Micromechanical characterization of the interphase layer in semi‐crystalline polyethylene

Abstract

Semi-crystalline polyethylene is composed of three domains: crystalline lamellae, the compliant amorphous phase, and the so-called "interphase" layer separating them. Among these three constituents, little is known about the mechanical properties of the interphase layer. This lack of knowledge is chiefly due to its mechanical instability as well as its nanometric thickness impeding any property measuring experiments. In this study, the Monte Carlo molecular simulation results for the interlamellar domain (i.e. amorphous+ interphases), reported in (in 't Veld et al. 2006) are employed. The amorphous elastic properties are adopted from the literature and then two distinct micromechanical homogenization approaches are utilized to dissociate the interphase stiffness from that of the interlamellar region. The results of the two approaches match perfectly, which validates the implemented dissociation methodology. Moreover, a hybrid numerical technique is proposed for one of the approaches when the recursive method poses numerical divergence problems. Interestingly, it is found that the dissociated interphase stiffness lacks the common feature of positive definiteness, which is attributed to its nature as a transitional domain between two coexisting phases. The sensitivity analyses carried out reveal that this property is insensitive to the non-orthotropic components of the interlamellar stiffness as well as the uncertainties existing in the interlamellar and amorphous stiffnesses. Finally, using the dissociated interphase stiffness, its effective Young's modulus is calculated. The evaluated Young's modulus compares well with the effective interlamellar Young's modulus for highly crystalline polyethylene, reported in an experimental study. This satisfactory agreement along with the identical results produced by the two micromechanical approaches confirms the validity of the new information about the interphase elastic properties in addition to making the proposed dissociation methodology quite reliable to be applied to similar problems.

Predicting experimental results for polyethylene by computer simulation

“…undertook the first theoretical estimates of the thermal and mechanical properties of the "interlamellar phase" of semicrystalline linear PE by MC simulations using the PYS-UA FF or modified versions [367,368]. Using this interface MC (IMC) model and micromechanical homogenization approaches [369], it is possible to dissociate interfacial stiffness from that of the whole interlamellar region. The interphase thickness and conformational aspects of the chain segments in this region, together with the phase volumes, can be also deduced.…”

All-atomic and coarse-grained molecular dynamics investigation of deformation in semi-crystalline lamellar polyethylene

“…To gain insight into the complex behaviour of semicrystalline polymers, atomistic modelling is a useful numerical modelling tool that has been widely used in the literature [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. Most of these works have been based on simplified and coarse-grained interaction models, such as the united atom (UA) interaction model.…”

Ab initio and classical atomistic modelling of structure and defects in crystalline orthorhombic polyethylene: Twin boundaries, slip interfaces, and nature of barriers

“…These force fields display different levels of atomic resolution and are commonly used for polymer modelling. Although there is a multitude of all-atom potentials available in the literature, the former was chosen for the present paper based on its common use, its simplicity and relatively low computational cost, while the latter was chosen because it has been used extensively for investigating the mechanical properties of amorphous and semi-crystalline polymers [32][33][34][35][36][37][38][39][40][41][42].…”