Thermally Switchable Liquid Crystals Based on Cellulose Nanocrystals with Patchy Polymer Grafts

Area of Science:

• Materials Science
• Polymer Chemistry
• Colloid Science

Background:

• Cellulose nanocrystals (CNCs) are rod-like nanoparticles with tunable properties.
• Thermoresponsive polymers, like poly(N-isopropylacrylamide) (PNIPAM), change conformation with temperature.
• Controlling nanoparticle interactions is key for developing advanced materials.

Purpose of the Study:

• To create cellulose nanocrystal (CNC) suspensions with thermally switchable liquid-crystalline (LC) phases.
• To investigate the effect of 'patchy' versus 'brush-like' PNIPAM grafting on CNC behavior.
• To explore potential applications in sensing and smart packaging.

Main Methods:

• Synthesized patchy PNIPAM-grafted CNCs using surface-initiated atom transfer radical polymerization (ATRP).
• Prepared 10 wt% aqueous suspensions of modified CNCs.
• Observed liquid-crystalline phase behavior using birefringence and monitored phase transitions with temperature changes.

Main Results:

• Patchy PNIPAM-grafted CNCs exhibited a reversible, thermally switchable liquid-crystalline phase.
• The liquid-crystalline phase disappeared above PNIPAM's lower critical solution temperature (LCST) due to polymer chain collapse.
• Patchy grafting provided higher colloidal stability above the LCST compared to brush-like grafting.

Conclusions:

• The reversible thermal switching of the liquid-crystalline phase in patchy PNIPAM-grafted CNCs is unprecedented.
• This phenomenon is driven by the temperature-induced collapse of PNIPAM chains, altering CNC packing and mobility.
• The findings suggest potential for these materials in responsive sensors and smart packaging.