13 research outputs found
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Control of nanomaterial self-assembly in ultrasonically levitated droplets
We demonstrate that acoustic trapping can be used to levitate and manipulate droplets of soft matter, in particular, lyotropic mesophases formed from selfassembly
of different surfactants and lipids, which can be analyzed in a contact-less manner by X-ray scattering in a controlled gas-phase environment. On the macroscopic length scale, the dimensions and the orientation of the particle are shaped by the ultrasonic field, while on the microscopic length scale the nanostructure can be controlled by varying the humidity of the atmosphere around the droplet. We demonstrate levitation and in situ
phase transitions of micellar, hexagonal, bicontinuous cubic, and lamellar phases. The technique opens up a wide range of new experimental approaches of fundamental
importance for environmental, biological, and chemical research
Unraveling the Structural Puzzle of the Giant Glutenin PolymerAn Interplay between Protein Polymerization, Nanomorphology, and Functional Properties in Bioplastic Films
Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops
Mesocrystals
composed of crystallographically aligned nanocrystals are present
in biominerals and assembled materials which show strongly directional
properties of importance for mechanical protection and functional
devices. Mesocrystals are commonly formed by complex biomineralization
processes and can also be generated by assembly of anisotropic nanocrystals.
Here, we follow the evaporation-induced assembly of maghemite nanocubes
into mesocrystals in real time in levitating drops. Analysis of time-resolved
small-angle X-ray scattering data and ex situ scanning electron microscopy
together with interparticle potential calculations show that the substrate-free,
particle-mediated crystallization process proceeds in two stages involving
the formation and rapid transformation of a dense, structurally disordered
phase into ordered mesocrystals. Controlling and tailoring the particle-mediated
formation of mesocrystals could be utilized to assemble designed nanoparticles
into new materials with unique functions
Unraveling the Structural Puzzle of the Giant Glutenin PolymerAn Interplay between Protein Polymerization, Nanomorphology, and Functional Properties in Bioplastic Films
A combination of
genotype, cultivation environment, and protein
separation procedure was used to modify the nanoscale morphology,
polymerization, and chemical structure of glutenin proteins from wheat.
A low-polymerized glutenin starting material was the key to protein–protein
interactions mainly via SS cross-links during film formation, resulting
in extended β-sheet structures and propensity toward the formation
of nanoscale morphologies at molecular level. The properties of glutenin
bioplastic films were enhanced by the selection of a genotype with
a high number of cysteine residues in its chemical structure and cultivation
environment with a short grain maturation period, both contributing
positively to gluten strength. Thus, a combination of factors affected
the structure of glutenins in bioplastic films by forming crystalline
β-sheets and propensity toward the ordered nanostructures, thereby
resulting in functional properties with high strength, stiffness,
and extensibility
Formation of Inverse Topology Lyotropic Phases in Dioleoylphosphatidylcholine/Oleic Acid and Dioleoylphosphatidylethanolamine/Oleic Acid Binary Mixtures
The addition of saturated fatty acids
(FA) to phosphatidylcholine
lipids (PC) that have saturated acyl chains has been shown to promote
the formation of lyotropic liquid-crystalline phases with negative
mean curvature. PC/FA mixtures may exhibit inverse bicontinuous cubic
phases (<i>Im</i>3<i>m</i>, <i>Pn</i>3<i>m</i>) or inverse topology hexagonal phases (H<sub>II</sub>), depending on the length of the acyl chains/fatty acid.
Here we report a detailed study of the phase behavior of binary mixtures
of dioleoylphosphatidylcholine (DOPC)/oleic acid (OA) and dioleoylphosphatidylethanolamine
(DOPE)/oleic acid at limiting hydration, constructed using small-angle
X-ray diffraction (SAXD) data. The phase diagrams of both systems
show a succession of phases with increasing negative mean curvature
with increasing OA content. At high OA concentrations, we have observed
the occurrence of an inverse micellar <i>Fd</i>3<i>m</i> phase in both systems. Hitherto, this phase had not been
reported for phosphatidylethanolamine/fatty acid mixtures, and as
such it highlights an additional route through which fatty acids may
increase the propensity of bilayer lipid membranes to curve. We also
propose a method that uses the temperature dependence of the lattice
parameters of the H<sub>II</sub> phases to estimate the spontaneous
radii of curvature (<i>R</i><sub>0</sub>) of the binary
mixtures and of the component lipids. Using this method, we calculated
the <i>R</i><sub>0</sub> values of the complexes comprising
one phospholipid molecule and two fatty acid molecules, which have
been postulated to drive the formation of inverse phases in PL/FA
mixtures. These are −1.8 nm (±0.4 nm) for DOPC(OA)<sub>2</sub> and −1.1 nm (±0.1 nm) for DOPE(OA)<sub>2</sub>. <i>R</i><sub>0</sub> values estimated in this way allow
the quantification of the contribution that different lipid species
make to membrane curvature elastic properties and hence of their effect
on the function of membrane-bound proteins
Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops
Mesocrystals
composed of crystallographically aligned nanocrystals are present
in biominerals and assembled materials which show strongly directional
properties of importance for mechanical protection and functional
devices. Mesocrystals are commonly formed by complex biomineralization
processes and can also be generated by assembly of anisotropic nanocrystals.
