At Zwartbas, about 10 km west of Vioolsdrif, southern Namibia, the Dwyka succession is composed of tillites and distal fossiliferous dropstone-bearing glacio-marine shales. The completely exposed Dwyka succession is interbedded with thin bentonites, altered distal pyroclastic deposits, which were derived from the magmatic arc at the southern rim of Gondwana. Dropstone-bearing and dropstonefree sequences intercalate with four diamictites, of which the two lowest were certainly recognised as tillites. Four events of deglaciation were proven at Zwartbas and thus consist with correlative deposits in southern Africa. Numerous fossilised fishes, trace fossils, and plant fragments appear frequently within the lower half of the Dwyka succession whereas trace fossils were principally found in the complete succession. Although the environmental determination is quite problematic, the fossil assemblage rather implies proximal, shallow water conditions with temporary restricted oxygenation. The hinterland was covered with considerable vegetation, which points to a moderate climate. Water salinity determinations based on shale geochemistry rectify contrary palaeontological results and point to rather brackish or non-marine conditions in comparison to present-day salinites. Geochemical analyses of the bentonites relate the pyroclastic deposits with acid to intermediate source magmas, as they are known from the magmatic arc in present-day Patagonia. Tectono-magmatic comparisons furthermore emphasise a syn-collision or volcanic-arc situation of the magma source. However, significant cyclicity in the production of the pyroclastic deposits was not observed. Radiometric age determinations of two tuff beds clearly date the onset of glacial activity into the Late Carboniferous.

The locality of Zwartbas is situated at the border of Namibia and South Africa about 15 km west of Noordoewer. The mapped area is confined by the Tandjieskoppe Mountains in the north and the Orange River in the south. Outcropping rocks are predominantly sediments of the Nama Group and of the Karoo Supergroup. During the compilation of this paper doubts arose about the correct classification of the Nama rocks as it is found in literature. Since no certain clues were found to revise the classification of the Nama rocks, the original classification remains still valid. Thus the Kuibis and Schwarzrand Subgroup constitute the Nama succession and date it to Vendian age. A glacial unconformity represents a hiatus for about 260 Ma. This is covered by sediments of the Karoo Supergroup. Late Carboniferous and early Permian glacial deposits of diamictitic shale of the Dwyka and shales of the Ecca Group overlie the unconformity. The shales of the Dwyka Group contain fossiliferous units and volcanic ash-layers. A sill of the Jurassic Tandjiesberg Dolerite Complex (also Karoo Supergroup) intruded rocks at the Dwyka-Ecca-boundary. Finally fluvial and aeolian deposits and calcretes of the Cretaceous to Tertiary Kalahari Group and recent depositionary events cover the older rocks occasionally. / Die Lokalität Zwartbas liegt an der namibisch-südafrikanischen Grenze, etwa 15 km westlich von Noordoewer. Das Kartiergebiet wird durch die Tandjiesberge im Norden und den Oranje Fluß im Süden begrenzt. Die anstehenden Gesteine bestehen hauptsächlich aus Sedimenten der Nama Gruppe und der Karoo Supergruppe. Während der Erarbeitung dieser Abhandlung entstanden Zweifel an der Klassifikation der Nama Gesteine, so wie sie in der Literatur zu finden ist. Da keine sicheren Hinweise zur Revision der Klassifikation der Nama Gesteine gefunden wurden, bleibt die ursprünglich Klassifikation jedoch gültig. Die Kuibis und Schwarzrand Untergruppe bilden also die Nama Abfolge und datieren sie ins Vendian. Eine glaziale Diskontinuität repräsentiert einen Hiatus von etwa 260 Mio Jahren. Sie wird überlagert von Sedimenten der Karoo Supergruppe. Spät-karbone und früh-permische glaziale Ablagerungen von diamiktitischen Tonsteinen der Dwyka Gruppe und Tonsteine der Ecca Gruppe liegen über dieser Diskontinuität. Die Sedimente der Dwyka Gruppe sind fossilführend und enthalten Tufflagen. Ein Sill des jurassischen Tandjiesberg Dolerit Komplex (auch Karoo Supergruppe) intrudierte in die Gesteine an der Dwyka-Ecca Grenze. Schließlich bedecken lokal fluviatile und äolische Ablagerungen und Kalkkrusten der kretazischen und tertiären Kalahari Gruppe und jüngerer Ablagerungsereignisse die älteren Gesteine.

