation) on cooling performance, and it was observed that convection plays a dominant role in cooling, with more than 90% of heat transferred by convection. In presence of MF-CNT coating, radiation heat transfer increases to &sim30% and lowers the steady state temperature by 10°C. It is illustrated that radiative cooling could be a significant factor in thermal management.Part III: Formulation of hard coatings for application on PVC. UV-curable coatings for PVC substrates are formulated and evaluated. It was observed that the water-borne systems were highly abrasion resistant and gave desired pencil hardness.