A hit-and-run Giant Impact scenario

The formation of the Moon from the debris of a slow and grazing giant impact of a Mars-sized impactor on the proto-Earth (Cameron & Ward 1976, Canup & Asphaug 2001) is widely accepted today. We present an alternative scenario with a hit-and-run collision (Asphaug 2010) with a fractionally increased impact velocity and a steeper impact angle.Comment: 11 pages, 2 figures, in press in ICARUS note

Evidence for temperature-independent triplet diffusion in a ladder-type conjugated polymer

Journal ArticleWe study the temperature dependence of triplet formation and decay by considering the phosphorescence dynamics in a prototypical conjugated polymer matrix. The dynamics of triplet formation as a function of temperature are unraveled by applying an electric field during optical singlet generation and recording the phosphorescence quenching. The diffusivity of triplet excitons in conjugated polymers is shown to be independent of temperature up to 200 K. We propose a diffusion model that describes the relaxation dynamics of triplet excitons at all times through triplet-triplet annihilation and spin orbit coupling at static heavy atom sites

Low-threshold polymeric distributed feedback lasers with metallic contacts

Journal ArticleOptical losses in waveguides comprising metallic contacts are thought to be a major hurdle to the realization of organic laser diodes. We demonstrate here that careful tuning of the waveguide mode in flexible distributed feedback lasers can allow lasing action to occur in organic thin films in the presence of contacting electrodes with virtually no difference when compared to metal free devices. A metallic electrode is most suited as the bottom contact between the polymer and the substrate as it reduces mode leakage into the substrate and enhances modal gain. In contrast, a thin transparent electrode such as a metal oxide is preferable for the top electrode, where confinement is not a problem

Stimulated emission depletion of triplet excitons in a phosphorescent organic laser

Journal ArticleTriplet formation is investigated in an optically pumped polymer laser by detecting the phosphorescence emission after excitation. A clear correlation is observed between the onset of lasing and a saturation of phosphorescence intensity due to stimulated emission depletion of the singlet state and the resulting reduction in intersystem crossing. The results are consistent with intersystem crossing constituting the dominant triplet formation pathway in conjugated polymers. Excitation at different wavelengths has no effect on the triplet saturation behavior, which allows the authors to exclude singlet fission or breaking as the origin of triplet formation. The method constitutes an implementation of a highly nondegenerate excitonic switch

Improved diffusing wave spectroscopy based on the automatized determination of the optical transport and absorption mean free path

Diffusing wave spectroscopy (DWS) can be employed as an optical rheology tool with numerous applications for studying the structure, dynamics and linear viscoelastic properties of complex fluids, foams, glasses and gels. To carry out DWS measurements, one first needs to quantify the static optical properties of the sample under investigation, i.e. the transport mean free path l* and the absorption length la. In the absence of absorption this can be done by comparing the diffuse optical transmission to a calibration sample whose l* is known. Performing this comparison however is cumbersome, time consuming, and prone to mistakes by the operator. Moreover, already weak absorption can lead to significant errors. In this paper, we demonstrate the implementation of an automatized approach, based on which the DWS measurement procedure can be simplified significantly. By comparison with a comprehensive set of calibration measurements we cover the entire parameter space relating measured count rates (CRt, CRb) to (l*, la). Based on this approach we can determine l* and la of an unknown sample accurately thus making the additional measurement of a calibration sample obsolete. We illustrate the use of this approach by monitoring the coarsening of a commercially available shaving foam with DWS

Formulation design of complex fluids based products through diffusing wave spectroscopy (DWS)

