@phdthesis{Andersen2005,
  author    = {Andersen, Audr{\´e}e},
  title     = {Surfactant dynamics at interfaces : a series of second harmonic generation experiments},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6553},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus. There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model. The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model. Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants.},
  subject      = {Tensid},
  language  = {en}
}
@phdthesis{Imranulhaq2008,
  author    = {Imran ul-haq, Muhammad},
  title     = {Synthesis of fluorinated polymers in supercritical carbon dioxide (scCO₂)},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19868},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {For the first time stabilizer-free vinylidene fluoride (VDF) polymerizations were carried out in homogeneous phase with supercritical CO₂. Polymerizations were carried out at 140°C, 1500 bar and were initiated with di-tert-butyl peroxide (DTBP). In-line FT-NIR (Fourier Transform- Near Infrared) spectroscopy showed that complete monomer conversion may be obtained. Molecular weights were determined via size-exclusion chromatography (SEC) and polymer end group analysis by 1H-NMR spectroscopy. The number average molecular weights were below 104 g∙mol-1 and polydispersities ranged from 3.1 to 5.7 depending on DTBP and VDF concentration. To allow for isothermal reactions high CO₂ contents ranging from 61 to 83 wt.\% were used. The high-temperature, high-pressure conditions were required for homogeneous phase polymerization. These conditions did not alter the amount of defects in VDF chaining. Scanning electron microscopy (SEM) indicated that regular stack-type particles were obtained upon expansion of the homogeneous polymerization mixture. To reduce the required amount of initiator, further VDF polymerizations using chain transfer agents (CTAs) to control molecular weights were carried out in homogeneous phase with supercritical carbon dioxide (scCO₂) at 120 °C and 1500 bar. Using perfluorinated hexyl iodide as CTA, polymers of low polydispersity ranging from 1.5 to 1.2 at the highest iodide concentration of 0.25 mol·L-1 were obtained. Electrospray ionization- mass spectroscopy (ESI-MS) indicates the absence of initiator derived end groups, supporting livingness of the system. The "livingness" is based on the labile C-I bond. However, due to the weakness of the C-I bond perfluorinated hexyl iodide also contributes to initiation. To allow for kinetic analyses of VDF polymerizations the CTA should not contribute to initiation. Therefore, additional CTAs were applied: BrCCl3, C6F13Br and C6F13H. It was found that C6F13H does not contribute to initiation. At 120°C and 1500 bar kp/kt0.5~ 0.64 (L·mol-1·s-1)0.5 was derived. The chain transfer constant (CT) at 120°C has been determined to be 8·10-1, 9·10-2 and 2·10-4 for C6F13I, C6F13Br and C6F13H, respectively. These CT values are associated with the bond energy of the C-X bond. Moreover, the labile C-I bond allows for functionalization of the polymer to triazole end groups applying click reactions. After substitution of the iodide end group by an azide group 1,3 dipolar cycloadditions with alkynes yield polymers with 1,2,3 triazole end groups. Using symmetrical alkynes the reactions may be carried out in the absence of any catalyst. This end-functionalized poly (vinylidene fluoride) (PVDF) has higher thermal stability as compared to the normal PVDF. PVDF samples from homogeneous phase polymerizations in supercritical CO₂ and subsequent expansion to ambient conditions were analyzed with respect to polymer end groups, crystallinity, type of polymorphs and morphology. Upon expansion the polymer was obtained as white powder. Scanning electron microscopy (SEM) showed that DTBP derived polymer end groups led to stack-type particles whereas sponge- or rose-type particles were obtained in case of CTA fragments as end groups. Fourier-Transform