The small angle x-ray scattering (SAXS) and wide angle x-ray scattering (WAXS) is measured for RTMS containing aliphatic quaternary ammonium cation; [RNMe{sub}3]{sup}+ (where R = n-C{sub}nH{sub}(2n+1); n=3-16 which are denoted as "N111n") and bis(trifluoromethyl sulfonyl) imide anion. It is shown that a new peak at low q-value is confirmed above n=5. It is suggested that this new peak is of the local ordering structure formed by van der Waals force between alkyl chains of ammonium cations. From DSC result, the local ordering structure forms in [N111n] TFSI above n=8. This behavior is due to the thermal mobility of the alkyl chains of which local ordering structure has a good thermal stability. The other room temperature molten salts such as [Nnnnn]{sup}+(n-5-6), [N1123]{sup}+, N-methyl-n-propyl piperidium cation [PP13]{sup}+ and N-methyl-n-propyl pyrrolidinium cation [P13]{sup}+ having the same anion; TFSI{sup}- were also used. The layer spacing (d) of this ordering structure is decrease with increase of the temperature. In the [Nnnnn] TFSI (n=5-6) systems, the peak of the local ordering structure is sharply confirmed around q=5 nm{sup}(-1) and this peak does not shift with increase of the temperature. From SAXS results of RTMSs ([Nnnnn] TFSI (n=5-6), [N1123] TFSI, [PP13] TFSI and [P13] TFSI), the peak around q=7 nm{sup}(-1) is assigned to the form factor of the electron density around N atom of aliphatic quaternary ammonium cation or the structure factor between the electron density around N atom of aliphatic quaternary ammonium cations.
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