Low Tg, strongly segregated, ABA triblock copolymers: a rheological and structural study.

ABA triblock copolymers can form microphase separated structures where the B blocks form bridges between A domains, leading to reversible networks interesting for a variety of applications such as pressure sensitive adhesives or thermoplastic elastomers. However, a major drawback of these systems is their rapid loss of mechanical properties upon temperature increase. A potential way to circumvent this limitation would be to design ABA triblock copolymers that keep their microphase separation at high temperatures. In this paper, we report on all-soft ABA triblock copolymers having a poly(n-butyl acrylate) (PnBA) central block and poly(heptafluorobutyl acrylate) (PHFBA) outer blocks. By introducing fluorinated units, the incompatibility between the blocks is largely increased, allowing strong segregation between the block domains, which preserve the microphase separation up to high temperatures despite the low glass transition temperature of the blocks, as shown by temperature dependent SAXS measurements. We study the properties of different copolymers, with similar PHFBA volume fractions but different block lengths. Linear shear rheology measurements revealed the presence of a second, low frequency, plateau whose onset and length depend on the PnBA and PHFBA length, respectively. This plateau also persists up to higher temperatures for longer PHFBA blocks.

Small-Angle Neutron Scattering Study of the Structural Relaxation of Elongationally Oriented, Moderately Stretched Three-Arm Star Polymers.

We present structural relaxation studies of a polystyrene star polymer after cessation of high-rate extensional flow. During the steady-state flow, the scattering pattern shows two sets of independent correlations peaks, reflecting the structure of a polymer confined in a fully oriented three-armed tube. Upon cessation of flow, the relaxation constitutes three distinct regimes. In a first regime, the perpendicular correlation peaks disappear, signifying disruption of the virtual tube. In a second regime, broad scattering arcs emerge, reflecting relaxation from highly aligned chains to more relaxed, still anisotropic form. New entanglements dominate the last relaxation regime where the scattering pattern evolves to a successively elliptical and circular pattern, reflecting relaxation via reptation.

Small-Angle X-Ray and Neutron Scattering on Photosynthetic Membranes.

Ultrastructural membrane arrangements in living cells and their dynamic remodeling in response to environmental changes remain an area of active research but are also subject to large uncertainty. The use of noninvasive methods such as X-ray and neutron scattering provides an attractive complimentary source of information to direct imaging because in vivo systems can be probed in near-natural conditions. However, without solid underlying structural modeling to properly interpret the indirect information extracted, scattering provides at best qualitative information and at worst direct misinterpretations. Here we review the current state of small-angle scattering applied to photosynthetic membrane systems with particular focus on data interpretation and modeling.

Insights into the composition of ancient Egyptian red and black inks on papyri achieved by synchrotron-based microanalyses.

A hitherto unknown composition is highlighted in the red and black inks preserved on ancient Egyptian papyri from the Roman period (circa 100 to 200 CE). Synchrotron-based macro-X-ray fluorescence (XRF) mapping brings to light the presence of iron (Fe) and lead (Pb) compounds in the majority of the red inks inscribed on 12 papyrus fragments from the Tebtunis temple library. The iron-based compounds in the inks can be assigned to ocher, notably due to the colocalization of Fe with aluminum, and the detection of hematite (Fe2O3) by micro-X-ray diffraction. Using the same techniques together with micro-Fourier transform infrared spectroscopy, Pb is shown to be associated with fatty acid phosphate, sulfate, chloride, and carboxylate ions. Moreover, micro-XRF maps reveal a peculiar distribution and colocalization of Pb, phosphorus (P), and sulfur (S), which are present at the micrometric scale resembling diffused "coffee rings" surrounding the ocher particles imbedded in the red letters, and at the submicrometric scale concentrated in the papyrus cell walls. A similar Pb, P, and S composition was found in three black inks, suggesting that the same lead components were employed in the manufacture of carbon-based inks. Bearing in mind that pigments such as red lead (Pb3O4) and lead white (hydrocerussite [Pb3(CO3)2(OH)2] and/or cerussite [PbCO3]) were not detected, the results presented here suggest that the lead compound in the ink was used as a drier rather than as a pigment. Accordingly, the study calls for a reassessment of the composition of lead-based components in ancient Mediterranean pigments.