Bei der geologischen Landesaufnahme im VEB Geologische Forschung und Erkundung Freiberg sind 1965 systematische palynologische Arbeiten an sächsischen Mooren begonnen und bis 2006 im Landesamt für Umwelt und Geologie fortgesetzt worden. Diese bislang nicht publizierten Arbeiten von Maria Seifert-Eulen werden nun der Öffentlichkeit zugänglich gemacht und für paläobotanische, stratigrafische, paläoklimatische und geschichtliche Fragestellungen zur Verfügung gestellt. Die Broschüre enthält außerdem die Analyse eines interdisziplinären Bearbeiterteams zum Zustand der heutigen Moore in Sachsen und neue Informationen zur Ausdehnung elstereiszeitlicher Gletscher im Vorfeld des Erzgebirges. Redaktionsschluss: 30.09.2016

There exist various glacial units in the Neoproterozoic strata of southern Namibia (Kalahari Craton). They were recognised and discussed in the scientific literature for at nearly 100 years (e.g. Coleman, 1926; Gevers, 1931; Schwellnuss, 1941; Martin, 1965). The Snowball Earth theory (Hoffman et al., 1998) had an huge impact on Neoproterozoic geosciences and especially outcrops of the Otavi Group in northern Namibia helped to strengthen and support this idea. Nevertheless, the Neoproterozoic glacial horizons in southern Namibia were difficult to interpret and even more difficult to correlate, due to their tectonic overprint and their scarce outcrops. In order to correlate and differentiate the various Neoproterozoic glacial units of southern Namibia (western rim of Kalahari Craton) a multi‐method approach based on isotopic analyses on zircon grains, whole rock geochemistry, grain size measurements combined with extensive field work, mapping and sampling was applied. In total, ten sections were mapped and measured from which 33 samples were chosen for further analyses. Two of these samples represent local basement rocks, 19 the siliciclastic Neoproterozoic sedimentary cover including glacial diamictites, and twelve carbonate samples. 3474 single zircon grains were picked and measured for their dimensions (width and length). Of those, 2404 zircons were analysed with LA‐ICP‐MS techniques for their U‐Pb and Th‐U ratios in order to calculate detrital zircon ages and to obtain information about the source magma. 1535 of those gave concordant ages (90‐110 % of concordance). Further, selected zircon grains (in total 346) with concordant U‐Pb ages were analyses for their εHf(t) values. To gather more information and to be able to provide absolute ages for the Neoproterozoic glacial units the new technique of LAICP‐MS U‐Pb dating on carbonate samples was tested and gave reliable results for ten out of twelve samples (representing seven different sample locations). Field work revealed two sections containing the Sturtian as well as the Marinoan glacial diamictites in relatively undisturbed succession that qualified as reference profiles for Neoproterozoic strata in southern Namibia: the Dreigratberg and the Namuskluft section in the Gariep Belt close to the Orange River. All analysed samples contain a very similar detrital zircon isotopic record and the whole rock geochemical analyses confirm this interpretation. All siliciclastic samples show a general felsic provenance, with zircon ages mainly divided into two age groups (Mesoproterozoic 1.0 – 105 Ga and Palaeoproterozoic 1.7 – 2.1 Ga), reflecting four different growth and recycling events of Mesoproterozoic to Archaean crustal units. The samples have a geochemical signature of continental island arc and the zircon grain dimensions (width vs. length) are also very similar for all samples. Direct age dating of the samples based on detrital zircons was not possible caused by the lack of ages reflecting deposition times. Nevertheless, the most important differences between the various glacial horizons were found in petrographic features (diamictite pebble contents) and the age peak shift of detrital zircon U‐Pb ages (P/M ratio). Based on these and the two