(a) Shear rate sweep data for PEG-BCA and PEG-CBCA hydrogels normalized by the Weissenberg number (x-axis) and the zero-shear viscosity (y-axis). To more easily visualize the data, error bars are omitted. (b) Degree of shear thickening (ηp/η0) for both hydrogel formulations. (c) Weissenberg number at the onset of shear thickening for both hydrogel formulations. (d) Weissenberg number at the onset of the flow instability for both hydrogel formulations.

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... characterize the rheological properties of the hydrogels when subjected to small deformations, the hydrogels were first measured using small amplitude oscillatory shear in the linear viscoelastic region at 1% strain ( Figure 1, Figure S4). The dynamic covalent crosslinks endowed the hydrogels with viscoelastic properties, as shown by the frequency dependence of the moduli during frequency sweeps (Figures 1a and 1b). ...

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... shear rate at the onset of shear thickening decreased with increasing concentration (Figure 3c), consistent with previous reports for telechelic polymers. 65 The shear rate at which the flow instability occurred (Figure 3d To further analyze the material behavior under steady shear, the rheological profiles were normalized by the zero-shear viscosity on the y-axis and scaled by the Weissenberg number, Wi=í µí»¾̇ × í µí¼ 0 , on the x-axis (Figure 4a). The Weissenberg number describes the degree of nonlinearity in a system, with Wi < 1 indicating linear behavior and Wi > 1 indicating nonlinear behavior. ...

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... this representation, the data for all formulations collapsed at shear rates below the onset of shear thickening, though differences emerged at higher shear rates. The degree of shear thickening, defined as the ratio of the peak viscosity (ηp) to the zero-shear viscosity (η0), was highest for the hydrogels at the lowest polymeric concentrations (Figure 4b). At slightly higher concentrations, the degree of shear thickening decreased. ...

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... In systems of telechelic polymers, the degree of shear thickening is often more modest at values up to about 1.4. 39,51,61,62,65 Additionally, the onset of shear thickening and the onset of the flow instability were examined in terms of the Weissenberg number (Figures 4c and 4d, respectively). For all hydrogel formulations (Figure 4c), shear thickening began at a similar Weissenberg number: 0.19 +/-0.04, which is comparable to solutions of telechelic polymers. ...

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... Additionally, the onset of shear thickening and the onset of the flow instability were examined in terms of the Weissenberg number (Figures 4c and 4d, respectively). For all hydrogel formulations (Figure 4c), shear thickening began at a similar Weissenberg number: 0.19 +/-0.04, which is comparable to solutions of telechelic polymers. 51,61,65 The maximum shear rate that was reached prior to the flow instability also occurred at a similar Weissenberg number for the PEG-BCA and PEG-CBCA hydrogels, though this trend showed a slight concentration dependence. ...

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... modulus scaling with concentration ( Figure S9) indicated significant network heterogeneity at low concentrations and suggests the chains are not largely extended at no shear. The hydrogels at lower concentrations shear thickened to a greater extent ( Figure 4b) and reached higher Weissenberg numbers before a flow instability occurred (Figure 4d), which may be due to increased chain stretching at lower concentrations. 67 Thus, the data suggest that non-Gaussian chain stretching drives the shear thickening behavior, though further efforts to measure the associated bond fraction under shear would provide a fuller picture of the molecular mechanism. ...

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... modulus scaling with concentration ( Figure S9) indicated significant network heterogeneity at low concentrations and suggests the chains are not largely extended at no shear. The hydrogels at lower concentrations shear thickened to a greater extent ( Figure 4b) and reached higher Weissenberg numbers before a flow instability occurred (Figure 4d), which may be due to increased chain stretching at lower concentrations. 67 Thus, the data suggest that non-Gaussian chain stretching drives the shear thickening behavior, though further efforts to measure the associated bond fraction under shear would provide a fuller picture of the molecular mechanism. ...