Electronic coarse graining is a technique improving the predictive power of molecular dynamics simulations by representing electrons via a quantum harmonic oscillator. This construction, known as a Quantum Drude Oscillator, provides all molecular long-range responses by uniting many-body dispersion, polarisation and cross interactions to all orders. To demonstrate the predictive power of electronic coarse graining and provide insights into the physics of water, a molecular model of water based on Quantum Drude Oscillators is developed. The model is parametrised to the properties of an isolated molecule and a single cut through the dimer energy surface. Such a parametrisation makes the condensed phase properties of the model a prediction rather than a fitting target. These properties are studied in four environments via two-temperature adiabatic path integral molecular dynamics: a proton ordered ice, the liquid{vapour interface, supercritical and supercooled water. In all these environments, the model predicts a condensed phase in excellent agreement with experiment, showing impressive transferability. It predicts correct densities and pressures in liquid water from 220 K to 647 K, and a correct temperature of maximum density. Furthermore, it predicts the surface tension, the liquid-vapour critical point, density of ice II, and radial distribution functions across all conditions studied. The model also provides insight into the relationship between the molecular structure of water and its condensed phase properties. An asymmetry between donor and acceptor hydrogen bonds is identified as the molecular scale mechanism responsible for the surface orientation of water molecules. The dipole moment is identified as a molecular scale signature of liquid-like and gas-like regions in supercritical water. Finally, a link between the coordination number and the anomalous thermal expansion of the second coordination shell is also presented.

Orientador: Maurice de Koning / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-13T12:16:33Z (GMT). No. of bitstreams: 1 CarvajalJara_DiegoAlejandro_M.pdf: 4649880 bytes, checksum: d014cd5c835938e4643e478fa70353be (MD5) Previous issue date: 2009 / Resumo: Recentemente tem sido proposta a existência de uma transição líquido-líquido em substâncias puras com o propósito de explicar alguns comportamentos anômalos como os incrementos de funções resposta (compressibilidade isotérmica, coeficiente de expansão térmica, calor específico) ao diminuir a temperatura de um líquido. A existência deste tipo de transição foi demostrada experimentalmente para o fósforo por dispersão de raios X, e através de simulações atomísticas ou de primeiros princípios para a água, o silício, o carbono, etc. A compreensão detalhada deste tipo de transição está intimamente relacionada à questão fundamental de quais fatores físicos controlam as propriedades de um líquido, e portanto o estudo desta é de grande importância para o desenvolvimento de novas tecnologias, a síntese de novos materiais e o controle de suas propriedades. Neste trabalho realizamos simulações atomísticas sobre um sistema de 1152 partículas de Gálio submetidas a um potencial semi-empírico MEAM, com condições periódicas de contorno. Com estas simulações procuramos uma transição líquido-líquido no Gálio através de um processo de eliminação de três teorias. Inicialmente mostramos que o limite de metaestabilidade do líquido super-aquecido tem um comportamento monótono decrescente no plano de fase P-T. Posteriormente nosso sistema apresenta histerese, uma descontinuidade no volume, estruturas locais diferentes, duas fases que fluem, e um calor latente característico de uma transição de fase de primeira ordem. Por todas estas razões concluímos que o sistema simulado apresenta um transição líquido-líquido de primeira ordem. Adicionalmente foram realizadas compressões e expansões isotérmicas para temperaturas diferentes, observando que estes processos também apresentam histerese e que ela diminui com o aumento da temperatura, indicando assim a possível existência de um segundo ponto crítico e a finalização da transição líquido-líquido. Finalizamos o trabalho com a obtenção e a caracterização de uma possível nova fase cristalina do Gálio cuja estrutura ainda não tem sido obtida experimentalmente. Esta fase foi obtida por casualidade durante o estudo da existência de uma transição líquido-líquido no Gálio ao tencionar o Gálio a -1.6GPa. Sua estrutura é do tipo ortorrômbica com uma simetria Cmcm (grupo espacial 63) e sua principal diferença do Gálio-I é a orientação dos dímeros de