The effect of plasma functionalization on the print performance and time stability of graphite nanoplatelet electrically conducting inks

Abstract

Carbon-based pastes and inks are used extensively in a wide range of printed electronics because of their widespread availability, electrical conductivity and low cost. Overcoming the inherent tendency of the nano-carbon to agglomerate to form a stable dispersion is necessary if these inks are to be taken from the lab scale to industrial production. Plasma functionalization of graphite nanoplatelets (GNP) adds functional groups to their surface to improve their interaction with the polymer resin. This offers an attractive method to overcome these problems when creating next generation inks. Both dynamic and oscillatory rheology were used to evaluate the stability of inks made with different loadings of functionalized and unfunctionalized GNP in a thin resin, typical of a production ink. The rheology and the printability tests showed the same level of dispersion and electrical performance had been achieved with both functionalized and unfunctionalized GNPs. The unfunctionalized GNPs agglomerate to form larger, lower aspect particles, reducing interparticle interactions and particle–medium interactions. Over a 12-week period, the viscosity, shear thinning behavior and viscoelastic properties of the unfunctionalized GNP inks fell, with decreases in viscosity at 1.17 s−1 of 24, 30, 39% for the ϕ = 0.071, 0.098, 0.127 GNP suspensions, respectively. However, the rheological properties of the functionalized GNP suspensions remained stable as the GNPs interacted better with the polymer in the resin to create a steric barrier which prevented the GNPs from approaching close enough for van der Waals forces to be effective.

Stretchable Carbon and Silver Inks for Wearable Applications

“…For the carbon composite ink, a blend of ammonia plasma functionalized Graphite Nanoplatelets (GNPs) and conductive Carbon Black (CB) was dispersed into a commercially available Thermoplastic Polyurethane (TPU) Resin in Diacetone alcohol. CB only [ 22 ] and GNP only [ 13 , 24 , 29 ] have been shown to have poor electrical performance, therefore as the aim of this study was to make a high conductivity, stretchable carbon ink. The ratio of GNP to CB was optimized for electrical conductivity with the most conductive GNP to CB ratio used in this study.…”

“…Shear viscosity values were taken from the down shear ramp from 100 to 0.1 s −1 . The experimental error on the Malvern Kinexus was examined to be <0.13 Pa·s at 1 s −1 across three measurements [ 24 ].…”

“…Graphite nanoplatelets (GNPs) are a high aspect ratio graphitic nanocarbon, with a surface that can be functionalized to give improved interaction with polymers and solvents [ 23 ]. In a previous work by the authors Ammonia plasma functionalized GNPs were shown to be well dispersed within the TPU resin system, with ammonia plasma functionalized GNPs shown to have better dispersion stability, hypothesized to be a result of improved interaction between the particles and the TPU [ 24 ]. Plasma functionalization offers a dry, scalable, non-polluting, fast, one-step method of surface modification for carbon nanomaterials [ 25 , 26 ].…”

“…Plasma functionalization offers a dry, scalable, non-polluting, fast, one-step method of surface modification for carbon nanomaterials [ 25 , 26 ]. GNP only inks have been shown to have relatively low electrical conductivity with bulk resistivities of ~3 Ohm·cm [ 24 ]. Hybridizing graphitic material with carbon black (CB) has been shown to improve the electrical properties of inks and nanocomposites [ 13 , 16 , 18 , 27 , 28 ], as the submicron CB improves interparticle contact between neighboring graphitic particles.…”

Graphene nanoplatelets/epoxy nanocomposites: A review on functionalization, characterization techniques, properties, and applications

“…109,110 This technique offers a dry, scalable, one-pot surface modification method, and by this process, carbon nanofillers become more hydrophilic by combining polar groups to aid dispersibility. 111 This method is connected to implementing the hydrophobic character of carbon structures to expand their dispersion with polymer polar matrices. 112 The main advantage of plasma treatment is that this process is not damaging the material, has no impurities, and enhances surface properties without changing the bulk composition.…”