Infrared spectroscopy and wide angle X-ray diffraction indicated that the type of polymorph, α or β crystal phase was significantly affected by the type of end group. The content of β-phase material, which is responsible for piezoelectricity of PVDF, is the highest for polymer with DTBP-derived end groups. In addition, the crystallinity of the material, as determined via differential scanning calorimetry is affected by the end groups and polymer molecular weights. For example, crystallinity ranges from around 26 \% for DTBP-derived end groups to a maximum of 62 \% for end groups originating from perfluorinated hexyl iodide for polymers with Mn ~2200 g·mol-1. Expansion of the homogeneous polymerization mixture results in particle formation by a non-optimized RESS (Rapid Expansion from Supercritical Solution) process. Thus, it was tested how polymer end groups affect the particles size distribution obtained from RESS process under controlled conditions (T = 50°C and P = 200 bar). In all RESS experiments, small primary PVDF with diameters less than 100 nm without the use of liquid solvents, surfactants, or other additives were produced. A strong correlation between particle size and particle size distribution with polymer end groups and molecular weight of the original material was observed. The smallest particles were found for RESS of PVDF with Mn~ 4000 g·mol-1 and PFHI (C6F13I) - derived end groups.},
  language  = {en}
}
@misc{DoscheMicklerLoehmannsroebenetal.2007,
  author    = {Dosche, Carsten and Mickler, Wulfhard and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Agenet, Nicolas and Vollhardt, K. Peter C.},
  title     = {Photoinduced electron transfer in [N]phenylenes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12463},
  year      = {2007},
  abstract  = {First studies of electron transfer in [N]phenylenes were performed in bimolecular quenching reactions of angular [3]- and triangular [4]phenylene with various electron acceptors. The relation between the quenching rate constants kq and the free energy change of the electron transfer (ΔG0CS ) could be described by the Rehm-Weller equation. From the experimental results, a reorganization energy λ of 0.7 eV was derived. Intramolecular electron transfer reactions were studied in an [N]phenylene bichomophore and a corresponding reference compound. Fluorescence lifetime and quantum yield of the bichromophor display a characteristic dependence on the solvent polarity, whereas the corresponding values of the reference compound remain constant. From the results, a nearly isoenergonic ΔG0CS can be determined. As the triplet quantum yield is nearly independent of the polarity, charge recombination leads to the population of the triplet state.},
  language  = {en}
}
@phdthesis{MichalikOnichimowska2022,
  author    = {Michalik-Onichimowska, Aleksandra},
  title     = {Real-time monitoring of (photo)chemical reactions in micro flow reactors and levitated droplets by IR-MALDI ion mobility and mass spectrometry},
  doi       = {10.25932/publishup-55729},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-557298},
  school      = {Universit{\"a}t Potsdam},
  pages     = {v, 68},
  year      = {2022},
  abstract  = {Eine nachhaltigere chemische Industrie erfordert eine Minimierung der L{\"o}sungsmittel und Chemikalien. Daher werden Optimierung und Entwicklung chemischer Prozesse vor einer Produktion in großem Maßstab in kleinen Chargen durchgef{\"u}hrt. Der entscheidende Schritt bei diesem Ansatz ist die Skalierbarkeit von kleinen Reaktionssystemen auf große, kosteneffiziente Reaktoren. Die Vergr{\"o}ßerung des Volumens des Reaktionsmediums geht immer mit der Vergr{\"o}ßerung der Oberfl{\"a}che einher, die mit dem begrenzenden Gef{\"a}ß in Kontakt steht. Da das Volumen kubisch, w{\"a}hrend die Oberfl{\"a}che quadratisch mit zunehmendem Radius skaliert, nimmt ihr Verh{\"a}ltnis nicht linear zu. Viele an der Grenzfl{\"a}che zwischen Oberfl{\"a}che und Fl{\"u}ssigkeit auftretende Ph{\"a}nomene