Self-organization of vapor-deposited polyolefins at the solid/vacuum interface

A Choukourov and I Melnichuk and I Gordeev and D Nikitin and R Tafiichuk and P Pleskunov and J Hanus and J Houska and T Kretkova and M Dopita, PROGRESS IN ORGANIC COATINGS, 143, 105630 (2020).

DOI: 10.1016/j.porgcoat.2020.105630

The self-organization of macromolecules on solid surfaces represents a topic of great current interest. Here, solvent-free interactions between polyolefins and silicon substrates are investigated upon their physical vapor deposition under vacuum. Molecular dynamics simulations show that polyolefins unfold upon adsorption and that two macromolecules suffice to produce a stable nucleus. Supersharp probe AFM measurements reveal the formation of 3.5 nm globular clusters that further transform into two-dimensional islands with compact shapes that possess a 3.5 nm thick rim and a 7.0 nm thick center. The islands grow via attachment-limited aggregation by accepting new molecules from the edge, keeping the thickness constant and expanding laterally. The evolution of the island growth is analyzed within the framework of capture zone distribution analysis using generalized Wigner scaling. The critical island size is found to be 1, confirming the results of molecular dynamics simulations. Upon longer deposition times, the islands coalesce, whereas their surface smoothens with a growth exponent of. =-0.33 and a dynamic exponent of 1/z = -0.21. Smoothening is accompanied by crystallization phenomena that result in the formation of orthorhombic polyolefin crystals, as detected by XRD.

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