This thesis deals with principles of thermochromism and its possible applications in heat distribution testing. Theoretical part describes mechanisms which allow the thermochromic properties of the substances. Particular attention is paid to cholesteric liquid crystals. Ability to measure the heat for this type of liquid crystals was varified. Also long service life in high humidity environment, enviroment with intense UV radiation, cyclic changes in temperature or immersion in water was tested. A possibility of their practical use in diagnosis was verified as well. Specifically mapping of heat distribution on an assembled PCB. Conclusion contains comparison and evaluation of this method in terms of accuracy, user comfort and economic advantages compared to conventional infrared sensors.

Master´s thesis covers introduction to the problems of materials with specific proprieties named liquid crystals. Theoretic part features primary fission these materials, theirs mechanical, electrotechnical and optical characteristics. Interesting chapter is description choice application including perhaps most interesting using liquid crystals - liquid crystal display. In this trend continues experimental part too, where there are first mentioned characteristics LCD, and after it alone metering capacitive characteristics display with active matrix. Main attention in experiment is however concentraded on evaluation frequency analysis of components complex permittivity regarding in plant temperature on submitted sample liquid crystals.

Diese Dissertation demonstriert die Nutzung von einzelnen optisch geheizten Goldnanopartikeln als Sensoren f ¨ur die Untersuchung von W¨armetransport und als Intensit¨atsmodulator f ¨ur Licht. Die beschriebenen Experimente basieren auf der photothermischen Mikroskopie, die die selektive Abbildung and Untersuchung von einzelnen absorbierenden Objekten erm¨oglicht. Goldnanopartikel werden optisch angeregt. Die Relaxation erfolgt durch nichtstrahlende Prozesse, die zu einer lokalen Erh¨ohung der Temperatur f ¨uhren. Die Erw¨armung f ¨uhrt zu einer Verringerung der Brechzahl, die als thermische Linse wirkt und dadurch die Ausbreitung eines zweiten nicht absorbierten Lichtstrahls vera¨ndert. Da die thermische A¨ nderung der Brechzahl sehr gering ist, wird das photothermische Signal durch das moduliertes Detektionsverfahren verst¨arkt. Der Heizlaserstrahl wird intensit¨atsmoduliert und erzeugt dadurch eine geringe Modulation der Strahlbreite des Detektionslaserstahls. Damit ver¨andert sich die Leistung, die durch eine Blende transmittiert wird. Diese Modulationsamplitude and Phaseverz¨ogerung werden mittels eines phasenempfindlichen Gleichrichters detektiert. Amplitude und Phase h¨angen von Modulationsfrequenz und thermischer Diffusivit¨at ab. Die frequenzaufgel¨oste Messung der beiden Gr¨oßen und deren Modellierung mittels einer verallgemeinerten Lorenz–Mie Theorie erm¨oglicht die Messung von der thermischen Diffusivit¨at des Mediums, das das Goldnanopartikel umgibt. In der zweiten Variante wird die Ausbreitung der W¨arme beobachtet. Ein Nanopartikel wird optisch geheizt und die ausgedehnte thermische Linse wird mit Hilfe der Ablenkung eines zweiten Laserstrahls vermessen. Das Ablenkungssignal wird mittels eines strahlenoptischen Models berechnet, um die thermische Diffusivit ¨at des Materials zu bestimmen, das das Nanopartikel umgibt. In einem weiteren Experiment wird das große Potential von optisch geheizten Nanopartikeln verdeutlicht. Einzelne Goldnanopartikel werden in eine d¨unne nematische Fl¨ussigkristallschicht eingebettet, deren Dicke darauf abgestimmt ist, dass die Schicht eine l/2-Platte darstellt. Die Goldnanopartikel werden optisch geheizt und steuern damit den Phasen¨ubergang von der nematischen zur isotropen Phase. Damit wird die Transmission eines zweiten Laserstrahls im Polarisationskontrast ge¨andert. Mit Hilfe dieser Anordnung kann die Intensit¨at eines Lichtstrahls um bis zu 100% moduliert werden. / This dissertation demonstrates the use of individual optically heated gold nanoparticles as sensors for investigations of heat transport and intensity modulation of light. The experiments employ the photothermal effect, which allows the selective detection and investigation of individual absorbers. The photothermal contrast is based on absorbing particles that are optically excited and relax via nonradiative processes. The absorbers act as nanosources of heat. The local temperature elevation leads to a local refractive index change due to thermal expansion which then acts as a lens. This thermal lens alters the propagation of a second non-absorbed beam of light. As the refractive index change with temperature is minuscule, the transmission changes of the detection are tiny as well. The photothermal signal is amplified by the use of a modulated detection scheme which enables the methods high sensitivity and provides a time scale for the measurement of thermal transport. The heating laser beam is intensity-modulated and thereby produces a small modulation of the beam waist of the detection laser beam and thus the transmitted power through an aperture. This modulation amplitude and phase are detected by a lock-in amplifier. Amplitude and phase depend on the modulation frequency and the thermal diffusivity of the material surrounding the nanoparticle. The frequency-resolved measurement of the two observables and their modeling using a generalized Lorenz–Mie theory allows the measurement of thermal diffusivities. In the second variant, the spread of heat into space is observed. A nanoparticle is optically heated, and the extended thermal lens is characterized by the deflection of a second laser beam. The deflection signal is modeled using ray optics to determine the thermal diffusivity of the material surrounding the nanoparticle. In a further experiment, the great potential of optically heated nanoparticles is demonstrated. Individual gold nanoparticles are embedded in a thin nematic liquid-crystal layer acting as a half-wave plate. The gold particles are optically heated. They control the transmission of a detection laser set up in polarization contrast. The intensity of the detection beam is modulated by up to 100%.

In this thesis, we aim to create a framework for the derivation of thermodynamically consistent anisotropic viscoelastic models. As an example we propose simple models extending the isotropic Oldroyd-B and Giesekus models to illustrate the models' behavior and the process of finding the correct equations. We show what behavior in sheer we can expect and continue with a 3D simulation inspired by the experiment on a real liquid crystal mixture. Finally, we compare the simulation and the experiment to find similarities and possible further research topics.

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