Phase change insulation for energy efficiency based on wax-halloysite composites Yafei Zhao, Suvhashis Thapa, Leland Weiss, Yuri Lvov Institute for Micromanufacturing, Louisiana Tech University, Ruston, LA 71270 Abstract Wax can be used as a phase change material in solar energy storage but has low thermal conductivity and cannot sustain shape at higher temperature (above 55 C). Introducing 50% halloysite clay nanotubes into wax yields a stable and homogenous phase change composite with thermal conductivity of 0.36 Wm-1K-1 and no leaking until 70 C (preserving layer-shape above the original wax melting point). Thermal conductivity of wax/halloysite/graphite (45/45/10%) composite showed a six-fold conductivity increase to 1.4 Wm-1K-1 compared to pure wax and had no liquid wax leakage until 81 C. Wax/halloysite/graphite/carbon nanotubes (45/45/5/10%) composite show thermal conductivity of 0.85 Wm-1K-1 while maintaining the original shape until 91 C. Vectorial thermal energy transfer for double layers of different phase change materials demonstrated heat flux difference in the opposite directions differed by 25%. This variance in layer conductivity allows for smart building roof insulators with increased absorption during hot weather but limited thermal losses during periods of cooler temperatures. The new wax-nanoclay composite is a promising heat storage material due to good heat capacity, high thermal conductivity and ability to preserve its shape during wax melting. Conclusions (1)Halloysite can offer as a support to maintain wax shape during heat absorption and phase change even when the temperature of the PCM exceeds the melting point. (2)Halloysite can also improve the thermal conductivity of wax. Shape stabilized temperature and thermal conductivity can be further enhanced by adding graphite or carbon nanotubes to wax/halloysite composite. (3)More than one phase change materials with different thermal conductivity and melting point can be combined to improve the performance of phase chage storage, and this design has a potential application in the building roof. Acknowledgements Support with NSF-1029147 and NSF- EPS1003897 grants are acknowledged. Authors are thankful to Applied Minerals Inc., USA for providing halloysite samples. Wax and Halloysite nanotubes Wax as a phase change material (PCM) Advantages: High heat of fusion (150-250 J/g), Appropriate melting temperature (51-53 C), Chemically inert and stable and noncorrosive and nontoxic Disadvantages: Low thermal conductivity (~0.25 W/ mK) For further information contact ylvov@latech.edu Experimental setup The composites were prepared by reflux blending and impregnation method. Wax was melted at 80 C and dissolved in 80 mL isooctane solution to form a homogenous solution under continuous stirring for 10 min. Halloysite (and graphite and carbon nanotubes) was added to the above solution and the resulting mixture was than stirred and refluxed under 80 C for 3 hours. Finally, the composites were sealed in a vacuum drier at room temperature for 3 days to evaporate isooctane solvent from the mixture. Results and discussion Table 2. Thermal conducivity of composites Figure 3. Images of pure wax (a) wax/halloysite (b) wax/graphite (c) wax/halloysite/graphite (d) wax/halloysite/graphite/carbon nanotubes at different temperature Reference [1] Y.M. Lvov, D.G. Shchukin, H. Möhwald, R.R. Price, ACS Nano. 2 (2008), 814-820. [2] E. Abdullayev, K. Sakakibara, K. Okamoto, W. Wei, K. Ariga, Y. Lvov, ACS Appl. Mater. Interface 3 (2011), 4040-4046. [3] B. Zhang, J. Zhang, et al. Solar Energy 86 (2012) 1142–1148. [4] M. Xiao, B. Feng, K. Gong. Energy conver. Manag.43 (2002) 103-108. [5] H. Kao, M. Li, X. Lv, J. Tan. J. Therm. Anal. Calorim .107 (2012) 299-303. W:HNT:G:CNT (w%) Melting Transition T (ºC) Melting point T (ºC) Melting latent heat ∆H (J/g) Total latent heat ∆H (J/g) 100:0:0:0 47.5 52.3 140.5 171.0 50:50:0:0 47.4 53.3 89.9 107.7 45:45:10:0 47.1 52.9 57.4 68.4 45:45:5: