2024 AIChE Annual Meeting
Investigating the Effect of Dispersity on the Conformation and Dynamics of Semiflexible Polymer Melts – Insights from Molecular Dynamics Simulations
Synthetic polymers inherently possess a distribution of molecular weights due to the statistical
nature of their polymerization path, which is typically described by dispersity (Ð). Mathematically,
Ð is the ratio between the weight average molecular weight Mw and number average molecular
weight Mn. Studies have shown that both high and low dispersity can offer complementary
characteristics, significantly impacting the polymer's processability and its mechanical properties.
However, the design space for manipulating this parameter is vast and performing experiments is
time consuming. An important feature of polymer melts is the degree of entanglement, or the
topological constraints that polymer chains exert on one another. By utilizing coarse-grained
molecular dynamics simulations, we study the structure and dynamics of chains spanning the
unentangled to marginally entangled regime as a function of dispersity, making comparisons with
that of chains in a monodisperse melt. We specifically use the bead – spring polymer model which
has been demonstrated to capture essential physics of polymer melts. In order to control the degree
of flexibility of the chains, which in turn affects observable macroscopic properties, we employ
the three-body bending potential. First, we investigate the structure by computing the static
structure factor and radius of gyration to benchmark these quantities with their behavior in the
corresponding monodisperse melts to assess any deviation from ideal chain behavior. Next, we
examine the effects of heterogeneity in surrounding test chain lengths on melt entanglement using
primitive path analysis. Lastly, we analyze the mobility of specific test chains through the mean
squared displacement to gain insights into molecular mechanisms that may contribute to the
diverse relaxation processes in a polymer melt. In summary, this work provides the necessary
foundation for an improved understanding of the behavior of chains in synthetic polymer melts to
guide the predictive design for future applications.
nature of their polymerization path, which is typically described by dispersity (Ð). Mathematically,
Ð is the ratio between the weight average molecular weight Mw and number average molecular
weight Mn. Studies have shown that both high and low dispersity can offer complementary
characteristics, significantly impacting the polymer's processability and its mechanical properties.
However, the design space for manipulating this parameter is vast and performing experiments is
time consuming. An important feature of polymer melts is the degree of entanglement, or the
topological constraints that polymer chains exert on one another. By utilizing coarse-grained
molecular dynamics simulations, we study the structure and dynamics of chains spanning the
unentangled to marginally entangled regime as a function of dispersity, making comparisons with
that of chains in a monodisperse melt. We specifically use the bead – spring polymer model which
has been demonstrated to capture essential physics of polymer melts. In order to control the degree
of flexibility of the chains, which in turn affects observable macroscopic properties, we employ
the three-body bending potential. First, we investigate the structure by computing the static
structure factor and radius of gyration to benchmark these quantities with their behavior in the
corresponding monodisperse melts to assess any deviation from ideal chain behavior. Next, we
examine the effects of heterogeneity in surrounding test chain lengths on melt entanglement using
primitive path analysis. Lastly, we analyze the mobility of specific test chains through the mean
squared displacement to gain insights into molecular mechanisms that may contribute to the
diverse relaxation processes in a polymer melt. In summary, this work provides the necessary
foundation for an improved understanding of the behavior of chains in synthetic polymer melts to
guide the predictive design for future applications.