Charge ordering and intermediate range order in ammonium ionic liquids

Molecular dynamics simulations were performed for ionic liquids based on the bis(trifluoromethylsulfonyl) imide anion, [NTf(2)], and ammonium cations with increasing length of the alkyl chain and ether functionalized chain. the signature of charge ordering is a sharp peak in the charge-charge structure factor, S(qq)(k), whose intensity is barely affected for longer carbon chain in tetraalkylammonium systems, but decreases in ether functionalized ionic liquids. the first sharp diffraction peak (FSDP) and the corresponding intermediate range order (IRO) are observed in the total S(k) of ionic liquids containing ammonium cations with relatively long chains. the intensity of the FSDP is lower in the total S(k) of the ether derivative in comparison with the tetraalkylammonium counterpart of the same chain length. It is shown that the nature of the IRO is structural heterogeneity of polar and non-polar domains, even though domains defined by chain interactions in the ether derivatives become more polar. Charge correlation in the ether derivative is modified because cations can be coordinated by oxygen atoms of the ether functionalized chain of neighboring cations. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662062]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Universidade Federal de São Paulo, Lab Mat Hibridos, Inst Ciencias Ambientais Quim Farm, BR-04024002 São Paulo, BrazilUniv São Paulo, Lab Espect Mol, Inst Quim, BR-05513970 São Paulo, BrazilUniversidade Federal de São Paulo, Lab Mat Hibridos, Inst Ciencias Ambientais Quim Farm, BR-04024002 São Paulo, BrazilFAPESP: 2008/08670-7FAPESP: 2006/58748-7Web of Scienc