k{\"o}nnen die Reaktionsgeschwindigkeiten und Ausbeuten beeinflussen, was zu falschen Prognosen aufgrund der kleinskaligen Optimierung f{\"u}hrt. Die Anwendung von schwebenden Tropfen als beh{\"a}lterlose Reaktionsgef{\"a}ße bietet eine vielversprechende M{\"o}glichkeit, die oben genannten Probleme zu vermeiden. In der vorgestellten Arbeit wurde eine effiziente Kopplung von akustisch schwebenden Tropfen und IM Spektrometer f{\"u}r die Echtzeit{\"u}berwachung chemischer Reaktionen entwickelt, bei denen akustisch schwebende Tropfen als Reaktionsgef{\"a}ße fungieren. Das Design des Systems umfasst die ber{\"u}hrungslose Probenahme und Ionisierung, die durch Laserdesorption und -ionisation bei 2,94 µm realisiert wird. Der Umfang der Arbeit umfasst grundlegende Studien zum Verst{\"a}ndnis der Laserbestrahlung von Tropfen im akustischen Feld. Das Verst{\"a}ndnis dieses Ph{\"a}nomens ist entscheidend, um den Effekt der zeitlichen und r{\"a}umlichen Aufl{\"o}sung der erzeugten Ionenwolke zu verstehen, die die Aufl{\"o}sung des Systems beeinflusst. Der Aufbau umfasst eine akustische Falle, Laserbestrahlung und elektrostatische Linsen, die bei hoher Spannung unter Umgebungsdruck arbeiten. Ein effektiver Ionentransfer im Grenzfl{\"a}chenbereich zwischen dem schwebenden Tropfen und dem IMS muss daher elektrostatische und akustische Felder vollst{\"a}ndig ber{\"u}cksichtigen. F{\"u}r die Probenahme und Ionisation wurden zwei unterschiedliche Laserpulsl{\"a}ngen untersucht, n{\"a}mlich im ns- und µs-Bereich. Die Bestrahlung {\"u}ber µs-Laserpulse bietet gegen{\"u}ber ns-Pulse mehrere Vorteile: i) das Tropfenvolumen wird nicht stark beeinflusst, was es erm{\"o}glichet, nur ein kleines Volumen des Tropfens abzutasten; ii) die geringere Fluenz f{\"u}hrt zu weniger ausgepr{\"a}gten Schwingungen des im akustischen Feld eingeschlossenen Tropfens und der Tropfen wird nicht aus dem akustischen Feld r{\"u}ckgeschlagen, was zum Verlust der Probe f{\"u}hren w{\"u}rde; iii) die milde Laserbestrahlung f{\"u}hrt zu einer besseren r{\"a}umlichen und zeitlichen Begrenzung der Ionenwolken, was zu einer besseren Aufl{\"o}sung der detektierten Ionenpakete f{\"u}hrt. Schließlich erm{\"o}glicht dieses Wissen die Anwendung der Ionenoptik, die erforderlich ist, um den Ionenfluss zwischen dem im akustischen Feld suspendierten Tropfen und dem IM Spektrometer zu induzieren. Die Ionenoptik aus 2 elektrostatischen Linsen in der N{\"a}he des Tropfens erm{\"o}glicht es, die Ionenwolke effektiv zu fokussieren und direkt zum IM Spektrometer-Eingang zu f{\"u}hren. Diese neuartige Kopplung hat sich beim Nachweis einiger basischer Molek{\"u}le als erfolgreich erwiesen. Um die Anwendbarkeit des Systems zu belegen, wurde die Reaktion zwischen N-Boc Cysteine Methylester und Allylalkohol in einem Chargenreaktor durchgef{\"u}hrt und online {\"u}berwacht. F{\"u}r eine Kalibrierung wurde der Reaktionsfortschritt parallel mittels 1H-NMR verfolgt. Der beobachtete Reaktionsumsatz von mehr als 50\% innerhalb der ersten 20 Minuten demonstrierte die Eignung der Reaktion, um die Einsatzpotentiale des entwickelten Systems zu bewerten.},
  language  = {en}
}
@phdthesis{Boerner2009,
  author    = {B{\"o}rner, Hans Gerhard},
  title     = {Exploiting self-organization and functionality of peptides for polymer science},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-29066},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {Controlling interactions in synthetic polymers as precisely as in proteins would have a strong impact on polymer science. Advanced structural and functional control can lead to rational design of, integrated nano- and microstructures. To achieve this, properties of monomer sequence defined oligopeptides were exploited. Through their incorporation as monodisperse segments into synthetic polymers we learned in recent four years how to program the structure formation of polymers, to adjust and exploit interactions in such polymers, to control inorganic-organic interfaces in fiber composites and induce structure in Biomacromolecules like DNA for biomedical applications.},
