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We report a colloid–polymer model system with tunable bridging interactions for microscopic studies of structure and dynamics using confocal imaging. The interactions between trifluoroethyl methacrylate-co-tert-butyl methacrylate copolymer particles and poly(acrylic acid) (PAA) polymers were controllable via polymer concentration and pH. The strength of adsorption of PAA on the particles, driven by pH-dependent interactions with polymer brush stabilizers on the particle surfaces, was tuned via solution pH. Particle–polymer suspensions formulated at low pH, where polymers strongly adsorbed to the particles, contained clusters or weak gels at particle volume fractions of ϕ = 0.15 and ϕ = 0.40. At high pH, where the PAA only weakly adsorbed to the particle surface, particles largely remained dispersed, and the suspensions behaved as a dense fluid. The ability to visualize the suspension structure is likely to provide insight into the role of polymer-driven bridging interactions in the behavior of colloidal suspensions.