4 research outputs found
Growth of Porous Anodic Alumina on Low-Index Surfaces of Al Single Crystals
The
pseudoepitaxial growth of amorphous anodic alumina with ordered
porous structure within single crystal grains of aluminum substrates
is an amazing feature of the self-organization process, which occurs
during anodization. Here, we used single crystal Al(100), Al(110),
and Al(111) substrates to inspect the effect of aluminum crystallography
on anodization rates and the morphology of the resulting alumina films
grown under different anodization conditions. The difference in the
kinetics of porous film growth on various substrates is described
in terms of the activation barrier of aluminum atom release from the
metal surface to the oxide layer. Scanning electron microscopy and
small-angle X-ray scattering are applied for quantitative characterization
of different kinds of ordering in anodic alumina films. The highest
number of straight channels was found in porous anodic alumina grown
on Al(100) substrates, whereas Al(111) was proved to induce the best
orientational order in anodic alumina with the formation of the single-domain-like
structures. Based on the obtained results, possible pathways for crystallographic
control of the anodic alumina porous structure for different practical
applications are discussed
Topological Connection between Vesicles and Nanotubes in Single-Molecule Lipid Membranes Driven by Head–Tail Interactions
Lipid
nanotube–vesicle networks are important
channels for
intercellular communication and transport of matter. Experimentally
observed in neighboring mammalian cells but also reproduced in model
membrane systems, a broad consensus exists on their formation and
stability. Lipid membranes must be composed of at least two molecular
components, each stabilizing low (generally a phospholipid) and high
curvatures. Strong anisotropy or enhanced conical shape of the second
amphiphile is crucial for the formation of nanotunnels. Anisotropic
driving forces generally favor nanotube protrusions from vesicles.
In this work, we report the unique case of topologically connected
nanotubes–vesicles obtained in the absence of directional forces,
in single-molecule membranes, composed of an anisotropic bolaform
glucolipid, above its melting temperature, Tm. Cryo-TEM and fluorescence confocal microscopy show the interconnection
between vesicles and nanotubes in a single-phase region, between 60
and 90 °C under diluted conditions. Solid-state NMR demonstrates
that the glucolipid can assume two distinct configurations, head–head
and head–tail. These arrangements, seemingly of comparable
energy above the Tm, could explain the
existence and stability of the topologically connected vesicles and
nanotubes, which are generally not observed for classical single-molecule
phospholipid-based membranes above their Tm
Effect of Self-Assembly of Oxalamide Based Organic Compounds on Melt Behavior, Nucleation, and Crystallization of Isotactic Polypropylene
We report on the
effect of an aliphatic oxalamide based nucleating
agent (<b>OXA3,6</b>) on the melt and crystallization behavior
of isotactic polypropylene (<i>i</i>PP) under defined shear
conditions. Through polarized optical microscopy, we demonstrate that <b>OXA3,6</b> self-assembles from the <i>i</i>PP melt into
rhombic crystals whereas their size and distribution proved highly
dependent on the employed cooling rates. The presence of 0.5 wt %
of <b>OXA3,6</b> in <i>i</i>PP results in a significant
suppression in <i>i</i>PP melt viscosity, which could not
be explained via molecular modeling. A possible cause for the drop
in viscosity in the presence of <b>OXA3,6</b> is attributed
to the interaction (absorption) of high molecular weight <i>i</i>PP chains with the nucleating agent, thereby suppressing their contribution
to the viscoelastic response of the melt. This proposed mechanism
for the suppression in melt viscosity appears similar to that encountered
by the homogeneous distribution of nanoparticles such as CNTs, graphene,
and silica. Shear experiments, performed using a slit flow device
combined with small-angle X-ray diffraction measurements, indicate
that crystallization is significantly enhanced in the presence of <b>OXA3,6</b> at relatively low shear rates despite its lowered sensitivity
to shear. This enhancement in crystallization is attributed to the
shear alignment of the rhombic <b>OXA3,6</b> crystals that provide
surface for <i>i</i>PP kebab growth upon cooling. Overall,
the suppression in melt viscosity in combination with enhanced nucleation
efficiency at low as well as high shear rates makes this self-assembling
oxalamide based nucleating agent a promising candidate for fast processing
Effect of the Aggregation on the Photophysical Properties of a Blue-Emitting Star-Shaped Molecule Based on 1,3,5-Tristyrylbenzene
In
this work we present a study on the effect of the aggregation
on the optical properties of star-shaped molecules. We analyzed the
modification of the absorption and fluorescent properties of a 1,3,5-tristyrylbenzene
core due to the formation of diverse aggregates. The nature of the
aggregates in solution was investigated by different spectroscopic
techniques such as electronic absorption, steady-state fluorescence,
fluorescence anisotropy, time-resolved fluorescence, small-angle X-ray
scattering, and dynamic light-scattering spectroscopy. In order to
simulate the molecular arrangement of the aggregates, the structure
and electronic properties of different clusters formed by stacking
of star-shaped molecules were studied by means of density functional
theory calculations. The theoretical insight was performed in the
gas phase as well as in solution through the polarizable continuum
model, and both linear response and state-specific polarization schemes
were applied. In the solid state, high quantum yields of up to 0.51
were measured for a 1,3,5-tristyrylbenzene derivative. Finally, the
morphological properties of different solid samples were analyzed
by differential scanning calorimetry, as well as scanning and transmission
electron microscopies