(383b) Tuning Colloidal Gel Mechanics By Active Doping.

Mechanical properties of disordered materials are fundamentally determined by the underlying free energy landscape. In contrast to external fields, embedding a small fraction of active particles within a disordered gel creates non-equilibrium internal fields to circumvent kinetic barriers and modulate the free energy landscape. Here, we computationally investigate the effect of internal activity on the mechanical response of the host gel. We show that brittle failure of deeply annealed gels is continuously modulated toward ductile yield-ing as we increase the swim force FS of the embedded active particles, accompanied by a nonlinear decrease of the elastic shear modulus that drops significantly above a critical swim force Fc. We rationalize this threshold force by an energetic argument and the weakening of the elastic modulus above Fc by the change in gel porosity and distributions of gel particle attractive forces. Below Fc, we explain the ductility enhancement by the increase of gel structural disorder. Above Fc, the gel is conspicuously heterogeneous with multiscale pore spaces. In this regime, the mechanical response de-couples from the homogenized degree of structural disorder due to dynamical heterogeneity. Finally, we contrast these results with a monodisperse gel that exhibits the opposite trend of ductility modulation.