Conducting polymers and hybrid materials for technological applications

Depletion of natural resources and non-renewable energy sources has recently accelerated due to the development of globalized economy and industrialization. During the last years, the scientific community has devoted much of its efforts to developing and improving renewable energy sources. In this context, electrochemical capacitors, or supercapacitors, have received great interest owing to their properties and potential applications. Supercapacitors and their different components constitute the main line of work of the present thesis. More specifically the thesis investigates the use of hydrogels in various distinct functions. The work done in the thesis has been developed both experimentally and corroborated by theoretical studies based on quantum mechanics and molecular dynamics. The main body of the thesis is divided into three parts. The first one includes the synthesis and characterization of a hydrogel derived from an unsaturated polyesteramide as a solid electrolyte in a supercapacitor. This part consists of the electrochemical characterization of the hydrogel obtained, evaluating the performance of the hydrogel when acting as a solid electrolyte, as well as a study of ion diffusion through the hydrogel carried out with molecular dynamics. These studies allow to obtain the optimal conditions for the synthesis and use of this hydrogel. The second part is based on the preparation and characterization of a multilayer system as an electrode in a supercapacitor. More specifically, it covers the preparation of a multilayer system consisting of PVA and the conductive polymer PEDOT, prepared by a layer-by-layer process. The chapter also consists of a theoretical study of quantum mechanics in which the movement and changes of a PEDOT monolayer are studied, and allows to elucidate the mechanisms and electronic properties that had not been fully understood at the experimental level. Finally, the third and last part incorporates the preparation of a multifunctional system consisting entirely of hydrogels. The chapter begins by detailing the preparation of an electrode of a supercapacitor based on a PEDOT hydrogel and alginate. After its characterization as an electrode, other functionalities that can be given to this system are explored. Among them, a reusable and recyclable pressure sensor is prepared to detect pressure changes linearly and with great sensitivity, as well as a controlled drug release system, in particular a controlled release by electrical stimulation of curcumin.Degut al desenvolupament de l'economia globalitzada i la industrialització, s'ha accelerat l'esgotament de recursos naturals i fonts d'energia no renovables. En els últims anys, la comunitat científica ha dedicat una gran part dels seus esforços a desenvolupar i millorar les fonts d'energia renovable. En aquest context, els capacitors electroquímics, o supercapacitors, han rebut un gran interès degut a les seves propietats i potencials aplicacions. El principal camp de treball d'aquesta tesis són els supercapacitors i les diferents parts que els constitueixen, més concretament la tesis estudia l'ús d'hidrogels en diverses funcions diferents. El treball fet a la tesis s'ha desenvolupat tant a nivell experimental com corroborat mitjançant estudis teòrics basats en la mecànica quàntica i la dinàmica molecular. El cos principal de la tesis està dividit en 3 parts. La primera part inclou la síntesis i caracterització d'un hidrogel derivat d'una poliesteramida insaturada com a electròlit sòlid en un supercapacitor. Aquesta part consta de la caracterització electroquímica de l'hidrogel obtingut, avaluant el rendiment de l'hidrogel a l'hora d'actuar com un electròlic sòlid, així com també consta d'un estudi de difusió dels ions a través d¿aquest dut a terme amb dinàmica molecular. Aquests estudis permeten obtenir les condicions òptimes per la síntesis i ús d'aquest hidrogel. La segona part està dedicada a la preparació i caracterització d'un sistema multicapa com a elèctrode en un supercapacitor. Més concretament, es basa en la preparació d'un sistema multicapa format per PVA i el polímer conductor PEDOT, preparat mitjançant un procés capa per capa. El capítol consta també d'un estudi teòric de mecànica quàntica en el que s'estudia el moviment i canvis d'una monocapa de PEDOT, i permet elucidar els mecanismes i propietats electròniques que no s'havien entès completament a nivell experimental. Finalment, l'última part es tracta de la preparació d'un sistema multifuncional format completament per hidrogels. El capítol comença detallant la preparació d'un elèctrode d'un supercapacitor basat en un hidrogel de PEDOT i alginat. Després de la seva caracterització com a elèctrode, s'exploren les altres funcionalitats que se li poden donar a aquest sistema. Es prepara un sensor de pressió reutilitzable i reciclable que permet detectar canvis de pressió linealment i amb una gran sensibilitat, i també es prepara un sistema d'alliberament controlat de fàrmacs, concretament l'alliberament controlat mitjançant estímul elèctric de curcuminaPostprint (published version

