# Additively Manufactured Polymers for Electronic Components
## 3 Polymers Used for AM in Electronic Applications
### Intrinsically Conductive Polymers (ICPs)
A PEDOT:PSS aqueous dispersion was employed for in situ printing using SL into a hydrogel matrix already formed by photopolymerising poly(ethylene glycol) diacrylate (PEGDA), as depicted in Figure 4. Computer-aided design-based architectural models featuring square pores and different line spacing options of 500, 600, and 800 \(\upmu\)m were chosen to guide the printing process of 3D strctures via UV laser exposure, resulting in well-integrated scaffolds with predefined geometries [50]. Recent research has focused on  
Figure 3: Chemical structure of PEDOT:PSS [46]. Figure 2: (**a**) Structures of typical conjugated polymers such as polyacetylene (**1**), poly(p-phenylene) (**2**), poly(p-phenylene vinylene) (**3**), poly(p-phenylene ethynylene) (**4**), and polyfluorene (**5**). (**b**) Examples of ICPs with higher contents of polycyclic aromatic hydrocarbon (PAH) building blocks (**6**), different positions of the substitutions on aromatic rings (**7** and **8**), and the inclusion of heteroatoms (**9–12**) [45]. the development of three-dimensional PEGDA:PEDOT structures produced using SL for the long-term monitoring of volatile organic compounds. The researchers demonstrated the feasibility of monitoring hazardous compounds by controlling variations in structure and conductivity [51]. Furthermore, wearable electronic devices have been produced using electrohydrodynamic (EHD) printing of inks based on PEDOT. One example is the utilisation of PEDOT:PSS ink mixed with poly(ethylene oxide) (PEO) to create a uniform EHD printing solution, where an electric field is employed to generate printed patterns. The inclusion of PEO resulted in an increase in ink viscosity. By printing PEO/PEDOT:PSS walls with varying numbers of layers, three-dimensional structures were achieved, featuring wall widths ranging from 49.5 to 62.5 \(\upmu\)m and wall heights spanning from 0.77 \(\upmu\)m to 57.25 \(\upmu\)m [52]. DIW is another technology that is suitable for AM of PEDOT:PSS. For this technology, PEDOT:PSS sinks are prepared by dissolving the polymer in a suitable solvent. As stated in Section 1, the ink needs to have shear thinning behaviour to allow the extrusion process. After extrusion, the ink should have sufficiently high viscosity to maintain its shape  
Figure 4: Light-based printing methods categorised into two types: DLP, which polymerises resins layer by layer when exposed to a light source in a vat, and SL, which cures resins point by point with a laser pulse in a vat. At the bottom, two examples of light-based printed materials: (**a**) PEDOT:PSS combined with ethylene glycol and PEGDA to form cross-linked structures using the SL printing method; and (**b**) composite ink based on polyaniline (PANI), graphene, and acrylic polymer (METAC) to be processed using DLP, showing complex and personalised structures. Adapted and reprinted with permission from ref. [48]. until the hardening process. One simple and efficient way to address this problem is to use conducting polymers, producing highly stable inks by simply adjusting the concentration [53; 54]. [PERSON] et al. reported the DIW of PEDOT:PSS to fabricate supercapacitors. Different PEDOT:PSS inks were fabricated, changing the polymer concentration from 1 wt% to 9 wt%. With increasing PEDOT:PSS concentration, a transition from a low-viscosity liquid-like state to a more dough-like state occurred due to the increased entanglement of the PEDOT:PSS chains (Figure 5a). Figure 5b illustrates the shear rate-dependent rheological viscosity of inks with different PEDOT:PSS contents. Higher viscosities were observed in inks with a higher quantity of PEDOT:PSS. Additionally, all inks exhibited shear thinning behaviour, with apparent viscosity decreasing as the shear rate increased. To assess ink printability, interdigitated electrode patterns were printed using all of the inks, and the relationship between viscosity and printing behaviour was summarised (Figure 5c).