Search

The adhesion behavior of perfluoropolyether (PFPE) on rough silica surfaces is investigated by steered molecular dynamics simulations. To reproduce bond breakage during sliding of PFPE, a dynamic bond breaking method is developed and applied to the PFPE–silica interface. Calculated results reveal that nanoscale roughness is a critical parameter that affects the adhesion strength due to the PFPE film thickness of 1 nm, and the adhesion strength also depends on the molecular density of PFPE on the silica surface. The effect of roughness amplitude, spacing, and molecular weight of PFPE are individually analyzed to find a key parameter for adhesion enhancement. Adhesion strength on a flat surface is highest and decreases with increasing roughness within the considered conditions. When Ra = 17.5 A, adhesion strength is 3 times lower than the flat surface, and vacant pores at the interface are observed, which implies a reduced molecular density of PFPE from 0.31 to 0.27 molecules/nm2. Increasing the roughness s...

Force fields developed with machine learning methods in tandem with quantum mechanics are beginning to find merit, given their (i) low cost, (ii) accuracy, and (iii) versatility. Recently, we proposed one such approach, wherein, the vectorial force on an atom is computed directly from its environment. Here, we discuss the multi-step workflow required for their construction, which begins with generating diverse reference atomic environments and force data, choosing a numerical representation for the atomic environments, down selecting a representative training set, and lastly the learning method itself, for the case of Al. The constructed force field is then validated by simulating complex materials phenomena such as surface melting and stress-strain behavior - that truly go beyond the realm of $ab\ initio$ methods both in length and time scales. To make such force fields truly versatile an attempt to estimate the uncertainty in force predictions is put forth, allowing one to identify areas of poor performance and paving the way for their continual improvement.