reference profiles correlations to other sections were achievable and the differentiation of four distinct Neoproterozoic glacial horizons for southern Namibia was possible. Furthermore, these new results provide new insights into the Neoproterozoic Gariep Belt formation comprising Tonian rifting events, Cryogenian formation of the Arachania Terrane and final Ediacaran collision of the Rio de la Plata and Kalahari cratons. The combination of all results reflects a continuous sedimentary recycling on the western Kalahari Craton. Comparison and statistical similarity tests based on zircon age data bases for possible source areas defined the Namaqua Natal and Gariep belts as the most likely sedimentary source areas, providing the rock material that got recycled for at least 200 Ma from Kaigas glaciation at ca. 750 Ma to Vingerbreek glaciation at ca. 550 Ma. In addition, the lack of exotic detrital zircon ages within the two Snowball Earth events of this study suggests the interpretation of none or only very minor glacial movement confirming the idea of a completely ice‐covered Earth. The assumed Sturtian and Marinoan ages of Numees Fm and Namaskluft Mbr diamictites were confirmed by the results of U‐Pb cap carbonate dating. Based on these, a minimum duration of ca. 8 Ma for the Sturtian and of ca. 14 Ma for the Marinoan glaciation can be assumed.:Abstract Kurzfassung Contents List of Figures List of Tables List of abbreviations Scientific question and thesis structure 1 Introduction 1.1 The Neoproterozoic era: Supercontinent dispersal and global glaciations 1.1.1 Rodinia supercontinent: Formation, dispersal, and location of Kalahari Craton 1.1.2 Glacial events during the Neoproterozoic era 1.1.2.1 A brief history on the discovery of Snowball Earth events 1.1.2.2 Formation and termination of a Snowball Earth event: The Snowball Earth flow chart 1.1.2.3 Hypotheses for cap carbonate formation 1.1.2.4 Survival of life during a Snowball Earth event 1.2 The Kalahari Craton 1.2.1 Evolution of the Kalahari Craton 1.3 Overview over the Geology of Namibia under special consideration of southern Namibia (Kalahari Craton) 2 Characteristics of southern Namibian Neoproterozoic glacial samples and sides 3 The problematic correlations of Neoproterozoic glacial deposits of the Kalahari Craton (southern Namibia) 4 Methods 4.1 Field work 4.2 Whole Rock geochemical analyses 4.3 Heavy mineral separation and SEM analyses on zircon grains of siliciclastic samples 4.4 Zircon grain size analyses 4.5 LA‐ICP‐MS analyses on zircon grains 4.5.1 U‐Pb analyses with LA‐SF‐ICP‐MS 4.5.2 Th‐U ratio determination on zircon grains 4.5.3 Hf‐isotope measurements with LA‐MS‐ICP‐MS 4.6 LA‐ICP‐MS U‐Pb dating on carbonates 4.7 Provenance interpretations and likeness tests based on zircon U‐Pb age data bases 5 Study I: “The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton, Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana” 5.1 Introduction and geological setting 5.2 Samples and methods 5.3 Results 5.4 Discussion and interpretation 5.5 Summary 6 Study II: “The four Neoproterozoic glaciations of southern Namibia and their detrital zircon record: The fingerprints of four crustal growth events during two supercontinent cycles” 6.1 Introduction 6.2 The samples 6.3 Methods 6.4 Results 6.5 Interpretation and discussion 6.6 Conclusion/Summary 7 Study III: “Correlation of Neoproterozoic diamictites in southern Namibia” 7.1 Introduction 7.2 Sample sites 7.2.1. The Kaigas and Sturtian Numees diamictites at the Orange River section 2.1.1. Outcrops of the Kaigas Fm diamictites 7.2.1.2 Outcrop of the Numees Fm diamictites (Sturtian) 7.2.2 The Sturtian diamcitite of the Blaubeker Fm (Witvlei Grp) at the farmgrounds Blaubeker and Tahiti 7.2.2.1 The Blaubeker diamictite at Blaubeker Farm (type locality) 7.2.2.2 The Blaubeker diamictite at Tahiti Farm (Gobabis‐syncline) 7.2.2.3 Correlation of Blaubeker diamictite at Blaubeker and Tahiti farms 7.2.3 The