Mechanical reinforcement of electrospun poly(vinyl alcohol) by α‐FeOOH nanowires

The authors kindly acknowledge the financial support of the Estonian Research Council for the post-doctoral research grants of personal research funding in projects PUT1096 and PUTJD578 as well as Institutional Research Funding Projects, IUT20-17, and IUT23-7.We report the mechanical performance of α‐FeOOH nanowire reinforced poly(vinyl alcohol) (PVA) composite nanofiber mat, fabricated using straightforward aqueous processing methods. Goethite (α‐FeOOH) nanocrystals have a high elastic modulus and –OH rich surface, ensuring strong interactions with hydrophilic polymers and effective reinforcement. Needle‐less electrospinning resulted in alignment of the nanowires along fibre axis, as confirmed by transmittance electron microscopy studies. Produced composite PVA nanofibers containing 10 wt% goethite nanoparticles exhibited an outstanding fivefold increase in Young's modulus and 2.5‐fold improvement of tensile strength compared to mats of neat PVA. The addition of α‐FeOOH had a significant influence on glass transition temperature indicating formation of interphase regions around nanowire inclusions. Observed properties are explained by nanowire grafting in the precursor solution, extensive interactions between the adsorbed PVA chains and the matrix and percolation of interphase regions at 10 wt% α‐FeOOH.Estonian Research Council PUT1096 and PUTJD578; Institutional Research Funding Projects, IUT20-17, and IUT23-7; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Hybrid Tribo-Piezo-Electric Nanogenerator with Unprecedented Performance Based on Ferroelectric Composite Contacting Layers

This research was supported by the European Regional Development Fund within the project ‘‘Hybrid energy harvesting systems’’ 1.1.1.1./16/A/013.It was recently reported that more efficient triboelectric nanogenerator (TENG)-like devices can be prepared using inversely polarized ferroelectric films made of same material as the contacting layers. In the present work, a clear correlation between the piezoelectric response of inversely polarized ferroelectric PVDF/BaTiO3 nanocomposite films and the performance of the TENG-like device based on these films is demonstrated. This observation is explained by magnified electrostatic induction that is driven by piezoelectric charges and ferroelectric properties of these films. A double capacitor model is proposed that effectively portrays the interactions between ferroelectric layers during contact-separation and subsequent charge redistributions in the external circuit. The new understanding has allowed the result of 3-fold higher open circuit voltages (2.7 kV from 5 cm2) as compared to that of a state of the art TENG. Furthermore, findings uncover the potential for vast improvement in the field of nanogenerators for mechanical energy harvesting as a significantly better piezoelectric performance of flexible nanogenerators has been reported elsewhere.ERDF 1.1.1.1./16/A/013; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Ohustatud sh kaitsealuste ja vääriskalaliikide seisundi parandamiseks vajalikud meetmed ja eelistatud tegevused

Eesti kalavaru, sh vähivaru kasutamine peab olema kooskõlas nii rahvusvaheliselt kui Eestis heakskiidetud säästva arengu põhimõtetega. Loodusvarade säästva kasutamise eesmärk on inimest rahuldava elukeskkonna ja majanduse arenguks vajalike ressursside tagamine, sealjuures oluliselt kahjustamata elukeskkonda ning säilitades looduslikku mitmekesisust. Kalavaru kaitset ja suurust saab mõjutada püügi reguleerimisega, elukeskkonna kaitse, parandamise või taastamisega ning kalakasvatusliku taastootmise abil. Viimane neist on kulukas tegevus, mis eeldab pikaajalist planeerimist ja otstarbekuse analüüsi. Selleks on vajalik kalavarude taastootmise tegevuskava. Tegevuskava koostamisel on lähtutud Eesti ja rahvusvahelistest valdkondlikest dokumentidest arvestades seejuures hetkeolukorda, kalavarude seisundit ja taastamise vajadust ning olemasolevaid võimalusi. Tegevuskava eesmärk on kalakasvatusliku taastootmise abil parandada ohustatud sh kaitsealuste kalaliikide seisundit ja suurendada nende arvukust, luues avaramad võimalused ka vääriskalaliikide püügiks Eestis. Tegevuskava elluviimist koordineerib ja selle eest vastutab Keskkonnaministeeriumi kalavarude osakond. Vastutav koordinaator koos tegevuskava täitjatega koostab iga nelja aasta tagant tegevuskava täitmise kokkuvõtte. Vastavalt saavutatud tulemustele ja ilmnenud puudustele muudetakse kava, et korrigeerida kalakasvatusliku taastootmise suundasid kalavarude olukorra parandamiseks ja bioloogilise mitmekesisuse hoidmiseks.Programmi koostamist finantseeris Keskonnainvesteeringute Kesku

