Thermoelectric properties and intrinsic conduction processes in DBSA and NaSIPA doped polyanilines

Seeking to gain fundamental understanding of the thermoelectric (TE) behavior of polyanilines (PANIs), structure- property relationships of PANI nanorods, doped with dodecylbenzenesulfonic acid (DBSA) and 5-sulfoisophtalic acid sodium salt (NaSIPA), and prepared by an indirect synthetic route, are discussed in terms of the contribution of the acid concentrations on the thermoelectric properties. The synergistic combination of high doping level and layer structure, accounts for the moderately high electrical conductivities (σ) and low constant Seebeck coefficients (α) of PANI-DBSA. Conversely, the poor doping ability of NaSIPA and low crystallinity degree explain the low electrical conductivities along with significant increases in Seebeck coefficient values. In relation to conduction mechanisms, PANI-DBSA shows a hopping behavior with a carrier concentration of c≈0.49 (hole type), while PANI-NaSIPA displays a diffusive regime, characteristic of degenerate metallic semiconductors, with an estimated charge carrier density of n≈3 × 1021 e/cm3

Printability Study of a Conductive Polyaniline/Acrylic Formulation for 3D Printing

[Abstract] There is need for developing novel conductive polymers for Digital Light Processing (DLP) 3D printing. In this work, photorheology, in combination with Jacobs working curves, efficaciously predict the printability of polyaniline (PANI)/acrylate formulations with different contents of PANI and photoinitiator. The adjustment of the layer thickness according to cure depth values (Cd) allows printing of most formulations, except those with the highest gel point times determined by photorheology. In the working conditions, the maximum amount of PANI embedded within the resin was ≃3 wt% with a conductivity of 10−5 S cm−1, three orders of magnitude higher than the pure resin. Higher PANI loadings hinder printing quality without improving electrical conductivity. The optimal photoinitiator concentration was found between 6 and 7 wt%. The mechanical properties of the acrylic matrix are maintained in the composites, confirming the viability of these simple, low-cost, conductive composites for applications in flexible electronic devices.Xunta de Galicia; ED481A-2019/001Xunta de Galicia; ED431C 2019/17Goretti Arias-Ferreiro thanks the financial funding received from the Xunta de Galicia and the European Union (Program to support the predoctoral stage at SUG 2019 (ED481A-2019/001)). The authors would like to thank the financial support from Xunta de Galicia-FEDER (Program of Consolidation and structuring competitive research units (ED431C 2019/17))

Lignin as a high-value bioaditive in 3D-DLP printable acrylic resins and polyaniline conductive composite

[Abstract]: With increasing environmental awareness, lignin will play a key role in the transition from the traditional materials industry towards sustainability and Industry 4.0, boosting the development of functional eco-friendly composites for future electronic devices. In this work, a detailed study of the effect of unmodified lignin on 3D printed light-curable acrylic composites was performed up to 4 wt.%. Lignin ratios below 3 wt.% could be easily and reproducibly printed on a digital light processing (DLP) printer, maintaining the flexibility and thermal stability of the pristine resin. These low lignin contents lead to 3D printed composites with smoother surfaces, improved hardness (Shore A increase ~5%), and higher wettability (contact angles decrease ~19.5%). Finally, 1 wt.% lignin was added into 3D printed acrylic resins containing 5 wt.% p-toluensulfonic doped polyaniline (pTSA-PANI). The lignin/pTSA-PANI/acrylic composite showed a clear improvement in the dispersion of the conductive filler, reducing the average surface roughness (Ra) by 61% and increasing the electrical conductivity by an order of magnitude (up to 10-6 S cm-1) compared to lignin free PANI composites. Thus, incorporating organosolv lignin from wood industry wastes as raw material into 3D printed photocurable resins represents a simple, low-cost potential application for the design of novel high-valued, bio-based products.Xunta de Galicia ; ED481A-2019/001Ministerio de Ciencia e Innovación ; PID2020-116976RB-I00Xunta de Galicia ; ED431C 2019/17Xunta de Galicia ; ED431B 2019/4

Extruded polyaniline/EVA blends: Enhancing electrical conductivity using gallate compatibilizers

The role played by alkyl gallate compatibilizers to enhance the conductivity of extruded polyaniline (PANI)–polyethylene-co-vinyl-acetate (EVA) composites was investigated. PANI doped with dodecylbenzensulfonic acid (DBSA) with 2 S cm−1 conductivity was synthetized via emulsion pathway. The achievement of doped emeraldine salt was confirmed by infrared and X-ray photoelectron spectroscopy. Two gallic acid compatibilizers, namely octyl gallate (OG) and lauryl gallate (LG) were studied by adding increasing amounts (0–20%) to the composite. Gallate compatibilizers enhanced the conductivity of the blend by one order of magnitude, achieving values similar to the pure polyaniline (1–2 S cm−1) using only 30% of PANI. Infrared spectral changes proved the formation of intermolecular hydrogen bonds between EVA and gallate esters and suggested additional interactions with PANI. These interactions improved the adhesion between PANI and EVA, thus explaining the better dispersion of the PANI observed by SEM and the increase in rheological viscosity and shear rate measurements

