4.1 Thermal conductivity and interfacial property of PTFE and PES membrane.
PTFE and PES both have good mechanical stability and outstanding chemical resistance50-52. In addition, they both exhibit excellent reliability for rapid temperature floatation and for long-term usage as reported53. The measured thermal conductivity of PTFE and PES hollow fiber membranes are shown in Figure 5a. PTFE membrane possesses higher thermal conductivity (0.1712±0.025 W/m·K, average value in the measured temperature range) than that of PES membrane (0.1246±0.013 W/m·K). And the thermal conductivity of PTFE membrane increases from 0.1464 W/(m·K) to 0.1959 W/(m·K) when the temperature increases from 10 ℃ to 80 ℃; while, the thermal conductivity of PES membrane is relatively stable when the temperature increases. Generally, the thermal conductivity of the membrane is influenced by the nature of the membrane material (solid phase) and the pores distributed of in the membrane (gas phase). The large void structure in the membrane will be a convective heat transfer heat transfer and a radiation heat transfer mode54,55. The XRD patterns of the two membranes in Figure 5b indicates that the PTFE membrane possesses a semi-crystalline structure, whose thermal conductivity changes greatly with temperature56-58. While, PES membrane has an amorphous polymer, which the glass transition temperature is as high as 230 °C51. Below this temperature, the temperature has no significant impact on PES membrane’s thermal conductivity. In the temperature operation range of 5 to 40 °C during MACC, the two hollow fiber membranes both have a stable thermal conductivity, which is important for the nucleation control at a wide temperature operation window.