Local structure and translational dynamics of NMF (N-methylformamide)-DMF (N,N-dimethylformamide) mixtures, via molecular dynamics simulation

In this work, the liquid amide mixture of N-methylformamide (NMF) with N,N-dimethylformamide (DMF) has been investigated by means of the molecular dynamics simulation method. The intermolecular structure and local mole fractions around any kind of the component molecules have been studied in terms of the calculated site-site correlation functions at three solvent compositions, XDMF, and ambient conditions. The hydrogen bonding network of the system has been extensively explored and the several hydrogen bond types formed between NMF-NMF, DMF-DMF and NMF-DMF in each mixture per molecule have been obtained with increasing XDMF. The results obtained reveal the notable effect of DMF molecules upon the formation of the hydrogen bonding network in each system. The investigated diffusion coefficients of both mixture components show clearly a linear increase of the diffusivity of all molecules while the DMF fraction increases. The intermolecular structure and hydrogen bonding properties studied validate the results from previous small angle neutron scattering studies on the system and support their conclusion that this amide mixture may be considered as an almost ideal one. Also, it may be concluded that DMF does not self-aggregate, because it acts as a hydrogen-bond breaker over the whole range of solvent composition. This finding is in accordance with the translational diffusive behavior of the molecules in the mixtures mentioned above. The detailed analysis of the hydrogen bonding network in DMF- rich and NMF-rich mixtures has revealed important information regarding the short range molecular aggregation in these diluted mixtures. This result is in general found to be comparable with corresponding predictions from previous experimental low-frequency raman spectroscopic studies of these mixtures.