Thermo-responsive properties driven by hydrogen bonding in aqueous cationic gemini surfactant systems

Area of Science:

• Colloid and Surface Chemistry
• Materials Science
• Physical Chemistry

Background:

• Cationic gemini surfactants, specifically 2-hydroxypropyl-1,3-bis(alkyldimethylammonium chloride) (n-3(OH)-n(2Cl), n = 14, 16), were studied in aqueous solutions.
• The presence of inorganic salts was found to influence the behavior of these surfactants.

Purpose of the Study:

• To investigate the unexpected thermo-responsive phenomena in aqueous solutions of n-3(OH)-n(2Cl) gemini surfactants.
• To analyze the viscosity changes and phase transitions in these systems as a function of temperature.

Main Methods:

• Rheological measurements
• Cryogenic transmission electron microscopy (cryo-TEM)
• Electric conductivity
• Differential scanning calorimetry

Main Results:

• The 14-3(OH)-14(2Cl) system showed a complex viscosity trend with a minimum at 27 °C and subsequent increase and decrease.
• The 16-3(OH)-16(2Cl) system exhibited similar viscosity changes and a gelling temperature (Tgel) above 27 °C.
• Reversible conversion between elastic hydrogel and wormlike micelles was observed in the 16-3(OH)-16(2Cl) system at low temperatures.

Conclusions:

• The observed thermo-responsive phenomena are attributed to the formation and destruction of intermolecular hydrogen bonds.
• The study provides insights into the aggregate transition mechanisms in gemini surfactant systems.