Realignment of Liquid Crystal Shells Driven by Temperature-Dependent Surfactant Solubility.

Area of Science:

• Materials Science
• Soft Matter Physics
• Physical Chemistry

Background:

• Nematic liquid crystals (LCs) exhibit dynamic director field variations.
• Shells of 4-cyano-4'-pentylbiphenyl LC are stabilized by cetyl trimethyl ammonium bromide (CTAB) and poly(vinyl alcohol) (PVA).
• CTAB and PVA typically induce orthogonal and tangential alignments, respectively, of the LC director.

Purpose of the Study:

• Investigate dynamic director field variations in LC shells.
• Study the effect of cooling/heating past CTAB's Krafft temperature (T_K) on LC director configuration.
• Explore the potential of LC shells to detect solutes.

Main Methods:

• Synthesis of LC shells with aqueous phases stabilized by CTAB and PVA.
• Controlled cooling and heating cycles around the Krafft temperature of CTAB (T_K ≈ 25 °C).
• Observation of LC director field configurations using optical microscopy.

Main Results:

• Cooling below T_K induces a switch from hybrid to uniformly orthogonal LC director alignment within a specific CTAB concentration range.
• This alignment change is attributed to CTAB migration into the inner PVA solution due to reduced water solubility below T_K.
• LC shells demonstrate sensitivity to solutes in the continuous phase.

Conclusions:

• The study demonstrates that liquid crystal shells can act as sensors for solutes in their surrounding environment.
• The observed director field reorientation is driven by temperature-induced changes in surfactant solubility and migration.
• This phenomenon highlights the potential of liquid crystal shells for developing novel detection systems.