Status of Biodiversity in the Baltic Sea

The brackish Baltic Sea hosts species of various origins and environmental tolerances. These immigrated to the sea 10,000 to 15,000 years ago or have been introduced to the area over the relatively recent history of the system. The Baltic Sea has only one known endemic species. While information on some abiotic parameters extends back as long as five centuries and first quantitative snapshot data on biota (on exploited fish populations) originate generally from the same time, international coordination of research began in the early twentieth century. Continuous, annual Baltic Sea-wide long-term datasets on several organism groups (plankton, benthos, fish) are generally available since the mid-1950s. Based on a variety of available data sources (published papers, reports, grey literature, unpublished data), the Baltic Sea, incl. Kattegat, hosts altogether at least 6,065 species, including at least 1,700 phytoplankton, 442 phytobenthos, at least 1,199 zooplankton, at least 569 meiozoobenthos, 1,476 macrozoobenthos, at least 380 vertebrate parasites, about 200 fish, 3 seal, and 83 bird species. In general, but not in all organism groups, high sub-regional total species richness is associated with elevated salinity. Although in comparison with fully marine areas the Baltic Sea supports fewer species, several facets of the system's diversity remain underexplored to this day, such as micro-organisms, foraminiferans, meiobenthos and parasites. In the future, climate change and its interactions with multiple anthropogenic forcings are likely to have major impacts on the Baltic biodiversity

Mikrorull-struktuuride moodustumine geel-kile rullumise teel Zr-, Ti- ja Hf- butoksiididest

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Õhukeste kilede rullumine mikro- ja nanotorudeks on kümne aasta vanune aktuaalne valdkond materjaliteaduses. Selle materjali vormimise ideoloogia ellurakendamiseks on seni kasutatud kõrgvaakumis läbiviidavaid materjali sadestamise ja vormimise meetodeid. Valmistatud struktuurid on potentsiaalselt kasutatavad mikrokanalite, optiliste resonaatorite, mikrosensorite või biomaterjalidena. Käesolev väitekiri käsitleb uudset ja originaalset sool-geel meetodit metalloksiidsete mikrorullide valmistamiseks metalli alkoksiididest saadavate geel-kilede rullumise teel. Meetod põhineb geelkile iseeneslikul jagunemisel segmentideks selle pragunemise tulemusena ja moodustunud materjali mehaanilistest pingetest tingitud spontaansel rullumisel. Tavapäraselt peetakse selliseid protsesse sool-geel meetodite puhul soovimatuteks. Käesolevas töös uuriti geelkile pragunemise protsesse, mis määravad rulluva kilesegmendi mõõtmed ning hinnati lähteine koostise ning geelistumisreaktsioonide kestvuse mõju rullumise teel saadavate struktuuride mõõtmetele. Meetod kohandati ka titaan- ja hafnium(IV)butoksiidist torujate mikrostruktuuride valmistamiseks, ühtlasi näidati et geelstruktuure on võimalik kuumutada oksiidmaterjali saamiseks ilma, et mikrostruktuurid laguneks. Tsirkooniumoksiidi puhul täheldati struktuuride lagunemist tetragonaalse ja monokliinse faasi vahelise siirde tõttu kuumutamisel 700 ºC kraadini. Ühtlasi näidati, et materjali lagunemist kuumutamisel on võimalik vältida üttriumi lisamise teel materjali koostisesse. Geelkile pragunemiskatsete tulemuste põhjal konstrueeriti plokk-vedru mudel, mis võimaldab eksperimendis nähtavate pragunemismustrite suhteliselt hea kokkulangevusega simuleerimist. Uudse kujuga metalloksiidse materjali võimalike rakendustena nähakse muu-hulgas optilisi resonaatoreid, elongeeritult vabastavaid materjale, mikrokonteinereid, katalüsaatoreid ja biomaterjale.Micro- and nanotubes by self-rolling of films is an exciting emerging field in materials science. This ideology of material forming was introduced a decade ago and has been since adapted to the preparation of nano- and microrolls from different materials by vacuum deposition and lithography methods with potential applications as microfluidic channels, optical resonators, microsensors or biomaterials. Present thesis is an overview of our studies on the formation of metal oxide microtubes by original metal alkoxide gel nanofilm rolling that opposes to previously reported approaches mainly by being simpler in its nature as no sophisticated material processing methods are required. The method is based on spontaneous gel cracking and rolling due to mechanical stress, phenomena that are conventionally considered as unwanted in sol-gel processes. Phenomenologic studies were conducted on gel film cracking that defines the dimensions of rolled film segments. Influence of precursor composition and precursor reacting time with humid air on the diameter of obtained roll structures and thickness of gel film was also estimated. The preparation method was also adapted to titanium(IV)butoxide and hafnium(IV)butoxide as starting compounds and the gel structures were successfully heat treated to achieve metal oxide composition. Roll shape was preserved despite shrinkage that is typical to sol-gel materials. Although the roll shape of structures prepared from zirconium(IV)butoxide did not withstand annealing at 700 ºC causing a transition from tetragonal to monoclinic phase they were found to be excellent hosts to Sm3+ ions in photoluminescence studies. As a successful solution to the problem of material fracture during heat treatment, yttria-doped zirconia microrolls were also prepared. Based on crack formation observation results, a discrete element method model was developed for cracking simulations. Relatively good concurrency with experimental data was achieved. Proposed applications of microtubular metal oxide structures include optical resonators, controlled release, microcontainers, catalysis and biomaterials