Evolution of local motifs and topological proximity in self-assembled quasi-crystalline phases.

Using methods from the field of topological data analysis, we investigate the self-assembly and emergence of three-dimensional quasi-crystalline structures in a single-component colloidal system. Combining molecular dynamics and persistent homology, we analyse the time evolution of persistence diagrams and particular local structural motifs. Our analysis reveals the formation and dissipation of specific particle constellations in these trajectories, and shows that the persistence diagrams are sensitive to nucleation and convergence to a final structure. Identification of local motifs allows quantification of the similarities between the final structures in a topological sense. This analysis reveals a continuous variation with density between crystalline clathrate, quasi-crystalline, and disordered phases quantified by 'topological proximity', a visualization of the Wasserstein distances between persistence diagrams. From a topological perspective, there is a subtle, but direct connection between quasi-crystalline, crystalline and disordered states. Our results demonstrate that topological data analysis provides detailed insights into molecular self-assembly.

Threading-Unthreading Transition of Linear-Ring Polymer Blends in Extensional Flow.

Adding small amounts of ring polymers to a matrix of their linear counterparts is known to increase the zero-shear-rate viscosity because of linear-ring threading. Uniaxial extensional rheology measurements show that, unlike its pure linear and ring constituents, the blend exhibits an overshoot in the stress growth coefficient. By combining these measurements with ex-situ small-angle neutron scattering and nonequilibrium molecular dynamics simulations, this overshoot is shown to be driven by a transient threading-unthreading transition of rings embedded within the linear entanglement network. Prior to unthreading, embedded rings deform affinely with the linear entanglement network and produce a measurably stronger elongation of the linear chains in the blend compared to the pure linear melt. Thus, rings uniquely alter the mechanisms of transient elongation in linear polymers.

Ultrastructural modeling of small angle scattering from photosynthetic membranes.

The last decade has seen a range of studies using non-invasive neutron and X-ray techniques to probe the ultrastructure of a variety of photosynthetic membrane systems. A common denominator in this work is the lack of an explicitly formulated underlying structural model, ultimately leading to ambiguity in the data interpretation. Here we formulate and implement a full mathematical model of the scattering from a stacked double bilayer membrane system taking instrumental resolution and polydispersity into account. We validate our model by direct simulation of scattering patterns from 3D structural models. Most importantly, we demonstrate that the full scattering curves from three structurally typical cyanobacterial thylakoid membrane systems measured in vivo can all be described within this framework. The model provides realistic estimates of key structural parameters in the thylakoid membrane, in particular the overall stacking distance and how this is divided between membranes, lumen and cytoplasmic liquid. Finally, from fitted scattering length densities it becomes clear that the protein content in the inner lumen has to be lower than in the outer cytoplasmic liquid and we extract the first quantitative measure of the luminal protein content in a living cyanobacteria.

Towards biomimics of cell membranes: Structural effect of phosphatidylinositol triphosphate (PIP3) on a lipid bilayer.