Gálio, que nesta nova fase estão dispostos paralelamente. Simulações por DFT mostraram que esta nova fase é metaestável a pressão nula e chega a ser estável a pressões negativas abaixo de ~ 1.5GPa. / Abstract: Recently, the existence of a liquid-liquid transition in pure substances has been proposed as an explanation of anomalous behaviors such as the increase of response functions (isothermal compressibility, coefficient of thermal expansion, specific heat) with decreasing temperature displayed by some liquids. The existence of this type of transition has been demonstrated experimentally for phosphorous by X-ray diÿraction, and through atomistic simulations for water, silicon and carbon. The detailed understanding of this type of transition is closely related to the fundamental question of which physical factors control the properties of a liquid. Therefore, the study of this phenomenon is of great importance for the development of new technologies, the synthesis of new materials and the control of their properties. In this work, we carry out a series of atomistic simulations of a system containing 1152 Gallium atoms described by a semi-empirical Modified Embedded-Atom Model subject to periodic boundary conditions. By means of these simulations we search for a liquid-liquid transition in Gallium by means of a process of elimination of three theories. Initially we show that the limit of metastability of the superheated liquid has a decreasing monotonous behavior in the pressure-temperature phase diagram. Subsequently, our system presents hysteresis, a discontinuity in volume, two phases that have different local atomic structures and display diffusion, and a latent heat, all characteristic of a first-order phase transition. For all these reasons we conclude that the simulated system presents a liquid-liquid phase transition of first-order in the supercooled regime. In addition, we carried out several simulations of isothermal compressions and expansions for different temperatures. These results also show hysteresis although it is found to decrease with increasing temperature, thus indicating the possible existence of a second critical point at which the liquid-liquid transition ends. We finish our studies with the discovery and characterization of a crystalline phase of Gallium whose structure has not been observed experimentally. This phase was obtained by chance during the study of the existence of a liquid-liquid transition in Gallium under tension of -1.6GPa. Its structure is of the orthorhombic type with Cmcm symmetry (space group 63). Its main difference with respect to the Gallium-I phase is that in the new phase the Gallium dimers are disposed in a parallel fashion. Subsequent DFT simulations show that this new phase is metastable at zero pressure and predict it to become stable with respect to Gallium-I arrives at negative pressures below ~1.5GPa. / Mestrado / Física da Matéria Condensada / Mestre em Física

Desenvolvemos dois modelos estatísticos para água, nos quais diferentes aspectos de sua estrutura são considerados. O modelo geométrico permite diferentes números de coordenação. Em uma aproximação de campo médio mostramos que sob pressão o modelo apresenta linha de coexistência entre fases de baixa e alta densidade, e ponto crítico. A entropia das ligações de hidrogênio tem papel fundamental na definição da inclinação da linha de coexistência. O comportamento do modelo pode estar realcionado como segundo ponto crítico da água super resfriada e com transições líquido-líquido em geral.O modelo da água quadrada é uma versão térmica do modelo do gelo, no qual considera-se a direcionalidade das ligações de hidrogênio. O modelo foi estudado na rede de Bethe e através de simulações de Monte Carlo em três situações diferentes: para a água pura e na presença de solutos polares e apolares. A água quadrada pura não apresenta transição de fase. No modelo para solvente com solutos apolares, medidas de frequência relativa de ligações e do tempo de correlação mostram que o modelo apresenta estruturação da camada de hidratação. Medidas de correlação temporal no modelo de Ising mostram comportamento oposto. Em um estudo preliminar para uma solução com solutos que realizam ligações de hidrogênio não conseguimos encontrar diagramas de coexistência com círculo fechado, para o conjunto de parâmetros utilizados, possivelmente devido à ausência de buracos. / We have developed two statistical models for water in which different features of water structure are considered. In the geometrical model different coordination numbers are present and the model allows