## 4 Conclusions  
To conclude, a series of hybrid fillers of CNT and CB loaded PS nanocomposites were prepared by melt blending. The weight ratio of CNT/CB was systematically varied at the same filler concentrations. Afterwards, the obtained blends were subjected to \(\upmu\)IM under a defined set of processing conditions. The distribution of carbon fillers within the micromoldings was evaluated by a combination of electrical conductivity measurements and morphology observations. Results indicated that both CB and CNT have a relatively uniform dispersion within PS. Although there is a shear-induced depletion effect in the shear layer of CB-containing microparts, the electrical conductivity measurements suggested that the high structure CB has a greater tendency to form conductive pathways within the microparts via self-assembly even under high shearing conditions of \(\upmu\)IM. However, no obvious synergistic effect of hybrid fillers on the construction of conductive pathways is detected, which is thought to be crucial to the enhancement of electrical conductivity for conductive polymer composites [11]. In addition to the weight ratios of CNT to CB in PS, further studies regarding the effect of intrinsic properties of polymer matrices on hybrid carbon fillers (i.e., CNT/CB) loaded polymer composites might be helpful to elucidate this phenomenon. Furthermore, the influence of annealing treatment on the electrical and morphological properties of as-molded microparts which have identical total filler concentration, i.e., 10 wt %, at various weight ratio of CNT/CB combinations was investigated as well. Results revealed that the electrical conductivity for CNT-containing samples increased after the thermal treatment whereas corresponding values for only CB-containing counterparts decreased.  
Figure 8: The morphology (TD) taken from the (**a,b**) core and (**c**) shear layers of the thick section of 5 wt %-PS/CNT50/CB50 microparts after the annealing treatment.  
Figure 7: The morphology (TD) taken from the (**a,b**) core and (**c**) shear layers of the thick section of 5 wt %-PS/CNT50/CB50 microparts before the annealing treatment.  
In this scenario, the occurrence of secondary agglomeration of CNT and the formation of CB aggregates are thought to be contributing factors. For example, a flow-induced orientation of CNT in microprats is expected due to the combined effects of high shearing and cooling in \(\upmu\)IM. Thus, the reorganization of orientated CNT and the occurrence of secondary agglomeration of CNT facilitate the construction of conductive pathways. Besides, the formation of CB aggregates further promotes the formation of conductive pathways within the host polymer matrix. However, the aggregation of CB particles in only CB-containing samples might break down the continuum of conductive pathways, thereby leading to a reduction of electrical conductivity after the thermal treatment.  
[PERSON] conceived the research idea, performed all experiments and analyzed research data. All authors contributed to the writing and discussion of the manuscript.  
This research was funded by the Natural Sciences and Engineering Research Council of Canada and the Network for Innovative Plastic Materials and Manufacturing Processes. S.Z. acknowledges financial support from China Scholarship Council.  
The authors declare no conflict of interest.