1,721,068 research outputs found
Assessment of Linearity Conditions in Thermal Field-Flow Fractionation by Peak Shape Analysis
No full textLinearity conditions in thermal-field flow fractionation, which are required for unambiguous results, are dealt with by a numerical and graphical peak shape analysis approach. Nonlinear effects, such as injected sample overloading as a function of sample concentration and field strength, can be detected by the Edgeworth-Cramér (EC) peak shape fitting method and the determination of relative statistical peak parameter determination. The physical implication of the nonlinearity effect is also discussed. Peak retention parameters by numerical integration are determined and the differences obtained by means of the above methods are compared
Characterization of Low-density Polybutadiene Latexes By Sedimentation Field-flow Fractionation
No full textA procedure based on sedimentation field-how fractionation for physical characterization of polydisperse latexes is presented. The particle density, dimensions, polydispersity, size distribution and aggregation can be determined for both narrow and wide polydispersities. The procedure is applied to the sample case of polybutadiene latexes with density lower than water. The results are compared with independent measurements obtained by electron microscopy. The relevance of significant steps of the procedure, such as the nonequilibrium corrections, are discussed
SEPARATION AND PURIFICATION OF FUNCTIONALISED WATER-SOLUBLE MULTI-WALLED CARBON NANOTUBES BY FLOW FIELD-FLOW FRACTIONATION
No full textWater-soluble, functionalised multi-walled carbon nanotubes (MWNT) have been separated and purified from amorphous material
through direct flow field-flow fractionation. MWNT subpopulations of relatively homogeneous, different length were obtained
by collecting fractions of the raw, highly polydispersed (200–5000 nm) functionalised MWNT sample
EVALUATION OF A STANDARDLESS METHOD OF DETERMINATION OF MOLECULAR WEIGHT AND POL YDISPERSITY OF A POLYSTYRENE SAMPLE BY THERMAL FIELD-FLOW FRACTIONATION
No full textThe possibility of an accurate determination of polymer molecular weight and polydispersity by thermal field-flow fractionation (ThFFF) retention measurements is' here discussed with reference to the use of only physicochemical data of ordinary and thermal diffusivity, but without need of prior calibration of the ThFFF system. Special emphasis is devoted to the check of linearity conditions of retention data determination, i.e., on the proper sample loading and thermal field strength to be chosen for unbiased polymer specifications determination. Different numerical methods of determining peak profile attributes (non¬linear peak fitting procedures by Edgeworth-Cramer series expansions, numerical integration, graphical determination) are compared. The approach is applied to a standard polystyrene sample, with ethylbenzene as polymer solvent and carrier liquid, as extensive physicochemical informations on this polymer-solvent system are available in the literature. In addition, it is shown that the combination of retention and plate height measurements provides an absolute and accurate method of determination of the thermal diffusion coefficient of the sample
Synthesis, Field-Flow Fractionation and Spectroscopic Charasterisation of TiO2 Nanoparticles Imprinted for Tyrosine
No full textContinuous split-flow thin cell and gravitational field-flow fractionation of wheat starch particles
No full textThe combined employment of the SPLITT (split-flow thin) cell — a relatively new system for fast, continuous binary separation — and of gravitational field-flow fractionation (GrFFF) — a fractionation technique suitable for micron particle size distribution determination — was investigated for starch separation and characterization. Emphasis is placed on the main advantages of both techniques: operating under gentle earth gravity field, low cost and ease of maintenance. The reproducibility of GrFFF is demonstrated. Both the SPLITT separation and GrFFF fractionation results were checked by optical microscopy. Application examples of typical starch fractionation experiments are reported and discussed
TiO2 Nanoparticles imprinted for tyrosine. Synthesis and their spectroscopic characterisation
No full textProperties of decalin as a solvent in thermal field-flow fractionation
No full textCis-trans-decahydronaphthalene (67.85% trans+ 32.15% cis, here briefly referred to ascis-trans-decalin) as a possible solvent for thermal field-flow fractionation is proposed. Different features such as solvent properties with respect to low polarity polymers, availability of basic physicochemical data (viscosity and thermal conductivity in a convenient temperature range), low toxicity and low cost are emphasized. Retention data over a wide range of cold wall temperatures and thermal gradients were collected. Thev correction factor and λ retention data were determined for polystyrene samples over a relative molecular mass range of 11,300–3,950,000 g mol−1.
From these data, selectivity values were determined and compared to the commonly found values for polystyrene in different solvent systems. The average value of −0.6 found here forcis-trans-decalin falls in the optimum selectivity solvent-domain.Cis-trans-decalin is thus fully proven as an optimum solvent for ThFFF
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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