for translational disorder. A mean-field treatment shows that under pressure the model exhibits phases of different densities and a coexistence line ending in a critical point. Entropy of the hydrogen network plays an essential role in defining the slope of the coexistence line. The model behavior might be related with the second critical point in supercooled water and to liquid-liquid transitions in general. The square water model is a thermal version of the ice model, and takes into account the directionality of the hydrogen bonds. The model was studied on a Bethe lattice and through Monte Carlo simulations, for three different situations: as pure water and in the presence of polar and apolar solutes. Pure square water does not present a phase transition. In the presence of apolar solutes, first shell square water presents ordering, as shown from comparison of relative frequency of bonds, as well as from study of time correlations. The latter was shown to present opposite behavior in case of an Ising system. In a preliminary study for a solution of hydrogen bonding solutes we were unable to find a closed loop for the sets of parameters chosen. Vacancies might need to be included.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere. / Science, Faculty of / Chemistry, Department of / Graduate

Nous nous sommes intéressés à la description de la dynamique d'un liquide surfondu en étudiant un modèle qui repose sur un ingrédient simple. En partant d'un système de Lennard-Jones monodisperse dans le plan euclidien, nous avons ajouté de la frustration en courbant le plan de sorte à former une sphère de rayon arbitraire. A l'aide d'un algorithme de dynamique moléculaire sphérique, nous avons montré que ce système présentait bien une dynamique vitreuse d'équilibre, caractérisée par la fonction de diffusion intermédiaire incohérente $F_s(k,t)$, qui ralentit fortement et change de comportement à basse température, pour une faible variation de la statique. Le système se comporte comme un verre fort pour les courbures les plus grandes, mais sa fragilité augmente lorsque la courbure diminue. L'allure de $F_s(k,t)$ est également modifiée quand la courbure diminue, ce que nous avons essayé d'expliquer par l'étude de la théorie de couplages de modes (MCT) sur la sphère. Nous avons dérivé l'équation dynamique de MCT sphérique puis étudié la limite aux temps longs de sa solution. On obtient une transition dynamique qui est similaire à celle de la MCT euclidienne, ce qui ne permet pas d'expliquer l'effet de courbure sur $F_s(k,t)$, bien que celle-ci ait une influence sur la valeur de la température de transition. Enfin, nous nous sommes intéressés au rôle des "défauts", dont un nombre minimal de $12$ est imposé par la topologie. A basse température, les défauts tendent à se réunir en structures linéaires, ce qui est prévu théoriquement et observé dans certaines expériences. Les défauts ont une contribution importante à la relaxation, sans pour autant que l'influence des autres particules ne soit négligeable. / We are interested in the description of the dynamics of a supercooled liquid through the study of a model which relies on a simple geometrical ingredient. Starting from a monodisperse Lennard-Jones system on the euclidean plane, we add frustration by curving the space to form a sphere of arbitrary radius. Using a molecular dynamics algorithm, we showed that this system indeed behaves like a glassy liquid at equilibrium. The dynamics, caracterized by the self-intermediate scattering function $F_s(k,t)$, slows down strongly and changes shape at low temperature, for a small variation of the statics. The system behaves like a strong glass for high curvatures, but its fragility increases when the curvature decreases. The shape of $F_s(k,t)$ is also modified when the curvature decreases, which we tried to explain theoretically through the study of the mode coupling theory (MCT) on the sphere. We derived the dynamical equation of spherical MCT and studied the long time limit of its solution. We predict a dynamic transition similar to the one predicted by euclidean MCT, which does not allow us to explain the effect of curvature on $F_s(k,t)$, though the curvature has an influence on the value of the transition temperature. Finally, we studied the role of "defects", among which a minimal number of $12$ is imposed by topology. At low temperature, the defects tend to form linear structures, as predicted theoretically and observed in some experiments. The defects have a strong contribution in the relaxation; however, the role of other particles is not negligible.

