IJS KOLOKVIJ, sreda, 4. 12. 2019, ob 13.00 uri, prof. dr. Vid Bobnar

[natasa.gosevac at ijs.si]

Vabimo vas na 4. predavanje iz sklopa "Kolokviji na IJS" v letu 2019/20, ki bo v sredo, 4. decembra 2019, ob 13. uri v Veliki predavalnici Instituta »Jožef Stefan«  na Jamovi cesti 39 v Ljubljani. Napovednik predavanja najdete tudi na naslovu  <http://www.ijs.si/ijsw/Koledar_prireditev> http://www.ijs.si/ijsw/Koledar_prireditev, posnetke preteklih predavanj pa na  <http://videolectures.net/kolokviji_ijs> http://videolectures.net/kolokviji_ijs. 

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prof. dr. Vid Bobnar

Institut Jožef Stefan, Ljubljana

Razvoj novih anorganskih in polimernih sistemov z ojačenim dielektričnim in elektromehanskim odzivom

V predavanju bomo na različnih primerih pokazali, da je mogoče nove materiale z visokim dielektričnim in piezoelektričnim odzivom, ki so nujno potrebni v sistemih za shranjevanje energije in v elektromehanskih aplikacijah, učinkovito razviti z upoštevanjem nekaterih osnovnih fizikalnih pojavov. (i) V heterogenem sistemu, sestavljenem iz dielektrične matrice in električno prevodnih vključkov, naboj na mejah med fazama deluje kot velik električni dipol. S takoimenovano Maxwell-Wagnerjevo polarizacijo smo učinkovito povečali dielektrično konstanto elektroaktivnih polimerov, sintetiziranih na osnovi PVDF, in tako znatno zmanjšali zunanje električno polje, potrebno za njihov velikanski elektrostrikcijski odziv. Analogno smo izdelali fleksibilne in okolju prijazne kompozite iz celuloznih nanovlaken in grafenovega oksida ter anorganske materiale, kot so keramični perkolativni kompoziti in tanke plasti s strukturo jedro-lupina, ki so sestavljene iz polprevodnih zrn, ločenih s tankimi neprevodnimi mejami. (ii) V tankih plasteh je elektromehanski odziv običajno močno zmanjšan zaradi njihovega mehanskega vpetja na podlago. Razvili smo preprosto in robustno metodo za pripravo poroznih feroelektričnih tankih plasti s sintezo iz raztopin. V teh plasteh se zaradi relaksacije mehanskih napetosti vrednosti piezoelektričnih koeficientov povečajo na vrednosti, tipične za keramične materiale v kosu. (iii) V sistemih z močno sklopljenimi električnimi dipoli se zaradi izrazite polarizacijske histereze povečajo tudi dielektrične izgube. Kot alternativo široko uporabljanim polimerom na osnovi PVDF bomo predstavili nov dielektrični polimer, aromatsko politiurejo, in primerjali odziv tega amorfnega polimera v steklasti fazi (s šibko sklopljenimi dipoli) z odzivom komercialno uporabljanih sistemov. 

Lepo vabljeni!

 

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We invite you to the 4th Institute colloquium in the academic year 2019/20. The colloquium will be held on Wednesday December 4, 2019 at 1 PM in the main Institute lecture hall, Jamova 39, Ljubljana. To read the abstract click   <http://www.ijs.si/ijsw/Koledar_prireditev> http://www.ijs.si/ijsw/Koledar_prireditev. Past colloquia are posted on   <http://videolectures.net/kolokviji_ijs> http://videolectures.net/kolokviji_ijs.

 

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prof. dr. Vid Bobnar

Institut Jožef Stefan, Ljubljana

 

Designing novel inorganic and polymer systems with enhanced dielectric and electromechanical response

 

The lecture will demonstrate, using various examples from our work, that novel materials with high dielectric and piezoelectric response, required in energy storage systems and electromechanical applications, can efficiently be developed by taking into account some basic physical phenomena. (i) In a heterogeneous system composed of dielectric matrix and electrically conductive inclusions, the charge accumulated at phase boundaries acts as a large electric dipole. Using this Maxwell-Wagner polarization we have effectively increased the dielectric permittivity of PVDF-based electroactive polymers and thus substantially reduced the electric field required for their giant electrostrictive response. Analogously, we have fabricated flexible, eco-friendly composites from cellulose nanofibrils and graphene oxide as well as inorganic materials such as bulk all-ceramic percolative composites and core-shell structured thin films that consist of semiconducting grains separated by thin insulating grain-boundaries. (ii) In thin films the electromechanical response is obstructed by the mechanical clamping of the substrate, resulting in a deterioration of the piezoelectric coefficients. We have thus developed a simple and robust method for the chemical solution deposition of highly porous ferroelectric thin films, where the porosity-mediated release of the substrate’s mechanical constraints enhances piezoelectric coefficients back to the level of bulk ceramics. (iii) Systems with strongly coupled dipoles also exhibit pronounced polarization hysteresis, which increases dielectric losses. As an alternative to the widely used PVDF-based polymers we will present a new class of dielectric polymer, aromatic polythiourea, and compare the response of this amorphous, glass-phase polymer (with weak coupling among the dipoles) with the response of commercially used systems.

 

 

Cordially invited!

 

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