Non-equilibrium conformations of dilute star polymers in shear flow

Polymer topology influences the structural and dynamic behavior of macromolecules, particularly under non-equilibrium conditions such as shear flow. As a result, conventional Gaussian chain models fail to capture the complex deformation and relaxation dynamics of polymers with branched architectures. In this study, we present a combination of Brownian dynamics simulations with Gram-Charlier (G-C) expansion analysis to quantify non-Gaussian features using two cumulant-based metrics: the standard deviation σ of the one-dimensional projected configurational distribution, where larger values indicate greater deformation, and the normalized fourth cumulant κ4/σ4, where larger values indicate stronger non-Gaussianity. Focusing on linear and star polymers in dilute solution, we systematically investigate how molecular architecture, finite extensibility, and hydrodynamic interactions (HI) influence their deformation and conformational response in shear flow. Our findings reveal that star polymers exhibit constrained global extension but enhanced local stretching near the core, resulting in reduced deviations from Gaussian behavior compared to linear chains. Finite extensibility imposes an upper limit on bond extension, which suppresses configurational deformation at high shear rates and leads to a non-monotonic trend in κ4/σ4. By contrast, hydrodynamic interactions introduce long-range segmental coupling that enhances coordinated motion and amplifies non-Gaussian character, resulting in higher values of κ4/σ4 under strong shear flow. Together, these results establish a robust framework for characterizing the influence of polymer topology on non-equilibrium conformations, offering new insights into the mechanics of branched polymer systems under flow.