3.2.3 Radial Distribution Function (RDF)
RDF has proved as an important approach for the assessment of the adsorption process type present during the inhibitor adsorption: either a physical or chemisorption. In advancement to the MD simulations, RDF is employed to measure the bond lengths between the heteroatoms and the alloy surface, which dictates the interaction modes (chemisorptions/physisorption).59 Further, this analysis reveals the degree of resistance/ rigidity of the adsorbed organics on the alloy surface.60 Emergence of the peak in the RDF graph offers a simple distinction of the involved process. The appearance of the peak from the distance 1 to 3.5 Å is an indication of a chemisorption process, whereas in the case of physisorption RDF peaks are expected at longer distances (> 3.5 Å). InFigure 6 , RDF values imparts the nature of intermolecular interactions (stronger/weaker) that occurred between alloy surface and the interacting atoms (nitrogen and oxygen atoms). Impressive findings are perceived in the presence of PPD molecule where the bond lengths of N-Ni-W & O-Ni-W shown less than 3.0 Å, from the surface plane of the material illustrating the chemisorption process; i.e, stronger interactive forces which aids in effective bounding of PPD molecule onto the alloy surface.61 However, the bond length of N-Ni-W & O-Ni-W for OPD molecule, recorded closer to 3.5 Å, pointing out the physisorption; i.e, weaker interactive forces exhibiting a tenuous affinity towards the alloy surface. Overall, the outcomes of RDF results, speculate that PPD molecule exert the action of corrosion inhibition through chemisorption, predominantly by the electrovalent bonds55 inferring the higher tendency of PPD adsorption onto the alloy surface, thus safeguarding the Ni-W alloy against degradation. The schematic representation of adsorption of additives onto the alloy surface was figured out in Figure 7.