Abstract
The compatibility and surface behavior of squalane–polybutadiene mixtures are studied by experimental cloud point and neutron reflectivity measurements, statistical associating fluid theory (SAFT), and molecular dynamics (MD) simulations. A SAFT-γ Mie model is shown to be successful in capturing the cloud point curves of squalane–polybutadiene and squalane–cis-polybutadiene binary mixtures, and the same SAFT-γ Mie model is used to develop a thermodynamically consistent top-down coarse-grained force field to describe squalane–polybutadiene. Coarse-grained molecular dynamics simulations are performed to study surface behavior for different concentrations of squalane, with the system exhibiting surface enrichment and a wetting transition. Simulated surface profiles are compared with those obtained by fitting to neutron reflectivity data obtained from thin films composed of deuterated squalane (d-sq)–polybutadiene. The presented top-down parametrization methodology is a fast and thermodynamically reliable approach for predicting properties of oligomer–polymer mixtures, which can be challenging for either theory or MD simulations alone.
Highlights
The molecular model in the statistical associating fluid theory (SAFT)-γ Mie equation of state (EoS) is a chain of tangentially connected beads interacting through Mie potentials, which can be expressed for the interaction between bead i and j as CijεijÄÇÅÅÅÅÅÅÅÅÅÅÅÅÅikjjjjjj σij rij y{zzzzzzλr ikjjjjjj σij rij y{zzzzzzλa,ij λrij λrij − λa
Pure component SAFT-γ models for squalane, PB, and cisPB were obtained by simultaneously fitting the εii, σii, λrii, and λaii Mie potential parameters to reproduce the experimental liquid densities across a wide range of temperatures and pressures (Figure 3)
SAFT-γ Mie leads to a single transferable set of Mie parameters that can be used to represent the entire range of experimental data (Table 2)
Summary
Oligomers play a significant role in influencing polymer properties both in the bulk and at an interface. Slow phase separation of oligomers can prove a major problem when designing stable polymer mixtures for specific applications.[8] oligomers exhibit a significant (sometimes beneficial) influence on polymer surfaces through surface migration, wetting transitions,[9] and surface segregation (including blooming).[10−15]
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