Orientadores: Alex Antonelli, Maurice de Koning / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-18T18:03:40Z (GMT). No. of bitstreams: 1 CajahuaringaMacollunco_OscarSamuel_M.pdf: 6673580 bytes, checksum: a344f89389b318a79fb73ef903615a6b (MD5) Previous issue date: 2011 / Resumo: A física dos líquidos super-resfriados é um dos problemas para o qual ainda não existe uma única teoria que tenha capturado com sucesso todas as características destes materiais, principalmente a origem da dinâmica complexa, e também a possível ocorrência de transições líquido-líquido nesse regime. Nosso trabalho está focado nas propriedades dinâmicas do gálio, que é evidenciada pelas funções de correlação temporais antes e depois da transição de fase líquido-líquido. Primeiro, foram feitas simulações atomísticas no gálio através de dinâmica molecular usando o modied embedded atom model (MEAM) e condições periódicas de contorno em uma super-célula contendo 1152 átomos, com o propósito de mostrar a transição de fase líquido-líquido obtida em recentes pesquisas teóricas. Para estudar a dinâmica do sistema como um todo, calculamos o deslocamento quadrático médio, que revela o platô em tempos intermediários, o qual se torna mais notório após a transição líquido-líquido. Esse comportamento pode ser originado por uma dinâmica espacialmente homogênea ou uma dinâmica espacialmente heterogênea. Para saber qual das duas hipóteses é mais relevante foi medido o parâmetro não-gaussiano de ordem 2, porque este nos fornece informação do grau de heterogeneidade dinâmica do sistema, e que mostrou que nosso sistema possui uma dinâmica heterogênea. Posteriormente, foi calculada a auto-função intermediária de espalhamento usando o método da transformada rápida de Fourier que é mas eciente para tempos de correlação longos. Esta função fornece a correlação na densidade de partículas no espaço recíproco, que mostra também um platô em tempos intermediários. Com o fim de analisar como relaxa cada partícula, baseados na ideia da dinâmica espacialmente heterogênea, foi possível separar as partículas pela sua dinâmica em dois grupos, um grupo que possui a dinâmica mais difusiva e outro que possui a dinâmica menos difusiva. Finalmente, foram caracterizados estruturalmente esses dois grupos e, comparando-os com as funções estruturais do sistema todo, concluímos que as duas fases presentes no líquido depois da transição, o líquido de alta densidade possui uma dinâmica mais difusiva e o líquido de baixa densidade possui uma dinâmica menos difusiva. Foi possível com estes resultados identicar espacialmente as duas fases líquidas e observar claramente os seus próprios domínios e que estes não estão misturados / Abstract: The physics of supercooled liquids still lacks a single theory which can successfully capture all features of these materials, mainly the cause for their complex dynamics and the possibility of liquid-liquid phase transitions in this regime. Our work is focused on the dynamics of liquid gallium, which was investigated through the correlation functions before and after the liquid-liquid phase transition. First, atomistic simulations were performed using the modied embedded atom model (MEAM) and periodical boundary conditions in a 1152-atom supercell, in order to obtain the liquid-liquid phase transition observed in recent previous simulations. To study the dynamics of the whole system, we calculate the mean square displacement, which shows the plateau for intermediate times that becomes much more noticeable after the liquidliquid transition. This behavior can be caused by either a spatially homogeneous dynamics or a spatially heterogeneous dynamics. In order to find out which hypothesis is more relevant for our case, the second order non-Gaussian parameter was determined, since it provides the degree of heterogeneity of the dynamics of the system, showing that system exhibits a heterogeneous dynamics. Later, the self-intermediate scattering function was calculated using the fast Fourier transform method, which is more ecient for long correlation times. This function gives the density particle correlation in reciprocal space, showing a plateau in intermediate times as well. In order to analyze how each particle relaxes, based on the idea of a spatially heterogeneous dynamics, it was possible to gather the particles according to their mobility in two groups, one which has a more diffuse dynamics and another which has a less diffuse dynamics. Finally, these two groups were structurally characterized and by comparing them with the structural functions of the whole system, it was possible to determine that the liquid of higher density has a more diffusive dynamics, whereas the lower density liquid has less diffusive dynamics. From these results we were able to spatially identify the two liquid phases, which clearly display their own domains that do not mix with each other / Mestrado / Física da Matéria Condensada / Mestre em Física

This master‘s thesis contains a comprehensive laboratory task about saving a heat energy with a use of changing a state of matter. The thesis is written for the object Chosen passages of renewable resources and saving a heat energy. Part one presents a theoretical part of the topic, terminology and relations needed to make this laboratory work. It also contains a created procedure of partial tasks necessary to take laboratory measurements. The second part of the thesis is about measuring and evaluation of acquired values according to procedure described in the theoretical part of the thesis. Different variations considered during the creation of measuring procedure are also named here. The final part of the thesis describes a laboratory equipment necessary to complete the task and an example of filled protocol is attached.

