Structural and Mechanical Properties of Ionic Di-block Copolymers via a Molecular Dynamics Approach

Abstract

Polymerized ionic copolymers have recently evolved as a new class of materials to overcome the limited range of mechanical properties of ionic homopolymers. In this paper, we investigate the structural and mechanical properties of charged ionic homopolymers and di-block copolymers, while using coarse-grained molecular dynamics simulation. Tensile and compressive deformation are applied to the homopolymers and copolymers in the glassy state. The effect of charge ratio and loading direction on the stress-strain behavior are studied. It is found that the electrostatic interactions among charged pairs play major roles, as evidenced by increased Young’s modulus and yield strength with charge ratio. Increased charge ratio lead to enhanced stress contribution from both bonding and pairwise (Van der Waals + coulombic) interaction. The increase in the gyration of the radius is observed with increasing charge ratio in homopolymers, yet a reversed tendency is observed in copolymers. Introduced charge pairs leads to an increased randomness in the segmental orientation in copolymers.

A Molecular Dynamics Study of the Mechanical Properties of Ionic Copolymers during Tension–Recovery Deformation

“…When the pressure in different coordinate directions is adjusted separately, the cubic simulation box changes its shape due to the anisotropic nature of the system. The length of the lamellar phase increases perpendicularly to the interface accompanied by the shrinkage along the other directions, as mentioned in our previous work [19] and similar to the work by Lee and co-workers. [20] The elongated direction has been observed to be in the direction perpendicular to the microphase interface.…”

“…As evidenced in our previous studies, the presence of ions will increase the , which has been shown to increase with the charge ratio up to 50%. [ 19,24 ] On the other hand, the interaction at the interface is weaker than that in the interior of the microphase. The larger interface area may also lower the glass transition temperature.…”

“…In our previous study, the of neutral homopolymers is around 0.35, and that of the 25% charged ones is around 0.49. [ 19 ] In the following study of the tension–recovery simulation, T* = 0.45 is chosen so that block A is in the glassy state and block B is in the rubbery state.…”

“…It has been shown in our previous studies that below the glass temperature, the effect of anisotropy only becomes apparent after the strain exceeds 10%. [ 19 ] It is likely that the effect of weak interface interaction at a moderate strain level is not significant enough to be observed. As mentioned previously, at the loading temperature of T* = 0.45, the charged A block is in the glassy state and the neutral B block is in the rubbery state.…”

Structure and Diffusion of Ionic PDMS Melts

“…It is used in biomedicine [ 3 , 4 ], microfluidics [ 5 , 6 , 7 ], MEMS [ 8 ], triboelectricity [ 9 ] and piezoelectrics [ 10 ]. Motivation to explore the structure and dynamics of ionic PDMS [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] or other melts [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], is very high since ionic interactions inherit polymers with a functionality that leads to a high performance and applications as gas-separating membranes [ 15 ], water purification membranes [ 13 , 14 , 16 ], energy storage devices [ 39 , 40 ] as well as in sensing [ 22 , 23 ], actuation [ 21 ], fuel cells [ 41 ], and others [ 18 , 19 , 24 , 42 ].…”