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Dynamic density functionals (DDFs) are popular tools for studying thedynamical evolution of inhomogeneous polymer systems. Here, we present asystematic evaluation of a set of diffusive DDF theories by comparing theirpredictions with data from particle-based Brownian dynamics (BD) simulationsfor two selected problems: Interface broadening in compressible A/B homopolymerblends after a sudden change of the incompatibility parameter, and microphaseseparation in compressible A:B diblock copolymer melts. Specifically, weexamine (i) a local dynamics model, where monomers are taken to moveindependently from each other, (ii) a nonlocal "chain dynamics" model, wheremonomers move jointly with correlation matrix given by the local chaincorrelator, and (iii,iv) two popular approximations to (ii), namely (iii) theDebye dynamics model, where the chain correlator is approximated by its valuein a homogeneous system, and (iv) the computationally efficient "externalpotential dynamics" (EPD) model. With the exception of EPD, the value of thecompressibility parameter has little influence on the results. In the interfacebroadening problem, the chain dynamics model reproduces the BD data best.However, the closely related EPD model produces large spurious artefacts. Theseartefacts disappear when the blend system becomes incompressible. In themicrophase separation problem, the predictions of the nonlocal models (ii-iv)agree with each other and significantly overestimate the ordering time, whereasthe local model (i) underestimates it. We attribute this to the multiscalecharacter of the ordering process, which involves both local and global chainrearrangements. To account for this, we propose a mixed local/nonlocal DDFscheme which quantitatively reproduces all BD simulation data considered here.

Dynamic density functional theories for inhomogeneous polymer systems compared to Brownian dynamics simulations