11 research outputs found
Simple Cubic Packing of Gold Nanoparticles through Rational Design of Their Dendrimeric Corona
The first simple-cubic liquid crystal was obtained by
coating monodisperse
Au nanoparticles (NPs) with a thick corona of amino-substituted
organic dendrons. This unusual structure was determined by grazing-incidence
diffraction and electron density reconstruction and explained by analyzing
the radial density profile of the corona. Another novel structure
is proposed for the phase preceding the cubic one: a hexagonal superlattice
composed of alternating dense and sparse strings of Au NPs
Characterizing Size and Porosity of Hollow Nanoparticles: SAXS, SANS, TEM, DLS, and Adsorption Isotherms Compared
A combination of experimental methods, including transmission
and
grazing incidence small-angle X-ray scattering (SAXS and GISAXS),
small-angle neutron scattering (SANS), transmission electron microscopy
(TEM), dynamic light scattering (DLS), and N<sub>2</sub> adsorption–desorption
isotherms, was used to characterize SiO<sub>2</sub>/TiO<sub>2</sub> hollow nanoparticles (HNPs) of sizes between 25 and 100 nm. In the
analysis of SAXS, SANS, and GISAXS data, the decoupling approximation
and the Percus–Yevick structure factor approximation were used.
Brunauer–Emmett–Teller, <i>t</i>-plot, and
a spherical pore model based on Kelvin equation were applied in the
treatment of N<sub>2</sub> isotherms. Extracted parameters from the
scattering and TEM methods are the average outer and inner diameters
and polydispersity. Good agreement was achieved between different
methods for these extracted parameters. Merits, advantages, and disadvantages
of the different methods are discussed. Furthermore, the combination
of these methods provided us with information on the porosity of the
shells of HNPs and the size of intrawall pores, which are critical
to the applications of HNPs as drug delivery vehicles and catalyst
supports
One-Step Synthesis and Self-Assembly of Metal Oxide Nanoparticles into 3D Superlattices
A simple one-pot approach based on the “benzyl alcohol route” is introduced for the fabrication of highly ordered supercrystals composed of highly uniform 3–4 nm zirconia and rare-earth stabilized zirconia nanoparticles. The as-fabricated supercrystals reach sizes larger than 10 μm and present well-defined 3D morphologies such as flower-like, rhombic dodecahedron, and bipyramids. This system is unique in that the supercrystals are formed in one-step directly in the reaction medium where the nanoparticles are synthesized. The uniformity in nanocrystal shape and size is attributed to the <i>in situ</i> formation of benzoate species that directs the nanoparticle growth and assembly. The low colloidal stabilization of the benzoate-capped nanoparticles in benzyl alcohol promotes the formation of supercrystals in solution by π–π interaction between the <i>in situ</i> formed benzoate ligands attached to neighboring particles. By varying the reaction temperature and the nature of the doping the way the nanobulding blocks assemble in the supercrystals could be controlled. Standard FCC superlattice packings were found together with more unusual ones with <i>P</i>6<i>/mmm</i> and <i>R</i>3̅<i>m</i> symmetries
Honeycombs in Honeycombs: Complex Liquid Crystal Alumina Composite Mesostructures
Small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM) were used to study orientation patterns of two polyphilic liquid crystals (LC) confined to cylindrical pores of anodic aluminum oxide (AAO). The hierarchical hybrid systems had the LC honeycomb (lattice parameter 3.5–4 nm) inside the pores of the AAO honeycomb (diameters 60 and 400 nm). By conducting complete reciprocal space mapping using SAXS, we conclude that the columns of both compounds align in planes normal to the AAO pore axis, with a specific crystallographic direction of the LC lattice aligning strictly parallel to the pore axis. AFM of LC-containing AAO fracture surfaces further revealed that the columns of the planar anchoring LC (compound <b>1</b>) formed concentric circles in the plane normal to the pore axis near the AAO wall. Toward the pore center, the circles become anisometric “racetrack” loops consisting of two straight segments and two semicircles. This mode compensates for slight ellipticity of the pore cross section. Indications are, however, that for perfectly circular pores, circular shape is maintained right to the center of the pore, the radius coming down to the size of a molecule. For the homeotropically anchoring compound <b>2</b>, the columns are to the most part straight and parallel to each other, arranged in layers normal to the AAO pore axis, like logs in an ordered pile. Only near the pore wall the columns splay somewhat. In both cases, columns are confined to layers strictly perpendicular to the AAO pore axis, and there is no sign of escape to the third dimension or of axial orientation, the latter having been reported previously for some discotic LCs. The main cause of the two new LC configurations, the “racetrack” and the “logpile”, and of their difference from those of confined nematic LC, is the very high splay energy and low bend energy of columnar phases
Induction of Thermotropic Bicontinuous Cubic Phases in Liquid-Crystalline Ammonium and Phosphonium Salts
Two series of wedge-shaped onium salts, one ammonium
and the other
phosphonium, having 3,4,5<b>-</b>tris(alkyloxy)benzyl moieties,
exhibit thermotropic bicontinuous “gyroid” cubic (Cub<sub>bi</sub>) and hexagonal columnar liquid-crystalline (LC) phases by
nanosegregation between ionophilic and ionophobic parts. The alkyl
chain lengths on the cationic moieties, anion species, and alkyl
chain lengths on the benzyl moieties have crucial effects on their
