Fak. 2 Mathematik und Naturwissenschaften

2145 Items

Recent Submissions
Macroscopic Internal Variables and Mesoscopic Theory: A Comparison Considering Liquid Crystals

Papenfuss, Christina ; Muschik, Wolfgang (2018-01-22)

Internal and mesoscopic variables differ fundamentally from each other: both are state space variables, but mesoscopic variables are additionally equipped with a distribution function introducing a statistical item into consideration which is missing in connection with internal variables. Thus, the alignment tensor of the liquid crystal theory can be introduced as an internal variable or as one...

Relations between Structure, Activity and Stability in C3N4 Based Photocatalysts Used for Solar Hydrogen Production

Sivasankaran, Ramesh P. ; Rockstroh, Nils ; Hollmann, Dirk ; Kreyenschulte, Carsten R. ; Agostini, Giovanni ; Lund, Henrik ; Acharjya, Amitava ; Rabeah, Jabor ; Bentrup, Ursula ; Junge, Henrik ; Thomas, Arne ; Brückner, Angelika (2018-01-29)

Solar hydrogen production from water could be a sustainable and environmentally friendly alternative to fossil energy carriers, yet so far photocatalysts active and stable enough for large-scale applications are not available, calling for advanced research efforts. In this work, H2 evolution rates of up to 1968 and 5188 μmol h−1 g−1 were obtained from aqueous solutions of triethanolamine (TEOA)...

Inner structure and dynamics of microgels with low and medium crosslinker content prepared via surfactant-free precipitation polymerization and continuous monomer feeding approach

Kyrey, Tetyana ; Witte, Judith ; Feoktystov, Artem ; Pipich, Vitaliy ; Wu, Baohu ; Pasini, Stefano ; Radulescu, Aurel ; Witt, Marcus U. ; Kruteva, Margarita ; Klitzing, Regine von ; Wellert, Stefan ; Holderer, Olaf (2019-07-17)

The preparation of poly(N-isopropylacrylamide) microgels via classical precipitation polymerization (batch method) and a continuous monomer feeding approach (feeding method) leads to different internal crosslinker distributions, i.e., from core–shell-like to a more homogeneous one. The internal structure and dynamics of these microgels with low and medium crosslinker concentrations are studied ...

Unraveling the protonation site of oxazole and solvation with hydrophobic ligands by infrared photodissociation spectroscopy

Chatterjee, Kuntal ; Dopfer, Otto (2019-01-19)

Protonation and solvation of heterocyclic aromatic building blocks control the structure and function of many biological macromolecules. Herein the infrared photodissociation (IRPD) spectra of protonated oxazole (H+Ox) microsolvated by nonpolar and quadrupolar ligands, H+Ox-Ln with L = Ar (n = 1–2) and L = N2 (n = 1–4), are analyzed by density functional theory calculations at the dispersion-co...

Experimental Activity Descriptors for Iridium-based Catalysts for the Electrochemical Oxygen Evolution Reaction (OER)

Spöri, Camillo Wolfgang ; Briois, Pascal ; Nong, Hong Nhan ; Reier, Tobias ; Billard, Alain ; Kühl, Stefanie ; Teschner, Detre ; Strasser, Peter (2019-06-13)

Recent progress in the activity improvement of anode catalysts for acidic electrochemical water splitting was largely achieved through empirical studies of iridium-based bimetallic oxides. However, practical, experimentally accessible, yet general predictors of catalytic OER activity are lacking. This study investigates iridium and iridium-nickel thin film model electrocatalysts for the OER and...

The Stability Challenges of Oxygen Evolving Catalysts: Towards a Common Fundamental Understanding and Mitigation of Catalyst Degradation

Spöri, Camillo Wolfgang ; Kwan, Jason Tai Hong ; Bonakdarpour, Arman ; Wilkinson, David P. ; Strasser, Peter (2017-05-04)

This review addresses the technical challenges, their scientific basis, as well as recent progress and the road ahead with respect to the stability and degradation of OER catalysts operating at electrolyzer anodes in acidic environments with an emphasis on MEA based operation. First, we start clarifying the complexity associated with the term “catalyst stability”, cover today’s performance targ...

