The preparation and mechanical properties of elastomeric nanocomposite hydrogels consisting of cellulose nanocrystals (CNCs) and poly(ethylene glycol) (PEG) are reported. The aqueous nanocomposite CNC/PEG precursor solutions covalently cross-linked through a one-stage photocross-linking process. The mechanical properties of nanocomposite hydrogels, including Young's modulus (E), fracture stress (σ), and fracture strain (ε), were measured as a function of CNC volume fraction (φCNC, 0.2-1.8%, v/v) within polymeric matrix. It was found that the homogeneously dispersed nanocomposite hydrogels can be prepared with φCNC being less than 1.5%, whereas the heterogeneous nanocomposite hydrogels were obtained with φCNC being higher than 1.5%. The nanocomposite hydrogels exhibited higher strengths and flexibilities when compared with neat PEG hydrogels, where the modulus, fracture stress, and fracture strain enhanced by a factor of 3.48, 5, and 3.28, respectively, over the matrix material alone at 1.2% v/v CNC loading. Oscillatory shear data indicated the CNC-PEG nanocomposite hydrogels were more viscous than the neat PEG hydrogels and were efficient at energy dissipation due to the reversible interactions between CNC and PEG polymer chains. It was proposed that the strong gel viscoelastic behavior and the mechanical reinforcement were related to "filler network", where the temporary interactions between CNC and PEG interfered with the covalent cross-links of PEG.

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The understanding of nanoparticle−polymer interaction is a key element to demystify the structure−property relationship for nanocomposites. The clusters composing poly(acrylamide) (PAM) grafted from silica nanoparticles (SNPs) were prepared according to the developed synthetic platform and analyzed by transmission electron microscopy and dielectric relaxation analysis. The morphological evolution of clusters was observed and correlated to the mechanical behaviors of nanocomposites. Dynamic dielectric analysis was conducted to examine the nature of the constrained polymer region in view of a reinforcement mechanism. The modulus enhancement of the nanocomposite hydrogels was found to correlate with the volume of constrained polymer chains, and a constrained region model for SNP/polymer nanocomposites was proposed. The strong interactions between SNPs and polymer chains affect the modulus of the nanocomposites that was predicted by the percolation model and contributed to the mechanical reinforcement. The interplay between filler−polymer interaction and network rearrangement during the deformations should be considered to propose the reinforcement mechanism. Article pubs.acs.org/JPCC