@phdthesis{Sand2021,
  author    = {Sand, Patrick},
  title     = {{\"U}bergangsmetallkatalysierte Funktionalisierungsreaktionen an Vinylsulfonylverbindungen},
  doi       = {10.25932/publishup-53687},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-536879},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 169},
  year      = {2021},
  abstract  = {Innerhalb dieser Arbeit erfolgte die erstmalige systematische Untersuchung von Vinylsulfons{\"a}ureethylester (1a), Phenylvinylsulfon (1b), N-Benzyl-N-methylethensulfonamid (1c) in der FUJIWARA-MORITANI Reaktion (alternativ als DHR bezeichnet). Bei dieser {\"u}bergangsmetallkatalysierten Reaktion erfolgt der Aufbau einer neuen C-C-Bindung unter der doppelten Aktivierung einer C-H-Bindung. Somit kann ein atom{\"o}konomischer Aufbau von Molek{\"u}len realisiert werden, da keine Beiprodukte in Form von Salzen entstehen. Als aromatischer Reaktant wurden Acetanilide (2) verwendet, damit eine regiospezifische Kupplung durch die katalysatordirigierende Acetamid-Gruppe (CDG) erfolgt. F{\"u}r die Pd-katalysierte DHR wurde eine umfangreiche Optimierung durchgef{\"u}hrt und anschließend konnten neun verschieden, substituierte 2 mit 1a und sieben verschieden, substituierte 2 mit 1b funktionalisiert werden. Da eine Reaktion mit 1c ausblieb, erfolgte ein Wechsel auf eine Ru-katalysierte Methode f{\"u}r die DHR. Mit dieser Methode konnte 1c mit Acetaniliden funktionalisiert werden und das Spektrum der verwendeten 2, in Form von deaktivierenden Substituenten erweitert werden. Im Anschluss wurden die sulfalkenylierten Acetanilide in weiterf{\"u}hrenden Reaktionen untersucht. Hierf{\"u}r wurde eine Reaktionssequenz bestehend aus einer DeacetylierungDiazotierung-Kupplungsreaktion verwendet, um die Acetamid-Gruppe in eine Abgangsgruppe zu {\"u}berf{\"u}hren und danach in einer MATSUDA-HECK Reaktion zu kuppeln. Mit dieser Methode konnten mehrere 1,2-Dialkenylbenzole erhalten werden und die CDG ein weiteres Mal genutzt werden. Neben der {\"U}berf{\"u}hrung der CDG in eine Abgangsgruppe konnte diese auch in die Synthese verschiedener Heterozyklen integriert werden. Daf{\"u}r erfolgte zun{\"a}chst eine 1,3-Zykloaddition durch deprotonierten Tosylmethylisocanid an der elektronenarmen Sulfalkenylgruppe zur Synthese von Pyrrolen. Anschließend erfolgte eine Kupplung der PyrrolFunktion und der CDG durch Zyklokondensation, wodurch Quinoline dargestellt wurden. Durch diese Synthesen konnten Schwefelanaloga des Naturstoffes Marinoquionolin A erhalten werden. Ein weitere {\"u}bergangsmetallkatalysierte C-H-Aktivierungsreaktion, die MATSUDA-HECK Reaktion, wurde genutzt, um 1b zu mit verschieden, subtituierten Diazoniumsalzen zu arylieren. Hier konnten zahlreichen Styrenylsulfone erhalten werden. Der erfolgreiche Einsatz der Vinylsulfonylverbindungen in der Kreuzmetathese konnte innerhalb dieser Arbeit nicht erreicht werden. Daher erfolgte die Synthese verschiedener dialkenylierter Sulfonamide. Hierf{\"u}r wurde die Kettenl{\"a}nge der Alkenyl-Gruppe am Schwefel zwischen 2-3 und am Stickstoff zwischen 3-4 variiert. Der Einsatz der dialkenylierten Sulfonamide erfolgte in den zuvor untersuchten C-H-Aktivierungsmethoden. N-Allyl-N-phenylethensulfonamid (3) konnte erfolgreich in der DHR und HECK Reaktion funktionalisiert werden. Hierbei erfolgte eine methodenspezifische Kupplung in Abh{\"a}ngigkeit von der Elektronendichte der entsprechenden Alkenyl-Gruppe. Die DHR f{\"u}hrte zur selektiven Arylierung der Vinyl-Gruppe und die HECK Reaktion zur Arylierung an der Allyl-Gruppe. Gemischte Produkte wurden nicht erhalten. F{\"u}r die weiteren Diolefine wurde komplexe Produktgemische erhalten. Des Weiteren wurden die Diolefine in der Ringschlussmetathese untersucht und die entsprechenden Sultame in sehr guten Ausbeuten erhalten. Die Verwendung der Sultame in der C-H-Aktivierung war erfolglos. Es wird vermutet, dass f{\"u}r diese zweifachsubstituierten Sulfonamide die vorhandenen Reaktionsbedingungen optimiert werden m{\"u}ssen. Abschließend wurden verschiedene, enantiomerenreine Olefine ausgehend von Levoglucosenon dargestellt. Hierf{\"u}r wurde Levoglucosenon zun{\"a}chst mit einem Allyl- und 3-Butenylgrignard Reagenz umgesetzt. Die entsprechenden Produkte wurden in moderaten Ausbeuten erhalten. Eine weitere Methode begann mit der Reduktion von Levoglucosenon zum Levoglucosenol. Dieser Alkohol wurde mit Allylbromid erfolgreich verethert. Neben der Untersuchungen zur Ethersynthese, erfolgte die Veresterung von Levoglucosenol mit verschiedenen Sulfonylchloriden zu den entsprechenden Sulfons{\"a}ureestern. Diese Olefine wurden in einer Dominometathesereaktion untersucht. Ausgehend vom Allyllevoglucosenylether erfolgte die Darstellung eines Dihydrofurans.},
  language  = {de}
}
@phdthesis{Saretia2021,
  author    = {Saretia, Shivam},
  title     = {Modulating ultrathin films of semi-crystalline oligomers by Langmuir technique},
