The Role of a Diluent in Deformation-Induced Bonding of Glassy Polymer Bidisperse Blends

TL;DR

This study uses molecular simulations to show that adding a low molecular weight diluent enhances deformation-induced bonding of glassy polymers at temperatures below their glass transition, improving interfacial entanglements and fracture energy.

Contribution

It demonstrates how diluents significantly improve bonding strength and interfacial entanglement formation in bidisperse glassy polymer blends during deformation below $T_g$.

Findings

Adding diluents increases interfacial chain-ends during deformation.

Bonding strength correlates with diluent concentration and entanglement density.

Enhanced bonding achieves about one-third of bulk strength below $T_g$.

Abstract

Bonding between polymers below the glass transition temperature through molecular-scale dilatation (or densification)-based interdiffusion of macromolecules has recently been introduced. In this mechanism, short timeframe plastic deformation enables polymer chains to interdiffuse and form entanglements at the interface, facilitating rapid bonding below the glass transition temperature ($T_g$). Here, we are addressing the role of a lower molecular weight diluent in bonding polymer interfaces of bidisperse blends through deformation-induced bonding (DIB) at temperatures well below both the surface and bulk glass transition temperatures, $T_g^s$ and $T_g^b$, respectively, by using molecular simulations. These simulations reveal that addition of the diluent ($\phi\le$20\%) drastically enhances the number of chain-ends at the interfacial region compared to a pure glass sample ($\phi=0\%$) during deformation below $T_g^s$, which improves the possibility of opposite side entanglement formation. The changes in stress-strain response of debonded samples correlate with the normalized entanglement density. Likewise, the maximum interfacial fracture energy $G_{I,max}$ of debonded samples is correlated with the diluent concentration ($\phi$), below $T_g^s$. Furthermore, the optimization of material and process conditions for DIB has yielded a notable advancement for the conditions tested here: achieving a higher bonding strength, approximately one-third of the bulk, all while remaining below $T_g$.