Affine Deformation and Self-Assembly Alignment in Hydrogel Nanocomposites

Abstract

Tailoring the order in hierarchical structures is a key goal of bioinspired nanocomposite design. Recently, nacre-like materials have been developed by solvent evaporation methods that are scalable and attain advanced functionalities. However, understanding the alignment mechanisms of 2D fillers, nanosheets, or platelets remains challenging. This work explores possible pathways for nanocomposite ordering via orientation distribution functions. We demonstrate how the immobilization of 2D materials via (pseudo)network formation is crucial to alignment based on evaporation. We show a modified affine deformation model that describes such evaporative methods. In this, a gel network develops enough yield stress and uniformly deforms as drying proceeds, along with the immobilized particles, causing an in-plane orientation. Herein, we tested the dominance of this approach by using a thermo-reversible gel for rapid montmorillonite (MMT) particle fixation. We researched gelatin/MMT as a model system to investigate the effects of high loadings, orientational order, and aspect ratio. The nacre-like nanocomposites showed a semiconstant order parameter (⟨P₂⟩ ∼ 0.7) over increasing nanofiller content up to 64 vol % filler. This remarkable alignment resulted in continuously improved mechanical and water vapor barrier properties over unusually large filler fractions. Some variations in stiffness and diffusion properties were observed, possibly correlated to the applied drying conditions of the hybrid hydrogels. The affine deformation strategy holds promise for developing next-generation advanced materials with tailored properties even at (very) high filler loadings. Furthermore, a gelling approach offers the advantages of simplicity and versatility in the formulation of the components, which is useful for large-scale fabrication methods.