Here, we follow the evaporation-induced assembly of maghemite nanocubes
into mesocrystals in real time in levitating drops. Analysis of time-resolved
small-angle X-ray scattering data and ex situ scanning electron microscopy
together with interparticle potential calculations show that the substrate-free,
particle-mediated crystallization process proceeds in two stages involving
the formation and rapid transformation of a dense, structurally disordered
phase into ordered mesocrystals. Controlling and tailoring the particle-mediated
formation of mesocrystals could be utilized to assemble designed nanoparticles
into new materials with unique functions
Experimental Confirmation of Transformation Pathways between Inverse Double Diamond and Gyroid Cubic Phases
A macroscopically oriented double
diamond inverse bicontinuous
cubic phase (Q<sub>II</sub><sup>D</sup>) of the lipid glycerol monooleate
is reversibly converted into a gyroid phase (Q<sub>II</sub><sup>G</sup>). The initial Q<sub>II</sub><sup>D</sup> phase is prepared in the
form of a film coating the inside of a capillary, deposited under
flow, which produces a sample uniaxially oriented with a ⟨110⟩
axis parallel to the symmetry axis of the sample. A transformation
is induced by replacing the water within the capillary tube with a
solution of poly(ethylene glycol), which draws water out of the Q<sub>II</sub><sup>D</sup> sample by osmotic stress. This converts the
Q<sub>II</sub><sup>D</sup> phase into a Q<sub>II</sub><sup>G</sup> phase with two coexisting orientations, with the ⟨100⟩
and ⟨111⟩ axes parallel to the symmetry axis, as demonstrated
by small-angle X-ray scattering. The process can then be reversed,
to recover the initial orientation of Q<sub>II</sub><sup>D</sup> phase.
The epitaxial relation between the two oriented mesophases is consistent
with topology-preserving geometric pathways that have previously been
hypothesized for the transformation. Furthermore, this has implications
for the production of macroscopically oriented Q<sub>II</sub><sup>G</sup> phases, in particular with applications as nanomaterial templates
Experimental Confirmation of Transformation Pathways between Inverse Double Diamond and Gyroid Cubic Phases
A macroscopically oriented double
diamond inverse bicontinuous
cubic phase (Q<sub>II</sub><sup>D</sup>) of the lipid glycerol monooleate
is reversibly converted into a gyroid phase (Q<sub>II</sub><sup>G</sup>). The initial Q<sub>II</sub><sup>D</sup> phase is prepared in the
form of a film coating the inside of a capillary, deposited under
flow, which produces a sample uniaxially oriented with a ⟨110⟩
axis parallel to the symmetry axis of the sample. A transformation
is induced by replacing the water within the capillary tube with a
solution of poly(ethylene glycol), which draws water out of the Q<sub>II</sub><sup>D</sup> sample by osmotic stress. This converts the
Q<sub>II</sub><sup>D</sup> phase into a Q<sub>II</sub><sup>G</sup> phase with two coexisting orientations, with the ⟨100⟩
and ⟨111⟩ axes parallel to the symmetry axis, as demonstrated
by small-angle X-ray scattering. The process can then be reversed,
to recover the initial orientation of Q<sub>II</sub><sup>D</sup> phase.
The epitaxial relation between the two oriented mesophases is consistent
with topology-preserving geometric pathways that have previously been
hypothesized for the transformation. Furthermore, this has implications
for the production of macroscopically oriented Q<sub>II</sub><sup>G</sup> phases, in particular with applications as nanomaterial templates
Effect of Clay Surface Charge on the Emerging Properties of Polystyrene–Organoclay Nanocomposites
A series of polystyrene–clay
nanocomposites, based on two
natural clay types (Na–Montmorillonite and Hectorite) and two
synthetic clays (Laponite and Li–Fluorohectorite), were prepared
via in situ intercalative polymerization after surface modification
with an organic ammonium cation (CTAB). The structural characteristics
of the organically modified clays as well as the nanocomposites were
investigated by means of wide-angle X-ray scattering (WAXS), and the
thermal properties were studied with TGA. In the organically modified
clays, the silicate interlayer spacing increases, and the magnitude
seems to be directly correlated with the amount of clay surface charge.
In the nanocomposites, polymer intercalation is also observed, but
partial exfoliation is present, modifying significantly the morphology
of the material. The degree of dispersion of the clay platelets, as
well as the resulting properties of the nanocomposites, were found
again to be systematically, and almost linearly, correlated with the
intrinsic surface charge of the clays, which varied between 44 and
120 meq/100 g. Increased dispersion was seen in the nanocomposites
made from clays with low surface charge, here Hectorite and Laponite,
suggesting that these can be suitable alternatives to the more employed
Montmorillonite for enhancement of thermal properties. The thermal
stability was found to be better for the nanocomposites than for the
pure polystyrene
Oxygen-Controlled Phase Segregation in Poly(<i>N</i>‑isopropylacrylamide)/Laponite Nanocomposite Hydrogels
The combination of nanoparticles and polymers into nanocomposite
gels has been shown to be a promising route to creating soft materials
with new or improved properties. In the present work, we have made
use of Laponite nanoparticles in combination with a poly(<i>N</i>-isopropylacrylamide) (PNIPAAM) polymer and describe a phenomenon
taking place during the polymerization and gelling of this system.
The presence of small amounts of oxygen in the process induces two
distinctly separated phases, one polymer-rich and one polymer-deficient
water–clay phase. Complex interactions among clay, oxygen,
and the polymer are found to govern the behavior of these phases.
It is also observed that the initial clay concentration can be used
to control the volume fraction of the polymer-deficient phase directly.
The dynamics of the phase boundary is found to be dependent on water
penetration and in general to exhibit non-Fickian behavior. An approach
using video recording to monitor hydrogel swelling is also presented,
and its advantages are addressed