Sturtian diamictite at the Trekpoort Farm section 7.2.4 The Sturtian and Marinoan diamictites at Namuskluft section (reference profile) 7.2.5 The Sturtian and Marinoan diamictites at Dreigratberg section 7.2.6 Sturtian diamictite and Marinoan‐type cap carbonate at Dreigratberg North section 7.2.7 The Marinoan diamictite at the Witputs Farm section 7.2.8 The post‐Gaskiers Vingerbreek diamictite 7.2.8.1 The Vingerbreek diamictite along the Orange River 7.2.8.2 The Vingerbreek diamictite at Tierkloof Farm (Klein Karas Mountains) 7.3 Methods 7.4 Data and Results 7.4.1 Results of the U‐Pb detrital zircon data 7.4.2 Results of the U‐Pb carbonate dating 7.4.3 Results of zircon grain width and length measurements 7.4.4 Results of the Th‐U zircon ratios 7.4.5 Results of Lu‐Hf isotopic measurements 7.4.6 Geochemical results of the siliciclastic and basement samples 7.4.7 Geochemical results of the carbonate samples 7.5 Discussion and Conclusion 8 Sediment provenance and Snowball Earth ice dynamics 9 Implications on the evolution of the Gariep Belt 10 Conclusions and outlook 11 References Supplementary Material / Die neoproterozoischen Einheiten des südlichen Namibias (Kalahari Kraton) umfassen verschiedene glaziale Einheiten, die schon seit fast 100 Jahren bekannt sind und wissenschaftlich beschrieben wurden (z.B. Coleman, 1926; Gevers, 1931; Schwellnuss, 1941; Martin, 1965). Die Schneeball Erde Theorie (Hoffman et al., 1998) hatte einen enormen Einfluss auf die geologischen Studien des Neoproterozoikums, wobei besonders Aufschlüsse der Otavi Gruppe Nordnamibias die Theorie stärken und bestätigen. Im Gegensatz dazu sind neoproterozoische glaziale Horizonte Südnamibias aufgrund ihrer tektonischen Überprägung und der wenigen Aufschlüsse schwer zu interpretieren und zu korrelieren. Mit dem Ziel, die neoproterozoischen glazialen Einheiten Südnamibias zu unterscheiden und zu korrelieren, wurde ein Multimethodenansatz basierend auf Isotopenanalysen an Zirkonmineralen, Gesamtgesteinsgeochemie, Mineralkorngrößenmessungen und intensiver Feldarbeit angewandt. Insgesamt wurden zehn Profile kartiert und vermessen, von denen 33 Proben zur weiteren Analyse ausgewählt wurden. Zwei dieser Proben stammen vom lokalen Grundgebirge, 19 aus den sedimentären Einheiten darüber (inklusive der glazialen Ablagerungen) und zwölf repräsentieren Karbonatgesteinsproben. 3474 Einzelzirkone wurden hinsichtlich ihrer Breite und Länge vermessen, wovon 2404 Minerale mittels LA‐ICP‐MS nach ihren U‐Pb und Th‐U‐Gehalten analysiert wurden. 1535 dieser Minerale ergaben konkordante Alter (90 – 110% Konkordanz). Darüber hinaus wurden von 346 ausgewählten konkordanten Zirkonen die εHf(t) Werte bestimmt. Um das Datenset zu vervollständigen wurden LA‐ICP‐MS U‐Pb Analysen an Karbonatgesteinen an zehn von zwölf Proben erfolgreich getestet. Im Zuge der Feldarbeiten kristallisierten sich zwei Profile nahe des Oranje heraus, welche die Sturtian und die Marinoan Vereisung in nahezu ungestörter Lagerung enthalten und sich deshalb als Referenzprofile qualifizieren. Alle analysierten Proben zeichnen sich durch sehr ähnliche Zirkonisotopenwerte aus, was durch die Gesamtgesteinsgeochemieanalysen weiterhin bestätigt wird. Alle siliziklastischen Proben zeigen eine generelle felsische Provenienz mit Zirkonaltern welche sich hauptsächlich in zwei Altersgruppen unterteilen lassen (mesoproterozoisch 1.0 – 1.5 Mrd Jahre, paläoproterozoisch 1.7 – 2.1 Mrd Jahre). Diese reflektieren vier verschiedene krustale Entwicklungsstadien vom Mesoproterozoikum bis Archaikum. Die geochemische Signatur aller Proben deutet auf einen kontinentalen Inselbogen hin und auch die Zirkonmineralgrößen sind für alle Proben ähnlich. Eine direkte Altersdatierung auf Grundlage der detritischen Zirkone war aufgrund fehlender junger Alter nicht möglich. Dennoch ist eine Unterscheidung der glazialen Schichten Südnamibias basierend auf den petrographischen Eigenschaften und dem sich verschiebenden