Structural arrest in an aging colloid-polymer mixture of charged colloidal disks and weakly interacting polymers is primarily governed by the spatial arrangement of microstructural domains in the system. Here we present a detailed ultra-small angle x-ray scattering (USAXS) study of the polymer induced microstructural changes occurring in systems containing laponite (R) and poly(ethylene oxide) (PEO). Laponite (R) suspensions are known to transition from a homogeneous fluid to an arrested phase as a function of time. USAXS results show that when polymer chains are added to this colloidal system, the microstructural changes are found to depend on (i) polymer-colloid size ratio, (ii) particle and polymer concentration. Large length scale structures (300-1000 nm) of non-uniformly varying size appear with increasing concentration of high molecular weight PEO (R-g/R similar to 2.4). However with shorter PEO chains (R-g/R similar to 0.5), we observe the formation of intermediary structures with a characteristic length scale of 50-60 nm. With increasing particle concentration, we observe a more compact structure for the high molecular weight PEO and no signature of a percolating network in the case of the low molecular PEO. We believe that these results add to our understanding of the complex aging behavior of clay-polymer systems. (C) 2016 Elsevier Ltd. All rights reserved.