Study on the control of porosity in films of polythiophene derivatives

Conducting polymers typically exhibit different oxidation states, which are easily interchangeable among them by means of the application of an electrical potential. In this work, we present a theoretical and experimental study to regulate the pore size of poly(3,4-ethylenedioxythiophene) (PEDOT) films doped with ClO4- ions by controlling their oxidation state. More specifically, different bulk and surface PEDOT models have been evaluated applying 2D- and 3-D periodic boundary conditions to density functional theory calculations. In highly oxidized PEDOT films, calculations predict that the incorporation of dopant ions increases the separation between neighboring chains, causing a structural re-organization. Thus, the calculated average pore size, which has been modeled as a structural defect in 2D surface models, increases by 15.1%. This increment is consistent with experimental measures of the nanopore size in PEDOT films with enhanced porosity, which reflect a difference of 25.2% between the oxidized and reduced forms. This superficial phenomenon could easily be used to retain and release controlled drugs through the application of different electric potentialsPeer ReviewedPostprint (author's final draft

Free-standing, flexible nanofeatured polymeric films prepared by spin-coating and anodic polymerization as electrodes for supercapacitors

Flexible and self-standing multilayered films made of nanoperforated poly(lactic acid) (PLA) layers separated by anodically polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) conducting layers have been prepared and used as electrodes for supercapacitors. The influence of the external layer has been evaluated by comparing the charge storage capacity of four- and five-layered films in which the external layer is made of PEDOT (PLA/PEDOT/PLA/PEDOT) and nanoperforated PLA (PLA/PEDOT/PLA/PEDOT/PLA), respectively. In spite of the amount of conducting polymer is the same for both four- and five-layered films, they exhibit significant differences. The electrochemical response in terms of electroactivity, areal specific capacitance, stability, and coulombic efficiency was greater for the four-layered electrodes than for the five-layered ones. Furthermore, the response in terms of leakage current and self-discharge was significantly better for the former electrodes than for the latter ones.Postprint (author's final draft

UV assisted photo reactive polyether-polyesteramide resin for future applications in 3D printing

Among additive manufacturing, photocuring 3D printing technologies are very relevant because of its high printing speed and high precision. However, the limited performance of photosensitive thermoset polymers is the bottleneck for the application of photocuring 3D printing in some fields, particularly in the biomedical sector. Thus, the development of biodegradable and biocompatible materials is highly desirable and of utmost importance. In this work, a biodegradable and non-cytotoxic thermoset polymer for photocuring 3D printing is reported. It consists of an unsaturated polyesteramide bearing phenylalanine, 2-butene-1,4-diol and fumarate building blocks, which is photocured under UV irradiation using a low molecular weight poly(ethylene glycol) diacrylate as crosslinker. The main characteristics of the new thermoset are: (1) very high volumetric and mechanical integrity stabilities, comparable to that of photocured epoxides; (2) very high degradation temperature; (3) very low water absorption capacity; (4) relatively fast enzymatic degradation, reaching 16.5% after 3¿months; and (5) non-cytotoxic response in presence of epithelial cells, even when soluble molecular fragments coming from biodegradation are considered. These properties favor the future utilization of the new polyether-polyesteramide resin in the manufacturing of more sustainable products via 3D printing methods, such as stereolithography, that uses UV sources.Postprint (published version

Electrical and chapacitive response of hydrogel solid-like electrolytes for supercapacitors

Flexible hydrogels are attracting significant interest as solid-like electrolytes for energy storage devices, especially for supercapacitors, because of their lightweight and anti-deformation features. Here, we present a comparative study of four ionic conductive hydrogels derived from biopolymers and doped with 0.1 M NaCl. More specifically, such hydrogels are constituted by κ-carrageenan (κC), carboxymethyl cellulose (CMC), poly-γ-glutamic acid (PGGA) or a phenylalanine-containing polyesteramide (PEA). After examining the morphology and the swelling ratio of the four hydrogels, which varies between 483% and 2356%, their electrical and capacitive behaviors were examined using electrochemical impedance spectroscopy. Measurements were conducted on devices where a hydrogel film was sandwiched between two identical poly(3,4-ethylenedioxythiophene) electrodes. The bulk conductivity of the prepared doped hydrogels is 76, 48, 36 and 34 mS/cm for PEA, PGGA, κC and CMC, respectively. Overall, the polyesteramide hydrogel exhibits the most adequate properties (i.e., low electrical resistance and high capacitance) to be used as semi-solid electrolyte for supercapacitors, which has been attributed to its distinctive structure based on the homogeneous and abundant distribution of both micro- and nanopores. Indeed, the morphology of the polyestermide hydrogel reduces the hydrogel resistance, enhances the transport of ions, and results in a better interfacial contact between the electrodes and solid electrolyte. The correlation between the supercapacitor performance and the hydrogel porous morphology is presented as an important design feature for the next generation of light and flexible energy storage devices for wearable electronics.Postprint (published version

