Characterization monodisperse

Erom Equations 12.46 and 12.47, one sees that ThEEE retention is related to (l/5j), but not specifically to a conventional analyte property, such as molar mass M or particle diameter d. However, since HSj depends on M or d, it also mediates the dependence between R and M or d. At constant Tq conditions, the relationship between X, M, and AT can be experimentally exploited by using standards. Eor instance, in polymers mass characterization, monodisperse or polydisperse standards can be employed for a specific polymer-solvent system. Once the relationship X vs. M, that is, the so-called calibration curve, is obtained, it is universal, that is, valid for any ThFFF instrument [3]. A typical calibration function, which relates the instrumental response to analyte property (in this case M), is... 

Well-Characterized Monodisperse Polystrene Latexes as Model Colloids... 

In order to make a better evaluation of the relative and absolute performance of various instruments, it was necessary to obtain well characterized, monodisperse latexes having a density greater than that of polystyrene. Polymethylmethacrylate PMMA) latex with a polymer density of approximately 1.21 gm/cm was selected for this purpose. 

In the section on the evolution of network, we described the visual development of strain patterns in the flow of interacting PEO solutions (Figure 10) leading to frilly developed flow instability (flare). Similar effects can be found in wejl-characterized monodisperse a-PS, as shown in Figure 30, for a 7.7 X 10 a-PS dissolved in decahydronaphthalene (0.35%) and its corresponding AP vs. e trace (Figure 27). Complex dilatant effects can be observed (curve b) when compared with pure solvent (curve a) and with dilute solutions (Figure 5). 

Experimental problems in FRAPP. The most difficult part of FRAPP experiments on synthetic polymers lies in the preparation of well characterized, monodisperse, labeled molecules. In addition, the necessity for using labeled molecules can lead to difficulties in the measurements themselves. For instance, the fluorescent labels may aggregate in the sample, or the bleaching reaction may alter the sample in some way. Fortunately, it is often possible to avoid this type of problem by working at sufficiently low concentrations of the labeled molecules. One can verify the absence of label-induced effects by measuring the... 

This equation is based on experience with liquid chromatography of low molecular weight samples displaying single peaks. Its application for the GPC of polymers, however, contains a disadvantage, as it mixes two inseparable properties the retention difference for the separation and the peak width for the contrary effect of band broadening. Such a procedure is acceptable if both effects are accessible for an experimental examination. For the GPC experiment, we do not possess polymer standards, consisting of molecules that are truly monodisperse. Therefore, we cannot determine the real peak width necessary for a reliable and reproducible peak resolution R,. This equation then is not qualified for a sufficient characterization of a GPC column. 

Aurora, T. S., Li, W., Cummins, H. Z., and Haines T. H. (1985). Prepai ation and characterization of monodisperse unilamellar phospholipid vesicles with selected diameters of from 300-600 nm, Biochim. Biophys. Acta. 820, 250-258. 

For the characterization of Langmuir films, Fulda and coworkers [75-77] used anionic and cationic core-shell particles prepared by emulsifier-free emulsion polymerization. These particles have several advantages over those used in early publications First, the particles do not contain any stabihzer or emulsifier, which is eventually desorbed upon spreading and disturbs the formation of a particle monolayer at the air-water interface. Second, the preparation is a one-step process leading directly to monodisperse particles 0.2-0.5 jim in diameter. Third, the nature of the shell can be easily varied by using different hydrophilic comonomers. In Table 1, the particles and their characteristic properties are hsted. Most of the studies were carried out using anionic particles with polystyrene as core material and polyacrylic acid in the shell. 

Murray CB, Norris DJ, Bawendi MG (1993) Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystaUites. J Am Chem Soc 115 8706-8715... 

Particle separation can be characterized by the separation factor, Rp, which is the ratio of eluant to particle elution volumes, or, by the difference in elution voliame, AV, between particle and eluant marker turbidity peaks. For polystyrene monodisperse standards, a linear relationship occ irs between the log of the particle diameter and AV, with a series of parallel lines resulting for different concentration of either salt or surfactant below its critical micelle concentration (IT>18,19) The separation factor has also been shown to be independent of eluant... 