Electrochemomechanical Behavior of Polypyrrole-Coated Nanofiber Scaffolds in Cell Culture Medium

Glucose-gelatin nanofiber scaffolds were made conductive and electroactive by chemical (conductive fiber scaffolds, CFS) and additionally electrochemical polypyrrole deposition (doped with triflouromethanesulfonate CF3SO3−, CFS-PPyTF). Both materials were investigated in their linear actuation properties in cell culture medium (CCM), as they could be potential electro-mechanically activated cell growth substrates. Independent of the deposition conditions, both materials showed relatively stable cation-driven actuation in CCM, based on the flux of mainly Na+ ions from CCM. The surprising result was attributed to re-doping by sulfate anions in CCM, as also indicated by energy-dispersive X-ray (EDX) spectroscopy results. Overall, the electrochemically coated material outperformed the one with just chemical coating in conductivity, charge density and actuation response

Concept of an artificial muscle design on polypyrrole nanofiber scaffolds.

Here we present the synthesis and characterization of two new conducting materials having a high electro-chemo-mechanical activity for possible applications as artificial muscles or soft smart actuators in biomimetic structures. Glucose-gelatin nanofiber scaffolds (CFS) were coated with polypyrrole (PPy) first by chemical polymerization followed by electrochemical polymerization doped with dodecylbenzensulfonate (DBS-) forming CFS-PPy/DBS films, or with trifluoromethanesulfonate (CF3SO3-, TF) giving CFS-PPy/TF films. The composition, electronic and ionic conductivity of the materials were determined using different techniques. The electro-chemo-mechanical characterization of the films was carried out by cyclic voltammetry and square wave potential steps in bis(trifluoromethane)sulfonimide lithium solutions of propylene carbonate (LiTFSI-PC). Linear actuation of the CFS-PPy/DBS material exhibited 20% of strain variation with a stress of 0.14 MPa, rather similar to skeletal muscles. After 1000 cycles, the creeping effect was as low as 0,2% having a good long-term stability showing a strain variation per cycle of -1.8% (after 1000 cycles). Those material properties are excellent for future technological applications as artificial muscles, batteries, smart membranes, and so on

Counterintuitive Increase in Optical Scattering Efficiency during Negentropic Orientational Transition in Dilute ZnO Nanowire Suspensions

We demonstrate experimentally that the electrophoretic manipulation of a ZnO nanowire (NW) suspension in polydimethylsiloxane (PDMS) causes a remarkable change in optical scattering. Counterintuitively, as an electric field is applied to the suspension and a negentropic orientational transition from a chaotically oriented state to a partially ordered (aligned) state is induced, the geometrical cross-section of the particles decreases whereas the scattering efficiency increases significantly, indicating an increase in the scattering cross-section. The alignment of the longer axis of oblong ZnO nanoparticles in the direction of incident light unexpectedly resulted in up to a 40% decrease in transmittance in the middle of the visible spectral range in the case of 150 mm thick composite films with below 0.1 vol% NW concentration. A prepared prototype smart window device exhibited spontaneous restoration of transmittance, persistent electro-optical performance (0% change in contrast after more than 10 cycles), and temporal stability against nanoparticle sedimentation and agglomeration