Thermomechanical properties and deformation of coarse-grained models of hard-soft block copolymers

In this paper, we investigate the enhancement mechanism of the mechanical properties for hard-soft block copolymers by using molecular dynamics simulations at various temperatures. A coarse-grained approach is adopted to study sufficiently generic models. Our numerical experiments demonstrate that the nonbond potential plays a more significant role in mechanical properties compared to the bond potential. This finding serves as a cornerstone to understand the hard-soft materials. To explore the effect of hard segments, four copolymers with different concentrations and energy factors that describe the interaction between hard beads are conducted. Simulation results show that the mechanical performances of the system with large attractive force and small concentration of hard segments could be improved dramatically in conjunction with a moderate increment of the glass transition temperature. In particular, the energy factor shows a substantial influence in determining the microphase separation as well as the morphology of hard domains. These observations are believed to provide design guidelines for polymeric materials in engineering practice.

Figure 1

Schematic representation of the approximation of the hard and soft phases for hard-soft copolymers.

Figure 2

Convergence of elastic constants of $C_{11}$, $C_{12}$, and $C_{44}$.

Figure 3

Volume $V\left(T\right)$ and nonbond potential energy per bead for chain length $N=100$ with respect to temperature.

Figure 4

(a) Bulk and (b) shear moduli as a function of temperature.

Figure 5

(a) Young's modulus and (b) Poisson's ratio as a function of temperature.

Figure 6

(a) Stress-strain behavior and (b) strain rate-dependent Young's moduli of an all-soft-beads polymer with a different strain rate at a temperature of 0.55.

Figure 7

Evaluation of average bond length of an all-soft bead polymer with a different strain rate at a temperature of 0.55.

Figure 8

Snapshots of two hard-soft block copolymers. Microphase separation of (a) H2S8-2 and (b) H2S8-5 into hard and soft domains.

Figure 9

RDFs between soft-soft, soft-hard, and hard-hard beads at a temperature of 1.0 for five polymers.

Figure 10

$\langle R_e^2\rangle$ and $\langle R_g^2\rangle$ at a temperature of 1.0 for five polymers.

Figure 11

(a) Volume and (b) the nonbond potential energy as a function of temperature for different hard-soft block copolymers.

Figure 12

(a) Bulk and (b) shear moduli as a function of temperature for hard-soft materials.

Figure 13

(a) Stress-strain behavior and (b) the average bond length of hard-soft polymers for the lowest strain rate at a temperature of 0.55.

Figure 14

Nonbond potential energies and bond potential energies for H2S8-5 and H2S3-2 structures for the lowest strain rate at a temperature of 0.55.