Alterstrend der detritischen Zirkone möglich (P/M Verhältnis). In Kombination mit den zwei Referenzprofilen ist eine umfassende Korrelation aller untersuchten Profile möglich und die Unterscheidung von vier Neoproterozoischen glazialen Schichten in Namibia gelungen. Die Ergebnisse geben weitere Einblicke in die neoproterozoische Entwicklung des Gariep Gürtels, welcher durch Riftvorgänge im Tonium, die Bildung des Arachania Terranes während des Cryogeniums und die ediakarische finale Kollision zwischen den Rio de la Plata und Kalahari Kratonen geprägt ist. Die Kombination aller Ergebnisse zeigt ein kontinuierliches Sedimentrecycling auf dem westlichen Kalahari Kraton. Vergleiche und statistische Ähnlichkeitsanalysen basierend auf U‐Pb Zirkonalterdatenbanken ergaben, dass der Namaqua Natal und der Gariep Gürtel die wahrscheinlichsten Liefergebiete sind. Das Recycling fand für mindestens 200 Millionen Jahre zwischen der Kaigas Vereisung (etwa vor 750 Millionen Jahren) und der Vingerbreek Vereisung (etwa vor 550 Millionen Jahren) statt. Darüber hinaus zeigt das Fehlen fremder Zirkonalter für die Schneeball Erde Proben, dass sich die Eispanzer kaum oder nur sehr wenig bewegt haben können, was die Theorie einer komplett zugefrorenen Erde unterstützt. Die Ergebnisse der U‐Pb Karbonatgesteinsdatierungen bestätigen des angenommene Sturtian und Marinoan Alter der Numees Fm und des Namaskluft Mbr. Basierend auf diesen Analysen kann eine Mindestlänge von etwa 8 Millionen Jahren für das Sturtian und etwa 14 Millionen Jahren für das Marinoan Schneeball Erde Ereignis angenommen werden.:Abstract Kurzfassung Contents List of Figures List of Tables List of abbreviations Scientific question and thesis structure 1 Introduction 1.1 The Neoproterozoic era: Supercontinent dispersal and global glaciations 1.1.1 Rodinia supercontinent: Formation, dispersal, and location of Kalahari Craton 1.1.2 Glacial events during the Neoproterozoic era 1.1.2.1 A brief history on the discovery of Snowball Earth events 1.1.2.2 Formation and termination of a Snowball Earth event: The Snowball Earth flow chart 1.1.2.3 Hypotheses for cap carbonate formation 1.1.2.4 Survival of life during a Snowball Earth event 1.2 The Kalahari Craton 1.2.1 Evolution of the Kalahari Craton 1.3 Overview over the Geology of Namibia under special consideration of southern Namibia (Kalahari Craton) 2 Characteristics of southern Namibian Neoproterozoic glacial samples and sides 3 The problematic correlations of Neoproterozoic glacial deposits of the Kalahari Craton (southern Namibia) 4 Methods 4.1 Field work 4.2 Whole Rock geochemical analyses 4.3 Heavy mineral separation and SEM analyses on zircon grains of siliciclastic samples 4.4 Zircon grain size analyses 4.5 LA‐ICP‐MS analyses on zircon grains 4.5.1 U‐Pb analyses with LA‐SF‐ICP‐MS 4.5.2 Th‐U ratio determination on zircon grains 4.5.3 Hf‐isotope measurements with LA‐MS‐ICP‐MS 4.6 LA‐ICP‐MS U‐Pb dating on carbonates 4.7 Provenance interpretations and likeness tests based on zircon U‐Pb age data bases 5 Study I: “The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton, Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana” 5.1 Introduction and geological setting 5.2 Samples and methods 5.3 Results 5.4 Discussion and interpretation 5.5 Summary 6 Study II: “The four Neoproterozoic glaciations of southern Namibia and their detrital zircon record: The fingerprints of four crustal growth events during two supercontinent cycles” 6.1 Introduction 6.2 The samples 6.3 Methods 6.4 Results 6.5 Interpretation and discussion 6.6 Conclusion/Summary 7 Study III: “Correlation of Neoproterozoic diamictites in southern Namibia” 7.1 Introduction 7.2 Sample sites 7.2.1. The Kaigas and Sturtian Numees diamictites at the Orange River section 2.1.1. Outcrops of the Kaigas Fm diamictites 7.2.1.2 Outcrop of the Numees Fm diamictites (Sturtian) 7.2.2 The Sturtian diamcitite of the Blaubeker Fm (Witvlei Grp) at the farmgrounds Blaubeker and