Design of Chemoresponsive Liquid Crystals Using Metal-Coordinating Polymer Surfaces.

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science
• Liquid Crystal Technology

Background:

• Liquid crystals (LCs) on functionalized surfaces offer optical readouts for chemical/physical changes.
• Existing metal cation-based LC interfaces suffer from cation leaching, reducing device reliability.
• Need for stable interfaces to prevent time-dependent property changes in LC-solid systems.

Purpose of the Study:

• To develop stable metal-coordinating polymer surfaces for chemoresponsive liquid crystals (LCs).
• To minimize metal cation dissolution into LCs and enhance interface stability.
• To characterize the impact of polymer interfaces on LC ordering and time-dependent properties.

Main Methods:

• Utilized poly(4-vinylpyridine-co-divinylbenzene) (P(4VP-co-DVB)) films to coordinate Ni²⁺.
• Combined theoretical (electronic structure calculations) and experimental (PMIRRAS) techniques.
• Investigated responses of nematic LC 5CB to DMMP vapor on different substrates (polymer vs. glass).

Main Results:

• Ni²⁺ coordination with polymer pyridine weakened binding with LC 5CB but maintained homeotropic orientation.
• LC films on polymer substrates showed triggered orientational transitions upon DMMP exposure, unlike glass.
• LC ordering on polymer substrates was stable and long-lived (>7 days) vs. unstable on glass (<14 h).

Conclusions:

• Metal-coordinating polymer films provide robust substrates for long-lived chemoresponsive LCs.
• The polymer interface kinetics, not thermodynamics, govern LC response to analytes like DMMP.
• This strategy enhances the reliability and longevity of LC-based chemical sensing devices.