Effects of Graphene Incorporation on the Nanoscale Structure and Mechanical Response of PVDF Membrane Models: A Molecular Dynamics Study

Poly(vinylidene fluoride) (PVDF) membranes require both suitable morphology and mechanical integrity, but changes in nanoscale geometry do not necessarily improve all loading responses. Atomistic molecular dynamics simulations were used to compare pristine PVDF and graphene/PVDF membrane models constructed from five-repeat-unit oligomers. A force-driven sedimentation procedure was used to examine the effects of lateral cell size and polymer-chain number on deposited morphology. The structural indicator was a two-dimensional projected void-area fraction. Increasing polymer-chain number reduced the projected void fraction, whereas increasing lateral cell size produced thinner deposits with greater uncovered area. Graphene-containing structures showed greater projected coverage under corresponding construction conditions. Separately prepared mechanical specimens were subjected to tensile and shear loading using identical PVDF parameters within the mechanical comparisons. The reported mean apparent tensile secant modulus was approximately 14.6% higher for the composite, a descriptive finite-rate comparison. Its peak stress averaged over three independent runs was 122.46 ± 32.57 MPa (mean ± sample standard deviation), whereas the peak of its average curve was 109.38 MPa. These results distinguish the reported initial-slope difference from peak-response variability and clarify the statistical meaning of peak load resistance. They provide an atomistic basis for discussing membrane-skeleton geometry and loading-dependent response, without constituting a prediction of water permeability, selectivity, or antifouling performance.