FIGURE 3 Dependence of a) CGand b) CG/CG,i onCG,i .
The effect of tM on FLG exfoliation was explored by fixing CP = 2.0 mg mL-1 and CG,i = 50 mg mL-1. As observed from Figure 4a,CG (thusCG/CG,i ) increases steadily from 0.092 mg mL-1 attM = 5 min to 0.33 mg mL-1 at tM = 80 min, showing an empirical correlation of CGtM 0.57. The exponents close to 0.5−0.7 were also noticed in sonication exfoliation and other instances of shear exfoliation and proposed to be process-independent, reflecting a more fundamental behavior.7,9,49 Above 80 min of tM ,CG tends to saturate. On the other hand, extension of tM decreases the lateral size of FLG. With tM extended from 5 to 20, 80, and 180 min, the average lateral size of FLG determined by DLS decreases from 829 ± 218 to 713 ± 180, 583 ± 115, and 304 ± 97 nm (Figure 4b). Larger lateral size thus higher aspect ratio is desired for many applications of FLG, such as polymer composites. Upon systematic consideration of FLG size, exfoliation efficiency, andCG/CG,i , the parameter combination of CP = 2.0 mg mL-1, CG,i = 50 mg mL-1, and tM = 80 min is preferred for subsequent scale-up production of FLG.