Novel All-Polymer Nanocomposites Enable Manipulation of Mechanical Properties via Self-Assembly

Abstract

Approaches to tailor the mechanical properties of polymer nanocomposites (PNCs) with various microstructures still remain limited. Herein, using coarse-grained molecular dynamics simulations, a new molecular design strategy is put forward to build a novel all-polymer nanocomposite (S_n-PNC) by grafting single-chain nanoparticles (SCNPs) as a block at both ends of a linear polymer chain. We investigated the effect of different volume fractions of SCNP (f_SCNP) and interfacial interaction strength (ε_AB) between SCNPs and the matrix on the phase separation behavior of the S_n-PNC. The results demonstrated that the morphology and degree of phase separation were predominantly dependent on f_SCNP and ε_AB, respectively. The dynamics of SCNPs in the typical phase separation morphologies, namely, lamellae, cylinder, and sphere, were similar at short time intervals, while at long time intervals, they exhibited a transition from ⟨Δr²⟩ ∼ t^0.47 to ⟨Δr²⟩ ∼ t^0.31. The mechanical response mechanisms of SCNPs and linear matrix chains under uniaxial tension were examined by defining the degree of asphericity and the degree of stretching, respectively. Primitive path analysis was further conducted to characterize the entanglement topology of spherical, cylindrical, and lamellar morphologies, exploring the influence of bridge and loop chains on the stress distribution. In addition, triaxial tension demonstrated that a spherical structure had the highest energy dissipation capacity, followed by a cylindrical one, and finally a lamellar structure. The volume fraction, number, and surface area of voids were quantified based on the Voronoi volume of beads. The nucleation of voids in the three self-assembled structures was primarily located in the polymer matrix. The tensile stress began to decrease when the small voids merged massively into large ones. The mechanical properties of the S_n-PNC designed in this work are better than those of the traditional composite systems. In general, this proposed new building block structure may open a door for the design and fabrication of novel PNCs with desirable mechanical properties.