This article reports the results obtained from an extensive experimental campaign aimed at investigating the effect of interparticle forces (IPFs) on the local flow structure of a gas-solid fluidized bed. A polymer coating approach was used to enhance and control the degree of cohesive IPFs in a gas-solid fluidized bed. In this work, the local transient solids concentration (bed voidage) was carefully measured with the help of an accurate optical fiber probe at different temperatures and gas velocities covering both bubbling and turbulent fluidization regimes. Also, the Radioactive Particle Tracking (RPT) technique was employed to track the trajectory of a tracer mimicking the behavior of solid particles in two systems, one with the least amount of IPFs in the bubbling regime and the other with the highest amount. Experimental results showed that by increasing the level of IPFs in the bed the fixed bed and emulsion phase voidage in the bubbling regime increased and demonstrated higher capacities in holding gas inside their structures. In addition, the emulsion phase fraction increased, the tendency of the fluidizing gas passing through the bed in the emulsion phase enhanced in the bubbling regime, the frequency of the bubble/emulsion phase cycle decreased, and the meso-scale transition from bubbling to turbulent fluidization regime delayed until reaching higher superficial gas velocities. (C) 2014 Elsevier Ltd. All rights reserved,