Cellulose nanocrystal (CNC) suspensions self-assemble into chiral nematic films when left to slowly evaporate over days through a process known as evaporation induced self-assembly. CNC films have been proposed for advanced optical applications, like photovoltaic cells, however additives may be needed to meet material performance requirements. The effects of additives on CNC film formation have been investigated, but rarely by varying the composition of more than one additive at a time. In this work we investigate multicomponent CNC films using a design of experiments approach, which can be a resource efficient way to investigate complex experimental spaces and explore non-obvious additive combinations and loadings that may otherwise be inaccessible. As this type of system is rather new to the construction and application of multivariate models, one goal of this project was to test the applicability of the approach in this environment. The aim was both to model and predict the optical and mechanical properties of multicomponent CNC-based films, connecting predictions to the underlying mechanisms from which these properties emerge. To do this, CNC suspensions containing differing compositions of four distinct plasticizing additives (glucose, glucuronic acid, glycerol, and locust bean gum) were prepared and used to cast films. Next, the optical and mechanical properties of the CNC films and the turbidity of CNC suspensions were measured. A predictive quantitative model was then constructed from the results. By tying the properties to underlying colloidal mechanisms during the drying process the relationship between these and the additives was also modeled. Supporting data that includes atomic force microscopy, dynamic light scattering, zeta potential, and polarized optical microscopy was collected to further affirm the picture that emerged from the model of how suspension colloidal properties connect to film outcomes. The overall aim was to design a reliable methodology that can be used to optimize for various film outcomes in multivariate systems, such as extensibility, photonic bandgap, transparency, and haze.

Using a design of experiments approach to investigate the influence of additives on cellulose nanocrystal film properties

ACS Spring Meeting 2021

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