No description available.

This thesis, which contains fourteen chapters in two parts, presents theoretical and computer simulation studies of dynamics in supercooled liquids and thermotropic liquid crystals. These two apparently diverse physical systems are unified by a startling similarity in their complex slow dynamics. Part I consists of six chapters on supercooled liquids while Part II comprises seven chapters on thermotropic liquid crystals. The fourteenth chapter provides a concluding note. Part I starts with an introduction to supercooled liquids given in chapter 1. This chapter discusses basic features of supercooled liquids and the glass transition and portrays some of the theoretical frameworks and formalisms that are widely recognized to have contributed to our present understanding. Chapter 2 introduces a new model of binary mixture in order to study dynamics across the supercooled regime. The system consists of an equimolar mixture of the Lennard-Jones spheres and the Gay-Berne ellipsoids of revolution, and thus one of its components has orientational degrees of freedom (ODOF). A decoupling between trans-lational diffusion and rotational diffusion is found to occur below a temperature where the second rank orientational correlation time starts showing a steady deviation from the Arrhenius temperature behavior. At low temperatures, the optical Kerr effect (OKE) signal derived from the system shows a short-to-intermediate time power law decay with a very weak dependence on temperature, if at all, of the power law exponent as has been observed experimentally. At the lowest temperature investigated, jump motion is found to occur in both the translational and orientational degrees of freedom. Chapter 3 studies how the binary mixture, introduced in the previous chapter, explores its underlying potential energy landscape. The study reveals correlations between the decoupling phenomena, observed almost universally in supercooled molecular liquids, and the manner of exploration of the energy landscape of the system. A significant deviation from the Debye model of rotational diffusion in the dynamics of ODOF is found to begin at a temperature at which the average inherent structure energy of the system starts falling as the temperature decreases. Further, the coupling between rotational diffusion and translational diffusion breaks down at a still lower temperature, where a change occurs in the temperature dependence of the average inherent structure energy. Chapters 4-6 describe analytical and numerical approaches to solve kinetic models of glassy dynamics for various observables. The β process is modeled as a thermally activated event in a two-level system and the a process is described as a β relaxation mediated cooperative transition in a double-well. The model resembles a landscape picture, conceived by Stillinger [Science 267, 1935 (1995)], where the a process is assumed to involve a concerted series of the β processes, the latter being identified as elementary relaxations involving transitions between contiguous basins. For suitable choice of parameter values, the model could reproduce many of the experimentally observed features of anomalous heat capacity behavior during a temperature cycle through the glass transition as described in chapter 4. The overshoot of the heat capacity during the heating scan that marks the glass transition is found to be caused by a delayed energy relaxation. Chapter 5 shows that the model can also predict a frequency dependent heat capacity that reflects the two-step relaxation behavior. The high-frequency peak in the heat capacity spectra appears with considerably larger amplitude than the low-frequency peak, the latter being due to the a relaxation. The model, when simplified with a modified description of the a process that involves an irreversible escape from a metabasin, can be solved analytically for the relaxation time. This version of the model captures salient features of the structural relaxation in glassy systems as described in chapter 6. In Part II, thermotropic liquid crystals are studied in molecular dynamics simulations using primarily the family of the Gay-Berne model systems. To start with, chapter 7 provides a brief introduction to thermotropic liquid crystals, especially from the perspective of the issues discussed in the following chapters. This chapter ends up with a detail description of the family of the Gay-Berne models. Chapter 8 demonstrates that a model system for calamitic liquid crystal (comprising rod-like molecules) could