(177af) Effect of Chain Stiffness and Dispersity on Interfacial Adhesion of Polymer Melts: A Molecular Dynamics Simulations Study

Understanding molecular mechanisms dictating interfacial adhesion properties is crucial for improved design of polymers used in applications such as polymeric coatings, adhesives, lubricants, and development of composites. Prior simulation studies have focused mainly on monodisperse melts; however, synthetic polymers usually exhibit some form of molecular weight distribution which can be characterized by dispersity Ð. It has been demonstrated that both low and high Ð melts are desirable and exhibit complementary properties. However, the design space is vast, even for specific applications such as in polymer interfaces, and performing experiments alone may be laborious. The goal of a good adhesive is to attain an interface that matches bulk properties, and an important way to strengthen the interface is the interdiffusion of polymers from one interface to the other. In this work, we perform extensive molecular dynamics simulations to study interfacial adhesion of unentangled to moderately entangled semiflexible polymer melts that follow Schulz – Zimm molecular weight distribution. We explore between melts in low dispersity regime Ð = 1.0 to high dispersity Ð = 2.0 and specifically use simple bead – spring polymer model which has been demonstrated to capture essential physics of linear polymers. We vary the dispersity and stiffness in order to observe how adhesion at the interface may be affected by heterogeneity of chains in the melt. Since chain rigidity plays a crucial role in the structure and dynamics of polymer chains and in turn affects observable macroscopic properties, we employ the three bending angle potential to account for stiffness. As the dynamics of bulk influences the dynamics at the interface, we study the self-diffusion in the bulk to identify relevant time and length scales of polymer diffusion. Then we estimate the distribution of chains near the film surface by computing the number density as a function of position. Further, to gain insights into how the polymer backbones are oriented near the surfaces, we analyze the overall orientation of the backbone bonds as a function of the positions. We probe the interface between two polymeric films by allowing the interface to heal. Since healing occurs by the diffusion of chains across the interface to create interfacial entanglements, we quantify this by calculating the mass uptake per unit area as a function of interdiffusion time. Future work will include analyzing interfacial strength by measuring the shear response of bulk polymers and comparing these with healed interfaces at different healing times to identify deviation from bulk response. In summary, this work provides the necessary foundation to guide the design of polymer melts with improved interfacial adhesion properties by using dispersity as a tuning parameter.

Keywords: Polymer melts, Interfacial Adhesion, Density Profile, Diffusion