Three-dimensional (3D) printing technology provides a simple and reasonably fast method to produce complex structures and hence is widely used in rapid prototyping. In addition, due to its ease of use and cost-effectiveness, the technology offers immense scope for personalization. Recently, there has been great interest in using 3D printing to print functional conductive microstructures for use as sensors [1] and for other microelectromechanical applications [2,3]. Past successes include using conductive nanocomposites for micromolding [4] and micropatterning [5]. In fact, large scale micropatterning on flexible substrates has been demonstrated [6]. The nanocomposites were prepared by mixing multi-walled carbon nanotubes in poly(dimethylsiloxane) and then crosslinking the linear polymer. In spite the aforementioned successes, this particular nanocomposite has some disadvantages. For one, it is not easy to prepare. Therefore, there is significant scope for improvement if effective use of the processing-properties-performace triad can be mastered. However, much remains to be understood even in the realm of materials design. Therefore, here we step back and focus on a more fundamental issue — the link between the processing undergone by a material intended for use in 3D printing and its effect on various properties. As it is already widely used, poly(acrylonitrile butadiene styrene) was chosen as the matrix polymer. To render the material electrically conductive, multi-walled carbon nanotubes (MWCNTs) were introduced at several concentrations. The polymer and the carbon nanotubes were blended and the nanocomposites prepared by three different methods: solvent casting, melt mixing and capillary extrusion. Solvent casting was unlikely to significantly orient the carbon nanotubes and hence was expected to function as the control. Melt mixing uses mostly shear deformations to disperse the carbon nanotubes in the sample. In capillary extrusion, in addition to shear flow, the sample also experiences significant elongational deformation. Therefore, these three methods are expected to yield polymer nanocomposites with different orientations of the carbon nanotubes and/or agglomerates and consequently, produce nanocomposites with different physical properties. The mechanical and electrical properties of the nanocomposites prepared by the three methods were compared. The structure and morphology of the nanocomposites were investigated by various techniques and several structural parameters that quantify the structure were measured. It was found that certain structural parameters were sensitive to the processing method used to prepare the samples. It will be argued that the aforementioned structural parameters can provide one route to rationally connect the processing method to the properties of the nanocomposite produced.
[1] S. Guo, X. Yang, M.-C. Heuzey, and D. Therriault, "3D printing of a multifunctional nanocomposite helical liquid sensor" Nanoscale, 7, 6451–6456 (2015). doi: 10.1039/C5NR00278H
[2] A. Khosla, "Nanoparticle-doped electrically-conducting polymers for flexible nano-micro systems" The Electrochemical Society Interface, 21, 67-20 (2012). doi: 10.1149/2.F04123-4if
[3] Khosla, A. (2011). "Micropatternable multifunctional nanocomposite polymers for flexible soft MEMS applications" (Doctoral dissertation, Applied Science: School of Engineering Science). http://summit.sfu.ca/item/12017
[4] A. Khosla, B.L. Gray, "Preparation, characterization and micromolding of multi-walled carbon nanotube polydimethylsiloxane conducting nanocomposite polymer" Materials Letters, 63, 1203-1206 (2009). doi: 10.1016/j.matlet.2009.02.043
[5] A. Khosla, B. L. Gray, "Preparation, micro-patterning and electrical characterization of functionalized carbon-nanotube polydimethylsiloxane nanocomposite polymer" Macromol. Symp., 297, 210–218 (2010). doi:10.1002/masy.200900165
[6] A. Khosla, D. Hilbich, C. Drewbrook, D. Chung, B. L. Gray, "Large scale micropatterning of multi-walled carbon nanotube/polydimethylsiloxane nanocomposite polymer on highly flexible 12×24 inch substrates" Proc. SPIE 7926, Micromachining and Microfabrication Process Technology XVI, 79260L (2011); doi:10.1117/12.876738.