Tahiti 7.2.2.1 The Blaubeker diamictite at Blaubeker Farm (type locality) 7.2.2.2 The Blaubeker diamictite at Tahiti Farm (Gobabis‐syncline) 7.2.2.3 Correlation of Blaubeker diamictite at Blaubeker and Tahiti farms 7.2.3 The Sturtian diamictite at the Trekpoort Farm section 7.2.4 The Sturtian and Marinoan diamictites at Namuskluft section (reference profile) 7.2.5 The Sturtian and Marinoan diamictites at Dreigratberg section 7.2.6 Sturtian diamictite and Marinoan‐type cap carbonate at Dreigratberg North section 7.2.7 The Marinoan diamictite at the Witputs Farm section 7.2.8 The post‐Gaskiers Vingerbreek diamictite 7.2.8.1 The Vingerbreek diamictite along the Orange River 7.2.8.2 The Vingerbreek diamictite at Tierkloof Farm (Klein Karas Mountains) 7.3 Methods 7.4 Data and Results 7.4.1 Results of the U‐Pb detrital zircon data 7.4.2 Results of the U‐Pb carbonate dating 7.4.3 Results of zircon grain width and length measurements 7.4.4 Results of the Th‐U zircon ratios 7.4.5 Results of Lu‐Hf isotopic measurements 7.4.6 Geochemical results of the siliciclastic and basement samples 7.4.7 Geochemical results of the carbonate samples 7.5 Discussion and Conclusion 8 Sediment provenance and Snowball Earth ice dynamics 9 Implications on the evolution of the Gariep Belt 10 Conclusions and outlook 11 References Supplementary Material

Icing on materials surface causes operational failures as well as technical and safety issues. Furthermore, it reduces the energy efficiency of the power supply and passenger/freight transportation systems. Conventional active deicing methods are widely used to remove ice, but are often associated with uneconomically high energy consumption and high maintenance costs, often not being aware of their environmental impact. Instead, passive anti-icing methods are being sought to prevent or delay ice formation by means of physico-chemical surface treatment. Pyroelectric materials can be used as possible anti-icing surfaces after their ability to inhibit ice nucleation has been experimentally demonstrated. This makes use of the effect of the pyroelectrically induced surface charge, which changes with the ambient temperature and thus, hypothetically, exerts an influence on the dipole orientation of the water molecules at the surface. This is expected to affect the hydrogen bonding network of the interfacial water in the supercooled liquid phase, depending on the sign of surface charge. However, the Classical Nucleation Theory predicts an increased nucleation rate with increasing electric field strength of the pyroelectric surface charge irrespective of its polarity, as confirmed by many experiments. This raises the question of what exactly influences the ice nucleation. The main purpose of this thesis is to find a relationship between the pyroelectricity and the ice nucleation rate. Various theoretical and experimental investigation methods have been used to examine which of the possible influencing factors related to the pyroelectric material surface plays a major role in promoting or inhibiting ice nucleation.:Contents Abstract i List of figures xi List of tables xv 1 Introduction 1 1.1 Motivation 1 1.2 Objective and Tasks 4 1.3 Structure of the thesis 6 2 Basics 7 2.1 Pyroelectric materials 7 2.1.1 Fundamental properties 7 2.1.2 Lithium niobate, LiNbO3 14 2.2 Ice nucleation and water freezing 21 2.2.1 Thermodynamics of ice nucleation 21 2.2.2 Factors influencing ice nucleation 26 3 Materials and Methods 29 3.1 Sample materials used for the investigation 29 3.2 Theoretical methods 31 3.2.1 Theoretical background of computational quantum mechanical modeling 31 3.2.2 LiNbO3 model system 38 3.2.3 DFT implementation in CP2K 41 3.3 Experimental methods 42 3.3.1 Optical and vibrational spectroscopy 43 3.3.2 X-ray spectroscopy 47 3.3.3 Atomic force microscopy 48 3.3.4 Environmental scanning electron spectroscopy 51 3.3.5 Pyroelectric measurement 52 3.3.6 Contact angle measurement 53 3.3.7 Icing