  doi       = {10.25932/publishup-54210},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-542108},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIII, 109},
  year      = {2021},
  abstract  = {Polymeric films and coatings derived from semi-crystalline oligomers are of relevance for medical and pharmaceutical applications. In this context, the material surface is of particular importance, as it mediates the interaction with the biological system. Two dimensional (2D) systems and ultrathin films are used to model this interface. However, conventional techniques for their preparation, such as spin coating or dip coating, have disadvantages, since the morphology and chain packing of the generated films can only be controlled to a limited extent and adsorption on the substrate used affects the behavior of the films. Detaching and transferring the films prepared by such techniques requires additional sacrificial or supporting layers, and free-standing or self supporting domains are usually of very limited lateral extension. The aim of this thesis is to study and modulate crystallization, melting, degradation and chemical reactions in ultrathin films of oligo(ε-caprolactone)s (OCL)s with different end-groups under ambient conditions. Here, oligomeric ultrathin films are assembled at the air-water interface using the Langmuir technique. The water surface allows lateral movement and aggregation of the oligomers, which, unlike solid substrates, enables dynamic physical and chemical interaction of the molecules. Parameters like surface pressure (π), temperature and mean molecular area (MMA) allow controlled assembly and manipulation of oligomer molecules when using the Langmuir technique. The π-MMA isotherms, Brewster angle microscopy (BAM), and interfacial infrared spectroscopy assist in detecting morphological and physicochemical changes in the film. Ultrathin films can be easily transferred to the solid silicon surface via Langmuir Schaefer (LS) method (horizontal substrate dipping). Here, the films transferred on silicon are investigated using atomic force microscopy (AFM) and optical microscopy and are compared to the films on the water surface. The semi-crystalline morphology (lamellar thicknesses, crystal number densities, and lateral crystal dimensions) is tuned by the chemical structure of the OCL end-groups (hydroxy or methacrylate) and by the crystallization temperature (Tc; 12 or 21 °C) or MMAs. Compression to lower MMA of ~2 {\AA}2, results in the formation of a highly crystalline film, which consists of tightly packed single crystals. Preparation of tightly packed single crystals on a cm2 scale is not possible by conventional techniques. Upon transfer to a solid surface, these films retain their crystalline morphology whereas amorphous films undergo dewetting. The melting temperature (Tm) of OCL single crystals at the water and the solid surface is found proportional to the inverse crystal thickness and is generally lower than the Tm of bulk PCL. The impact of OCL end-groups on melting behavior is most noticeable at the air-solid interface, where the methacrylate end-capped OCL (OCDME) melted at lower temperatures than the hydroxy end-capped OCL (OCDOL). When comparing the underlying substrate, melting/recrystallization of OCL ultrathin films is possible at lower temperatures at the air water interface than at the air-solid interface, where recrystallization is not visible. Recrystallization at the air-water interface usually occurs at a higher temperature than the initial Tc. Controlled degradation is crucial for the predictable performance of degradable polymeric biomaterials. Degradation of ultrathin films is carried out under acidic (pH ~ 1) or enzymatic catalysis (lipase from Pseudomonas cepcia) on the water surface or on a silicon surface as transferred films. A high crystallinity strongly reduces the hydrolytic but not the enzymatic degradation rate. As an influence of end-groups, the methacrylate end-capped linear oligomer, OCDME (~85 ± 2 \% end-group functionalization) hydrolytically degrades faster than the hydroxy end capped linear oligomer, OCDOL (~95 ± 3 \% end-group functionalization) at different temperatures. Differences in the acceleration of hydrolytic degradation of semi-crystalline films were observed upon complete melting, partial melting of the crystals, or by heating to temperatures close to Tm. Therefore, films of densely packed single crystals are suitable as barrier layers with thermally switchable degradation rates. Chemical modification in ultrathin films is an intricate process applicable to connect functionalized molecules, impart stability or create stimuli-sensitive cross-links. The reaction of end-groups is explored for transferred single crystals on a solid surface or amorphous monolayer at the air-water interface. Bulky methacrylate end-groups are expelled to the crystal