Isotropic nematic transitions for different effective microtubule widths. (a) Almost direct transition from disorder I phase to nematic N_I phase for W = 0 nm with the increase of growth rate k_g. The transition is discontinuous characterized by the coexistence regime near k_g = 44 nm/s. (b) For W = 25 nm, the transition from disorder I phase to N_II phase, then jumping into N_I phase with the increase of growth rate k_g. The N_II and N_I phase transition is discontinuous, with a bistable regime near k_g = 60 nm/s. The order parameter S is obtained by time and sample average (20 samples). Errors bar for 20 independent samples are given and most are within the symbol. Red circles represent that simulation samples undergo phase transition process and do not reach the steady state within the simulation time ∼ 5× 10⁵ s, giving the strong discontinuous nature of the transition, which is not included for averaging. Other parameters not listed here are the same as those in Fig. 2.