Monitoring the chemistry of self-healing by vibrational spectroscopy - Current state and perspectives

Self-healing materials are designed to heal damage caused by, for example, mechanical stress or aging such that the original functionality of the material is at least partially restored. Thus, self-healing materials hold great promise for prolonging the lifetime of machines, particularly those in remote locations, as well as in increasing the reliability and safety associated with functional materials in, for example, aeronautics applications. Recent material science applications of self-healing have led to an increased interest in the field and, consequently, the spectroscopic characterization of a wide range of self-healing materials with respect to their mechanical properties such as stress and strain resistance and elasticity was in the focus. However, the characterization of the chemical mechanisms underlying various self-healing processes locally within the damaged region of materials still presents a major challenge. This requires experimental techniques that work non-destructively in situ and are capable of revealing the chemical composition of a sample with sufficient spatial and temporal resolution without disturbing the healing process. Along these lines, vibrational spectroscopy and, in particular Raman spectroscopy, holds great promise, largely due to the high spatial resolution in the order of several hundreds of nanometers that can be obtained. This article aims to summarize the state of the art and prospective of Raman spectroscopy to contribute significant insights to the research on self-healing materials - in particular focusing on polymer and biopolymer materials

Phase Coherence and Control of Stored Photonic Information

We report the demonstration of phase coherence and control for the recently developed "light storage" technique. Specifically, we use a pulsed magnetic field to vary the phase of atomic spin excitations which result from the deceleration and storing of a light pulse in warm Rb vapor. We then convert the spin excitations back into light and detect the resultant phase shift in an optical interferometric measurement. The coherent storage of photon states in matter is essential for the practical realization of many basic concepts in quantum information processing.Comment: 5 pages, 3 figures. Submitted to Phys. Rev. Let

Systems theory of Smad signaling

Transforming Growth Factor-beta (TGF-beta) signalling is an important regulator of cellular growth and differentiation. The principal intracellular mediators of TGF-beta signalling are the Smad proteins, which upon TGF-beta stimulation accumulate in the nucleus and regulate transcription of target genes. To investigate the mechanisms of Smad nuclear accumulation, we developed a simple mathematical model of canonical Smad signalling. The model was built using both published data and our experimentally determined cellular Smad concentrations (isoforms 2, 3, and 4). We found in mink lung epithelial cells that Smad2 (8.5-12 x 10^4 molecules/cell) was present in similar amounts to Smad4 (9.3-12 x 10^4 molecules/cell), while both were in excess of Smad3 (1.1-2.0 x 10^4 molecules/cell). Variation of the model parameters and statistical analysis showed that Smad nuclear accumulation is most sensitive to parameters affecting the rates of RSmad phosphorylation and dephosphorylation and Smad complex formation/dissociation in the nucleus. Deleting Smad4 from the model revealed that rate-limiting phospho-R-Smad dephosphorylation could be an important mechanism for Smad nuclear accumulation. Furthermore, we observed that binding factors constitutively localised to the nucleus do not efficiently mediate Smad nuclear accumulation if dephosphorylation is rapid. We therefore conclude that an imbalance in the rates of R-Smad phosphorylation and dephosphorylation is likely an important mechanism of Smad nuclear accumulation during TGF-beta signalling.Comment: To appear in IEE Proceedings Systems Biology. 12 pages of text, 36 pages tota

3D microstructure characterization of polymer battery electrodes by statistical image analysis based on synchrotron X ray tomography

Polymer based batteries represent a promising concept for next generation energy storage due to their potentially higher power densities and smaller ecological footprint, compared to classical Li ion batteries. Since the microstructure of electrodes is a key factor for the performance of battery cells, a detailed understanding of this microstructure is essential for the improvement of manufacturing processes. In the present contribution, the 3D microstructure of electrodes for polymer based batteries is quantitatively characterized for the first time, where synchrotron X ray tomography is combined with statistical image analysis. In particular, 3D imaging is performed for two porous electrodes, which both consist of the redox active polymer PTMA as well as conductive additives, but differ regarding their binder materials. The focus is put on local heterogeneity of volume fractions of the constituents, surface area per unit volume of the polymer phase and the length of shortest transportation paths through both, polymer and binder additive phase. It is shown that using different binder materials leads to significant differences regarding the 3D electrode microstructures. In this way, statistical analysis of image data helps to gain further insight into the influence of manufacturing processes on electrode microstructures and thus, on the performance of battery cell