  language  = {en}
}
@phdthesis{Popovic2011,
  author    = {Popovic, Jelena},
  title     = {Novel lithium iron phosphate materials for lithium-ion batteries},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-54591},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Conventional energy sources are diminishing and non-renewable, take million years to form and cause environmental degradation. In the 21st century, we have to aim at achieving sustainable, environmentally friendly and cheap energy supply by employing renewable energy technologies associated with portable energy storage devices. Lithium-ion batteries can repeatedly generate clean energy from stored materials and convert reversely electric into chemical energy. The performance of lithium-ion batteries depends intimately on the properties of their materials. Presently used battery electrodes are expensive to be produced; they offer limited energy storage possibility and are unsafe to be used in larger dimensions restraining the diversity of application, especially in hybrid electric vehicles (HEVs) and electric vehicles (EVs). This thesis presents a major progress in the development of LiFePO4 as a cathode material for lithium-ion batteries. Using simple procedure, a completely novel morphology has been synthesized (mesocrystals of LiFePO4) and excellent electrochemical behavior was recorded (nanostructured LiFePO4). The newly developed reactions for synthesis of LiFePO4 are single-step processes and are taking place in an autoclave at significantly lower temperature (200 deg. C) compared to the conventional solid-state method (multi-step and up to 800 deg. C). The use of inexpensive environmentally benign precursors offers a green manufacturing approach for a large scale production. These newly developed experimental procedures can also be extended to other phospho-olivine materials, such as LiCoPO4 and LiMnPO4. The material with the best electrochemical behavior (nanostructured LiFePO4 with carbon coating) was able to delive a stable 94\% of the theoretically known capacity.},
  language  = {en}
}
@phdthesis{ChaleawlertUmpon2018,
  author    = {Chaleawlert-Umpon, Saowaluk},
  title     = {Sustainable electrode materials based on lignin},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-411793},
  school      = {Universit{\"a}t Potsdam},
  pages     = {114},
  year      = {2018},
  abstract  = {The utilization of lignin as renewable electrode material for electrochemical energy storage is a sustainable approach for future batteries and supercapacitors. The composite electrode was fabricated from Kraft lignin and conductive carbon and the charge storage contribution was determined in terms of electrical double layer (EDL) and redox reactions. The important factors at play for achieving high faradaic charge storage capacity contribute to high surface area, accessibility of redox sites in lignin and their interaction with conductive additives. A thinner layer of lignin covering the high surface area of carbon facilitates the electron transfer process with a shorter pathway from the active sites of nonconductive lignin to the current collector leading to the improvement of faradaic charge storage capacity. Composite electrodes from lignin and carbon would be even more sustainable if the fluorinated binder can be omitted. A new route to fabricate a binder-free composite electrode from Kraft lignin and high surface area carbon has been proposed by crosslinking lignin with glyoxal. A high molecular weight of lignin is obtained to enhance both electroactivity and binder capability in composite electrodes. The order of the processing step of crosslinking lignin on the composite electrode plays a crucial role in achieving a stable electrode and high charge storage capacity. The crosslinked lignin based electrodes are promising since they allow for more stable, sustainable, halogen-free and environmentally benign devices for energy storage applications. Furthermore, improvement of the amount of redox active groups (quinone groups) in lignin is useful to enhance the capacity in lithium battery applications. Direct oxidative demethylation by cerium ammonium nitrate has been carried out under mild conditions. This proves that an increase of quinone groups is able to enhance the performance of lithium battery. Thus, lignin is a promising material and could be a good candidate for application in sustainable energy storage devices.},
