Search results for "colloid"
showing 10 items of 1288 documents
Electron-Transfer Kinetics for Generation of Organoiron(IV) Porphyrins and the Iron(IV) Porphyrin π Radical Cations
1999
Homogeneous electron-transfer kinetics for the oxidation of seven different iron(III) porphyrins using three different oxidants were examined in deaerated acetonitrile, and the resulting data were evaluated in light of the Marcus theory of electron transfer to determine reorganization energies of the rate-determining oxidation of iron(III) to iron(IV). The investigated compounds are represented as (P)Fe(R), where P = the dianion of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin (OETPP) and R = C6H5, 3,5-C6F2H3, 2,4,6-C6F3H2, or C6F5 or P = the dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) and R = C6H5, 2,4,6-C6F3H2, or 2,3,5,6-C6F4H. The first one-electron transfer …
Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers.
2007
Abstract In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)2(tmphen)]PF6, (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air–water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as π – A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. B…
Molecular adhesion interactions between Langmuir monolayers and solid substrates
1998
Abstract Substrate-monolayer adhesion interactions between differently prepared SiO2 surfaces and Langmuir monolayers were investigated. From the relation between the contact angle and the surface tension of a Langmuir monolayer in the configuration of Langmuir wetting the work of adhesion between the substrate and the monolayer as a function of the molecular packing and the transfer ratios was determined. Thus the molecular work of adhesion of different SiO2-dimyristoylphosphatidylethanolamine surfaces was quantified. The relation between the local adhesion interactions and the molecular packing and structure is presented and substrate-induced phase transitions are discussed.
Incorporation of CrIII into a Keggin Polyoxometalate as a Chemical Strategy to Stabilize a Labile {CrIIIO4} Tetrahedral Conformation and Promote Unat…
2020
Polyoxometalates (POMs) provide rigid and highly symmetric coordination sites and can be used as a strategy for the stabilization of magnetic ions. Herein, we report a new member of the Keggin archetype, the Cr-centered Keggin anion [α-CrW12O40]5– (CrW12), with the unusual tetrahedral coordination of CrIII reported for the first time in POMs conferring unattended magnetic properties. POM chemistry has recently presented excellent examples of single-molecule and single-ion magnets (SMMs and SIMs) as well as molecular spin qubits; however, the majority of POM-based SIMs reported to date contain lanthanoid ions. CrW12, as the first example of a chromium(III) SIM, exhibits slow relaxation of ma…
Lanthanoid single-ion magnets based on polyoxometalates with a 5-fold symmetry: The series [LnP5W30O110]12– (Ln3+ = Tb, Dy, Ho, Er, Tm, and Yb)
2012
A robust, stable and processable family of mononuclear lanthanoid complexes based on polyoxometalates (POMs) that exhibit single-molecule magnetic behavior is described here. Preyssler polyanions of general formula [LnP 5W 30O 110] 12- (Ln 3+ = Tb, Dy, Ho, Er, Tm, and Yb) have been characterized with static and dynamic magnetic measurements and heat capacity experiments. For the Dy and Ho derivatives, slow relaxation of the magnetization has been found. A simple interpretation of these properties is achieved by using crystal field theory. © 2012 American Chemical Society.
Stratification Dynamics in Drying Colloidal Mixtures
2017
Stratification in binary colloidal mixtures was investigated using implicit-solvent molecular dynamics simulations. For large particle size ratios and film Péclet numbers greater than unity, smaller colloids migrated to the top of the film, while big colloids were pushed to the bottom, creating an "inverted" stratification. This peculiar behavior was observed in recent simulations and experiments conducted by Fortini et al. [ Phys. Rev. Lett. 2016 , 116 , 118301 ]. To rationalize this behavior, particle size ratios and drying rates spanning qualitatively different Péclet number regimes were systematically studied, and the dynamics of the inverted stratification were quantified in detail. Th…
Opale: Photonische Kristalle
2007
Opale sind selbstorganisierte, kubisch dichtest gepackte Kolloidkristalle mit Kolloid-Durchmessern im Nanometer- und Submikrometerbereich. Aufgrund der periodisch modulierten Dielektrizitatskonstante bilden sich photonische Bandlucken aus, so dass die Ausbreitung von Licht mit Wellenlangen in der Grosenordnung der Gitterkonstanten unterdruckt wird. Dies erklart u.a. den brillianten Farbeindruck. Opale konnen synthetisch aus Polymer- oder Metalloxidkolloiden in einem Bottom-up-Prozess hergestellt und auf vielfaltige Weise chemisch funktionalisiert, strukturiert oder als Template fur ihre invertierten Strukturen verwendet werden. Anwendungsgebiete reichen von optischen Chips, Farbdisplays und…
Orientation of polybutadiene chains in a thermoplastic elastomer
1996
The orientation of polybutadiene chains in thermoplastic elastomers based on hydrogen bonding complexes is investigated under uniaxial deformation by two-dimensional small-angle neutron scattering (SANS), deuteron magnetic resonance spectroscopy (2H-NMR), optical birefringence and infrared dichroism spectroscopy (FTIR-D). While SANS probes orientation on the length scale of the radius of gyration,2H-NMR, birefringence and FTIR-D monitor orientation on a segmental scale. The deformation of the elastomer chains appears to be affine on the different length scales.
An Improved Empirical Relation to Determine the Particle Number Density of Fluid-Like Ordered Charge-Stabilized Suspensions
2001
Polystyrene as an archetypal charge-stabilized colloid model system was used in this work under well defined preparation conditions. A continuous preparation technique was used to control the suspension parameters salt concentration c and particle number density n. Measurements of n were performed using both conductivity in the completely deionized state and static light scattering. We found a significant deviation between the position of the first maximum of the static structure factor qmax=2π/L and an estimate identifying the relevant length scale L with the average inter-particle distance d¯=n−1/3. Instead, qmax was observed to follow the relation qmax=(2.20±0.03)π/d¯, which is equivalen…
Prodrug based on halloysite delivery systems to improve the antitumor ability of methotrexate in leukemia cell lines
2021
The prodrug approach, as well as the development of specific systems able to deliver a chemotherapeutic agent in the target site, decreasing the side effects often associated with its administration, are still a challenging. In this context, both methotrexate drug molecules (MTX) and biotin ligand moieties, whose receptors are overexpressed on the surface of several cancer cells, were loaded on halloysite nanotubes (HNTs) to develop nanomaterial based on multifunctional and "smart" delivery systems. To highlight the crucial role played by biotin, carrier systems based on HNTs and MTX were also synthetized. In detail, several approaches were envisaged: i) a supramolecular interaction between…