Interactions and structure of poly(dimethylsiloxane) at silicon dioxide surfaces: Electronic structure and molecular dynamics studies

Electronic structure studies are used to probe the interactions and molecular dynamics simulations are used to study the structure of thin poly(dimethylsiloxane) (PDMS) films near hydroxylated SiO2 substrates. Results of the electronic structure calculations show that the PDMS end groups, rather than atoms such as oxygen in the PDMS backbone structure, dominate interactions at the interface. Methyl–terminated PDMS binds weakly with the substrate via interactions between H atoms on PDMS methyl groups and O atoms on the substrate hydroxyl groups, while hydroxyl–terminated PDMS binds strongly with the substrate via hydrogen bonding between hydroxyl groups on PDMS and the substrate. To study the effect of temperature and type of substrate on the structural ordering of the PDMS liquid near the solid/liquid and liquid/air interfaces, molecular dynamics simulations for two temperatures (300 and 400 K) are carried out for three hydroxylated SiO2 substrates (α–quartz, β–cristobalite and amorphous SiO2). A direct correlation between the amount of ordering in the liquid near the solid/liquid interface and both the roughness of the substrate and the temperature is found. Furthermore the type of terminal end groups on the PDMS molecule also plays a role in the ordering of the PDMS segments near the interface.