Structural transitions induced by shear flow and temperature variation in a nonionic surfactant/water system

Area of Science:

• Materials Science
• Physical Chemistry
• Soft Matter Physics

Background:

• Nonionic surfactants like tetraethylene glycol monohexadecyl ether (C(16)E(4)) exhibit complex phase behavior.
• Understanding their structural transitions under external stimuli is crucial for applications.

Purpose of the Study:

• To investigate the structural transitions of C(16)E(4) in D(2)O under shear flow and varying temperatures.
• To compare the shear flow behavior of C(16)E(4) with other nonionic surfactants.

Main Methods:

• Rheology to measure flow properties.
• Rheo-small-angle neutron scattering (rheo-SANS) to probe nanoscale structures.
• Rheo-small-angle light scattering (rheo-SALS) to analyze larger structures.

Main Results:

• Competition between multi-lamellar vesicles, planar lamellae, and a sponge phase was observed.
• A new transient lamellar phase with increased spacing coexists with the initial lamellar phase in a narrow temperature-time window.
• The shear flow behavior of C(16)E(4) resembles that of longer chain surfactants (C(16)E(7)) rather than shorter ones (C(10)E(3), C(12)E(4)).

Conclusions:

• Shear flow and temperature are key factors driving structural evolution in C(16)E(4) solutions.
• The formation of a transient lamellar phase and its coexistence with other phases highlight complex self-assembly mechanisms.
• C(16)E(4) exhibits distinct shear-induced phase behavior influenced by its long alkyl chain length.