Designing Pickering Emulsions for Interfacial Catalysis

Pickering emulsions (PEs) are emulsions stabilized by solid or soft (nano-)particles. The high adsorption energy of the particles at the interface results in outstanding stability of PEs. This attribute makes them ideal candidates as an environment for interfacial catalysis. In PEs that are used for interfacial catalysis, usually, a water-soluble catalyst is enclosed in water droplets that are surrounded by the substrate/product containing oil phase. The reaction takes place at the interface of the droplets. The large internal interfacial area of PEs benefits the contact between substrate and catalyst, while the catalyst itself is conserved and protected in the dispersed phase. This increases the product yield and reduces the catalyst loss. Most important, the inherent stability of PEs allows the application of energy-efficient separation strategies, e. g., membrane filtration, to retain the catalyst phase and simultaneously extract the product phase. Despite the growing interest in this topic over the last decade, the connection between emulsion structure and reaction performance remains unclear and general conclusions are missing. This thesis addresses the influence of the emulsion structure on the reaction and filtration performance and suggests a new improved PE structure based on the gained findings. It resembles a bottom-up approach: First, the used nano-particles are characterized regarding their size, charge, hydrophobicity, density and other geometrical characteristics. As a model system, mono-disperse silica nano-spheres (SNs) are synthesized to enable the calculation of values for the particle coverage and the particle-liquid contact area in the PEs. Second, these particles are used to stabilize water in 1-dodecene emulsions and a connection between the nano-scale particle properties and the micro-scale PE structure is drawn. Third, the PEs are tested as an environment for the hydroformylation of 1-dodecene into tridecanal via the water-soluble ligand-metal catalyst Rhodium-Sulfoxantphos and subsequent membrane filtration is carried out. The knowledge about the geometry and structure of the PEs enables the development of a detailed and quantitative model of the reaction process. Finally, a novel emulsion structure is designed based on the findings by combining solid hydrophobic SNs and soft hydrophilic microgel particles (MGs) to synergistically stabilize PEs. The hydrophobic SNs enable the formation of water in oil emulsions while MGs act as a spacer between the SNs to improve the catalyst-substrate contact area. These findings may contribute to a fundamental understanding and offer new impulses for the optimization of interfacial catalysis in PEs

Impact of Ultrasound on the Motion of Compact Particles and Acousto-responsive Microgels

In this study, we investigate dynamic light scattering (DLS) from both randomly diffusing silica particles and acousto-responsive microgels in aqueous dispersions under ultrasonic vibration. Employing high-frequency ultrasound (US) with low amplitude ensures that the polymers remain intact without damage. We derive theoretical expressions for the homodyne autocorrelation function, incorporating the US term alongside the diffusion term. Subsequently, we successfully combine US with a conventional DLS system to experimentally characterize compact silica particles and microgels under the influence of US. Our model allows us to extract essential parameters, including particle size, frequency, and amplitude of particle vibration, based on the correlation function of the scattered light intensity. The studies involving non-responsive silica particles demonstrate that US does not disrupt size determination, establishing them as suitable reference systems. Microgels show the same swelling/shrinking behavior as that induced by temperature, but with significantly faster kinetics. The findings of this study have potential applications in various industrial and biomedical fields that benefit from the characterization of macromolecules subjected to US

A Tale of Two Headers: A Formal Analysis of Inconsistent Click-Jacking Protection on the Web

Click-jacking protection on the modern Web is commonly enforced via client-side security mechanisms for framing control, like the X-Frame-Options header (XFO) and Content Security Policy (CSP). Though these client-side security mechanisms are certainly useful and successful, delegating protection to web browsers opens room for inconsistencies in the security guarantees offered to users of different browsers. In particular, inconsistencies might arise due to the lack of support for CSP and the different implementations of the underspecified XFO header. In this paper, we formally study the problem of inconsistencies in framing control policies across different browsers and we implement an automated policy analyzer based on our theory, which we use to assess the state of click-jacking protection on the Web. Our analysis shows that 10% of the (distinct) framing control policies in the wild are inconsistent and most often do not provide any level of protection to at least one browser. We thus propose recommendations for web developers and browser vendors to mitigate this issue. Finally, we design and implement a server-side proxy to retrofit security in web applications

Simulation-based Inference for Model Parameterization on Analog Neuromorphic Hardware

The BrainScaleS-2 (BSS-2) system implements physical models of neurons as well as synapses and aims for an energy-efficient and fast emulation of biological neurons. When replicating neuroscientific experiment results, a major challenge is finding suitable model parameters. This study investigates the suitability of the sequential neural posterior estimation (SNPE) algorithm for parameterizing a multi-compartmental neuron model emulated on the BSS-2 analog neuromorphic hardware system. In contrast to other optimization methods such as genetic algorithms or stochastic searches, the SNPE algorithms belongs to the class of approximate Bayesian computing (ABC) methods and estimates the posterior distribution of the model parameters; access to the posterior allows classifying the confidence in parameter estimations and unveiling correlation between model parameters. In previous applications, the SNPE algorithm showed a higher computational efficiency than traditional ABC methods. For our multi-compartmental model, we show that the approximated posterior is in agreement with experimental observations and that the identified correlation between parameters is in agreement with theoretical expectations. Furthermore, we show that the algorithm can deal with high-dimensional observations and parameter spaces. These results suggest that the SNPE algorithm is a promising approach for automating the parameterization of complex models, especially when dealing with characteristic properties of analog neuromorphic substrates, such as trial-to-trial variations or limited parameter ranges

Eradicating DNS Rebinding with the Extended Same-Origin Policy

The Web’s principal security policy is the Same-Origin Policy (SOP), which enforces origin-based isolation of mutually distrusting Web applications. Since the early days, the SOP was repeatedly undermined with variants of the DNS Rebinding attack, allowing untrusted script code to gain illegitimate access to protected network resources. To counter these attacks, the browser vendors introduced countermeasures, such as DNS Pinning, to mitigate the attack. In this paper, we present a novel DNS Rebinding attack method leveraging the HTML5 Application Cache. Our attack allows reliable DNS Rebinding attacks, circumventing all currently deployed browser-based defense measures. Furthermore, we analyze the fundamental problem which allows DNS Rebinding to work in the first place: The SOP’s main purpose is to ensure security boundaries of Web servers. However, the Web servers themselves are only indirectly involved in the corresponding security decision. Instead, the SOP relies on information obtained from the domain name system, which is not necessarily controlled by the Web server’s owners. This mismatch is exploited by DNS Rebinding. Based on this insight, we propose a light-weight extension to the SOP which takes Web server provided information into account. We successfully implemented our extended SOP for the Chromium Web browser and report on our implementation’s interoperability and security properties