  Low-density "equilibrium" gels that consist of a percolated, kinetically
arrested network of colloidal particles and are resilient to aging can be
fabricated by restricting the number of effective bonds that form between the
colloids. Valence-restricted patchy particles have long served as one
archetypal example of such materials, but equilibrium gels can also be realized
through a synthetically simpler and scalable strategy that introduces a
secondary linker, such as a small ditopic molecule, to mediate the bonds
between the colloids. Here, we consider the case where the ditopic linker
molecules are low-molecular-weight polymers and demonstrate using a model
colloid-polymer mixture how macroscopic properties such as the phase behavior
as well as the microstructure of the gel can be designed through the polymer
molecular weight and concentration. The low-density window for equilibrium gel
formation is favorably expanded using longer linkers, while necessarily
increasing the spacing between all colloids. However, we show that blends of
linkers with different sizes enable wider variation in microstructure for a
given target phase behavior. Our computational study suggests a robust and
tunable strategy for the experimental realization of equilibrium colloidal
gels.
