Biopolümeeridest ja mittetoksilistest ioonvedelikest koosneva polümeerse ajami arendamine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneEdendades inimkonna tehnoloogilist progressi ning olles samas loodussäästlikud, peame välja töötama lahendused, mis ainult ei täida funktsiooni, vaid ei kehtesta ka liigset koormat loodusele. Pehmed täiturid on kasulikud biomeditsiinilistes rakendustes nende madalpingetarbimise ja mitteinvasiivse liikumise tõttu. Elektrolüütide ehk ioonsete vedelike, toksilisus materjalis, mis on vajalikud pehmete polümeeride täiturmootori liigutamiseks, on täiturite kasutusvõimalusi piiranud. Üks viis selle piirangu ületamiseks on kasutada elektrolüütidena koliin ioonseid vedelikke. Selline lähenemine võimaldaks saavutada täielikult toimiva bioühilduvat pehmet polümeertäituri. Bioühilduv pehme polümeertäitur saavutati pärast järgmisi toiminguid. Esiteks testiti üksikuid koliin ioonseid vedelikke mitmete bakteritüvede ja rakuliini peal, mida kõiki on toksikoloogia uuringutes laialdaselt kasutatud. Teiseks prooviti koliin ioonseid vedelikke kombineerida segudeks, millel on madalam sulamistemperatuur kui üksikutel komponentidel. See lihtsustab nende kasutamist madala temperatuuriga keskkonnas. Täielikult bioühilduv pehme polümeertäitur saavutati lõpuks kõikide bioühilduvate komponentide kombineerimisega ning täituri elektromehaaniliste ja toksikoloogiliste omaduste põhjaliku testimisega. Sünteesitud koliin ioonsed vedelikud olid kõikide testitud katseorganismide suhtes ohutud. Peamiseks toksilisust mõjutavaks teguriks oli toitelahuse pH muutus. Koliin ioonsete vedelike segamisel tuvastati viis kahekomponendilist segu, millel on madalam sulamistemperatuur kui nende üksikutel komponentidel. Sulamispunkti languse hulk sõltus üksikute komponentide molekulaarsest kujust. Valmistatud bioühilduv täitur ületas oma võimekuselt võrdluseks valitud täiturit, mis oli valmistatud laiemalt kasutust leiduvatest materjalidest. Samuti kinnitati, et bioühilduv täitur tervikuna ei ohusta kokkupuutel elusorganisme.For the conservation of earth, while keeping up the technological progress of humanity, we need to come up with solutions that not only fill a function, but also do not impose a penalty on nature. Soft actuators are useful in biomedical applications because of their low voltage consumption and non-invasive movement. The toxicity of the electrolytes in the material, called ionic liquids, necessary to make the soft polymer actuator move, has limited their applications. One way to overcome this limitation, is to swap the toxic components for choline ionic liquids. This approach would make it possible to achieve a fully functioning biofriendly soft polymer actuator. The biofriendly soft polymer actuator was achieved after the following research steps. First, the individual choline ionic liquids were tested against several bacterial strains and a human cell-line, which are all widely used in toxicology studies. Second, the choline ionic liquids were attempted to be combined into mixtures that have a lower melting point than the individual components. This makes them easy to use in low temperature environments. The fully biofriendly soft polymer actuator was finally achieved by combining the biofriendly components and thoroughly testing its electromechanical and toxicological properties. The synthesized choline ionic liquids were all harmless towards the selected test organisms. Moreover, the main factor influencing the toxicity, was the change in feeding solution pH. By mixing the choline ionic liquids five two-component mixtures were identified that have a lower melting point than their individual components. The amount of melting point depression depended on the molecular shape of the individual components. Lastly, the biofriendly soft polymer actuator outperformed the comparison made from more widely used soft polymer actuator materials. It was also confirmed that the biofriendly actuator as a whole was suitable for contact with living organisms.https://www.ester.ee/record=b542876

Süsinik-tselluloos komposiit tsüanobakteri elutegevuse pärssimiseks

http://www.ester.ee/record=b4610831*es

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures

Mixing ionic liquids is a suitable strategy to tailor properties, e.g., to reduce melting points. The present study aims to widen the application range of low-toxic choline-based ionic liquids by studying eight binary phase diagrams of six different choline carboxylates. Five of them show eutectic points with melting points dropping by 13 to 45 °C. The eutectic mixtures of choline acetate and choline 2-methylbutarate were found to melt at 45 °C, which represents a remarkable melting point depression compared to the pure compounds with melting points of 81 (choline acetate) and 90 °C (choline 2-methylbutarate), respectively. Besides melting points, the thermal stabilities of the choline salt mixtures were investigated to define the thermal operation range for potential practical applications of these mixtures. Typical decomposition temperatures were found between 165 and 207 °C, with choline lactate exhibiting the highest thermal stability

Predicting Melting Points of Biofriendly Choline-Based Ionic Liquids with Molecular Dynamics

In this work, we introduce a simulation-based method for predicting the melting point of ionic liquids without prior knowledge of their crystal structure. We run molecular dynamics simulations of biofriendly, choline cation-based ionic liquids and apply the method to predict their melting point. The root-mean-square error of the predicted values is below 24 K. We advocate that such precision is sufficient for designing ionic liquids with relatively low melting points. The workflow for simulations is available for everyone and can be adopted for any species from the wide chemical space of ionic liquids

Wider Potential Windows of Cellulose Multiwall Carbon Nanotube Fibers Leading to Qualitative Multifunctional Changes in an Organic Electrolyte