Phosphoinositide (PIP) lipids are anionic phospholipids playing a fundamental role for the activity of several transmembrane and soluble proteins. Among all, phosphoinositol-3',4',5'-trisphosphate (PIP3) is a secondary signaling messenger that regulates the function of proteins involved in cell growth and gene transcription. The present study aims to reveal the structure of PIP-containing lipid membranes, which so far has been little explored. For this purpose, supported lipid bilayers (SLBs) containing 1,2-dioleoyl-sn-glycero-3-phospho-(1'-myo-inositol-3',4',5'-trisphosphate (DOPIP3) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were used as mimics of biomembranes. Surface sensitive techniques, i.e. Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), Atomic Force Microscopy (AFM) and Neutron Reflectometry (NR), provided detailed information on the formation of the SLB and the location of DOPIP3 in the lipid membrane. Specifically, QCM-D and AFM were used to identify the best condition for lipid deposition and to estimate the total bilayer thickness. On the other hand, NR was used to collect experimental structural data on the DOPIP3 location and orientation within the lipid membrane. The two bilayer leaflets showed the same DOPIP3 concentration, thus suggesting the formation of a symmetric bilayer. The headgroup layer thicknesses of the pure POPC and the mixed POPC/DOPIP3 bilayer suggest that the DOPIP3-headgroups have a preferred orientation, which is not perpendicular to the membrane surface, but instead it is close to the surrounding lipid headgroups. These results support the proposed PIP3 tendency to interact with the other lipid headgroups as PC, so far exclusively suggested by MD simulations.

Structural Studies of Three-Arm Star Block Copolymers Exposed to Extreme Stretch Suggests a Persistent Polymer Tube.

We present structural small-angle neutron scattering studies of a three-armed polystyrene star polymer with short deuterated segments at the end of each arm. We show that the form factor of the three-armed star molecules in the relaxed state agrees with that of the random phase approximation of Gaussian chains. Upon exposure to large extensional flow conditions, the star polymers change conformation resulting in a highly stretched structure that mimics a fully extended three-armed tube model. All three arms are parallel to the flow, one arm being either in positive or negative stretching direction, while the two other arms are oriented parallel, right next to each other in the direction opposite to the first arm.

Cutting edges and weaving threads in the gene editing (Я)evolution: reconciling scientific progress with legal, ethical, and social concerns.

Gene-editing technology, such as CRISPR/Cas9, holds great promise for the advancement of science and many useful applications technology. This foundational technology enables modification of the genetic structure of any living organisms with unprecedented precision. Yet, in order to enhance its potential for societal benefit, it is necessary to adapt rules and produce adequate regulations. This requires an interdisciplinary effort in legal thinking. Any legislative initiative needs to consider both the benefits and the problematic aspects of gene editing, from a broader societal and value-based perspective. This paper stems from an interdisciplinary research project seeking to identify and discuss some of the most pressing legal implications of gene-editing technology and how to address these. While the questions raised by gene editing are global, laws and regulations are to a great extent bound by national borders. This paper presents a European perspective, written for a global audience, and intends to contribute to the global debate. The analysis will include brief references to corresponding USA rules in order to place these European debates in the broader international context. Our legal analysis incorporates interdisciplinary contributes concerning the scientific state of the art, philosophical thinking regarding the precautionary principle and dual-use issues as well as the importance of communication, social perception, and public debate. Focusing mainly in the main regulatory and patent law issues, we will argue that (a) general moratoriums and blank prohibitions do a disservice to science and innovation; (b) it is crucial to carefully consider a complex body of international and European fundamental rights norms applicable to gene editing;

Highly Anisotropic Glassy Polystyrenes Are Flexible.

We show that stretching polystyrene melts at a rate faster than the inverse Rouse time, followed by rapid quenching below the glass transition temperature, results in a material that is flexible and remains so for at least six months. Oriented micro/nanofibers are observed in the flexible samples after the mechanical tests. The fibers are probably related to the highly aligned molecules in melt stretching. At room temperature, a tensile strength over 300 MPa has been achieved for the flexible polystyrenes.

Stretching PEO-PPO Type of Star Block Copolymer Gels: Rheology and Small-Angle Scattering.

