Effect of aromatic spacer groups and counterions on aqueous micellar and thermal properties of the synthesized quaternary ammonium gemini surfactants

One of the major challenges for the oil industry in the 21st century is to get the desired surfactants that are soluble in high saline water (220, 000 ppm) and stable at high temperature (100 °C). Most commercial surfactants suffering due to hydrolysis at high temperature and the monovalent and divalent reservoir ions leads to surfactant precipitation. In order to address these issues, a new series of cationic gemini surfactants with a different number of aromatic rings in the spacer group as well as different counter ions were synthesized and characterized with the aid of MALDI-TOF MS, FTIR, ¹H NMR, and ¹³C NMR spectroscopy. The effect of number of phenyl aromatic rings in the spacer and counterions on thermal and surface properties was determined. Thermogravimetric results showed the decomposition temperature of all the gemini surfactant near to 300 °C which is larger than the existing oilfield temperature (≥100 °C). The insertion of ethoxy units between the lipophilic tail and lipophobic headgroup resulted in good solubility of cationic gemini surfactants in high saline and normal water without cloudiness or precipitation. The critical micelle concentration and the corresponding surface tension were lower for gemini surfactants containing bromide counterions compared to the surfactants containing chloride counterions. The gemini surfactants containing two aromatic phenyl rings in the spacer have lower critical micelle concentration compared to the gemini surfactants with one phenyl ring. The properties of the synthesized cationic gemini surfactants mark them a material of choice for high salinity/temperature reservoirs.