147 research outputs found
Visualization of flow-aligned type I collagen self-assembly in tunable pH gradients
No full textCollagen is a major component of the extracellular matrix that exhibits unique hierarchical organization at multiple length scales ranging from nano to macroscale. Despite numerous methods to create collagen-based biomaterials, the self-assembly process of collagen ex vivo is poorly understood. Here, we describe a system that uses a microfluidic method to investigate the dynamics of collagen self-assembly. A main inlet stream of semidilute soluble collagen-I is hydrodynamically focused by two side inlet streams, which gradually increases the pH in the main stream. This enables dynamic nonequilibrium investigation of the self-assembly process simultaneously at different positions and therefore different stages in the assembly process within the same system. The device is designed for in situ monitoring and characterization of collagen assembly using polarization microscopy and X-ray diffraction: the continuous extensional flow provides highly ordered phases of the macromolecules over a large distance in the outlet microchannel and allows for data collection without material damage. We further demonstrate that finite element method simulations provide a good description of our experimental results regarding the diffusive phenomena, flow profile, and pH distribution. Our approach has broad impact, since it provides a powerful means of controlling and investigating the dynamic self-assembly process of biomacromolecules
Microfluidics of soft matter investigated by small-angle scattering
No full textThe combination of X-ray microdiffraction and microfluidics is used to investigate the dynamic behaviour of soft materials. A microfocused X-ray beam enables the observation of the influence of droplet formation on the nanostructure of a smectic liquid crystal in water. Using a hydrodynamic focusing device, the evolution of the intercalation of DNA into multilamellar membranes can be studied. Owing to the elongational flow at the centre of this device, alignment of the material is induced which allows for an improved structural characterization. Furthermore, the influence of strain applied to these materials can be tested
Evolution of DNA compaction in microchannels
No full textCombining microfluidics with x-ray microdiffraction and Raman microscopy, the dynamic behaviour of soft matter, with specific consideration of the molecular structure, can be investigated. Microfluidic systems enable a reduction of sample volume and shorter reaction times. By performing experiments under continuous microflow, material damage is avoided and the influence of external stress on biomacromolecules can be analysed. The generated elongated flow induces alignment of the investigated materials, allowing for an improved structural characterization. Here, the dynamics of the compaction of DNA by polypropyleneimine dotriacontaamine dendrimers, generation 4 is studied. As a consequence of the laminar flow inside the microchannels, highly defined, diffusion-controlled compaction of the DNA occurs enabling the study of different states of the reaction during one measurement by varying the observation position in the channels. The evolution of a columnar mesophase with an in-plane square symmetry is monitored by x-ray microdiffraction and the molecular interaction between the two reactants is traced using Raman microscopy, leading to a more profound comprehension of the condensation reaction. The experimental results are in accordance with finite element method simulations of the flow and diffusion profiles in the elongated flow device
Sharp symmetry-change marks the mechanical failure transition of glasses
Get PDFGlasses acquire their solid-like properties by cooling from the supercooled liquid via a continuous transition known as the glass transition. Recent research on soft glasses indicates that besides temperature, another route to liquify glasses is by application of stress that drives relaxation and flow. Here, we show that unlike the continuous glass transition, the failure of glasses to applied stress occurs by a sharp symmetry change that reminds of first-order equilibrium transitions. Using simultaneous x-ray scattering during the oscillatory rheology of a colloidal glass, we identify a sharp symmetry change from anisotropic solid to isotropic liquid structure at the crossing of the storage and loss moduli. Concomitantly, intensity fluctuations sharply acquire Gaussian distributions characteristic of liquids. Our observations and theoretical framework identify mechanical failure as a sharp atomic affine-to-nonaffine transition, providing a new conceptual paradigm of the oscillatory yielding of this technologically important class of materials, and offering new perspectives on the glass transition
In situ observation of maghemite nanoparticle adsorption at the water/gas interface
No full textThe adsorption of (maghemite) nanoparticles at the aqueous solution/gas interface was investigated by x-ray reflectivity. Two different concentrations (0.07 g/L and 0.7 g/L) were probed. The x-ray reflectivities indicate the adsorption of nanoparticles at the liquid surface for the highly concentrated solution, while no nanoparticle adsorption could be detected at the surface of the low concentrated solution within several hours. The vertical electron density profile of the high concentration solution/gas interface indicates the formation of a low ordered monolayer of nanoparticles occupying only 6% of the interfacial region
Reversibility and hysteresis of the sharp yielding transition of a colloidal glass under oscillatory shear.
Get PDFThe mechanical response of glasses remains challenging to understand. Recent results indicate that the oscillatory rheology of soft glasses is accompanied by a sharp non-equilibrium transition in the microscopic dynamics. Here, we use simultaneous x-ray scattering and rheology to investigate the reversibility and hysteresis of the sharp symmetry change from anisotropic solid to isotropic liquid dynamics observed in the oscillatory shear of colloidal glasses (D. Denisov, M.T. Dang, B. Struth, A. Zaccone, P. Schall, Sci. Rep. 5 14359 (2015)). We use strain sweeps with increasing and decreasing strain amplitude to show that, in analogy with equilibrium transitions, this sharp symmetry change is reversible and exhibits systematic frequency-dependent hysteresis. Using the non-affine response formalism of amorphous solids, we show that these hysteresis effects arise from frequency-dependent non-affine structural cage rearrangements at large strain. These results consolidate the first-order-like nature of the oscillatory shear transition and quantify related hysteresis effects both via measurements and theoretical modelling
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