  We introduce a model gel system in which colloidal forces, structure, and
rheology are measured by balancing the requirements of rheological and
microscopy techniques with those of optical tweezers. Sterically stabilized
poly(methyl methacrylate) (PMMA) colloids are suspended in cyclohexane (CH) and
cyclohexyl bromide (CHB) with dilute polystyrene serving as a depletion agent.
A solvent comprising of 37% weight fraction CH provides sufficient refractive
index contrast to enable optical trapping, while maintaining good confocal
imaging quality and minimal sedimentation effects on the bulk rheology. At this
condition, and at a depletant concentration c = 8.64 mg/mL (c/c* = 0.81),
results from optical trapping show that 50% of bonds rupture at 3.3 pN. The
linear strain-dependent elastic modulus of the corresponding gel (volume
fraction = 0.20) is G' = 1.8 Pa, and the mean contact number of the particles
in the gel structure is 5.4. These structural and rheological parameters are
similar to colloidal gels that are weakly aggregating and cluster-like. Thus,
the model gel yields a concomitant characterization of the interparticle
forces, microstructure, and bulk rheology in a single experimental system,
thereby introducing the simultaneous comparison of these experimental measures
to models and simulations.
