Novel Dynamic Viscoelastic Measurements of Polyurethane Copolymer Melts and Their Implication to Tack Results

Summary: A series of polyurethane multiblock copolymers with different proportions of hard segments (urethane) to soft segments (polyadipate of hexane‐1,6‐diol), are investigated. Dynamic viscoelastic functions of homogeneous melts in the terminal zone are determined. For the first time, entanglement modulus values of such copolymers are reported, which allows estimation of the packing length. These parameters do not vary with changing the hard‐to‐soft segment ratio, a result that is explained by a compensating effect of the chain architecture. For samples of similar molecular weight, the relaxation time of the terminal zone increases as the hard‐to‐soft segment ratio augments. The adhesives obtained from PUR solutions show a correlation between the elastic modulus and the debonding stress‐strain curves in tack experiments.

The storage modulus of the adhesives as a function of frequency at 70 °C.     

Reversible active switching of the mechanical properties of a peptide film at a fluid-fluid interface

Designer peptides have recently been developed as building blocks for novel self-assembled materials with stimuli-responsive properties. To date, such materials have been based on self-assembly in bulk aqueous solution or at solid-fluid interfaces. We have designed a 21-residue peptide, AM1, as a stimuli-responsive surfactant that switches molecular architectures at a fluid-fluid interface in response to changes in bulk aqueous solution composition. In the presence of divalent zinc at neutral pH, the peptide forms a mechanically strong 'film state'. In the absence of metal ions or at acid pH, the peptide adsorbs to form a mobile 'detergent state'. The two interfacial states can be actively and reversibly switched. Switching between the two states by a change in pH or the addition of a chelating agent leads to rapid emulsion coalescence or foam collapse. This work introduces a new class of surfactants that offer an environmentally friendly approach to control the stability of interfaces in foams, emulsions and fluid-fluid interfaces more generally.     

Simple method for the stretching and alignment of single adsorbed synthetic polycations

Spin-coating of isolated positively charged macromolecules onto mica in the presence of octylamine was found to be a simple and general method of stretching and aligning the macromolecular chains. The contour length and molar mass for the stretched macromolecules can be directly measured by atomic force microscopy, which makes this method a very useful analytical tool. Moreover, the molecular height is increased by co-deposition with octylamine, which drastically improves the molecular resolution and allows even ultrathin polycations to be visualized. The reason for the key role of the octylamine is found in the formation of an ultrathin liquidlike alkylamine film, which reduces the surface energy of mica and weakens the interactions between the surface and the charged macromolecules.     

Towards Continuous Flow,Highly Enantioselective Allylic Amination: Ligand Design,Optimization and Supporting

A family of enantiopure diphenylphosphinooxazolines (PHOX) containing in their structures a sterically tunable alkoxymethyl group (‐CH₂OR) has been optimized for the palladium‐catalyzed asymmetric allylic amination. The optimal catalyst (R=CH₃), depicting very high catalytic activity and broad scope applicability, has been further modified to include an ω‐alkynyloxy substituent of variable length for polymer supporting via click chemistry, and has been anchored onto slightly cross‐linked azidomethyl poly(styrene). The length of a polymethylene chain connecting the PHOX unit with the 1,2,3‐triazole linker has been optimized, and the first polymer‐supported PHOX ligands for the highly enantioselective allylic amination have been prepared in this manner. Conditions for catalyst recovery and reuse in microwave‐promoted amination reactions have been established, and the system has been finally adapted to continuous flow operation.     

Das städtische Mikroklima: Analyse für die Stadt‐ und Gebäudeplanung

In the face of global warming, human thermal comfort has become an increasing important aspect in applied urban planning. As the urban heat island is not a homogenous factor the microclimate conditions play an important role also for single buildings and the situation inside. For a better consideration of this aspect in the planning process, qualitative and especially quantitative assessment tools are required. To get a better knowledge about the quantitative dimension of urban climates investigations on thermal comfort in outdoor and indoor spaces are carried out in selected city quarters in the city of Kassel in Germany. These studies consist of experimental investigations including field interviews about usage of urban open spaces and thermal sensation and numerical simulations on thermal comfort under recent as well as future regional climate conditions. The added‐value of the interdisciplinary research project is based on the correlation of findings from human‐biometeorology with the outcomes from sociologic questionnaires and building physics, which will be used to plan and design structures in a high spatial resolution. The thermal conditions outside continue inside the building, a combination of internal and external climate considerations must be made. The aim of a research at the University of Kassel is the examination and presentation of different microclimate and its influence on the thermal behavior of buildings.     

