Nanocellulose Fragmentation Mechanisms and Inversion of Chirality from the Single Particle to the Cholesteric Phase

Understanding how nanostructure and nanomechanics influence physical material properties on the micro- and macroscale is an essential goal in soft condensed matter research. Mechanisms governing fragmentation and chirality inversion of filamentous colloids are of specific interest because of their critical role in load-bearing and self-organizing functionalities of soft nanomaterials. Here we provide a fundamental insight into the self-organization across several length scales of nanocellulose, an important bio-colloid system with wide-ranging applications as structural, insulating and functional material. Through a combined microscopic and statistical analysis of nanocellulose fibrils at the single particle level, we show how mechanically and chemically induced fragmentation proceed in this system. Moreover, by studying the bottom-up self-assembly of fragmented carboxylated cellulose nanofibrils into cholesteric liquid crystals, we show via direct microscopic observations, that the chirality is inverted from right-handed at the nanofibril level to left-handed at the level of the liquid crystal phase. These results improve our fundamental understanding of nanocellulose and provide an important rationale for their application in colloidal systems, liquid crystals and nanomaterials

Phase equilibrium liquid-vapor in three-component system UF6-IF5-BrF3 at complete mutual components solubility

The results of studying phase equilibrium liquid-vapor at 353,15 K in the system of uranium hexafluoride, iodine pentafluoride, bromine trifluoride have been presented. The dependences of saturated vapor pressure on condensed phase composition, the results of analysis of studied system deviation from error-free behavior, the data on equilibrium vapor phase are give

Dynamics of the photoinduced insulator-to-metal transition in a nickelate film

The control of materials properties with light is a promising approach towards the realization of faster and smaller electronic devices. With phases that can be controlled via strain, pressure, chemical composition or dimensionality, nickelates are good candidates for the development of a new generation of high performance and low consumption devices. Here we analyze the photoinduced dynamics in a single crystalline NdNiO$_3$ film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally we compare our results to similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced phase transitions.Comment: 17 pages, 6 figure

Dynamics of the photoinduced insulator-to-metal transition in a nickelate film

Material properties can be controlled via strain, pressure, chemical composition, or dimensionality. Nickelates are particularly susceptible due to their strong variations of the electronic and magnetic properties on such external stimuli. Here, we analyze the photoinduced dynamics in a single crystalline NdNiO3 film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally, we compare our results with similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced electronic ordering phase transitions. © 2018 Author(s)

FiberApp: An Open-Source Software for Tracking and Analyzing Polymers, Filaments, Biomacromolecules, and Fibrous Objects

Biological semiflexible polymers and filaments such as collagen, fibronectin, actin, microtubules, coiled-coil proteins, DNA, siRNA, amyloid fibrils, etc., are ubiquitous in nature. In biology, these systems have a direct relation to critical processes ranging from the movement of actin or assembly of viruses at cellular interfaces to the growth of amyloid plaques in neurodegenerative diseases. In technology and applied sciences, synthetic macromolecules or fibrous objects such as carbon nanotubes are involved in countless applications. Accessing their intrinsic properties at the single molecule level, such as their molecular conformations or intrinsic stiffness, is central to the understanding of these systems, their properties, and the design of related applications. In this Perspective we introduce FiberAppa new tracking and analysis software based on a cascade of algorithms describing structural and topological features of objects characterized by a very high length-to-width aspect ratio, generally described as “fiber-like objects”. The program operates on images from any microscopic source (atomic force or transmission electron microscopy, optical, fluorescence, confocal, etc.), acquiring the spatial coordinates of objects by a semiautomated tracking procedure based on A* pathfinding algorithm followed by the application of active contour models and generating virtually any statistical, topological, and graphical output derivable from these coordinates. Demonstrative features of the software include statistical polymer physics analysis of fiber conformations, height, bond and pair correlation functions, mean-squared end-to-end distance and midpoint displacement, 2D order parameter, excess kurtosis, fractal exponent, height profile and its discrete Fourier transform, orientation, length, height, curvature, and kink angle distributions, providing an unprecedented structural description of filamentous synthetic and biological objects

Polymorphism Complexity and Handedness Inversion in Serum Albumin Amyloid Fibrils