Calculations for Rp as a function of the relevant experimental parameters (eluant ionic species concentration-including surfactant, packing diameter, eluant flow rate) and particle physical and electrochemical properties (Hamaker constant and surface potential) show good agreement with published data (l8,19) Of particiilar interest is the calculation which shows that at very low ionic concentration the separation factor becomes independent of the particle Hamaker constant. This result indicates the feasibility of xmiversal calibration based on well characterized latices such as the monodisperse polystyrenes. In the following section we present some recent results obtained with our HDC system using several, monodisperse standards and various surfactant conditions. 

Since the modified iterative method is completely numerical, data can be used directly from the monodisperse chromatograms to characterize the axial dispersion, eliminating the need for a specific axial dispersion function. The monodisperse standards were used to represent the spreading behavior for particle ranges as given in reference (27). 

Calibration refers to characterizing the residence time in the GPC as a function of molecular weight. Axial dispersion refers to the chromatogram being a spread curve even for a monodisperse sample. A polydisperse sample then is the result of a series of overlapping, unseen, spread curves. 

One possibility is that although averages for polystyrene standards require correction, those for PMMA would not According to symmetrical axial dispersion theory (5) the correction depends upon both the slope of the calibration curve (different for each polymer type) and the variance of the chromatogram of a truly monodisperse sample. Furthermore, the calibration curve to be utilized can be obtained from a broad standard as well as from monodisperse samples. The broad standard method may itself incorporate some axial dispersion correction depending upon how the standard was characterized. 

Axial dispersion characterization is a valuable by-product of coupling GPCs. By sampling chromatograms with the second GPC, extremely monodisperse fractions can be obtained and the concentration of misplaced molecules in any chromatogram slice revealed. 

Murray, C. B., Kagan, C. R. and Bawendi, M. G. (2000) Synthesis and characterization of monodisperse nanocrystals and close-packed nanocrystal assemblies. Anna. Rev. Mater. Sci., 30, 545-610. 

An interesting 3D superlattice of the main group metal tin has recently been generated [36]. When Sn(NMe2)2 is treated with hexadecylamine and HCl, perfect 3D superstructures of monodisperse 18 x 15nm Sn nanoparticles could be characterized. 

The preparation of ZnSe materials is an area of interest and study. The coordinating ability of the solvent used in the solvothermal synthesis of zinc selenide was demonstrated to play an important role in the nucleation and growth of nanocrystalline ZnSe.604 Thermolysis of bis [methyl( -hexyl)di-seleno]carbamato]zinc gave highly monodispersed particles characterized by electronic spectroscopy, photoluminescence, X-ray diffraction, and electron microscopy.605... 

Besides MALDI-TOF mass spectroscopy, by which the monodispersity of all the above described dendritic compounds was proven, H-NMR spectroscopy was again found to be a most informative characterization method, since most signals from the hydrogens at the different stereogenic centers have unique shifts. The resonances from analogous protons of the peripheral, interior and central units were always well separated and shifted towards lower field on going from outside to inside (for detailed discussion see our recent full paper [90]). 

Simple homopolymers, where monodisperse standards and suitable solvents are available, are easily characterized by SEC. Homopolymers for which no monodisperse standards are available additionally require some more elaborate detection system for transformation of the retention time into molecular weight. This can be done by, e.g., universal calibration. Alternatively, an absolute molar mass detector, like an on-line light scattering detector or mass spectrometer, can be used. 

Table 2. Characterization of monodisperse poly(MMA) synthesized by [SmH(C5Me5)2]2 initiator...

Over the past few years, both at the Weizmann Institute and in the Cavendish Laboratory, we have used a modification of the mica approach to measure the interaction forces F(D) between two mica surfaces,a distance D apart,immersed in organic and aqueous liquid media, both in the absence and in the presence of polymer layers absorbed onto the mica from the liquid. We have studied a number of model systems covering a wide range of conditions, using monodispersed, well characterized polymers. 

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