Binary mixtures of homologous room-temperature ionic liquids: Temperature and composition evolution of the nanoscale structure

•Extensive X-ray measurements of the nanoscale structure over full composition range.•First RTIL mixtures’ structure study spanning a broad, 20–100 °C, temperature range.•Components differ in chain length only, excluding geometry & shape effects.•Microscopic structure’s deviations from ideal mixtures measured and discussed.