Design of Chemoresponsive Soft Matter Using Hydrogen-Bonded Liquid Crystals

Area of Science:

• Soft Matter Physics
• Materials Science
• Chemical Sensing

Background:

• Soft matter with programmed responses to analytes is valuable for health and safety.
• Liquid crystals (LCs) can be engineered for specific chemical interactions.

Purpose of the Study:

• Design a nematic liquid crystal (LC) that undergoes a visible phase transition upon exposure to organoamine vapors.
• Investigate the mechanism and selectivity of this chemoresponsive phase transition.

Main Methods:

• Screening of carboxylic acid mixtures to form a stable nematic LC phase.
• Infrared (IR) spectroscopy and density functional theory (DFT) to analyze LC composition and dimerization.
• Differential scanning calorimetry (DSC) to confirm phase behavior.
• Exposure to various analytes (e.g., triethylamine) to trigger and characterize phase transitions.

Main Results:

• A stable, long-lived nematic LC phase was formed from specific carboxylic acid mixtures, dominated by heterodimers.
• Exposure to triethylamine (TEA) induced a phase transition to an isotropic phase via an acid-base reaction, forming ammonium carboxylate salts.
• The phase transition proceeded through nucleation, growth, and coalescence of isotropic domains.
• The LC selectively responded to volatile amines, not to hydrogen bonding molecules like water.

Conclusions:

• A chemoresponsive soft matter system based on hydrogen-bonded LCs was successfully designed.
• The system provides a facile and chemically selective method for detecting volatile amines.
• This approach offers a basis for developing low-cost visual indicators for chemical environments.