Cross-linked Tetronic star block copolymer gels, based on poly(ethylene oxide) and poly(propylene oxide), behave quite regular with respect to mechanical properties, but exhibits unusual absence of structural response to strain. The elastic response is linear up to more than 100% strain, with a steady-state modulus of the order of 0.01 MPa after an initial stress relaxation. Neutron and X-ray scattering experiments show a consistent but unexpected response to uniaxial strain, with no changes in characteristic molecular dimensions. Upon strain beyond about 100%, that is, when the stress-strain curve is no longer linear, structural texture appears and becomes even more pronounced upon further strain, thus, indicating alignment of the self-assembled hexagonally ordered cylindrical micelles with the cylinder-axis perpendicular to the strain. It is proposed that the main structural response to large-amplitude strain is related to a layer-dominated structure of cross-linked star molecules.

The nature of ancient Egyptian copper-containing carbon inks is revealed by synchrotron radiation based X-ray microscopy.

For the first time it is shown that carbon black inks on ancient Egyptian papyri from different time periods and geographical regions contain copper. The inks have been investigated using synchrotron-based micro X-ray fluorescence (XRF) and micro X-ray absorption near-edge structure spectroscopy (XANES) at the European Synchrotron Radiation Facility (ESRF). The composition of the copper-containing carbon inks showed no significant differences that could be related to time periods or the geographical locations. This renders it probable that the same technology for ink production was used throughout Egypt for a period spanning at least 300 years. It is argued that the black pigment material (soot) for these inks was obtained as by-products of technical metallurgy. The copper (Cu) can be correlated with the following three main components: cuprite (Cu2O), azurite (Cu3[CO3]2[OH]2) and malachite (Cu2CO3[OH]2).

Cross-Linked Amylose Bio-Plastic: A Transgenic-Based Compostable Plastic Alternative.

Bio-plastics and bio-materials are composed of natural or biomass derived polymers, offering solutions to solve immediate environmental issues. Polysaccharide-based bio-plastics represent important alternatives to conventional plastic because of their intrinsic biodegradable nature. Amylose-only (AO), an engineered barley starch with 99% amylose, was tested to produce cross-linked all-natural bioplastic using normal barley starch as a control. Glycerol was used as plasticizer and citrate cross-linking was used to improve the mechanical properties of cross-linked AO starch extrudates. Extrusion converted the control starch from A-type to Vh- and B-type crystals, showing a complete melting of the starch crystals in the raw starch granules. The cross-linked AO and control starch specimens displayed an additional wide-angle diffraction reflection. Phospholipids complexed with Vh-type single helices constituted an integrated part of the AO starch specimens. Gas permeability tests of selected starch-based prototypes demonstrated properties comparable to that of commercial Mater-Bi© plastic. The cross-linked AO prototypes had composting characteristics not different from the control, indicating that the modified starch behaves the same as normal starch. The data shows the feasibility of producing all-natural bioplastic using designer starch as raw material.

All-natural bio-plastics using starch-betaglucan composites.

Grain polysaccharides represent potential valuable raw materials for next-generation advanced and environmentally friendly plastics. Thermoplastic starch (TPS) is processed using conventional plastic technology, such as casting, extrusion, and molding. However, to adapt the starch to specific functionalities chemical modifications or blending with synthetic polymers, such as polycaprolactone are required (e.g. Mater-Bi). As an alternative, all-natural and compostable bio-plastics can be produced by blending starch with other polysaccharides. In this study, we used a maize starch (ST) and an oat ß-glucan (BG) composite system to produce bio-plastic prototype films. To optimize performing conditions, we investigated the full range of ST:BG ratios for the casting (100:0, 75:25, 50:50, 25:75 and 0:100 BG). The plasticizer used was glycerol. Electron Paramagnetic Resonance (EPR), using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a spin probe, showed that the composite films with high BG content had a flexible chemical environment. They showed decreased brittleness and improved cohesiveness with high stress and strain values at the break. Wide-angle X-ray diffraction displayed a decrease in crystallinity at high BG content. Our data show that the blending of starch with other natural polysaccharides is a noteworthy path to improve the functionality of all-natural polysaccharide bio-plastics systems.

