10,529 research outputs found
Generation of silicone poly-HIPES with controlled pore sizes via reactive emulsion stabilization
Macrocellular silicone polymers are obtained after solidification of the
continuous phase of a PDMS (polydimethylsiloxane) emulsion, which contains PEG
(polyethylene glycol) drops of sub-millimetric dimensions. Coalescence of the
liquid template emulsion is prohibited by a reactive blending approach. We
investigate in detail the relationship between the interfacial properties and
the emulsion stability, and we use micro- and millifluidic techniques to
generation macro-cellular polymers with controlled structural properties over a
wider range of cell-sizes (0.2-2mm) and volume fractions of the continuous
phase (0.1-40%). This approach could easily be transferred to a wide range of
polymeric systems
Molecular-Level Switching of Polymer/Nanocrystal Non-Covalent Interactions and Application in Hybrid Solar Cells
Hy brid composites obtained upon blending conjugated polymers and colloidal
inorganic semiconductor nanocrystals are regarded as attractive photo-active
materials for optoelectronic applications. Here we demonstrate that tailoring
nanocrystal surface chemistry permits to exert control on non-covalent bonding
and electronic interactions between organic and inorganic components. The
pendant moieties of organic ligands at the nanocrystal surface do not merely
confer colloidal stability while hindering charge separation and transport, but
drastically impact morphology of hybrid composites during formation from blend
solutions. The relevance of our approach to photovoltaic applications is
demonstrated for composites based on poly(3-hexylthiophene) and Pbs
nanocrystals, considered as inadequate before the submission of this
manuscript, which enable the fabrication of hybrid solar cells displaying a
power conversion efficiency that reaches 3 %. Upon (quasi)steady-state and
time-resolved analisys of the photo-induced processes in the nanocomposites and
their organic and inorganic components, we ascertained that electron transfer
occurs at the hybrid interface yielding long-lived separated charge carriers,
whereas interfacial hole transfer appears slow. Here we provide a reliable
alternative aiming at gaining control over macroscopic optoelectronic
properties of polymer/nanocrystal composites by acting at the molecular-level
via ligands' pendant moieties, thus opening new possibilities towards efficient
solution-processed hybrid solar cells
UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization
Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular
weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the
FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as
filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15
prior polymerization. A study on polymerization activity of this catalyst has been performed under
homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous
particles and of the immobilization method is also carried out. Moreover, the thermal characterization,
phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials
have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and
final SBA-15 content have been established
Rotation, magnetism, and metallicity of M dwarf systems
Close M-dwarf binaries and higher multiples allow the investigation of
rotational evolution and mean magnetic flux unbiased from scatter in
inclination angle and age since the orientation of the spin axis of the
components is most likely parallel and the individual systems are coeval.
Systems composed of an early (M0.0 -- M4.0) and a late (M4.0 -- M8.0) type
component offer the possibility to study differences in rotation and magnetism
between partially and fully convective stars. We have selected 10 of the
closest dM systems to determine the rotation velocities and the mean magnetic
field strengths based on spectroscopic analysis of FeH lines of Wing-Ford
transitions at 1 m observed with VLT/CRIRES. We also studied the quality
of our spectroscopic model regarding atmospheric parameters including
metallicity. A modified version of the Molecular Zeeman Library (MZL) was used
to compute Land\'e g-factors for FeH lines. Magnetic spectral synthesis was
performed with the Synmast code. We confirmed previously reported findings that
less massive M-dwarfs are braked less effectively than objects of earlier
types. Strong surface magnetic fields were detected in primaries of four
systems (GJ 852, GJ 234, LP 717-36, GJ 3322), and in the secondary of the
triple system GJ 852. We also confirm strong 2 kG magnetic field in the primary
of the triple system GJ 2005. No fields could be accurately determined in
rapidly rotating stars with \vsini>10 \kms. For slow and moderately rotating
stars we find the surface magnetic field strength to increase with the
rotational velocity \vsini which is consistent with other results from
studying field stars.Comment: Accepted by MNRAS, 10 pages, 4 figures, 4 table
Grid sensitivity for aerodynamic optimization and flow analysis
After reviewing relevant literature, it is apparent that one aspect of aerodynamic sensitivity analysis, namely grid sensitivity, has not been investigated extensively. The grid sensitivity algorithms in most of these studies are based on structural design models. Such models, although sufficient for preliminary or conceptional design, are not acceptable for detailed design analysis. Careless grid sensitivity evaluations, would introduce gradient errors within the sensitivity module, therefore, infecting the overall optimization process. Development of an efficient and reliable grid sensitivity module with special emphasis on aerodynamic applications appear essential. The organization of this study is as follows. The physical and geometric representations of a typical model are derived in chapter 2. The grid generation algorithm and boundary grid distribution are developed in chapter 3. Chapter 4 discusses the theoretical formulation and aerodynamic sensitivity equation. The method of solution is provided in chapter 5. The results are presented and discussed in chapter 6. Finally, some concluding remarks are provided in chapter 7
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