Berlin 2024 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 2: Modeling and Simulation of Soft Matter I

CPP 2.2: Vortrag

Montag, 18. März 2024, 10:00–10:15, H 0107

Phase-Behaviour of Polymer Grafted Colloidal Nano-Crystals with Variable Grafting Density — •William Fall and Henricus Wensink — Laboratoire de Physique des Solides UMR 8502, CNRS, Université Paris-Saclay, 91405, Orsay, France

The effect of short chain grafting on the liquid crystalline ordering of colloidal nano-crystals is investigated using molecular dynamics simulations. Nano-rods with aspect ratios of typical of cellulose nano-crystals (CNCs) are grafted randomly with short oligomers at 5 different grafting densities. Each system is crystallised from the isotropic phase in solution and slowly compressed until the nano-rods spontaneously order. The liquid crystalline behaviour depends strongly on the grafting density as the effective shape and softness of the nano-rods is modified. Ungrafted rods exhibit complex biaxial Nematic and Smectic-C phases at very low volume fractions, which are then preserved upon grafting with at least a 50% occupation of surface sites with oligomers, forming a Nematic and a tilted Smectic-I phase. Heavier grafting results in the disappearance of the Nematic phase and a direct transition to a complex Smectic-B. Interesting behaviour is observed at extremely low grafting densities, around 25%, with the disappearance of Smectic phases and a persistent Nematic phase induced by patchy grafting, which transitions to a Lamellar phase at high concentration. Such systems fall outside of the traditional hard or soft rod descriptions of phase-transitions in rod-like LC systems. Our findings point to as yet undiscovered LC behaviour in grafted and ungrafted rod-like nanocrystals.

Keywords: Nano Crystals; Polymers; Liquid Crystals; Complex Smectics; Cellulose