Confinement effect on spatio-temporal growth of spherulites from cellulose/ionic liquid solutions

Abstract

In this study, we investigate the growth kinetics and through-the width-distribution of polycrystalline morphologies developed in the confined microcrystalline cellulose (MCC)/1-allyl-3-methylimidazolium chloride (AmimCl) solution films at controlled temperature and humidity. Being an anti-solvent, the diffusion of moisture from the edges to the interior of the cellulose film causes the aggregation and rearrangement of cellulose molecules. When the confined films of thickness varying between 100 μm and 850 μm are incubated for over 25 days, different polycrystalline morphologies evolve. While a skin-transition-core morphological distribution is observed in the films of thickness ≥ 700 μm, interesting morphologies such as cylindrites, shish-kebab, deformed spherulites are observed in confined films of thickness ≤ 500 μm. The formation of concentric rings called terraces is also observed on the spherulites in highly confined films, signaling two dimensional (2-D) growth. The growth kinetics is observed to follow the classical Avrami theory. The Avrami exponent value, n, in the highly confined film (100 μm) is found to be close to 2, indicating 2-D growth.