Protein-based amyloid fibrils can show a great variety of polymorphic structures within the same protein precursor, although the origins of these structural homologues remain poorly understood. In this work we investigate the fibrillation of bovine serum albumina model globular proteinand we follow the polymorphic evolution by a statistical analysis of high-resolution atomic force microscopy images, complemented, at larger length scales, by concepts based on polymer physics formalism. We identify six distinct classes of coexisting amyloid fibrils, including flexible left-handed twisted ribbons, rigid right-handed helical ribbons and nanotubes. We show that the rigid fibrils originate from flexible fibrils through two diverse polymorphic transitions, first, via a single-fibril transformation when the flexible left-handed twisted ribbons turn into the helical left-handed ribbons, to finally evolve into nanotube-like structures, and second, via a double-fibril transformation when two flexible left-handed twisted ribbons wind together resulting in a right-handed twisted ribbon, followed by a rigid right-handed helical ribbon polymorphic conformation. Hence, the change in handedness occurs with an increase in the level of the fibril’s structural organization

Anomalous Stiffening and Ion-Induced Coil–Helix Transition of Carrageenans under Monovalent Salt Conditions

The macromolecular conformations of anionic polysaccharides with decreasing linear charge densities − lambda, iota, and kappa carrageenan −, at varying NaCl concentrations, are studied by single-chain statistical analysis of high-resolution atomic force microscopy (AFM) images. Lambda remains in the random coil conformation, whereas iota and kappa undergo ion-induced coil–helix transitions, with a 2–3-fold increase in chain rigidity. At low ionic strengths, <i>I</i>, the polymer chains sequester Na⁺, leading to a greater flexibility, and beyond a critical <i>I</i> to the formation of an intramolecular single helix. The persistence length exhibits a sublinear dependence on the Debye screening length, κ^–1, <i>L</i>_p^e ∼ κ^–<i>y</i> (with 0 < <i>y</i> < 1), deviating from the classical polyelectrolyte behavior expressed by Odijk–Skolnick–Fixman or Barrat–Joanny models. Above a certain <i>I</i>, the <i>L</i>_p shows an upturn, resulting in polymer stiffening and nonmonotonic behavior. This phenomenon is inferred from specific ion–polymer interactions and/or nonlinear electrostatic physics involving ion–ion correlations

Understanding nanocellulose chirality and structure-properties relationship at the single fibril level

Nanocellulose fibrils are ubiquitous in nature and nanotechnologies but their mesoscopic structural assembly is not yet fully understood. Here we study the structural features of rod-like cellulose nanoparticles on a single particle level, by applying statistical polymer physics concepts on electron and atomic force microscopy images, and we assess their physical properties via quantitative nanomechanical mapping. We show evidence of right-handed chirality, observed on both bundles and on single fibrils. Statistical analysis of contours from microscopy images shows a non-Gaussian kink angle distribution. This is inconsistent with a structure consisting of alternating amorphous and crystalline domains along the contour and supports process-induced kink formation. The intrinsic mechanical properties of nanocellulose are extracted from nanoindentation and persistence length method for transversal and longitudinal directions, respectively. The structural analysis is pushed to the level of single cellulose polymer chains, and their smallest associated unit with a proposed 2 × 2 chain-packing arrangement.ISSN:2041-172

Small-angle X-ray scattering tensor tomography: model of the three-dimensional reciprocal-space map, reconstruction algorithm and angular sampling requirements

Small-angle X-ray scattering tensor tomography, which allows reconstruction of the local three-dimensional reciprocal-space map within a three-dimensional sample as introduced by Liebi et al. [Nature (2015), 527, 349-352], is described in more detail with regard to the mathematical framework and the optimization algorithm. For the case of trabecular bone samples from vertebrae it is shown that the model of the three-dimensional reciprocal-space map using spherical harmonics can adequately describe the measured data. The method enables the determination of nanostructure orientation and degree of orientation as demonstrated previously in a single momentum transfer q range. This article presents a reconstruction of the complete reciprocal-space map for the case of bone over extended ranges of q. In addition, it is shown that uniform angular sampling and advanced regularization strategies help to reduce the amount of data required.The mathematical framework and reconstruction algorithm for small-angle scattering tensor tomography are introduced in detail, as well as strategies which help to reduce the amount of data and therewith the measurement time required. Experimental validation is provided for the application to trabecular bone