Ultrasound response of aqueous poly(ionic liquid) solution

• US effect on the aqueous poly(ionic liquid) was studies by FT-IR spectroscopy.
• US could change the viscosity of poly(ionic liquid) periodically.
• US could break the hydrogen bond in the aqueous poly(ionic liquid).

Ultrasound (US) effects on aqueous poly(ionic liquid) (PIL) solution were investigated using viscosity and FT-IR spectroscopy after exposure to US of 23, 43, and 96 kHz frequencies at 50 W. The viscosity of the poly(1-vinyl-3-butyl-imidazolium chloride) (PIL) aqueous solution decreased during exposure to US. It then increased gradually within about 10 min as US stopped. The aqueous PIL behavior was then observed using FT-IR spectroscopy. The US exposure enhanced the FT-IR band intensity of the OH stretching. The band intensity returned to its original value after the US stopped. These results responded cyclically to the US on/off. Analysis of the FT-IR spectra revealed that US influenced the breakage and reformation of hydrogen bonds in the PIL and water. Two-dimensional correlation and deconvolution were used to analyze the change of components in the region of 3000–3700 cm−1 for US exposure. Results of these analyses suggest that US exposure might break hydrogen bonds between PIL segments and water. In the absence of US, hydrogen bonds reformation was also observed between the PIL and water.