Photocurable printed piezocapacitive pressure sensor based on an acrylic resin modified with polyaniline and lignin

The design of suitable materials for the manufacture of pressure sensors with high sensitivity and flexibility in wearable electronics is still a challenge. In this study, a flexible and portable pressure sensor has been developed based on a photopolymeric formulation of polyaniline (PANI) /Lignin/acrylate. The amount of photoinitiator and the presence of lignin within the filler were investigated in order to obtain the best printability and capacitive response. Low PANI contents drastically increased the dielectric constant and 4 wt.% photoinitiator improved the signal and sensitivity. A sensitivity of 0.012 kPa-1 was achieved in a linear range (0 to 10 kPa) with only 3.5 wt.% PANI. Lignin improved both the dispersion of the filler within the matrix and the printability of the resin, due to lower absorptivity at the UV wavelength of the 3D printer. Thus, the PANI-Lignin filler was selected for the fabrication of a piezocapacitive prototype transducer. The pressure transducer demonstrated its practical application by responding to a human footfall and transmitting its corresponding electrical signal. This study shows the enhanced properties of lignin modified PANI acrylate composites. Based on lignin, an abundant natural waste, a sustainable photocurable cost-effective polymer is proposed for the fabrication of printable, wearable electronicsG.A.-F. would like to thank the financial funding received from the Xunta de Galicia and the European Union (Program to support the predoctoral stage at SUG 2019 (ED481A-2019/001)) and the Iacobus program (Candidature n degrees 35, 2020/2021 edition). The authors would like to thank the financial support from Ministerio de Ciencia e Innovacion/FEDER (project ref; PID2020-116976RB-I00) and Xunta de Galicia-FEDER (Program of Consolidation and structuring competitive research units (ED431C 2019/17 and ED431B 2019/44)). Furthermore, the authors thank FCT - Portuguese Foundation for Science and Technology for funding under Strategic Funding UIDB/00319/2021 and grant SFRH/BPD/110914/2015 (P.C.). Financial support from the Basque Government Industry under the ELKARTEK program is also acknowledged. Funding for open access charge: Universidade da Coruna/CISUG

Effects of silane functionalization of alumina whiskers on high-density polyethylene composites

New polyethylene matrix and alumina whiskers composites have been designed in order to combine the processability of common thermoplastics with improved physical properties. This work analyzes the influence of the composite formulation on the morphological, rheological and thermal properties of the new materials. Concerning rheological properties, a significant increase in viscosity and storage modulus is observed for high alumina whiskers content. Furthermore, the whiskers were functionalized with silane coupling agent in order to improve compatibility with the matrix. Two surface treatments were used for comparison purposes, and Fourier transform infrared spectroscopy was applied for evaluating the chemical changes on the surface of whiskers. Pre-treatment with the silane coupling agent brought about beneficial changes in morphology and rheology, related with improved dispersion of whiskers and increased filler–matrix interface. Finally, the inclusion of only 5 wt.% filler, functionalized with 100 wt.% silane, increased the thermal stability of matrix around 37%

Flexible 3D printed acrylic composites based on polyaniline/multiwalled carbon nanotubes for piezoresistive pressure sensors

The development of tunable UV-curable polymeric composites for functional applications, taking into consideration environmental issues and additive manufacturing technologies, is a research topic with relevant challenges yet to be solved. Herein, acrylic composites filled with 0–3 wt.%. polyaniline/ multiwalled carbon nanotubes (PANI/MWCNT) are prepared by Digital Light Processing (DLP) in order to tailor morphology, thermal, mechanical, and electromechanical properties. Viscosity, real-time infrared spectroscopy, and cure depth tests allow optimizing resin composition for suitable DLP printing. 2 wt.% is the maximum filler content reproducibly embedded in the polymer matrix. The advantages of PANI/MWCNT (50/50 wt.%) compared with single-component composites include safety issues, enhanced printability, increased electrical conductivity and thermal stability, and lower electrical percolation threshold (0.83 wt.%). Above this threshold the composites display excellent piezoresistive response, no hysteresis, and stability for over 400 compression cycles. The pressure sensibility (PS) of 2 wt.% composites decreases with applied pressure from PS ≈ 15 to 0.8 Mpa−1 for maximum pressures of 0.02 and 0.57 MPa, respectively. A proof-of-concept of the functionality of the novel materials is developed in the form of a tactile sensor, demonstrating their potential for pressure sensing applications as cost-effective, sustainable, and flexible materials for printed electronics.Goretti Arias-Ferreiro would like to thank the financial funding received from the Xunta de Galicia and the European Union (ED481A-2019/001). The authors would like to thank the financial support from Ministerio de Ciencia e Innovacion/FEDER (reLiCom3D project ref PID2020-116976RB-I00) and Xunta de GaliciaFEDER (ED431C 2019/17). Furthermore, the authors thank FCT - Portuguese Foundation for Science and Technology for funding under Strategic Funding UIDB/00319/2021 and grant SFRH/BPD/110914/2015 (P.C.). Financial support from the Basque Government Industry under the ELKARTEK program is also acknowledged. Funding for open access charge: Universidade da Coruña/CISUG