surface during chain-folded crystallization. The density of end-groups is inversely proportional to molecular weight and hence very pronounced for oligomers. The methacrylate end-groups at the crystal surface, which are present at high concentration, can be used for further chemical functionalization. This is demonstrated by fluorescence microscopy after reaction with fluorescein dimethacrylate. The thermoswitching behavior (melting and recrystallization) of fluorescein functionalized single crystals shows the temperature-dependent distribution of the chemically linked fluorescein moieties, which are accumulated on the surfaces of crystals, and homogeneously dispersed when the crystals are molten. In amorphous monolayers at the air-water interface, reversible cross-linking of hydroxy-terminated oligo(ε-caprolactone) monolayers using dialdehyde (glyoxal) lead to the formation of 2D networks. Pronounced contraction in the area occurred for 2D OCL films in dependence of surface pressure and time indicating the reaction progress. Cross linking inhibited crystallization and retarded enzymatic degradation of the OCL film. Altering the subphase pH to ~2 led to cleavage of the covalent acetal cross-links. Besides as model systems, these reversibly cross-linked films are applicable for drug delivery systems or cell substrates modulating adhesion at biointerfaces.},
  language  = {en}
}
@phdthesis{Schutjajew2021,
  author    = {Schutjajew, Konstantin},
  title     = {Electrochemical sodium storage in non-graphitizing carbons - insights into mechanisms and synthetic approaches towards high-energy density materials},
  doi       = {10.25932/publishup-54189},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-541894},
  school      = {Universit{\"a}t Potsdam},
  pages     = {v, 148},
  year      = {2021},
  abstract  = {To achieve a sustainable energy economy, it is necessary to turn back on the combustion of fossil fuels as a means of energy production and switch to renewable sources. However, their temporal availability does not match societal consumption needs, meaning that renewably generated energy must be stored in its main generation times and allocated during peak consumption periods. Electrochemical energy storage (EES) in general is well suited due to its infrastructural independence and scalability. The lithium ion battery (LIB) takes a special place, among EES systems due to its energy density and efficiency, but the scarcity and uneven geological occurrence of minerals and ores vital for many cell components, and hence the high and fluctuating costs will decelerate its further distribution. The sodium ion battery (SIB) is a promising successor to LIB technology, as the fundamental setup and cell chemistry is similar in the two systems. Yet, the most widespread negative electrode material in LIBs, graphite, cannot be used in SIBs, as it cannot store sufficient amounts of sodium at reasonable potentials. Hence, another carbon allotrope, non-graphitizing or hard carbon (HC) is used in SIBs. This material consists of turbostratically disordered, curved graphene layers, forming regions of graphitic stacking and zones of deviating layers, so-called internal or closed pores. The structural features of HC have a substantial impact of the charge-potential curve exhibited by the carbon when it is used as the negative electrode in an SIB. At defects and edges an adsorption-like mechanism of sodium storage is prevalent, causing a sloping voltage curve, ill-suited for the practical application in SIBs, whereas a constant voltage plateau of relatively high capacities is found immediately after the sloping region, which recent research attributed to the deposition of quasimetallic sodium into the closed pores of HC. Literature on the general mechanism of sodium storage in HCs and especially the role of the closed pore is abundant, but the influence of the pore geometry and chemical nature of the HC on the low-potential sodium deposition is yet in an early stage. Therefore, the scope of this thesis is to investigate these relationships using suitable synthetic and characterization methods. Materials of precisely known morphology, porosity, and chemical structure are prepared in clear distinction to commonly obtained ones and their impact on the sodium storage characteristics is observed. Electrochemical impedance spectroscopy in combination with distribution of relaxation times analysis is further established as a technique to study the sodium storage process, in addition to classical direct current techniques, and an equivalent circuit model is proposed to qualitatively describe the HC sodiation mechanism, based on the recorded data. The obtained knowledge is used to develop a method for the preparation of closed porous and non-porous materials from open porous ones, proving not only the necessity of closed pores for efficient sodium storage, but also providing a method for effective pore closure and hence the increase of the sodium storage capacity and efficiency of carbon materials. The insights obtained and methods developed within this work hence not only contribute to the better understanding of the sodium storage mechanism in carbon materials of SIBs, but can also serve as guidance for the design of efficient electrode materials.},
  language  = {en}
}
@phdthesis{Yan2021,
  author    = {Yan, Wan},
  title     = {Shape-Memory effects of thermoplatic multiblock copolymers with overlapping thermal transitions},
  year      = {2021},
  language  = {en}
}
@phdthesis{Zhao2021,
  author    = {Zhao, Yuhang},
  title     = {Synthesis and surface functionalization on plasmonic nanoparticles for optical applications},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 149},
  year      = {2021},
  abstract  = {This thesis focuses on the synthesis of novel functional materials based on plasmonic nanoparticles. Three systems with targeted surface modification and functionalization have been designed and synthesized, involving modified perylenediimide doped silica-coated silver nanowires, polydopamine or TiO2 coated gold-palladium nanorods and thiolated poly(ethylene glycol) (PEG-SH)/dodecanethiol (DDT) modified silver nanospheres. Their possible applications as plasmonic resonators, chiral sensors as well as photo-catalysts have been studied. In addition, the interaction between silver nanospheres and 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) molecules has also been investigated in detail. In the first part of the thesis, surface modification on Ag nanowires (NWs) with optimized silica coating through a modified St{\"o}ber method has been firstly conducted, employing sodium hydroxide (NaOH) to replace ammonia solution (NH4OH). The coated silver nanowires with a smooth silica shell have been investigated by single-particle dark-field scattering spectroscopy, transmission electron microscopy and electron-energy loss spectroscopy to characterize the morphologies and structural components. The silica-coated silver nanowires can be further functionalized with fluorescent molecules in the silica shell via a facile one-step coating method. The as-synthesized nanowire is further coupled with a gold nanosphere by spin-coating for the application of the sub-diffractional chiral sensor for the first time. The exciton-plasmon-photon interconversion in the system eases the signal detection in the perfectly matched 1D nanostructure and contributes to the high contrast of the subwavelength chiral sensing for the polarized light. In the second part of the thesis, dumbbell-shaped Au-Pd nanorods coated with a layer of polydopamine (PDA) or titanium dioxide (TiO2) have been constructed. The PDA- and TiO2- coated Au-Pd nanorods show a strong photothermal conversion performance under NIR illumination. Moreover, the catalytic performance of the particles has been investigated using the reduction of 4-nitrophenol (4-NP) as the model reaction. Under light irradiation, the PDA-coated Au-Pd nanorods exhibit a superior catalytic activity by increasing the reaction rate constant of 3 times. The Arrhenius-like behavior of the reaction with similar activation energies in the presence and absence of light irradiation indicates the photoheating effect to be the dominant mechanism of the reaction acceleration. Thus, we attribute the enhanced performance of the catalysis to the strong photothermal effect that is driven by the optical excitation of the gold surface plasmon as well as the synergy with the PDA layer. In the third part, the kinetic study on the adsorption of 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquino-dimethane (F4TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been reported in detail. Based on the results obtained from the UV-vis-NIR absorption spectroscopy, cryogenic transmission electron microscopy (cryo-TEM), scanning nano-beam electron diffraction (NBED) and electron energy loss spectroscopy (EELS), a two-step interaction kinetics has been proposed for the Ag NPs and F4TCNQ molecules. It includes the first step of electron transfer from Ag NPs to F4TCNQ indicated by the ionization of F4TCNQ, and the second step of the formation of Ag-F4TCNQ complex. The whole process has been followed via UV-vis-NIR absorption spectroscopy, which reveals distinct kinetics at two stages: the instantaneous ionization and the long-term complex formation. The kinetics and the influence of the molar ratio of Ag NPs/F4TCNQ molecules on the interaction between Ag NPs and F4TCNQ molecules in the organic solution are reported herein for the first time. Furthermore, the control experiment with silica-coated Ag NPs indicates that the charge transfer at the surface between Ag NPs and F4TCNQ molecules has been prohibited by a silica layer of 18 nm.},
  language  = {en}
}