temperature measurement 54 3.4 Tabular overview of the different methods 57 ix4 Results and Discussion 59 4.1 Results 59 4.1.1 Several results of DFT calculations 59 4.1.2 MD simulations of interfacial water 75 4.1.3 Results of optical and vibrational spectroscopy 80 4.1.4 X-ray spectroscopy on LiNbO3 surfaces 96 4.1.5 Extended treatment of the Classical Nucleation Theory 100 4.1.6 Results of atomic force microscopy 108 4.1.7 ESEM images of ice crystals grown on LiNbO3 116 4.1.8 Results of pyroelectric measurements 122 4.1.9 Results of contact angle measurements 124 4.1.10 Results of icing temperature measurements 126 4.2 Discussion 135 4.2.1 Surface charge 135 4.2.2 Surface structure 144 4.2.3 Surface reactivity 149 4.3 Conclusion of the findings and remarks 151 5 Summary and Outlook 157 5.1 Conclusion of the thesis 157 5.2 Recommendations for further investigations 161 5.3 Outlook 164 Appendix 167 A.1 Additional information to the DFT calculations 167 A.2 Background spectrum for ATR spectroscopy 175 A.3 Additional information to SFG/SHG spectroscopy 176 A.4 Additional information to the XPS results 181 A.5 Additional information to the AFM measurement 182 A.6 ESEM images of ice accretion in the sample system 187 A.7 FEM simulation of local temperature and flow velocity distribution 190 A.8 Additional information to the icing temperature measurement 203 A.9 Temperature-dependent pH variation of water at LiNbO3 surface 207 List of abbreviations and symbols 213 References 217 Publications 276 Acknowledgements 277 Erklärung 281 / Vereisung auf Werkstoffoberflächen führt einerseits zu Betriebsausfällen und andererseits zur Reduzierung der Energieeffizienz von Energieversorgungs- sowie Personen- und Gütertransportsystemen. Sie stellt nicht selten ein sicherheitstechnisches und gesundheitliches Risiko dar. Da die konventionellen aktiven Enteisungsmethoden mit hohem Energieaufwand und hohen Wartungskosten verbunden sind, wird nach passiven Anti-icing-Methoden als vorbeugende Maßnahmen zur Vermeidung/Verzögerung von Eisbildung auf physikalisch-chemisch behandelten Oberflächen gesucht. Der Einsatz dieser Werkstoffoberflächen senkt nicht nur den Energieverbrauch, sondern soll auch die Umwelt schonen. Pyroelektrische Materialien kommen als passive Anti-icing-Oberflächen in Frage, nachdem ihre eiskeimbildungshemmende Fähigkeit experimentell nachgewiesen wurde. Dabei wird der Effekt der pyroelektrisch induzierten Oberflächenladung ausgenutzt, die sich mit der Umgebungstemperatur ändert und somit, hypothetisch gesehen, einen Einfluss auf die Dipolorientierung der Wassermoleküle an der Oberfläche ausübt. Das hat je nach Vorzeichen der Oberflächenladung Auswirkungen auf das Wassermolekülbindungsnetzwerk des Grenzflächenwassers in der unterkühlten flüssigen Phase. Da die klassische Keimbildungstheorie jedoch eine erhöhte Keimbildungswahrscheinlichkeit mit zunehmender Stärke des elektrischen Feldes der pyroelektrischen Oberflächenladung unabhängig von ihrem Vorzeichen voraussagt, wie es ebenfalls in vielen Experimenten nachgewiesen wurde, stellt sich die Frage, was genau die Eiskeimbildung beeinflusst. Das Hauptanliegen dieser Arbeit ist, einen Zusammenhang zwischen der Pyroelektrizität der Oberfläche und der Eiskeimbildungsrate zu finden. Mithilfe einer Vielzahl von verschiedenen theoretischen und experimentellen Methoden wird untersucht, welcher der möglichen Einflussfaktoren im Zusammenhang mit der pyroelektrischen Materialoberfläche eine große Rolle bei der Eiskeimbildung spielt.:Contents Abstract i List of figures xi List of tables xv 1 Introduction 1 1.1 Motivation 1 1.2 Objective and Tasks 4 1.3 Structure of the thesis 6 2 Basics 7 2.1 Pyroelectric materials 7 2.1.1 Fundamental properties 7 2.1.2 Lithium niobate, LiNbO3 14 2.2 Ice nucleation and water freezing 21 2.2.1 Thermodynamics of ice nucleation 21 2.2.2 Factors influencing ice nucleation 26 3 Materials and Methods 29 3.1 Sample materials used for the