Anisotropy in the spatial arrangement of species and also geometric anisotropy in the components of liquid and soft matter systems gives rise to complex phase and non-trivial dynamic behaviors. Many systems are encompassed by this description including polymers, guest molecules in porous gels or nano-structured materials and also orientable fluids. In order to understand these systems, computational studies provide valuable insight. The study of such systems computationally is difficult if not prohibitive thus it is necessary to reduce these systems to simple models that capture the essential physical processes that govern the dynamics and phase behavior. Two simple models fit into this category: systems where the surrounding solvent is held stationary, a Lorentz model and also systems where a liquid crystal is formed from hard spherocylinders and is driven by an electric field. The Lorentz models studied provide a description of the dynamical regimes accessible when the probe and/or scatterers are given geometric anisotropy. The resulting dynamics are studied when order is present in the stationary solvent, i.e. structured versus isotropic solvent structure. Effective channels depending upon the competition of length scales as well as the structure of the stationary solvent leads to transitions in the dynamics of the traversing probe. Geometric anisotropy in nematogens in liquid crystals leads to the formation of mesophases indicative of a liquid crystal. When coupled to a rotating electric field, the dynamics and phase of the nematogens can be controlled.

Semi-crystalline polymers have shown increased crystalline order and size when confined in multilayered films by coextrusion1. The resulting large crystals lead to dramatic improvements in gas barrier properties. Ordered polymers whose characteristics are between that of the liquid phase and the crystalline phase are known as liquid crystalline polymers. The highly ordered mesogens in liquid crystalline polymers contribute to their exceptional bulk properties. In this research, side-chain liquid crystalline polymers were confined in multilayered films, made by either multilayer coextrusion or spin coating, with a non-liquid crystalline polymer in an attempt to improve the ordering of the liquid crystalline mesogens. The liquid crystalline behavior and morphology was studied to understand the correlation between the confinement size and the properties of the multilayer films. Commercial main chain liquid crystalline polymers and hydrogen bonded liquid crystalline polymers were also explored in this research for their use in multilayer coextrusion. / text

Carbon nanotubes (CNTs) exhibit unique and fascinating intrinsic electrical, optical, thermal or mechanical properties that lead to a plethora of potential applications in composite materials, electronics, energy storage, medicine, among others. However, the manipulation of nanotubes is not trivial and there are significant difficulties to overcome before achieving their full potential in applications. Because of their high aspect ratio and strong tube-to-tube van der Waals interactions, nanotubes form bundles and ropes that are difficult to disperse in liquids. In this thesis, the topic of dispersing carbon nanotubes in water was addressed by several experimental methods such as nuclear magnetic resonance (NMR) diffusometry and light/electron microcopy. The main goal was to obtain molecular information on how the dispersants interact with carbon nanotubes. In dispersions of single-walled carbon nanotubes (SWNTs) in water, only a small fraction of the polymeric dispersant (Pluronic F127) was shown to be adsorbed at the CNT surface. Regarding dynamic features, the residence time of F127 on the SWNT surface was measured to be in the order of hundred milliseconds, and the lateral diffusion coefficient of the polymer along the nanotube surface proved to be an order of magnitude slower than that in the solution. The surface coverage of SWNTs by F127 was also investigated and the competitive adsorption of F127 and the protein bovine serum albumin, BSA, was assessed. F127 was found to bind stronger to the CNT surface than BSA does. Low molecular weight dispersants, viz. surfactants, were also investigated. Using carefully controlled conditions for the sonication and centrifugation steps, reproducible sigmoidal dispersibility curves were obtained, that exhibited an interesting variation with molecular properties of the surfactants. Various metrics that quantify the ability of different surfactants to disperse CNTs were obtained. In particular, the concentration of surfactant required to attain maximal dispersibility depends linearly on alkyl chain length, which indicates that the CNT-surfactant association, although hydrophobic in nature, is different from a micellization process. No correlation between dispersibility and the critical micellization concentration, cmc, of the surfactants was found. For gemini surfactants of the n-s-n type with spacer length s and hydrophobic tail length n, the dispersibility of multiwalled carbon nanotubes (MWNTs) also followed sigmoidal curves that were compared to those obtained with single-tailed homologues. The increase in spacer length caused an increase in the dispersion efficiency. The observations indicate a loose type of monolayer adsorption rather than the formation of micelle-like aggregates on the nanotube surface. With the future goal of embedding nanotubes in liquid crystal (LC) phases and thereby creating nanocomposites, the effect of the spacer length on the thermotropic behavior of the gemini 12-s-12 surfactant was investigated. Different mesophases were observed and a non-monotonic effect of the spacer length was found and rationalized within a model of the surfactant packing in the solid state. The relative binding strength of simple surfactants to CNTs was assessed by the amount of F127 they displace from the CNT surface upon addition. Anionic surfactants were found to replace more F127, which was interpreted as a sign of stronger binding to CNT. The data collected for all surfactants showed a good correlation with their critical dispersibility concentration that suggests the existence of a surface coverage threshold for dispersing nanotubes. On the macroscopic scale, the formation of weakly bound CNT aggregates in homogeneous dispersions was found to be induced by vortex-shaking. These aggregates could quickly and easily be re-dispersed by mild sonication. This counterintuitive behavior was related to the type of dispersant used and of the duration of mechanical agitation and was explained as a result of loose coverage by the dispersant. / <p>This Ph.D thesis was completed under the Thesis Co-supervision Agreement between KTH Royal Institute of Technology and the University of Port. QC 20151105</p>