  language  = {en}
}
@phdthesis{Milke2012,
  author    = {Milke, Bettina},
  title     = {Synthese von Metallnitrid- und Metalloxinitridnanopartikeln f{\"u}r energierelevante Anwendungen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-60008},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {Ein viel diskutiertes Thema unserer Zeit ist die Zukunft der Energiegewinnung und Speicherung. Dabei nimmt die Nanowissenschaft eine bedeutende Rolle ein; sie f{\"u}hrt zu einer Effizienzsteigerung bei der Speicherung und Gewinnung durch bereits bekannte Materialien und durch neue Materialien. In diesem Zusammenhang ist die Chemie Wegbereiter f{\"u}r Nanomaterialien. Allerdings f{\"u}hren bisher die meisten bekannten Synthesen von Nanopartikeln zu undefinierten Partikeln. Eine einfache, kosteng{\"u}nstige und sichere Synthese w{\"u}rde die M{\"o}glichkeit einer breiten Anwendung und Skalierbarkeit bieten. In dieser Arbeit soll daher die Darstellung der einfachen Synthese von Mangannitrid-, Aluminiumnitrid-, Lithiummangansilicat-, Zirkonium-oxinitrid- und Mangancarbonatnanopartikel betrachtet werden. Dabei werden die sogenannte Harnstoff-Glas-Route als eine Festphasensynthese und die Solvothermalsynthese als typische Fl{\"u}ssigphasensynthese eingesetzt. Beide Synthesewege f{\"u}hren zu definierten Partikelgr{\"o}ßen und interessanten Morphologien und erm{\"o}glichen eine Einflussnahme auf die Produkte. Im Falle der Synthese der Mangannitridnanopartikel mithilfe der Harnstoff-Glas-Route f{\"u}hrt diese zu Nanopartikeln mit Kern-H{\"u}lle-Struktur, deren Einsatz als Konversionsmaterial erstmalig vorgestellt wird. Mit dem Ziel einer leichteren Anwendung von Nanopartikeln wird eine einfache Beschichtung von Oberfl{\"a}chen mit Nanopartikeln mithilfe der Rotationsbeschichtung beschrieben. Es entstand ein Gemisch aus MnN0,43/MnO-Nanopartikeln, eingebettet in einem Kohlenstofffilm, dessen Untersuchung als Konversionsmaterial hohe spezifische Kapazit{\"a}ten (811 mAh/g) zeigt, die die von dem konventionellen Anodenmaterial Graphit (372 mAh/g) {\"u}bersteigt. Neben der Synthese des Anodenmaterials wurde ebenfalls die des Kathodenmaterials Li2MnSiO4-Nanopartikeln mithilfe der Harnstoff-Glas-Route vorgestellt. Mithilfe der Synthese von Zirkoniumoxinitridnanopartikeln Zr2ON2 kann eine einfache Einflussnahme auf das gew{\"u}nschte Produkt durch die Variation derReaktionsbedingungen, wie Harnstoffmenge oder Reaktionstemperatur, bei der Harnstoff-Glas-Route demonstriert werden. Der Zusatz von kleinsten Mengen an Ammoniumchlorid vermeidet, dass sich Kohlenstoff im Endprodukt bildet und f{\"u}hrt so zu gelben Zr2ON2-Nanopartikeln mit einer Gr{\"o}ße d = 8 nm, die Halbleitereigen-schaften besitzen. Die Synthese von Aluminiumnitridnanopartikeln f{\"u}hrt zu kristallinen Nanopartikeln, die in eine amorphe Matrix eingebettet sind. Die Solvothermalsynthese von Mangancarbonatnanopartikel l{\"a}sst neue Morphologien in Form von Nanost{\"a}bchen entstehen, die zu schuppenartigen sph{\"a}rischen {\"U}berstrukturen agglomeriert sind.},
  language  = {de}
}
@phdthesis{Gaebert2022,
  author    = {G{\"a}bert, Chris},
  title     = {Light-responsive polymer systems aiming towards programmable friction},
  doi       = {10.25932/publishup-55338},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-553380},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVI, 108, XXVI},
  year      = {2022},
