The Interface Between Platinum(111) and Poly(vinyl Alcohol) Melt: A Molecular Dynamics Study

Molecular dynamics simulations are used to study the structure and dynamics of the platinum(111)/poly(vinyl alcohol) (PVA) oligomers (10 monomers long) interface at 400 K. The mass density and number density distribution of separate atoms along the surface normal resemble, in general, the distributions obtained for the platinum(111)/liquid isopropanol interface 28. The small discrepancies are dictated by the chemical bonds between monomers within PVA chains. The differences between PVA and isopropanol in the orientational structure of O‐H and O‐C bond vectors are large immediately at the platinum surface. The connectivity of monomers within PVA chains is also the main driving force of these changes. At longer distances, the structure of the PVA melt resembles approximately that of liquid isopropnaol. The PVA chains, which are directly adsorbed on the surface, extend into the bulk up to 2.25  nm. There exists a region where adsorbed chains mix with nonadsorbed ones and, therefore, form very likely hydrogen bonds between each other. Thus, it is expected that PVA melt, unlike liquid isopropanol, attaches relatively strongly onto the metal surface.

Keywords:

• Metal
• Surface
• Platinum
• Polymer
• Melt
• Poly (vinyl‐alcohol)
• PVA
• Bulk
• Interface
• Adsorption
• Simulations
• Molecular dynamics

Acknowledgments

The authors thank Volker C. Weiß for helpful scientific discussions. The authors are thankful to the Hochschulrechenzentrum der Technische Universität Darmstadt for the granted time on the IBM Regatta p575 machines (HHLR) located at the TU Darmstadt, Darmstadt, Germany and also to the John von Neumann‐Institut für Computing (NIC) for the granted time on IBM Regatta p690+ machines (JUMP) located at the ZAM Center.

Notes

¹The density of real amorphous PVA is 1.26 g/cm³ at 298 K [see Ref. 54]. For 200 PVA oligomers at 300 K and 101.3 kPa, we obtained density of about 1.105 g/cm³. The order analysis was performed as proposed in Ref. 55 Eq. (1) (crystallization of polyethylene). It confirmed that our system of 200PVA oligomers at 300 K is amorphous. One can expect, therefore, that the density of PVA will increase with chain length (density of isopropanol is 0.7827 g/cm³). Since our oligomers are only 10 monomers long and in reality polymer chains are built of few hundreds of monomers, the obtained lower density is an expected result. For the higher temperatures lower density can be expected. For 200 PVA oligomers at 400 K and 101.3 kPa, we obtained density of 1.084 g/cm³).