Azobenzene upon photochemical E/Z isomerization changes both its shape and size. The E-azobenzene moiety falls in the class of calamitic liquid crystalline mesogens, producing a wide variety of mesophases. Two series of linear bis(azobenzene) compounds, one with phenyl benzoate linkage and the other with benzyl benzoate linkage were synthesized. The termini of these molecules ranged from a dodecyloxy chain to hydrophobic amphiphilic dendrons up to first generation. We determined the effects of both the linkages and generation number on the mesogenic properties of these compounds. Our results show that the mesogenic behavior of these bis(azobenzene) compounds are highly dependent on the linkages between individual azobenzenes and that for the bis(azobenzene) compounds of the phenyl benzoate series, generation number had an effect on the liquid crystalline mesophase of the compounds

There are inherent tradeoffs in size, weight, and adaptability for many military imaging systems. In some cases, active optical devices provide new alternatives external to the traditional trade-space. Applications of interest include remote wide-area surveillance, tactical use of high altitude and space-based sensors, remote navigation of unmanned ground and air vehicles, and night vision systems.My goal is to demonstrate that by augmenting or replacing static dioptric, catatropic, or catadioptric optical designs, mechanical complexity can be reduced while either maintaining or increasing performance in three areas:(1). Spectral Resolution(2). Spatial Resolution(3). MagnificationI present here three different imaging systems to showcase these capabilities.

This dissertation describes the study of organic thin-film solar cells in pursuit of affordable, renewable, and environmentally-friendly energy sources. Particular emphasis is given to the molecular ordering found in liquid crystalline or polycrystalline films as a way to leverage the efficiencies of these types of cells. Maximum efficiencies estimated based on excitonic character of organic solar cells show power conversion efficiencies larger than 10% are possible in principle. However, their performance is often limited due to small exciton diffusion lengths and poor transport properties which may be attributed to the amorphous nature of most organic semiconductors.Discotic liquid crystal (DLC) copper phthalocyanine was investigated as an easily processible building block for solar cells in which ordered molecular arrangements are enabled by a self-organization in its mesophases. An increase in photocurrent and a reduction in series resistance have been observed in a cell which underwent an annealing process. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements suggest that structural and morphological changes induced after the annealing process are related to these improvements.In an alternative approach, p-type pentacene thin films prepared by physical vapor deposition were incorporated into heterojunction solar cells with C60 as n-type layers. Power conversion efficiencies of 2.7 % under broadband illumination (350-900 nm) with a peak external quantum efficiency of 58 % have been achieved with the broad spectral coverage across the visible spectrum. Analysis using an exciton diffusion model shows this efficient carrier generation is mainly due to the large exciton diffusion length of pentacene films. Joint XRD and AFM studies reveal that the highly crystalline nature of pentacene films can account for the observed large exciton diffusion length. In addition, the electrical characteristics are studied as a function of light intensity using the equivalent circuit model used for inorganic pn-junction solar cells. Dependences of equivalent-circuit parameters on light intensity are further investigated using a modified equivalent circuit model, and their effects on the overall photovoltaic performance are discussed.