Hydrogels for flexible and compressible free standing cellulose supercapacitors

Cellulose-based supercapacitors display important advantages in comparison with devices fabricated with other materials, regarding environmental friendliness, flexibility, cost and versatility. Recent progress in the field has been mainly focused on the utilization of cellulose fibres as: structural mechanical reinforcement of electrodes; precursors of electrically active carbon-based materials; or primary electrolytes that act as reservoirs of secondary electrolytes. In this work, a flexible, lightweight, robust, portable and manageable all-carboxymethyl cellulose symmetric supercapacitor has been obtained by assembling two electrodes based on carboxymethyl cellulose hydrogels to a solid electrolytic medium formulated with the same material. Hydrogels, which were made by cross-linking carboxymethyl cellulose paste with citric acid in water, rendered not only effective solid electrolytic media by simply loading NaCl but also electroactive electrodes. For the latter, conducting polymer microparticles, which were loaded into the hydrogel network during the physical cross-linking step, were appropriately connected through the in situ anodic polymerization of a similar conducting polymer in aqueous medium, thus creating conduction paths. The performance of the assembled supercapacitors has been proved by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. This design opens a new window for the green and mass production of flexible cellulose-based supercapacitorsPeer ReviewedPostprint (author's final draft

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Conductive, self-healable and reusable poly(3,4-ethylenedioxythiophene)-based hydrogels for highly sensitive pressure arrays

Although challenging, the preparation of pure conducting polymer (CP) hydrogels as conductive flexible networks for developing high-performance functional platforms is an outstanding alternative to conventional approaches, as for example those based on the cross-linking of insulating polymers with CP segments and the simple utilization of CPs as fillers of insulating hydrogel networks. In this work, we propose the employment of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to prepare conductive hydrogels by partially replacing the PSS dopant by alginate (Alg) chains, which is energetically favoured. The capacity of Alg chains to be electrostatically cross-linked by Ca2+ ions has allowed us to obtain hydrogels with good electrical percolation response and mechanical properties. Hydrogels were prepared in a very simple one-step process by adding CaCl2 to different mixtures of PEDOT : PSS and alginic acid (1 : 3, 1 : 1 and 3 : 1). After structural, chemical and physical characterization, the 1 : 3 PEDOT/Alg hydrogel was moulded to fabricate stretchable touch-pressure sensor arrays, which exhibited fast response and good spatial resolution of the pressure distribution. In addition, the PEDOT/Alg hydrogel is self-healable which allowed us to prepare reusable pressure sensors (i.e. devices that can be reprocessed to be used in their original application) thanks to the reversibility of the noncovalent Ca2+ crosslinks. Reusable devices are different to reclaimed and recycled devices as these are no longer used for the same application because the materials lose their properties. With our hydrogels we are a step closer to a circular economy by allowing the reuse of electronic devices and reducing electronic waste worldwide. Moreover, the superior performance of the PEDOT/Alg hydrogel opens up its utilization as an efficient and flexible pressure sensor for wearable human-electronic interfaces, in which reusability would be an added value.Postprint (author's final draft

Self-healable and eco-friendly hydrogels for flexible supercapacitors

One limitation of wearable electronics, and at the same time a challenge, is the lack of energy storage devices with multiple functionalities produced using clean and environmental-friendly strategies. Here, a multifunctional conductive hydrogel containing poly(3,4-ethylenedioxythiophene) (PEDOT) and alginate was fabricated, to be used as electrodes in supercapacitors, by applying water-mediated self-assembly and polymerization processes at room temperature. The interpenetration of both polymers allowed combining flexibility and self-healing properties within the same hydrogel together with the intrinsic biocompatibility and sustainability of such materials. Initially, PEDOT : polystyrene sulfonate and alginate aqueous solutions were mixed in two different proportions (1:1 and 1:3) and ionically cross-linked with CaCl2. Subsequently, re-interpenetration of poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PHMeDOT) by anodic polymerization in CaCl2 aqueous solution was achieved. Re-interpenetrated 1:3 PEDOT/alginate hydrogels showed excellent capacitance values (35 mF/cm2) and good capacitance retention. On the other hand, the electrochemical properties were not significantly changed after many cutting/self-healing cycles as was observed by cyclic voltammetry. Therefore, this sustainably produced hydrogel shows promising properties as wearable energy storage devices.Postprint (author's final draft

Electroresponsive alginate-based hydrogels for controlled release of hydrophobic drugs

Stimuli-responsive biomaterials have attracted significant attention for the construction of on-demand drug release systems. The possibility of using external stimulation to trigger drug release is particularly enticing for hydrophobic compounds, which are not easily released by simple diffusion. In this work, an electrochemically active hydrogel, which has been prepared by gelling a mixture of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and alginate (Alg), has been loaded with curcumin (CUR), a hydrophobic drug with a wide spectrum of clinical applications. The PEDOT/Alg hydrogel is electrochemically active and organizes as segregated PEDOT- and Alg-rich domains, explaining its behavior as an electroresponsive drug delivery system. When loaded with CUR, the hydrogel demonstrates a controlled drug release upon application of a negative electrical voltage. Comparison with the release profiles obtained applying a positive voltage and in the absence of electrical stimuli indicates that the release mechanism dominating this system is complex because of not only the intermolecular interactions between the drug and the polymeric network but also the loading of a hydrophobic drug in a water-containing delivery system.Peer ReviewedPostprint (author's final draft