A review of Monte Carlo simulations of polymers with PERM

In this review, we describe applications of the pruned-enriched Rosenbluth method (PERM), a sequential Monte Carlo algorithm with resampling, to various problems in polymer physics. PERM produces samples according to any given prescribed weight distribution, by growing configurations step by step with controlled bias, and correcting "bad" configurations by "population control". The latter is implemented, in contrast to other population based algorithms like e.g. genetic algorithms, by depth-first recursion which avoids storing all members of the population at the same time in computer memory. The problems we discuss all concern single polymers (with one exception), but under various conditions: Homopolymers in good solvents and at the $\Theta$ point, semi-stiff polymers, polymers in confining geometries, stretched polymers undergoing a forced globule-linear transition, star polymers, bottle brushes, lattice animals as a model for randomly branched polymers, DNA melting, and finally -- as the only system at low temperatures, lattice heteropolymers as simple models for protein folding. PERM is for some of these problems the method of choice, but it can also fail. We discuss how to recognize when a result is reliable, and we discuss also some types of bias that can be crucial in guiding the growth into the right directions.Comment: 29 pages, 26 figures, to be published in J. Stat. Phys. (2011

Stromspeicher : Radikal organisch = Power storage : radically organic

Lithiumionenbatterie, Bleiakku und Co. sind für den Sprung von der konventionellen zur flexiblen, gedruckten organischen Elektronik wenig geeignet. Polymerbasierte, organische Radikalbatterien bieten einen effizienten Ausweg

Synthesis of rigid pi-conjugated mono-, bis-, tris-, and tetrakis(terpyridine)s: influence of the degree and pattern of substitution on the photophysical properties

A series of rigid pi-conjugated mono-, bis-, tris-, and tetrakis(terpyridine)s 3-8 was synthesized in high yields by means of Horner-Wadsworth-Emmons (HWE) reactions between benzyl phosphonates 1 and an aldehyde-functionalized terpyridine deriv. 2. The photophys. properties of the materials in soln. and in the solid state depend strongly both on the nos. of terpyridine moieties attached to the central Ph cores and on the geometries of the compds. The photophys. behavior of the ortho-substituted compds. 5 and 8 indicated significant changes in the geometries, together with major extensions of the effective pi-conjugated systems upon excitation. Bright green emission with high quantum yields was obsd. for the tetrakis(terpyridine) deriv. 8. [on SciFinder (R)

One-component intrinsic self-healing polymer for coatings based on reversible crosslinking by Diels-Alder-cycloadditions

Self-healing can be achieved in polymer coatings by the incorporation of extrinsic materials, i.e. a healing agent is embedded into the coating (e.g., within capsules). In contrast the polymeric coating itself can feature the ability for healing \u96 for instance if reversible covalent bonds are introduced into the polymer network. The Diels-.Alder reaction is one prominent example to obtain reversibility within self-healing/mendable materials. In this context, a novel acrylic-based one-component polymer system has been synthesized, which contains both binding units for the Diels-Alder reaction (i.e. the maleimide and the furan moiety) as well as comonomers to tune the mechanical as well as thermal properties. The ATRP (atom transfer radical polymerization) of maleimide methacrylate (MIMA), furfuryl methacrylate (FMA) as well as of different alkylmethacrylates was utilized to synthesize well-defined functional terpolymers, which could be crosslinked subsequently via thermal treatment. The mechanical and thermal properties of these polymers have been investigated in detail. Moreover, the healing ability of these polymer coatings was studied. The influence of the crosslinking density, the kind of the comonomer and the healing temperature was investigated in detail. An efficient healing of these coatings could be observed. Additionally first attempts to tune the healing temperature of these coatings have been performed. The comonomers can also influence the required temperature for the retro-Diels-Alder reaction