  abstract  = {The development of novel programmable materials aiming to control friction in real-time holds potential to facilitate innovative lubrication solutions for reducing wear and energy losses. This work describes the integration of light-responsiveness into two lubricating materials, silicon oils and polymer brush surfaces. The first part focusses on the assessment on 9-anthracene ester-terminated polydimethylsiloxanes (PDMS-A) and, in particular, on the variability of rheological properties and the implications that arise with UV-light as external trigger. The applied rheometer setup contains an UV-transparent quartz-plate, which enables radiation and simultaneous measurement of the dynamic moduli. UV-A radiation (354 nm) triggers the cycloaddition reaction between the terminal functionalities of linear PDMS, resulting in chain extension. The newly-formed anthracene dimers cleave by UV-C radiation (254 nm) or at elevated temperatures (T > 130 °C). The sequential UV-A radiation and thermal reprogramming over three cycles demonstrate high conversions and reproducible programming of rheological properties. In contrast, the photochemical back reaction by UV-C is incomplete and can only partially restore the initial rheological properties. The dynamic moduli increase with each cycle in photochemical programming, presumably resulting from a chain segment re-arrangement as a result of the repeated partial photocleavage and subsequent chain length-dependent dimerization. In addition, long periods of radiation cause photooxidative degradation, which damages photo-responsive functions and consequently reduces the programming range. The absence of oxygen, however, reduces undesired side reactions. Anthracene-functionalized PDMS and native PDMS mix depending on the anthracene ester content and chain length, respectively, and allow fine-tuning of programmable rheological properties. The work shows the influence of mixing conditions during the photoprogramming step on the rheological properties, indicating that material property gradients induced by light attenuation along the beam have to be considered. Accordingly, thin lubricant films are suggested as potential application for light-programmable silicon fluids. The second part compares strategies for the grafting of spiropyran (SP) containing copolymer brushes from Si wafers and evaluates the light-responsiveness of the surfaces. Pre-experiments on the kinetics of the thermally initiated RAFT copolymerization of 2-hydroxyethyl acrylate (HEA) and spiropyran acrylate (SPA) in solution show, first, a strong retardation by SP and, second, the dependence of SPA polymerization on light. Surprisingly, the copolymerization of SPA is inhibited in the dark. These findings contribute to improve the synthesis of polar, spiropyran-containing copolymers. The comparison between initiator systems for the grafting-from approach indicates PET-RAFT superior to thermally initiated RAFT, suggesting a more efficient initiation of surface-bound CTA by light. Surface-initiated polymerization via PET-RAFT with an initiator system of EosinY (EoY) and ascorbic acid (AscA) facilitates copolymer synthesis from HEA and 5-25 mol\% SPA. The resulting polymer film with a thickness of a few nanometers was detected by atomic force microscopy (AFM) and ellipsometry. Water contact angle (CA) measurements demonstrate photo-switchable surface polarity, which is attributed to the photoisomerization between non-polar spiropyran and zwitterionic merocyanine isomer. Furthermore, the obtained spiropyran brushes show potential for further studies on light-programmable properties. In this context, it would be interesting to investigate whether swollen spiropyran-containing polymers change their configuration and thus their film thickness under the influence of light. In addition, further experiments using an AFM or microtribometer should evaluate whether light-programmable solvation enables a change in frictional properties between polymer brush surfaces.},
  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}
}