Transition of the bounded polymer layer to a rigid amorphous phase: A computational and DSC study

•Modification of the Sanchez-Lacombe equation of state.•Transition of the bounded layer to a rigid amorphous phase.•Examination of the glass transition in semicrystalline polymer nanocomposites.

The study focuses on the transition of the bounded to solid surfaces polymer layer to a rigid amorphous phase (RAP). Based on previous Monte Carlo (MC) simulation studies on bulk polyethylene (PE), we refine our numerical variable density Self Consistent Field (nSCF) method in order the calculated density in bulk to follow the predictions of the MC simulation. The proposed modification of the Sanchez-Lacombe equation of state allows us to examine thermodynamic aspects of the glass transition. By imposing a glass transition (Tg = 220 K) in the bulk we predict an earlier (during cooling), stronger transition of the bounded layer to a RAP, at ∼350 K. Also at short separation distances we record the appearance of undisturbed polymer bridges. Differential scanning calorimetry (DSC) experiments on polydimethylsiloxane (PDMS) and polyamide 6 (PA6) nanocomposites suggest that although the crystallization can be significantly suppressed by the addition of nanoparticles, the RAP layer may locally equilibrate, above Tg, for long experimental times with the melt phase. Our results support the idea that a significant free energy barrier of entropic origin appears due to the RAP formation, below the melting temperature (Tm) and above the Tg.

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