thermotropic phase behavior. For example, triethyl-[3,4,5-tris(dodecyloxy)benzyl]ammonium
hexafluorophosphate forms the thermotropic <i>Ia</i>3̅<i>d</i> Cub<sub>bi</sub> LC phase, whereas an analogous compound
with trifluoromethanesulfonate anion shows no LC properties. Synchrotron
small-angle diffraction intensities from the <i>Ia</i>3̅<i>d</i> Cub<sub>bi</sub> LC materials provide electron density
maps in the bulk state. The resulting maps show convincingly that
the <i>Ia</i>3̅<i>d</i> Cub<sub>bi</sub> structure is composed of three-dimensionally interconnected ion
nanochannel networks surrounded by aliphatic domains. A novel differential
mapping technique has been applied successfully. The map of triethyl-[3,4,5-tris(decyloxy)benzyl]ammonium
tetrafluoroborate has been subtracted from that of the analogous ammonium
salt with hexafluorophosphate anion in the <i>Ia</i>3̅<i>d</i> Cub<sub>bi</sub> phases. The differential map shows that
the counteranions are located in the core of the three-dimensionally
interconnected nanochannel networks. Changing from trimethyl- via
triethyl- to tripropylammonium cation changes the phase from columnar
to Cub<sub>bi</sub> to no mesophase, respectively. This sensitivity
to the widened shape for the narrow end of the molecule is explained
successfully by the previously proposed semiquantitative geometric
model based on the radial distribution of volume in wedge-shaped molecules.
The LC onium salts dissolve lithium tetrafluoroborate without losing
the <i>Ia</i>3̅<i>d</i> Cub<sub>bi</sub> LC phase. The Cub<sub>bi</sub> LC materials exhibit efficient ion-transporting
behavior as a result of their 3D interconnected ion nanochannel networks.
The <i>Ia</i>3̅<i>d</i> Cub<sub>bi</sub> LC material formed by triethyl-[3,4,5-tris(decyloxy)benzyl]phosphonium
tetrafluoroborate shows ionic conductivities higher than the analogous <i>Ia</i>3̅<i>d</i> Cub<sub>bi</sub> material based
on ammonium salts. The present study indicates great potential of
Cub<sub>bi</sub> LC nanostructures consisting of ionic molecules for
development of transportation nanochannel materials
Comparison of the A-T rich regions and the Bacillus subtilis RNA polymerase binding sites in phage ø29
By using a modification of the BAC spreading method for mounting the DNA for electron microscopy, partial denaturation maps of protein-free ø29 DNA and of ø29 DNA containing protein p3 were obtained. In ø29 P3-DNA1 the protein does not seem to influence the melting of the ends of the molecules.
The comparison of the partial denaturation map and the B. subtilis RNA polymerase binding sites indicates that five of the seven early promoters (Al, A2, A3, B2 and C2) are located in A-T rich DNA regions whereas the other two early promoters (Bl and Cl) are located in less A-T rich sites.Peer reviewe
Columnar Liquid Crystals in Cylindrical Nanoconfinement
Axial orientation of discotic columnar liquid crystals in nanopores of inorganic templates, with the columns parallel to the axis of the nanochannels, is considered desirable for applications such as production of molecular wires. Here, we evaluate experimentally the role of the rigidity of the LC columns in achieving such orientation in nanopores where the planar anchoring (<i>i.e.</i>, columns parallel to wall surface) is enforced. We studied the columnar phase of several discotic compounds with increasing column rigidity in the following order: dendronized carbazole, hexakis(hexyloxy)triphenylene (HAT6), a 1:1 HAT6-trinitrofluorenone (TNF) complex, and a helicene derivative. Using 2-D X-ray diffraction, AFM, grazing incidence diffraction, and polarized microscopy, we observed that the orientation of the columns changes from circular concentric to axial with increasing column rigidity. Additionally, when the rigidity is borderline, increasing pore diameter can change the configuration from axial back to circular. We derive expressions for distortion free energy that suggest that the orientation is determined by the competition between, on the one hand, the distortion energy of the 2-d lattice and the mismatch of its crystallographic facets with the curved pore wall in the axial orientation and, on the other hand, the bend energy of the columns in the circular configuration. Furthermore, the highly detailed AFM images of the core of the disclinations of strength +1 and +1/2 in the center of the pore reveal that the columns spiral down to the very center of the disclination and that there is no amorphous or misaligned region at the core, as suggested previously
Transformation from Kinetically into Thermodynamically Controlled Self-Organization of Complex Helical Columns with 3D Periodicity Assembled from Dendronized Perylene Bisimides
The
dendronized perylene 3,4:9,10-tetracarboxylic acid bisimide
(PBI), (3,4,5)12G1-1-PBI, was reported by our laboratory to self-assemble
into complex helical columns containing dimers of dendronized PBI
with one molecule in each stratum, with different intra- and interdimer
rotation angles but identical intra- and interdimer distance of 3.5
Å, exhibiting a four-strata 2<sub>1</sub> helical repeat. A thermodynamically
controlled 2D columnar hexagonal phase with short-range intracolumnar
order represents the thermodynamic product at high temperature, while
a kinetically controlled monoclinic columnar array with 3D periodicity
is the thermodynamic product at low temperature. With heating and
cooling rates higher than 10 °C/min to 1 °C/min, at low
temperature the 2D columnar periodic array is the kinetic product
for this dendronized PBI. Here the synthesis and structural analysis
of a library of (3,4,5)<i>n</i>G1-<i>m</i>-PBI
with <i>n</i> = 12 to 6 and <i>m</i> = 1 are reported.
