Morphology and Dynamics of Dense Nanometric Precursor Films of Polymer Melts

Nanometer-thick supported films of polymer melts spontaneously form and spread around sessile droplets that are deposited on oxidized silicon wafers. At steady state, the films become dense and adopt a uniform thickness, which is equal to twice the gyration radius of the free polymer. Remarkably, this law applies to a wide variety of melts and does not depend on the polymer chemistry nor on the surface state (oxide layer thickness, temperature, presence of water adsorbed, etc.). We show that existing theoretical descriptions cannot reproduce this experimental result. Conversely, the evolution toward this equilibrium state witnesses the specificity of the interactions at stake in these confined polymer films. The chain spreading dynamics can be modeled by taking into account both the polymer/surface friction and the polymer/polymer friction.