Ultrafast Nanoscale Polymer Coating on Porous 3D Structures Using Microwave Irradiation

Thin polymer coatings are very popular, but the coatings on uneven surfaces or porous 3D structures are difficult to obtain with traditional methods. The pores are easily clogged due to nonuniform polymer curing processes caused by inevitable macroscale temperature gradients from their hotter outer to colder inner sides. Here an ultrafast and simple fabrication method is developed to obtain nanoscale coating layers on the inner and outer surfaces of a porous 3D sponge-like carbon nanotube (CNT). Microwave irradiation rapidly and selectively heats the CNT immersed in a mixture solution of an uncured polymer and a diluent solvent, solidifying the polymer only adjacent to the CNT with five repeated 3 s microwave irradiation. The coating layers can be controlled by adjusting the concentration of the uncured polymer in the solution and controlling the CNT temperature via microwave power and irradiation time. The nanoscale coating strongly ties the junction between CNTs without filling the pores with the polymer, resulting in excellent resilience to compressive stress with large strains (≈180 kPa at 60%), which is maintained throughout repeated 8000 cycles of 0–60% strain. The unfilled pores allow for maintaining the low thermal conductivity, ≈26 mW m−1 K−1, and the electrical resistance is varied with strain. This facile selective polymer curing methodology can be utilized in processing various materials with uneven surfaces or pores.