The trend across the whole of society is to focus on natural and/or biodegradable materials such as cellulose (Cell) over synthetic polymers. Among other usage scenarios, Cell can be combined with electroactive components such as multiwall carbon nanotubes (CNT) to form composites, such as Cell-CNT fibers, for applications in actuators, sensors, and energy storage devices. In this work, we aim to show that by changing the potential window, qualitative multifunctionality of the composites can be invoked, in both electromechanical response as well as energy storage capability. Cell-CNT fibers were investigated in different potential ranges (0.8 V to −0.3 V, 0.55 V to −0.8 V, 1 V to −0.8 V, and 1.5 V to −0.8 V), revealing the transfer from cation-active to anion-active as the potential window shifted towards more positive potentials. Moreover, increasing the driving frequency also shifts the mode from cation- to anion-active. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy were conducted to determine the ion species participating in charge compensation under different conditions

Cellulose-Multiwall Carbon Nanotube Fiber Actuator Behavior in Aqueous and Organic Electrolyte

As both consumers and producers are shifting from fossil-derived materials to other, more sustainable approaches, there is a growing interest in bio-origin and biodegradable polymers. In search of bio-degradable electro-mechanically active materials, cellulose-multi wall carbon nanotube (Cell-CNT) composites are a focus for the development of actuators and sensors. In the current study, our aim was to fabricate Cell-CNT composite fibers and study their electro-mechanical response as linear actuators in aqueous and propylene carbonate-based electrolyte solutions. While the response was (expectedly) strongly solvent dependent, the different solvents also revealed unexpected phenomena. Cell-CNT fibers in propylene carbonate revealed a strong back-relaxation process at low frequencies, and also a frequency dependent response direction change (change of actuation direction). Cell-CNT fibers operated in aqueous electrolyte showed response typical to electrochemical capacitors including expansion at discharging with controllable actuation dependence on charge density. While the response was similarly stable in both electrolyte solution systems, the aqueous electrolytes were clearly favorable for Cell-CNT with 3.4 times higher conductivities, 4.3 times higher charge densities and 11 times higher strain

Sustainability of Multiwall Carbon Nanotube Fibers and Their Cellulose Composite

Nowadays, the research community envisions smart materials composed of biodegradable, biocompatible, and sustainable natural polymers, such as cellulose. Most applications of cellulose electroactive materials are developed for energy storage and sensors, while only a few are reported for linear actuators. Therefore, we introduce here cellulose-multiwall carbon nanotube composite (Cell-CNT) fibers compared with pristine multiwall carbon nanotube (CNT) fibers made by dielectrophoresis (DEP) in their linear actuation in an organic electrolyte. Electrochemical measurements (cyclic voltammetry, square wave potential steps, and chronopotentiometry) were performed with electromechanical deformation (EMD) measurements. The linear actuation of Cell-CNT outperformed the main actuation at discharging, having 7.9 kPa stress and 0.062% strain, making this composite more sustainable in smart materials, textiles, or robotics. The CNT fiber depends on scan rates switching from mixed actuation to main expansion at negative charging. The CNT fiber-specific capacitance was much enhanced with 278 F g−1, and had a capacity retention of 96% after 5000 cycles, making this fiber more sustainable in energy storage than the Cell-CNT fiber. The fiber samples were characterized by scanning electron microscopy (SEM), BET (Braunauer-Emmett-Teller) measurement, energy dispersive X-ray (EDX) spectroscopy, FTIR, and Raman spectroscopy

A Biomimetic Approach to Increasing Soft Actuator Performance by Friction Reduction

While increasing power output is the most straight-forward solution for faster and stronger motion in technology, sports, or elsewhere, efficiency is what separates the best from the rest. In nature, where the possibilities of power increase are limited, efficiency of motion is particularly important; the same principle can be applied to the emerging biomimetic and bio-interacting technologies. In this work, by applying hints from nature, we consider possible approaches of increasing the efficiency of motion through liquid medium of bilayer ionic electroactive polymer actuations, focusing on the reduction of friction by means of surface tension and hydrophobicity. Conducting polyethylene terephthalate (PET) bilayers were chosen as the model actuator system. The actuation medium consisted of aqueous solutions containing tetramethylammonium chloride and sodium dodecylbenzenesulfonate in different ratios. The roles of ion concentrations and the surface tension are discussed. Hydrophobicity of the PET support layer was further tuned by adding a spin-coated silicone layer to it. As expected, both approaches increased the displacement-the best results having been obtained by combining both, nearly doubling the bending displacement. The simple approaches for greatly increasing actuation motion efficiency can be used in any actuator system operating in a liquid medium

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures

Mixing ionic liquids is a suitable strategy to tailor properties, e.g., to reduce melting points. The present study aims to widen the application range of low-toxic choline-based ionic liquids by studying eight binary phase diagrams of six different choline carboxylates. Five of them show eutectic points with melting points dropping by 13 to 45 °C. The eutectic mixtures of choline acetate and choline 2-methylbutarate were found to melt at 45 °C, which represents a remarkable melting point depression compared to the pure compounds with melting points of 81 (choline acetate) and 90 °C (choline 2-methylbutarate), respectively. Besides melting points, the thermal stabilities of the choline salt mixtures were investigated to define the thermal operation range for potential practical applications of these mixtures. Typical decomposition temperatures were found between 165 and 207 °C, with choline lactate exhibiting the highest thermal stability