Complex fluids and soft matter systems are ubiquitous in consumer and cosmetic products and also in products found across many other industrial sectors encompassing foods, paints, coatings, biopharmaceutiucals etc. A critical aspect in the formulation design and optimization of these complex fluids based products is the maintenance of stability and enhancement of the sensory and functional performance. This requires establishing and optimizing the microstructure-property-performance linkages in these complex fluids. Since complex fluids are structured on multiple length scales and undergo dynamics over a wide range of timescales, the establishment of such linkages requires experimental tools that allow access to these length and time scales. Diffusing Wave Spectroscopy has emerged as a versatile experimental technique that allows unique insights into the microstructure/dynamics/rheology of complex fluid based products, allowing the design and optimization of formulations for enhanced performance benefits. This talk reviews a number of different examples and applications of DWS that are relevant for formulation design. This will include sizing, rheology and stability monitoring in emulsions, rheology of polymers to understand short time dynamics and monitoring the effect active/drug release has on the evolution of a micellar system. M. Reufer Journal OF Pharmaceutical Sciences 103:3902–3913, 2014 D. Gaudino et al., PCCP, 19, 2017, 782. LS Instruments Application Note

Temperature-sensitive poly(N-Isopropyl-Acrylamide) microgel particles: A light scattering study

We present a light scattering study of aqueous suspensions of microgel particles consisting of poly(N-Isopropyl-Acrylamide) cross-linked gels. The solvent quality for the particles depends on temperature and thus allows tuning of the particle size. The particle synthesis parameters are chosen such that the resulting high surface charge of the particles prevents aggregation even in the maximally collapsed state. We present results on static and dynamic light scattering (SLS/DLS) for a highly diluted sample and for diffuse optical transmission on a more concentrated system. In the maximally collapsed state the scattering properties are well described by Mie theory for homogenous hard spheres. Upon swelling we find that a radially inhomogeneous density profile develop

On the origin and composition of Theia: Constraints from new models of the Giant Impact

Knowing the isotopic composition of Theia, the proto-planet which collided with the Earth in the Giant Impact that formed the Moon, could provide interesting insights on the state of homogenization of the inner solar system at the late stages of terrestrial planet formation. We use the known isotopic and modeled chemical compositions of the bulk silicate mantles of Earth and Moon and combine them with different Giant Impact models, to calculate the possible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in each model. We compare these ranges to the isotopic composition of carbonaceous chondrites, Mars, and other solar system materials. In the absence of post-impact isotopic re-equilibration, the recently proposed high angular momentum models of the Giant Impact ("impact-fission", Cuk & Stewart, 2012; and "merger", Canup, 2012) allow - by a narrow margin - for a Theia similar to CI-chondrites, and Mars. The "hit-and-run" model (Reufer et al., 2012) allows for a Theia similar to enstatite-chondrites and other Earth-like materials. If the Earth and Moon inherited their different mantle FeO contents from the bulk mantles of the proto-Earth and Theia, the high angular momentum models cannot explain the observed difference. However, both the hit-and-run as well as the classical or "canonical" Giant Impact model naturally explain this difference as the consequence of a simple mixture of two mantles with different FeO. Therefore, the simplest way to reconcile the isotopic similarity, and FeO dissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic composition and a higher (~20%) mantle FeO content.Comment: 53 Pages, 10 Figures, 1 Table, 3 Supplementary Table

Transport of light in amorphous photonic materials

Amorphous photonic materials based on dense assemblies of high refractive index spherical particles are presented. Light transmission through these photonic glasses shows a nontrivial wavelength dependence. The transmission spectra can be quantitatively reproduced by modeling the optical properties starting from their building blocks. Our results emphasize the relevance of including short range order correlations and an appropriate effective refractive index in the analysis of light transmission through amorphous photonic materials

Soft Nanotechnology – from Colloid Physics to Nanostructured Functional Materials

We demonstrate how we can tune the size, shape, surface functionality and properties of nanoparticles and use them as ideal model systems for fundamental investigations as well as for materials applications. In particular we describe ways to create functionalized core-shell particles with various degree of anisotropy and interesting magnetic properties. We show how we can use these particles in order to study the equilibrium and non-equilibrium phase behavior of colloidal suspensions with different interaction potentials and summarize our current understanding of the phenomenon of dynamical arrest, i.e. gel and glass formation. While different nanoparticles are vital for fundamental studies of various aspects of soft condensed matter, they also offer fascinating possibilities in materials science. We will demonstrate this with the example of nanocomposites made through an in situ polymerization reaction