The kinetics of dipolar nonradiative energy transfer (DET) between dyes confined to the core−corona interface region of poly(isoprene-b-methyl methacrylate) block copolymers (PI−PMMA) in acetonitrile ...was analyzed using a new distribution model for energy transfer in spherical micelles. The distribution of block junction points was described by the model of Helfand and Tagami (HT) for the strong segregation limit, adapted for the spherical geometry of the core−corona interface. We used this model to analyze experimental fluorescence decay curves for block copolymer micelles made up of polymers containing a donor dye or an acceptor dye covalently attached to the PI−PMMA junction. The analysis yielded an interface thickness between the PI core and the PMMA corona of δ = (0.9 ± 0.1) nm. In the past, the experimental fluorescence decay curves measured for similar systems have been fitted with the Klafter and Blumen (KB) equation for energy transfer, which has a stretched exponential form. To relate these results to topological characteristics of the system, we simulated donor decay profiles for different interface thickness values using the new distribution model for energy transfer and a modified HT equation. Subsequent analysis by the stretched exponential KB equation proved that the magnitude of the fitted exponent is directly related to the interface thickness between the blocks for a given dye concentration in the core−corona interface. Within a certain range of interface thickness values, this relation can be used to determine the interface thickness from the fitting parameters of the KB equation.
Micellenanaloga von Bolaamphiphilen sind die Titelsysteme, die durch Kristallisations‐getriebene lebende Selbstorganisation von Diblockcopolymeren mit kernbildenden Polyferrocenylsilanblöcken ...erhalten werden können. Diese neuartigen Co‐Micellen‐Bausteine bilden – abhängig von den relativen Längen der A‐ und B‐Segmente – in polaren Medien reguläre gekreuzte oder sphärische Supermicellen oder gestreckte Netzwerke (siehe Bild).
It's elemental: A water‐soluble polymer bearing multiple metal‐chelating ligands has been used as a tag for bioassays with inductively coupled plasma mass spectrometry. The tag was covalently ...conjugated to antibodies, and the polymer–antibody constructs were loaded with lanthanide ions (Ln3+) and used for the simultaneous assay of five orthogonally labeled antibodies against cell surface antigens that differ in abundance by more than two orders of magnitude.
Poly(methyl methacrylate)-polystyrene (PS-PMMA) core-shell latex particles were prepared by two-stage emulsion polymerization under monomer-starved conditions. These particles were examined by three ...different transmission electron microscopy techniques; cryosectioning, beam damage in ice, and freeze-fracture (FFTEM). This is the first reported application of FFTEM to the study of composite latex morphology. From these experiments we learn that the second stage polymer forms a shell surrounding the seed. In addition, we infer that some second stage monomer polymerizes within the latex seed. A very interesting observation is that when MMA is polymerized in the presence of PS seed latex, some polystyrene migrates to the surface of the PMMA shell. These results are explained in terms of a combination of thermodynamic and kinetic factors affecting the polymerization and morphology evolution process.
5,6-Dimethyl-pyrazine-2,3-dicarbonitrile Bardajee, Ghasem Rezanejade; Lough, Alan J; Winnik, Mitchell A
Acta crystallographica. Section E, Structure reports online,
2012-Nov-01, Letnik:
68, Številka:
Pt 11
Journal Article
Odprti dostop
The asymmetric unit of the title compound, C(8)H(6)N(4), contains two almost planar independent mol-ecules (r.m.s. deviations = 0.026 and 0.030 Å). The crystal studied was a non-merohedral twin with ...the components in a 0.513 (2):0.487 (2) ratio.
A novel class of materials that self-assemble in water into equilibrium network structures with a well-defined mesh size consist of polyethylene glycols (PEG's) end-capped with micelle-forming ...fluorocarbon tails. These micellar systems form flowable aqueous gel-like networks that permit electrophoretic DNA sequencing in capillary columns. The gels have unusual rheological properties, including network breakdown under shear, resulting in plug flow that allows columns refill with complete ejection of byproducts of the previous sequencing analysis. In this system, DNA fragment electrophoretic mobilities are unaffected by the hydrophobicity of the polymer tails. Low molecular weight (M) PEG chains (M 8000) show catastrophic resolution loss for DNA fragments larger than 100 bases due to band broadening. For a longer PEG segment (M 35000) separating the end groups, band broadening occurs for DNA fragments larger than 300 bases, implying that the PEG segment length controls the mesh size in the equilibrium network structure. Optimum sequencing results were obtained from a 6% solution of a 1:1 mixture of C6F13 end-capped- and C8F17 end-capped PEG 35,000. The resolution limit of fluorescent-dye-labeled sequencing products in this formulation was 450 bases in 75 microns capillaries at 200 V/cm.
Polyferrocenyldimethylsilane (PFS) diblock copolymers with polyisoprene (PFS-PI) or with polydimethylsiloxane
(PFS-PDMS) self-assemble in simple alkane solvents to form what appear by TEM to be dense ...flexible
cylinders (nanowires) or “nanotube-like” structures. Typical widths are on the order
of 20 to 30 nm, with variable lengths often greater than 10 μm. The structures that
form, and the dimensions of the “tube-like” structures or wires, depend upon the composition
of the polymers and the lengths of the blocks. Light scattering experiments show that the PFS-PDMS
(block ratio 1:12) solutions aged at 25°C contain long thin objects 950 nm in length. These
structures probably rearrange on the TEM grid as the solvent evaporates to form elongated structures.
Establishing a mechanistic connection between the objects present in solution and those seen
in the TEM images, as well as understanding the factors that lead to these unusual self-assembled
structures, remain a challenge.
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