2025/12/11 by Syed Shuja Hasan Zaidi, Zaidi, Syed Shuja Hasan, Hema Teherpuria +5
Materials Science · Engineering · Physics and Astronomy · #Block Copolymer Self-Assembly #Fluid Dynamics and Thin Films #Theoretical and Computational Physics
paper · pdf · doi:10.48550/arxiv.2512.10542
We employ a molecular dynamics (MD) study to explore pattern selection in binary fluid mixtures (AB) undergoing surface-directed spinodal decomposition on a chemically patterned amorphous substrate. We chose a checkerboard pattern with chemically distinct square patches of a side M, with neighboring patches preferring different particle types. We report the efficient transposition of the substrate's pattern as a registry to the fluid cross sections in its vicinity when the pattern's periodicity λ/σ≃ 2M (σ being the fluid particle size) is larger than the mixture's spinodal length scale λc/σ≃ 2π/ξB (ξB being the bulk correlation length). Our correlation analysis between the surface field and the surface-registries in the substrate's normal direction shows that the associated decay length, L⊥(t), increases with decreasing pattern periodicity (λ). L⊥(t) also exhibits diffusive growth with time ∼ t1/3, similar to wetting-layer growth for chemically homogeneous walls. Our MD results also show the emergence of composition waves parallel to the substrate, whose wavelength exhibits dynamical scaling with a power-law growth in time L||(z,t)∼ tα. L||(z,t) shows dynamical crossovers from a transient surface-registry regime to universal phase-separation regimes for cross-sections with registries. We also give an account of the scaling of registry's formation and melting times with patch sizes.