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) colloids are suspended in cyclohexane (CH) and cyclohexyl bromide (CHB) with dilute polystyrene serving as a depletion agent. A study of the optical trap strength, rheology, and microscopic structure of the gels as a function of CH/CHB solvent composition identifies the conditions for which these measurements can be applied to characterize gel properties. The results indicate that a solvent comprising 37% weight fraction CH (wCH = 0.37) provides sufficient refractive index contrast to enable optical trapping, while maintaining good confocal microscopy 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 in a dilute sample show that 50% of bonds rupture at (3.3 ± 0.5) pN. The linear strain-dependent elastic modulus of the corresponding gel (ϕ = 0.20) is G′ = (1.8 ± 0.6) Pa, and the mean contact number of the colloids in the gel structure is 〈z〉 = 5.4 ± 0.1. The development of this model colloidal gel system yields a concomitant characterization of the interparticle forces, microstructure, and bulk rheology in a single experimental system, thereby allowing the simultaneous comparison of these different measures.
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