Kinetic study of dry reforming of Methane with Ni over different supports and Pt/Al2O3

Guan, Chengyue (2019)

This thesis presents a kinetic study on Ni series catalysts for dry reforming of methane (DRM) and comparison with a commercially noble metal catalyst Pt/Al2O3. For each catalyst, a corresponding kinetic model needs to be established. These kinetic schemes should be sophisticated enough to describe the consumption rates, meanwhile rather simple for industrial applications. In this thesis, we in...

Collective dynamics in a monolayer of squirmers confined to a boundary by gravity

Kuhr, Jan-Timm ; Rühle, Felix ; Stark, Holger (2019-06-21)

We present a hydrodynamic study of a monolayer of squirmer model microswimmers confined to a boundary by strong gravity using the simulation method of multi-particle collision dynamics. The squirmers interact with each other via their self-generated hydrodynamic flow fields and thereby form a variety of fascinating dynamic states when density and squirmer type are varied. Weak pushers, neutral ...

Effect of Electron Blocking Layer Doping and Composition on the Performance of 310 nm Light Emitting Diodes

Kolbe, Tim ; Knauer, Arne ; Rass, Jens ; Cho, Hyun ; Hagedorn, Sylvia ; Einfeldt, Sven ; Kneissl, Michael ; Weyers, Markus (2017-12-06)

The effects of composition and p-doping profile of the AlGaN:Mg electron blocking layer (EBL) in 310 nm ultraviolet B (UV-B) light emitting diodes (LEDs) have been investigated. The carrier injection and internal quantum efficiency of the LEDs were simulated and compared to electroluminescence measurements. The light output power depends strongly on the temporal biscyclopentadienylmagnesium (Cp...

Direct utilization of methane: from mechanism understanding to process optimization

Parishan, Samira (2019)

Methane, which is a promising alternative to replace crude oil, is currently underutilized. Industrialization of either OCM or DMTM could realize utilization of methane to value-added chemicals. But, unfortunately, none of these reactions have still an industrially acceptable yield. In this thesis, it was searched for the solutions to overcome these yield barriers. The focus in the OCM projec...

Second Law and Non-Equilibrium Entropy of Schottky Systems—Doubts and Verification−

Muschik, Wolfgang (2018-09-28)

Meixner’s historical remark in 1969 “... it can be shown that the concept of entropy in the absence of equilibrium is in fact not only questionable but that it cannot even be defined....” is investigated from today’s insight. Several statements—such as the three laws of phenomenological thermodynamics, the embedding theorem and the adiabatical uniqueness—are used to get rid of non-equilibrium e...

Structural Dynamics of Spin Crossover in Iron(II) Complexes with Extended-Tripod Ligands

Stock, Philipp ; Wiedemann, Dennis ; Petzold, Holm ; Hörner, Gerald (2017-09-05)

Selective manipulation of spin states in iron(II) complexes by thermal or photonic energy is a desirable goal in the context of developing molecular functional materials. As dynamic spin-state equilibration in isolated iron(II) complexes typically limits the lifetime of a given spin state to nanoseconds, synthetic strategies need to be developed that aim at inhibited relaxation. Herein we show ...

Synthese und Anwendung kationischer bor- und phosphorbasierter LEWIS-Säurekatalysatoren

Vogler, Maria (2019)

Die vorliegende Arbeit widmet sich zum einen der Synthese und Anwendung neuer axial chiraler Boreniumkationen und zum anderen der Anwendung verschiedener achiraler Phosphoniumkationen in DIELS–ALDER-Reaktionen und NAZAROV-Cyclisierungen. Für chirale Boreniumkationen und deren Anwendung als LEWIS-Säurekatalysatoren gibt es bisher nur vereinzelte Beispiele mit eher niedrigen Enantiomerenüberschü...