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Baigiamajame magistro darbe nagrinėjama skystųjų kristalų priedo įtaka tepimo aušinimo skysčio savybėms. Pateikiama sintetinės emulsijos su cholesterolio stearato kristalų priedais ir be jų tribologinių tyrimų rezultatų analizė. Tyrimai buvo atlikti tekinant plieninį strypą esant tokioms sąlygoms: pastūma – 0,1 mm/aps, špindelio apsisukimų dažnis buvo keičiamas nuo 710 aps/min iki 2240 aps/min, cholesterolio stearato kristalų koncentracija emulsijoje – nuo 0,1 iki 0,5 proc. Ruošiniai pagaminti iš 45 plieno. Eksperimentas buvo atliekamas pagal dviejų veiksnių ortogonalinį eksperimento planą. Rezultatai pateikti kaip tekinto paviršiaus šiurkštumo parametro Ra priklausomybė nuo pjovimo greičio ir cholesterolio stearato koncentracijos tepimo aušinimo skystyje. Darbe nustatyta, kad skystųjų kristalų priedai pagerina tepimo aušinimo skysčio antifrikcines savybes, nepriklausomai nuo jų koncentracijos. Darbą sudaro keturios dalys: įvadas, literatūros analizė, eksperimentiniai tyrimai, išvados. Darbo apimtis: 59 psl., 15 lent., 23 pav. / Subject of this Master Thesis is investigation of influence of additive of liquid crystals to properties of coolants. There are results of analysis of tribological investigations of coolant with additive of liquid crystals and without them presented in this work. Investigations realized by turning of steel core in such: delivery output – 0,1 mm/rotation, cutting speed interval: 85 m/min – 267 m/min, concentration of cholesteric liquid crystals in coolant – from 0,1 by 0,5 percent. Experiment was conducted according to two factors orthogonal experimental plan. Results are provided as equation, which shows dependence of ruggedness parameter of faced surface Ra of cutting speed and concentration of cholesteric liquid crystals in coolant. Results of experiment show that liquid crystals additives improve anti-frictional properties of coolants independently of concentration of liquid crystals. This work consists of four parts: introduction, theoretical review, experiential investigations, and conclusions. The Annex is attached on the end of work. Size of work: 59 pages., 15 tables, 23 figures.

Paskutiniais dešimtmečiais puslaidininkių fizika vaidino svarbų vaidmenį beveik kiekvienoje šiuolaikinių technologijų srityje. Šiame greitai besikeičiančiame pasaulyje mūsų jau nebetenkina supantys buities ir darbo prietaisai, valdomi naudojantis elektronais. Mums reikalingas didesnis kompiuterių operatyvumas, didesnė atminties talpa, greitesnis telekomunikacinis ryšys, ir todėl reikalingos naujos technologijos bei sprendimai. Naujas žingsnis fotoninės struktūros. Žinių ir technologijų pasiekimai leidžia fotoninių sturktūrų savybes taikyti šviesos valdymui. Dabartiniame optinės fizikos tyrinėjimų etape šviesos sąveika su medžiaga labai aktuali: ji gali atrodyti universali ir invariantiška, kadangi šviesa jau kontroliuojama pasitelkus hibridinius fotoninius kristalus. Šių darinių tyrimai patrauklūs tiek fundamentaliam, tiek taikomajam mokslui. Į opalą infiltravę skystąjį kristalą, gauname hibridinį fotoninį kristalą. Jo optines savybes galima keisti priklausomai nuo infiltruotos medžiagos lūžio rodiklio. Fotoniniai kristalai, reikia tikėtis, bus taikomi ateities fotoniniuose įrenginiuose, telekomunikacijoje. Su šia sritimi siejamos tokios pat ar net didesnės viltys, kokios buvo siejamos su prieš 50 metų išrastu puslaidininkiniu tranzistoriumi, pakeitusiu techniką ir davusiu impulsą naujoms mokslo kryptims. Teoriškai fotoninių kristalų egzistavimą nepriklausomai vienas nuo kito 1987 metais pirmieji aprašė E.Jablonovičius ir S. Johnas. Tačiau prireikė dar dešimt metų, kol buvo... [toliau žr. visą tekstą] / We live in the rapidly developing technological world. However, fields of communication, computer memory, and data processing require considerable improvements. The speed of data transportation is acceptable but capacity is low. There is a growing need for new technologies that rapidly detect and treat diseases at an early stage or even pre-stage. When we get accustomed to the advance, we demand more compact, energy-efficient, rapidly-responding and environmentally-safe technologies. During the last century this problem was solved by switching to transportation of electronic data, which connected people around the world. This approach had changed our lives, but about twenty years ago this technology reached its limits, while need for an even higher transportation capacity increases. Now we need faster computers and other state-of-the-art technological solutions: electrons are too slow and we have to use photons. Over the last decade, the steady progress regarding ability to fabricate hybrid photonic nanostructures led to a rich variety of different one-, two-, and three-dimensional dielectric/organic and/or metallic periodic structures. They demonstrate qualitatively new and fascinating linear-optical, nonlinear-optical, and quantum-optical features which provide an unprecedented control of light propagation and light-matter interaction. Photonic-based technology, coupled with nanotechnology, can meet many of these challenges. In this work fabrication of hybrid photonic... [to full text]

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