A combination of differential scanning calorimetry, X-ray diffraction
on powder and orientated fibers, including pattern simulation and
electron density map reconstruction, and solid-state NMR, all as a
function of temperature and heating and cooling rate, was employed
for their structural analysis. It was discovered that at low temperature
the as-prepared <i>n</i> = 12 to 10 exhibit a 3D layered
array that transforms irreversibly into columnar periodicities during
heating and cooling. Also the kinetically controlled 3D columnar phase
of <i>n</i> = 12 becomes thermodynamically controlled for <i>n</i> = 10, 9, 8, 7, and 6. This unprecedented transformation
is expected to facilitate the design of functions from dendronized
PBI and other self-assembling building blocks
Mesoscale Graphene-like Honeycomb Mono- and Multilayers Constructed via Self-Assembly of Coclusters
Honeycomb
structure endows graphene with extraordinary properties.
But could a honeycomb monolayer superlattice also be generated via
self-assembly of colloids or nanoparticles? Here we report the construction
of mono- and multilayer molecular films with honeycomb structure that
can be regarded as self-assembled artificial graphene (SAAG). We construct
fan-shaped molecular building blocks by covalently connecting two
kinds of clusters, one polyoxometalate and four polyhedral oligomeric
silsesquioxanes. The precise shape control enables these complex molecules
to self-assemble into a monolayer 2D honeycomb superlattice that mirrors
that of graphene but on the mesoscale. The self-assembly of the SAAG
was also reproduced via coarse-grained molecular simulations of a
fan-shaped building block. It revealed a hierarchical process and
the key role of intermediate states in determining the honeycomb structure.
Experimental images also show a diversity of bi- and trilayer stacking
modes. The successful creation of SAAG and its stacks opens up prospects
for the preparation of novel self-assembled nanomaterials with unique
properties
Complex Columnar Hexagonal Polymorphism in Supramolecular Assemblies of a Semifluorinated Electron-Accepting Naphthalene Bisimide
Simple synthetic
methods for a strongly electron-accepting naphthalene
bisimide (NBI) derivative functionalized with a new environmentally
friendly chiral racemic semifluorinated alkyl group and with AB<sub>3</sub> minidendrons containing the same semifluorinated group are
reported. The semifluorinated dendron was attached to the imide groups
of the NBI via one, two, and three (<i>m</i> = 1, 2, 3)
methylenic units. The NBI-containing semifluorinated groups and the
dendronized NBI with <i>m</i> = 1 and 2 self-organize into
lamellar crystals. The dendronized NBI with <i>m</i> = 3
self-assembles into an unprecedentedly complex and ordered column
that self-organizes in a columnar hexagonal periodic array. This array
undergoes a continuous transition to a columnar hexagonal superlattice
that does not display a first-order phase transition during analysis
by differential scanning calorimetry at heating and cooling rates
of 10 and 1 °C/min. These complex columnar hexagonal periodic
arrays with intramolecular order could be elucidated only by a combination
of powder and fiber X-ray diffraction studies and solid-state NMR
experiments. The lamellar crystals self-organized from <i>m</i> = 1 and the two highly ordered columnar hexagonal periodic arrays
of <i>m</i> = 3 are assembled via thermodynamically controlled
processes. Since strongly electron-accepting derivatives are of great
interest to replace fullerene acceptors in organic photovoltaics and
for other supramolecular electronic materials, the multitechnique
structural analysis methodology elaborated here must be taken into
consideration in all related studies