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Title:Zlom simetrije: aplikacija v optimizaciji energijskih procesov in detekciji nanodelcev
Authors:ID Klemenčič, Eva (Author)
ID Slavinec, Mitja (Mentor) More about this mentor... New window
ID Kralj, Samo (Comentor)
Files:.pdf DOK_Klemencic_Eva_2019.pdf (3,55 MB)
MD5: DD9C4898E2C4A722557B972BE3F5EA8E
PID: 20.500.12556/dkum/04f6eb01-2ece-4094-923b-2bd827a2deef
 
Language:Slovenian
Work type:Doctoral dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FNM - Faculty of Natural Sciences and Mathematics
Abstract:Doktorska disertacija zajema teoretično študijo treh primerov zloma simetrije v aplikativne namene. Osredotočimo se na možne aplikacije v sistemu tekočih kristalov, ki združujejo unikatno kombinacijo optične anizotropije, delnega značaja tekočine in »mehkobe«. Slednja opisuje možnost relativno močnega makroskopskega odziva na sorazmerno majhne motnje. Kot prvo obravnavamo uporabo fazno spremenljivih materialov v gradbenih kompozitih. Z numeričnimi simulacijami pokažemo, da s fazno spremenljivimi materiali lahko zagotovimo manjša temperaturna nihanja v prostoru in tako izboljšamo toplotno stabilnost prostora, pri čemer ima ključni pomen ustrezno izbrana temperatura faznega prehoda. Nadalje predstavimo dve možni izboljšavi. Prva izboljšava je kombinacija dveh fazno spremenljivih materialov, ki preideta fazni prehod pri različnih temperaturah, kar podaljša časovno konstantno toplotne stabilizacije. Pri drugi izboljšavi manipuliramo temperaturo faznega prehoda z zunanjimi perturbacijami. Na sistemu tekočih kristalov ograjenih v celico analitično prikažemo odvisnost temperature faznega prehoda od karakteristične razdalje celice, na katero lahko vplivamo z zunanjimi perturbacijami kot je na primer zunanje električno polje. S predlaganima izboljšavama razširimo območje optimalnega delovanja kompozita s fazno spremenljivimi materiali. Druga aplikacija zloma simetrije je elektrokalorični pojav, ki ga podrobneje preučimo na sistemu tekočih kristalov v bližini faznih prehodov in v bližini kritične točke z dodajanjem nanodelcev. Za teoretično obravnavo elektrokaloričnega pojava uporabimo Landau-de Gennes – Ginzburgov model na mezoskopski skali. Rezultati numeričnih simulacij razkrivajo, da se s približevanjem temperaturi faznega prehoda iz izotropne v nematsko fazo elektrokalorični odziv sistema veča kot posledica večje spremembe v orientacijski entropiji sistema. Analitično in numerično dokažemo, da lahko elektrokalorični odziv povečamo z direktnim faznim prehodom med izotropno in smektično A fazo. V slednji smektična urejenost efektivno deluje kot zunanje električno polje, kar posledično lahko vodi v ojačenje elektrokaloričnega odziva. Jakost odziva je močno odvisna od jakosti nezveznega prehoda med tekmujočima fazama. Fazno obnašanje v preučevanih sistemih kontroliramo z jakostjo sklopitve med orientacijskim in translacijskim redom. Za vrednosti nad kritično dosežemo direktni fazni prehod 1. reda iz izotropne v smektično A fazo, ki rezultira v povečanju elektrokaloričnega odziva sistema. Predstavimo tudi hladilni sistem in aktivni regenerator, ki delujeta na principu elektrokaloričnega pojava v tekočih kristalih, s čimer dosežemo večje razmerje med hladilno močjo in maso hladilnega sistema. Pri analizi elektrokaloričnega pojava v bližini kritične točke v sistem tekočih kristalov naključno porazdelimo različno koncentracijo nanodelcev. Sistem obravnavamo na semi- mikroskopski skali z Lebwohl Lasherjevim mrežnim modelom. Ugotovimo, da prisotnost nanodelcev ne prispeva k povečanju elektrokaloričnega odziva. Razlog je zmanjševanje možne električno povzročene spremembe orientacijske entropije, kar prevlada nad mehanizmom večjega odziva v bližini kritične točke. Kot tretjo aplikacijo zloma simetrije obravnavamo možnost detekcije nanodelcev. Prisotnost nanodelcev v celici tekočega kristala v nematski fazi povzroči frustracijo, ki se odraža v lokalno dvoosni urejenosti sistema. Posledično s spreminjanjem zunanjih pogojev kot so zunanje električno polje, temperatura in pozicija nanodelca, dobimo kvalitativno različne konfiguracije, kar lahko uporabimo za detekcijo nanodelcev. Rezultati doktorske disertacije prispevajo k boljšemu razumevanju obnašanja sistema tekočih kristalov v bližini faznih prehodov pod vplivom zunanjih dejavnikov.
Keywords:zlom simetrije, optimizacija energijskih procesov, detekcija nanodelcev, tekoči kristali, elektrokalorični pojav, fazno spremenljivi materiali, inovativni fasadni sistemi, modeliranje
Place of publishing:[Maribor
Publisher:[E. Klemenčič]
Year of publishing:2019
PID:20.500.12556/DKUM-73894 New window
UDC:539.2:532.783(043.3)
COBISS.SI-ID:24917256 New window
NUK URN:URN:SI:UM:DK:NDSLSTT9
Publication date in DKUM:20.11.2019
Views:4014
Downloads:137
Metadata:XML DC-XML DC-RDF
Categories:FNM
:
KLEMENČIČ, Eva, 2019, Zlom simetrije: aplikacija v optimizaciji energijskih procesov in detekciji nanodelcev [online]. Doctoral dissertation. Maribor : E. Klemenčič. [Accessed 26 March 2025]. Retrieved from: https://dk.um.si/IzpisGradiva.php?lang=eng&id=73894
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Licences

License:CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Link:http://creativecommons.org/licenses/by-nc-nd/4.0/
Description:The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.
Licensing start date:27.06.2019

Secondary language

Language:English
Title:Symmetry breaking: application in optimization of energy process and detection of nanoparticles
Abstract:The doctoral thesis covers a theoretical study of three cases of symmetry breaking phenomenon for applicative purposes. We focus on possible applications in liquid crystals, which combine a unique combination of optical anisotropy, the partial character of the liquid and the "softness". The latter describes the possibility of a relatively strong macroscopic response to relatively small external perturbations. First, we consider the use of phase change materials in construction composites. With numerical simulations, we show that phase change materials can decrease room temperature fluctuations and thereby improve the thermal stability of the room. In the latter, the phase transition temperature has a key role. Furthermore, we present two possible improvements. The first improvement is a combination of two different phase change materials that undergo phase transitions at different temperatures, which prolongs the time constant of the heat stabilization. The second improvement is the manipulation of the phase transition temperature with external perturbations. For liquid crystals enclosed in a cell, we show that the phase transition temperature depends on the characteristic length of the cell. The following can be manipulated by external perturbations, for example, the external electric field. With proposed improvements, we expand the optimal operation interval of innovative composites with phase change materials. The second symmetry breaking application is an electrocaloric effect. In the doctoral thesis, we study electrocaloric effect in liquid crystals near the phase transitions and near the critical point by the addition of nanoparticles. For a theoretical study, we use the Landau-de Gennes – Ginzburg model at the mesoscopic scale. Numerical results reveal that by approaching the phase transition temperature from an isotropic to a nematic phase, the electrocaloric response of the system increases because of the increase in the orientational entropy change. We prove that the electrocaloric response increases for a direct phase transition between the isotropic and the smectic A phase both analytically and numerically. In the latter, the smectic ordering effectively acts as an external electric field. Consequently, it can enhance the electrocaloric response, which strongly depends on the intensity of discontinuous transitions between the competing phases. The phase behaviour is controlled by the coupling strength between the orientational and the translational order. In addition, we present an electrocaloric based cooling system and an active regenerator, which can increase performance and cooling power yield per mass. We analyse the electrocaloric effect near a critical point by randomly distributing different concentrations of nanoparticles in the liquid crystal system. Numerical simulations are based on Lebwohl Lasher model at a semi- microscopic scale. We reveal that the presence of nanoparticles does not contribute to an increase in electrocaloric response. The reasoning behind this is a decrease in the electrically induced change in orientational entropy, which prevails over the possible increase due to the critical point. The third symmetry breaking application is the detection of nanoparticles. The presence of nanoparticles in a nematic liquid crystal cell causes frustration, which results in a local biaxiality. At varying external conditions such as the external electric field, temperature, and position of the nanoparticle, we obtain qualitatively different configurations, which can be used to detect nanoparticles. The results of the doctoral thesis contribute to a better understanding of the behaviour of the liquid crystal system in the vicinity of phase transitions under the influence of external factors.
Keywords:symmetry breaking, optimization of energy process, detection of nanoparticles, liquid crystals, electrocaloric effect, phase change materials, innovative facade systems, modeling


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