capture the short-to-intermediate time power law decay in the OKE signal near the isotropic-nematic (I-N) phase transition as observed experimentally. The single-particle second rank orientational time correlation function (OTCF) for the model liquid crystalline system is also found to sustain a power law decay regime in the isotropic phase near the I-N transition. On transit across the I-N phase boundary, two power law decay regimes, separated by a plateau, emerge giving rise to a step-like feature in the single-particle second rank OTCF. When the time evolution of the rotational non-Gaussian parameter is monitored as a diagnostic of spatially heterogeneous dynamics, a dominant peak is found to appear following a shoulder at short times, signaling the growth of pseudonematic domains. These observations are compared with those relevant ones obtained for the supercooled binary mixture, as discussed in chapter 2, in the spirit of the analogy suggested recently by Fayer and coworkers [J. Chem. Phys. 118, 9303 (2003)]. In chapter 9, orientational dynamics across the I-N transition are investigated in a variety of model systems of thermotropic liquid crystals. A model discotic system that consists of disc-like molecules as well as a lattice system have been considered in the quest of a universal short-to-intermediate time power law decay in orientational relaxation, if any. A surprisingly general power law decay at short to intermediate times in orientational relaxation is observed in all these systems. While the power law decay of the OKE signal has been recently observed experimentally in calamitic systems near the I-N phase boundary and in the nematic phase by Fayer and coworkers [J. Chem. Phys. 116, 6339 (2002), J. Phys. Chem. B 109, 6514 (2005)], the prediction for the discotic system can be tested in experiments. Chapter 10 presents the energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals by determining the inherent structures of a family of one-component Gay-Berne model systems. This study throws light on the interplay between the orientational order and the translational order in the mesophases the systems exhibit. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures. The inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the I-N transition and this breakdown is found to occur at a temperature below which the system explores increasingly deeper potential energy minima. There exists a remarkable similarity in the manner of exploration of the potential energy landscape between the Gay-Berne systems studied here and the well known Kob-Andersen binary mixture reported previously [Nature, 393, 554 (1998)]. In search of a dynamical signature of the coupling between orientational order and translational order, anisotropic translational diffusion in the nematic phase has been investigated in the Gay-Berne model systems as described in chapter 11. The translational diffusion coefficient parallel to the director D// is found to first increase and then decrease as the temperature drops through the nematic phase. This reversal occurs where the smectic order parameter of the underlying inherent structures becomes significant for the first time. The non-monotonic temperature behavior of D// can thus be viewed from an energy landscape analysis as a dynamical signature of the coupling between orientational and translational order at the microscopic level. Such a view is likely to form the foundation of a theoretical framework to explain the anisotropic translation diffusion. Chapter 12 investigates the validity of the Debye model of rotational diffusion near the I-N phase boundary with a molecular dynamics simulation study of a Gay-Berne model system for calamitic liquid crystals. The Debye model is found to break down near the I-N phase transition. The breakdown, unlike the one observed in supercooled molecular liquids where a jump diffusion model is often invoked, is attributed to the growth of orientational pair correlation. A mode-coupling theory analysis is provided in support of the explanation. Chapter 13 presents a molecular dynamics study of a binary mixture of prolate ellipsoids of revolution with different aspect ratios interacting with each other through a generalized Gay-Berne potential. Such a study allows to investigate directly the aspect ratio dependence of the dynamical behavior. In the concluding note, chapter 14 starts with a brief summary of the outcome of the thesis and ends up with suggestion of a few relevant problems that may prove worthwhile to be addressed in future.

