372 research outputs found
Challenges and opportunities from water under soft nanoconfinement
Nanoconfined water differs significantly from bulk water and challenges our common understanding of liquid water in both its most fundamental features, as well as in many applied aspects which stem out from its peculiar behavior. This brief perspective pinpoints both challenges associated with the study of water under soft nanoconfinement as well as some opportunities which arise from it, and which would not be at reach with standard bulk water. A special focus is given to the strong nanoconfinement (âŒ1â10 nm) offered by inverse lipidic mesophases, viewed as a natural soft nanoconfinement environment for water
Hybrid protein membranes: Snatch contaminants from water and strike gold
Industrial development, energy production and mining have led to dramatically increased levels of environmental pollutants such as heavy metal ions, metal cyanides and nuclear waste. Current technologies for purifying contaminated waters are typically expensive and ion specific, and there is therefore a significant need for new approaches. Here, we report inexpensive hybrid membranes made from protein amyloid fibrils and activated porous carbon that can be used to remove heavy metal ions and radioactive waste from water. During filtration, the concentration of heavy metal ions drops by three to five orders of magnitude per passage and the process can be repeated numerous times. Notably, their efficiency remains unaltered when filtering several ions simultaneously. The performance of the membrane is enabled by the ability of the amyloids to selectively absorb heavy metal pollutants from solutions. We also show that our membranes can be used to recycle valuable heavy metal contaminants by thermally reducing ions trapped in saturated membranes, leading to the creation of elemental metal nanoparticles and films.
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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
Flow-induced order-order transitions in amyloid fibril liquid crystalline tactoids
Understanding and controlling the director field configuration, shape, and
orientation in nematic and cholesteric liquid crystals is of fundamental
importance in several branches of science. Liquid crystalline droplets, also
known as tactoids, which spontaneously form by nucleation and growth within the
biphasic region of the phase diagram where isotropic and nematic phases
coexist, challenge our current understanding of liquid crystals under
confinement, due to the influence of anisotropic surface boundaries at
vanishingly small interfacial tension and are mostly studied under quiescent,
quasi-equilibrium conditions. Here, we show that different classes of amyloid
fibril nematic and cholesteric tactoids undergo out-of-equilibrium order-order
transitions by flow-induced deformations of their shape. The tactoids align
under extensional flow and undergo extreme deformation into highly elongated
oblate shapes, allowing the cholesteric pitch to decrease as an inverse power
law of the tactoids aspect ratio. Energy functional theory and experimental
measurements are combined to rationalize the critical elongation ratio above
which the director-field configuration of tactoids transforms from bipolar and
uniaxial cholesteric to homogenous and to debate on the thermodynamic nature of
these transitions. Our findings suggest new opportunities in designing
self-assembled liquid crystalline materials where structural and dynamical
properties may be tuned by non-equilibrium phase transitions
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Modulating self-assembly of a nanotape-forming peptide amphiphile with an oppositely charged surfactant
A peptide amphiphile (PA) C16-KTTKS, containing a pentapeptide headgroup based on a sequence from procollagen I attached to a hexadecyl lipid chain, self-assembles into extended nanotapes in aqueous solution. The tapes are based on bilayer structures, with a 5.2 nm spacing. Here, we investigate the effect of addition of the oppositely charged anionic surfactant sodium dodecyl sulfate (SDS) via
AFM, electron microscopic methods, small-angle X-ray scattering and X-ray diffraction among other methods. We show that addition of SDS leads to a transition from tapes to fibrils, via intermediate states that include twisted ribbons. Addition of SDS is also shown to enhance the development of remarkable lateral ââstripesââ on the nanostructures, which have a 4 nm periodicity. This is ascribed to counterion condensation. The transition in the nanostructure leads to changes in macroscopic
properties, in particular a transition from sol to gel is noted on increasing SDS (with a further reentrant
transition to sol on further increase of SDS concentration). Formation of a gel may be useful in
applications of this PA in skincare applications and we show that this can be controlled via development of a network of fine stranded fibrils
Interfacial activity and interfacial shear rheology of native Ă-lactoglobulin monomers and their heat-induced fibers
Interfacial properties of native ÎČ-lactoglobulin monomers and their heat-induced fibers, of two different lengths, were investigated at pH 2, through surface tension measurements at waterâair and waterâoil interfaces and interfacial shear rheology at the waterâoil interface. The applied heat treatment generates a mixed system of fibers with unconverted monomers and hydrolyzed peptides. The surface tension of this system at the waterâair interface decreased more rapidly than the surface tension of native monomers, especially at short times (10â»Âł to 10ÂČs). This behavior was not observed when the unconverted monomers and peptides were removed by dialysis. At the waterâoil interface, the adsorption kinetics was much faster than at the waterâair interface, with a plateau interfacial pressure value reached after 1 h of adsorption. For all the systems, interfacial shear rheology showed the formation of a highly elastic interface, with solid-like behavior at 1â10Âł s time scales. The highest modulus was observed for the long fibers and the lowest for the native monomers. Creepâcompliance curves in the linear regime could be reduced to a single master curve, showing similar spectra of relaxation times for all investigated systems. Upon large deformations, the interfaces formed with long fibers showed the most rigid and fragile behavior. This rigidity was even more pronounced in the presence of unconverted monomers
Self-assembly of rod-coil block copolymers from weakly to moderately segregated regimes
We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a Ï -conjugated polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions, Ï , while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter and the total polymerization degree, ÏN . Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self- assembly of rod-coil block copolymers in a weakly segregated regime. The two rod- coil block copolymer systems investigated were poly(DEH-p-phenylenevinylene-b- styrene), whose self-assembly takes place in the very weakly segregated regime, and poly(DEH-p-phenylenevinylene-b-4vinylpyridine), for which the self-assembly behaviour occurs under increased tendency towards microphase separation, hereby referred to as moderately segregated regime. Experimental results for both systems are compared with predictions based on Landau expansion theories
a new level of hierarchical structure control by use of supramolecular self-assembled dendronized block copolymers
Complexation of dendronized block copolymers with sulfate alkyl tails forms unprecedented hierarchically ordered bulk structures, including rectangular-in-lamellar, tetragonal-in-lamellar, hexagonal-in-lamellar and lamellar-in-lamellar. These novel liquid-crystalline morphologies, which can be designed at low length scales in these systems, are expected to provide final materials with not only unprecedented structural complexity, but also tunable physical properties
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