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

Bonding between polymers below the glass transition temperature through dilatational-plasticity has recently been introduced. In the deformation-induced bonding (DIB) mechanism, molecular-scale dilatation (or densification) with enhanced chain mobility enables polymer chain segments to interdiffuse and form entanglements at the interface, facilitating rapid bonding below the glass transition temperature (Tg). Here, we are addressing the role of a diluent in bidisperse blends which further amplifies the molecular mobility, interchain interactions, and the overall free volume, while simultaneously diluting the overall number of entanglements in the system as the number of host polymer chains is reduced. These simulations reveal that moderate addition (ϕ ≤ 20%) of a low molecular weight diluent drastically enhances the number of host polymer chain ends during deformation at the interfacial region compared to a pure glass sample (ϕ = 0%), which improves the possibility of opposite side entanglement formation. At higher diluent concentrations, the mobility further increases, yet the system suffers a greater loss of number of host polymer chains; optimization is found in a balance of these effects. The maximum strength of bonded samples with respect to bulk GI,max/Gb is thus correlated with the diluent concentration (ϕ). 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 in a short-time frame, approximately one-third of the bulk, all while remaining below Tg.