Icing severely affects society, especially in the Nordic countries. Iceaccumulation can result in critical performance problems and safetyconcerns for instance in road, air and sea transportation, transmissionlines, marine and offshore structures, wind turbines and heat exchangers.Present active ice-combating approaches possess environmental,efficiency and cost drawbacks. Thus, fabricating icephobic surfaces orcoatings impeding ice formation (anti-icing), but facilitating ice removal(de-icing) is desired. However, different conditions in the environmentduring ice formation and growth add to the complexity of the problem.An icephobic surface that works for a certain application might not be agood candidate for another. These surfaces and the challenges are infocus in this thesis.Wetting properties are important for ice formation on surfaces fromthe liquid phase (often supercooled water), where the water repellency ofthe surfaces could enhance their anti-icing effect. Considering this,different hydrophobic and superhydrophobic surfaces with differentchemistry, morphology and roughness scale were prepared. Since anyinduced wetting state hysteresis on hydrophobic surfaces could influencetheir performance, the wetting stability was investigated. In particulardynamic wetting studies of the hydrophobic surfaces revealed whatsurface characteristics benefit a stable wetting performance. Further, theeffect of temperature, particularly sub-zero temperatures, on the wettingstate of flat and nanostructured hydrophobic surfaces was investigated.This was complemented with studies of the wetting stability of sessilewater droplets on flat to micro- and multi-scale (micro-nano) roughhydrophobic samples in a freeze-thaw cycle. To be consistent with mostapplications, all temperature-controlled experiments were performed inan environmental condition facilitating frost formation. Further, antiicingproperties of hydrophobic surfaces with different topography butsimilar chemistry were studied by freezing delay measurements.A dynamic wetting study using hydrophobic samples with similarchemistry but different topography revealed that multi-scale roughnesscould benefit the wetting stability. However, when these surfaces areutilized at low temperatures the wetting hysteresis observed during acooling/heating cycle is significant. Such a temperature-inducedhysteresis is also significant on superhydrophobic surfaces. I attributethis to condensation followed by frost formation facilitating spreading of  the supercooled water droplet. The freezing delay measurementsdemonstrate no significant effect of surface topography on anti-icingproperties of hydrophobic surfaces, however the flat surfaces showed thelongest delay. These findings are in agreement with heterogeneous icenucleation theory, suggesting preferential ice nucleation in concave sites,provided they are wetted.In the second part of this thesis, I consider the findings from theprevious part illustrating the limitations of (super)hydrophobic surfaces.The de-icing properties of hydrophilic surfaces with a hydration waterlayer, hypothesized to lubricate the interface with ice, were studied. Heretemperature-controlled shear ice adhesion measurements, down to -25oC, were performed on an adsorbed layer of a polymer, either bottle-brushstructured poly(ethylene oxide) or linear poly(ethylene oxide). The iceadhesion strength was reduced significantly on the bottle-brushstructured polymer layer, specifically at temperatures above -15 oC,whereas less adhesion reduction was observed on the layer formed by thelinear polymer. These findings are consistent with differential scanningcalorimetry (DSC) data, demonstrating that the hydration water, boundto the bottle-brush structured polymer, is in the liquid state at thetemperatures where de-icing benefit is observed. Further, continuingwith the hypothesis of the advantage of surfaces with a natural lubricantlayer for de-icing targets, I studied shear ice adhesion on the molecularlyflat basal plane of hydrophilic mica down to -35 oC. Interestingly, ultralowice adhesion strength was measured on this surface. I relate this to theproposed distinct structure of the first ice-like but fluid water layer onmica, with no free OH groups, followed by more bulk liquid-like layers.This combined with the molecularly smooth nature of mica results in aperfect plane for ice sliding. / Isbildning har en stark inverkan på