Thickening of T1 Precipitates during Aging of a High Purity Al−4Cu−1Li−0.25Mn Alloy

Häusler, Ines ; Kamachali, Reza Darvishi ; Hetaba, Walid ; Skrotzki, Birgit (2018-12-21)

The age hardening response of a high-purity Al–4Cu–1Li–0.25Mn alloy (wt. %) during isothermal aging without and with an applied external load was investigated. Plate shaped nanometer size T1 (Al2CuLi) and θ′ (Al2Cu) hardening phases were formed. The precipitates were analyzed with respect to the development of their structure, size, number density, volume fraction and associated transformation ...

Structural characteristics of InGaAs/GaP quantum dots and related materials on the atomic scale

Prohl, Christopher (2019)

Self-assembled (In,Ga)As quantum dots (QDs) embedded in a GaP matrix are a promising semiconductor material for possible applications in optoelectronics and nanomemory cells. Even more, GaP with its particular low lattice mismatch to silicon offers the possibility to monolithically integrate III-V semiconductor nanotechnology into silicon. In this thesis, cross-sectional scanning tunneling mic...

Geometrie, Spinzustand und Reaktivität verzerrt-oktaedrischer Eisen-Komplexe im Lichte des Liganddesigns

Kroll, Nicole (2019)

Im Rahmen dieser Arbeit wurden drei Themenbereiche, die sich mit dem Einfluss der Ligandumgebung von pentadentaten Liganden auf die Geometrie, den Spinzustand und die Reaktivität von Eisen-Komplexen befassen, bearbeitet. Einerseits konnte der isolierte Einfluss der Donoratome auf die Ligandumgebung und damit auf die Struktur der Chelatkomplexe eindeutig gezeigt werden. Dazu wurde der Ligand TPS...

Surface Patterning of Gold Nanoparticles on PEG-Based Hydrogels to Control Cell Adhesion

Ren, Fang ; Yesildag, Cigdem ; Zhang, Zhenfang ; Lensen, Marga C. (2017-04-26)

We report on a versatile and easy approach to micro-pattern gold nanoparticles (Au NPs) on 8-arm poly(ethylene glycol)-vinyl sulfone thiol (8PEG-VS-SH) hydrogels, and the application of these patterned Au NPs stripes in controlling cell adhesion. Firstly, the Au NPs were patterned on silicon wafers, and then they were transferred onto reactive, multifunctional 8PEG-VS-SH hydrogels. The patterne...

Droplets, Evaporation and a Superhydrophobic Surface: Simple Tools for Guiding Colloidal Particles into Complex Materials

Sperling, Marcel ; Gradzielski, Michael (2017-05-04)

The formation of complexly structured and shaped supraparticles can be achieved by evaporation-induced self-assembly (EISA) starting from colloidal dispersions deposited on a solid surface; often a superhydrophobic one. This versatile and interesting approach allows for generating rather complex particles with corresponding functionality in a simple and scalable fashion. The versatility is base...

Surface Plasmon Resonance Immunosensor for the Detection of Campylobacter jejuni

Masdor, Noor Azlina ; Altintas, Zeynep ; Tothill, Ibtisam E. (2017-05-16)

Campylobacteriosis is an internationally important foodborne disease caused by Campylobacter jejuni. The bacterium is prevalent in chicken meat and it is estimated that as much as 90% of chicken meat on the market may be contaminated with the bacterium. The current gold standard for the detection of C. jejuni is the culturing method, which takes at least 48 h to confirm the presence of the bact...

Volume Hologram Formation in SU-8 Photoresist

Sabel, Tina (2017-05-30)

In order to further understand the mechanism of volume hologram formation in photosensitive polymers, light-induced material response is analyzed in commonly used epoxy-based negative photoresist Epon SU-8. For this purpose, time-resolved investigation of volume holographic grating growth is performed in the SU-8 based host–guest system and in the pure SU-8 material, respectively. The compariso...