Influence of diurnal photosynthetic activity on the morphology, structure, and thermal properties of normal and waxy barley starch.

This study investigated the influence of diurnal photosynthetic activity on the morphology, molecular composition, crystallinity, and gelatinization properties of normal barley starch (NBS) and waxy barley starch (WBS) granules from plants cultivated in a greenhouse under normal diurnal (16h light) or constant light photosynthetic conditions. Growth rings were observed in all starch samples regardless of lighting conditions. The size distribution of whole and debranched WBS analyzed by gel-permeation chromatography did not appear to be influenced by the different lighting regimes, however, a greater relative crystallinity measured by wide-angle X-ray scattering and greater crystalline quality as judged by differential scanning calorimetry was observed under the diurnal lighting regime. NBS cultivated under the diurnal photosynthetic lighting regime displayed lower amylose content (18.7%), and shorter amylose chains than its counterpart grown under constant light. Although the relative crystallinity of NBS was not influenced by lighting conditions, lower onset, peak, and completion gelatinization temperatures were observed in diurnally grown NBS compared to constant light conditions. It is concluded that normal barley starch is less influenced by the diurnal photosynthetic lighting regime than amylose-free barley starch suggesting a role of amylose to prevent structural disorder and increase starch granule robustness against environmental cues.

Rheological Link Between Polymer Melts with a High Molecular Weight Tail and Enhanced Formation of Shish-Kebabs.

Presence of an ultra high molecular weight (UHMw) fraction in flowing polymer melts is known to facilitate formation of oriented crystalline structures significantly. The UHMw fraction manifests itself as a minor tail in the molar mass distribution and is hardly detectable in the canonical characterization methods. In this study, alternatively, we demonstrate how the nonlinear extensional rheology reveals to be a very sensitive characterization tool for investigating the effect of the UHMw-tail on the structural ordering mechanism. Samples containing a UHMw-tail relative to samples without, exhibit a clear increase in extensional stress that is directly correlated with the crystalline orientation of the quenched samples. Extensional rheology, particularly, in combination with linear creep measurements, thus, enables the conformational evolution of the UHMw-tail to be studied and linked to the enhanced formation of oriented structures.

Recent advances in X-ray compatible microfluidics for applications in soft materials and life sciences.

The increasingly narrow and brilliant beams at X-ray facilities reduce the requirements for both sample volume and data acquisition time. This creates new possibilities for the types and number of sample conditions that can be examined but simultaneously increases the demands in terms of sample preparation. Microfluidic-based sample preparation techniques have emerged as elegant alternatives that can be integrated directly into the experimental X-ray setup remedying several shortcomings of more traditional methods. We review the use of microfluidic devices in conjunction with X-ray measurements at synchrotron facilities in the context of 1) mapping large parameter spaces, 2) performing time resolved studies of mixing-induced kinetics, and 3) manipulating/processing samples in ways which are more demanding or not accessible on the macroscale. The review covers the past 15 years and focuses on applications where synchrotron data collection is performed in situ, i.e. directly on the microfluidic platform or on a sample jet from the microfluidic device. Considerations such as the choice of materials and microfluidic designs are addressed. The combination of microfluidic devices and measurements at large scale X-ray facilities is still emerging and far from mature, but it definitely offers an exciting array of new possibilities.

Nematic effects and strain coupling in entangled polymer melts under strong flow.

We use small-angle neutron scattering (SANS) to study labeled short chains with and without the influence of an entangled and highly stretched surrounding environment of longer chains. We find unequivocal evidence of nematic effects as the blend chains in steady state flow are stretched a factor ∼1.5 more from the presence of the long chain nematic field. In the pure melt we confirm that the nonaffine mean-field result ν=0.5 for the strain coupling is still valid for very fast flows, while in the nematic system our analysis predicts an increased coupling constant. We provide a structural explanation for the two first regimes of the nonlinear relaxation, particularly a transition regime where the long chains are relaxing in a sea of reptating short chains.