Figure 2.

Hierarchical deformation. (a) LBL self-assembly is regulated by molecular (n_bb, n_sc, n_L) and morphological (R_sc, D_L, R_in, l) parameters, where Rsc - brush radius, D_L - L-block domain diameter, and l - distance between neighboring side chains along the bottlebrush contour. (b) The cascade of deformation mechanisms during uniaxial extension of LBL networks: (1) unfolding of bottlebrush filaments limited by f_unfold < k_BT/b_K ≅ k_BT/R_sc ≅ 0.5 pN (for n_sc = 70), (2) stretching of backbones inside brush envelops ranging within k_BT/R_sc < f_stretch < k_BT/l₀ ≅ 20 pN, where l₀ = 0.25 nm is the monomer projection length, and (3) pulling linear chains from microdomains creating a new interface between exposed linear block sections and the bottlebrush matrix. The two-head arrow indicates that chain pulling may overlap with backbone stretching. The pulling force is on the order of f_pull ≅ γ_LBl₀ ≅ 2.5 pN, where γ_LB ≅ 10 mN is the surface energy of the L–B interface. The actual f_pull value may be higher due to kinetic barriers imparted by glassy L-domains.