Determination of surface free energy components of ε-CL-20 by thin-layer wicking technique

The solid surface free energy components of ε-CL-20 were determined by the Washburn equation with the thin-layer wicking technique. The results show that the surface free energy components of ε-CL-20 from different liquids are in good agreement with each other. The total surface free energy r_s^T of ε-CL-20 is 42.65 mJ · m^-2, which accords with the theoretic calculation result 41.28 mJ · m^-2. The other determined values are dispersive component r_s^LW = 40.61 mJ · m^-2, polar component r_s^AB = 2.042 mJ · m^-2, electron acceptor component r_s⁺= 0.32 mJ· m^-2 and electron donor component r_s^- = 13.02 mJ · m^-2. The results also show that the apolar component is the main part in the surface free energy and ε-CL-20 is a bipolar solid, which is more basic than acid.