EFFECTS OF MOLECULAR CHAIN COVERAGE AND MOLECULAR CHAIN LENGTH ON STRENGTH AND PACKING OF SURFACE COATING MATERIALS: DFT CALCULATIONS

Self-assembled monolayers (SAMs) on an SiO2 surface were investigated using periodic DFT calculations. The stability of SAMs on SiO2 surfaces was influenced by modifications in head groups, coverage, and space group length. Three molecules were considered as trial molecular chains: methyltrichlorosilane (CH3SiCl3), acetyl chloride (CH3COCl), and methylphosphonic acid (CH3PO(OH)2), with CH3SiCl3 being chosen because of the stable chemisorption complex of its -SiCl3 functional group to the surface and the nonpolar hydrophobic nature of CH3. The stability of each SAM was evaluated using the molecular chain length in terms of CH3(CH2)nSiCl3, where n = 0-9, and three distinct coverages (1/4, 1/2, and 1 ML). Our findings revealed that coverage and molecular chain length had a major influence on SAM stability, with van der Waals interactions outweighing steric interactions during molecular chain lengthening.