samhället, speciellt i de nordiskaländerna. Isuppbyggnad kan resultera i kritiska prestandaproblem ochsäkerhetsrisker inom t.ex. väg-, luft-, och sjötransport, kraftledningar,marina- och offshorestrukturer, vindkraftverk och värmeväxlare.Nuvarande aktiva isbekämpningsmetoder uppvisar brister i avseende påmiljö, effektivitet och kostnad. Det finns därmed ett behov av attframställa ytor eller ytbeläggningar som förhindrar isbildning (antiisning)eller underlättar borttagandet av redan bildad is (avisning). Dockkompliceras problemet av de många olika förhållanden under vilka is kanbildas. En beläggning som fungerar för en viss tillämpning behöver intenödvändigtvis vara en bra kandidat för en annan. Dessa ytor ochutmaningar relaterade till dem är i fokus i denna avhandling.Vätningsegenskaper är viktiga för isbildning på ytor från vätskefas(ofta underkylt vatten), och det har visats att vattenavstötande ytor i vissasammanhang kan motverka isbildning. Med detta i åtanke framställdesolika hydrofoba och superhydrofoba ytor, med varierande kemi,morfologi och ytråhet. Eftersom en förändring i de hydrofoba ytornasvätningsegenskaper kan påverka deras funktion studerades vätningsstabilitetenför dessa ytor. I synnerhet dynamiska vätningsstudier av dehydrofoba ytorna avslöjade vilka ytegenskaper som är fördelaktiga förvätningsstabiliteten. Vidare studerades hur temperaturen, särskilt undernoll grader, påverkar vätningstillståndet på släta och nanostruktureradehydrofoba ytor. Arbetet kompletterades med studier av vätningsstabilitetenför vattendroppar på släta samt mikro- och multistrukturerade(mikro-nano) hydrofoba ytor under flera frysningsupptiningscykler.För att vara i linje med de flesta tillämpningar, utfördesalla temperaturkontrollerade mätningar i en miljö där frost kunde bildaspå ytorna. Anti-isegenskaperna hos de hydrofoba ytorna med varierandetopografi men samma kemi studerades vidare genom att studera hur långtid det dröjde innan en vattendroppe på ytan fryste vid en visstemperatur.De dynamiska vätningsstudierna på hydrofoba ytor med samma kemimen olika topografi avslöjade att en ytråhet på flera längdskalor kan haen positiv inverkan på vätningsstabiliteten. När dessa ytor är exponeradeför låga temperaturer är dock vätningshysteresen under en nedkylnings-/uppvärmnings-cykel significant. Den temperatur-inducerade hysteresenär också betydande för superhydrofoba ytor. Detta tillskriver jag  kondensation på ytan som följs av frostbildning, vilket i sin tur möjliggörspridning av den underkylda vattendroppen på ytan. Mätning avfördröjningen i frysningsförloppet påvisade ingen betydande effekt avyttopografin för hydrofoba ytor, men släta hydrofoba ytor uppvisade denlängsta fördröjningen. Dessa resultat är i överensstämmelse med rådandeheterogen iskärnbildningsteori, som visar på fördelaktig iskärnbildningpå konkava delar av ytan, förutsatt att dessa väts.I den andra delen av avhandlingen utnyttjar jag observationerna frånden första delen vilka illustrerade begränsningarna för superhydrofobaytor, och söker en annan lösning. Avisningsegenskaper för hydrofilastarkt hydratiserade ytor studerades, med hypotesen att hydratiseringkan smörja gränsskiktet med is. Temperatur-kontrolleradeisadhesionsmätningar ned till -25 °C utfördes på adsorberade skikt av enpolymer med många sidokedjor av polyetylenoxid (”bottle-brush”), såvälsom på ett skikt av linjär polyetylenoxid. Isadhesionen blev kraftigtreducerad på ”bottle-brush”-polymeren, speciellt vid temperaturer högreän -15°C. Däremot kunde knappast ingen minskad isadhesion observerasför den linjära polymeren. Dessa observationer överensstämmer meddifferentialskanningskalorimetri (DSC) data, som visar att dethydratiserade vattenskiktet, vilket är bundet till ”bottle-brush”-polymeren, är i vätskeform vid de temperaturer där avisningsfördelar ärobserverade. För att vidare undersöka hypotesen att det vore fördelaktigtmed ett naturligt smörjande skikt på ytan för att uppnå godaavisningsegenskaper, utförde jag isadhesionsmätningar på molekylärtsläta glimmerytor ner till -35 °C. Intressant nog uppmättes extremt lågisadhesion på denna yta. Detta relaterar jag till den föreslagna utprägladehydratiseringsstrukturen, bestående av ett första is-liknande vattenskiktutan fria OH-grupper, följt av ett mer bulkliknande skikt. Detta ikombination med den molekylärt släta naturen hos glimmer resulterar iett perfekt plan för isen att glida på. / <p>QC 20160504</p> / TopNano