investigation 29 3.2 Theoretical methods 31 3.2.1 Theoretical background of computational quantum mechanical modeling 31 3.2.2 LiNbO3 model system 38 3.2.3 DFT implementation in CP2K 41 3.3 Experimental methods 42 3.3.1 Optical and vibrational spectroscopy 43 3.3.2 X-ray spectroscopy 47 3.3.3 Atomic force microscopy 48 3.3.4 Environmental scanning electron spectroscopy 51 3.3.5 Pyroelectric measurement 52 3.3.6 Contact angle measurement 53 3.3.7 Icing temperature measurement 54 3.4 Tabular overview of the different methods 57 ix4 Results and Discussion 59 4.1 Results 59 4.1.1 Several results of DFT calculations 59 4.1.2 MD simulations of interfacial water 75 4.1.3 Results of optical and vibrational spectroscopy 80 4.1.4 X-ray spectroscopy on LiNbO3 surfaces 96 4.1.5 Extended treatment of the Classical Nucleation Theory 100 4.1.6 Results of atomic force microscopy 108 4.1.7 ESEM images of ice crystals grown on LiNbO3 116 4.1.8 Results of pyroelectric measurements 122 4.1.9 Results of contact angle measurements 124 4.1.10 Results of icing temperature measurements 126 4.2 Discussion 135 4.2.1 Surface charge 135 4.2.2 Surface structure 144 4.2.3 Surface reactivity 149 4.3 Conclusion of the findings and remarks 151 5 Summary and Outlook 157 5.1 Conclusion of the thesis 157 5.2 Recommendations for further investigations 161 5.3 Outlook 164 Appendix 167 A.1 Additional information to the DFT calculations 167 A.2 Background spectrum for ATR spectroscopy 175 A.3 Additional information to SFG/SHG spectroscopy 176 A.4 Additional information to the XPS results 181 A.5 Additional information to the AFM measurement 182 A.6 ESEM images of ice accretion in the sample system 187 A.7 FEM simulation of local temperature and flow velocity distribution 190 A.8 Additional information to the icing temperature measurement 203 A.9 Temperature-dependent pH variation of water at LiNbO3 surface 207 List of abbreviations and symbols 213 References 217 Publications 276 Acknowledgements 277 Erklärung 281

Icing is an important problem, which often leads to emergency situations in northern countries. The reduction of icing requires a detailed understanding of this process. In this work, we report on a systematic investigation of the effects of geometry and chemical properties of surfaces on the formation of an ice layer, its properties, and thawing. We compare in detail icing and ice thawing on flat and rough hydrophilic and hydrophobic surfaces. We also show advantages and disadvantages of the surfaces of each kind. We demonstrate that water condenses in a liquid form, leading to the formation of a thin continuous water layer on a hydrophilic surface. Meanwhile, separated rounded water droplets are formed on hydrophobic surfaces. As a result of slower heat exchange, the freezing of rounded water droplets on a hydrophobic surface occurs later than the freezing of the continuous water layer on a hydrophilic one. Moreover, growth of ice on hydrophobic surfaces is slower than on the hydrophilic ones, because ice grows due to the condensation of water vapor on already formed ice crystals, and not due to the condensation on the polymer surface. Rough hydrophobic surfaces also demonstrate a very low ice adhesion value, which is because of the reduced contact area with ice. The main disadvantage of hydrophobic and superhydrophobic surfaces is the pinning of water droplets on them after thawing. Flat hydrophilic poly(ethylene glycol)-modified surfaces also exhibit very low ice adhesion, which is due to the very low freezing point of the water–poly(ethylene glycol) mixtures. Water easily leaves from flat hydrophilic poly(ethylene glycol)-modified surfaces, and they quickly become dry. However, the ice growth rate on poly(ethylene glycol)-modified hydrophilic surfaces is the highest. These results indicate that neither purely (super)hydrophobic polymeric surfaces, nor ‘‘antifreeze’’ hydrophilic ones provide an ideal solution to the problem of icing.