Strong practical stability and stabilization of discrete linear repetitive processes

This paper considers two-dimensional (2D) discrete linear systems recursive over the upper right quadrant described by well known state-space models. Included are discrete linear repetitive processes that evolve over subset of this quadrant. A stability theory exists for these processes based on a bounded-input bounded-output approach and there has also been work on the design of stabilizing control laws, elements of which have led to the assertion that this stability theory is too strong in many cases of applications interest. This paper develops so-called strong practical stability as an alternative in such cases. The analysis includes computationally efficient tests that lead directly to the design of stabilizing control laws, including the case when there is uncertainty associated with the process model. The results are illustrated by application to a linear model approximation of the dynamics of a metal rolling process.

What Genetics Has Told Us and How It Can Inform Future Experiments for Spinal Muscular Atrophy,a Perspective

Proximal spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder characterized by motor neuron loss and subsequent atrophy of skeletal muscle. SMA is caused by deficiency of the essential survival motor neuron (SMN) protein, canonically responsible for the assembly of the spliceosomal small nuclear ribonucleoproteins (snRNPs). Therapeutics aimed at increasing SMN protein levels are efficacious in treating SMA. However, it remains unknown how deficiency of SMN results in motor neuron loss, resulting in many reported cellular functions of SMN and pathways affected in SMA. Herein is a perspective detailing what genetics and biochemistry have told us about SMA and SMN, from identifying the SMA determinant region of the genome, to the development of therapeutics. Furthermore, we will discuss how genetics and biochemistry have been used to understand SMN function and how we can determine which of these are critical to SMA moving forward.     

Quorum Sensing of Bacteria and Trans-Kingdom Interactions of N-Acyl Homoserine Lactones with Eukaryotes

Many environmental and interactive important traits of bacteria, such as antibiotic, siderophore or exoenzyme (like cellulose, pectinase) production, virulence factors of pathogens, as well as symbiotic interactions, are regulated in a population density-dependent manner by using small signaling molecules. This phenomenon, called quorum sensing (QS), is widespread among bacteria. Many different bacterial species are communicating or "speaking" through diffusible small molecules. The production often is sophisticatedly regulated via an autoinducing mechanism. A good example is the production of N-acyl homoserine lactones (AHL), which occur in many variations of molecular structure in a wide variety of Gram-negative bacteria. In Gram-positive bacteria, other compounds, such as peptides, regulate cellular activity and behavior by sensing the cell density. The degradation of the signaling molecule--called quorum quenching--is probably another important integral part in the complex quorum sensing circuit. Most interestingly, bacterial quorum sensing molecules also are recognized by eukaryotes that are colonized by QS-active bacteria. In this case, the cross-kingdom interaction can lead to specific adjustment and physiological adaptations in the colonized eukaryote. The responses are manifold, such as modifications of the defense system, modulation of the immune response, or changes in the hormonal status and growth responses. Thus, the interaction with the quorum sensing signaling molecules of bacteria can profoundly change the physiology of higher organisms too. Higher organisms are obligatorily associated with microbial communities, and these truly multi-organismic consortia, which are also called holobionts, can actually be steered via multiple interlinked signaling substances that originate not only from the host but also from the associated bacteria.     

Morphological structure and surface properties of maleated ethylene propylene diene monomer/organoclay nanocomposites

The phase morphology and surface properties of some maleated ethylene propylene‐diene/organoclay nanocomposites (EPDM‐g‐MA/OC) were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. The effect of organoclay and/or compatibilizing agent [maleic anhydride‐grafted polypropylene (PP‐g‐MA)] on the properties of the EPDM‐g‐MA nanocomposites was investigated. The quality and uniformity of nanoclay dispersion were analyzed by SEM and AFM images. The experimental results showed an intercalate structure and biphasic morphology for the binary blends based on EPDM and clay. The surface properties of the studied composites are significantly influenced by the presence of a compatibilizing agent—PP‐g‐MA. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers