Thermal field flow fractionation TFFF

TFFF can be used for the separation and molecular-weight distribution determination of polymers in the molecular weight range lO -lO. As a tech- 

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Most data about the Ludwig-Soret effect of polymers in solution have been obtained from thermal field-flow fractionation (TFFF), developed by Giddings and coworkers [17,18]. TFFF is one member of the family of field-flow fractionation techniques, which are all characterized by a laminar flow of the polymer solution or colloidal suspension within a relatively narrow channel. An external field, which may be gravitation, cross-flow, or temperature as in TFFF, is applied... 

In thermal field flow fractionation (TFFF), a temperature gradient is applied. The primary potential advantage of this technique is that it can be used to size particles in the range 0.01 pm to 0.001 pm, an order of magnitude smaller than SFFF. Fffractionation market a TFFF polymer fractionator channel module with 286/16 MHz IBM compatible PC, super VGA color monitor workstation to include data acquisition software, hardware and data analysis software. A linear UV detector and single channel high performance pump are optional. 

Thermal field-flow fractionation (TFFF) belongs to the historically oldest subtechniques of FFF. It is based on the principle of thermal diffusion. In early works... 

Thermophoresis is applied in industry for the separation of (large) molecules or small particles from their solvent in the so-called thermal field-flow fractioning (TFFF) [13]. A downscaled version of this process to microscopic scales demonstrated thermophoretic separation on microscopic scales [14, 15]. The advantage of using the very small confinement in a microfluidic device is that the separation times can be reduced, so that thermophoretic separation can be used. Braun and Libchaber [16] use a combination of thermophoresis and convection to concentrate DNA samples. The disadvantage of this approach is that it is a batch process. 

It is discussed in more detail below. The most basic chromatographic technique is adsorption chromatography [82,83], in which separation arises from variation in the retention of the chain units or functional groups, due to their interaction with a stationary surface. Other techniques rely on rates of sedimentation [84,85], and diffusion-adsorption phenomena (thin layer chromatography [TT-C]) [86, 87]. Thermal diffusion is the basis for thermal field flow fractionation (TFFF) [88-91], discussed later. 

The thermal field-flow fractionation (TFFF) was also coupled off-line with MALDI. This particular technique is especially able to separate large polymers according to their molecular masses, chemical composition, and microstructure. Routine MALDI-TOF MS analyses of PS polymers up to 575 kDa could be performed. 

Thermal field-flow fractionation was invented by Giddings. The universal applicability of thermal FFF for the analysis of various polymers had been already demonstrated in 1979. Several applications of TFFF to the analysis of polymers and colloidal particles were published (see Refs. for a review) but the contemporary TFFF channels have practically the same dimensions (roughly 50 X 2 X 0.01 cm) as those constructed at the very beginning. Giddings concluded, in 1993, that the miniaturization of the FFF channels could provide only some limited advantages. The experimental studydealt only with the effect of the reduced channel thickness on the performance of TFFF. 

Field flow techniques have been reviewed in a number of articles [148-150]. Sedimentation field flow fractionation has found use in the separation of PVC [151, 152], polystyrene [151-153], poly(methyl methacrylate) [153, 154], poly (vinyl toluene) [155] and poly(glycidyl methacrylate) latexes [156] to produce particle-size distributions and particle densities. It has also been applied in polymer-aggregation studies [157], pigment [157] quality control and in the separation of silica particles [158] and its performance has been compared with that of ultracentrifugation [159]. Thermal field flow fractionation has been used successfully in the characterisation of ultra-high-molecular-weight polystyrenes [160, 161], poly(methyl methacrylate), polyisoprene, polysulphane, polycarbonate, nitrocellulose, polybutadiene and polyolefins [162]. In the difficult area of water-soluble polymers, poly(ethylene glycol), poly(ethylene oxide), poly(vinyl pyrrolidone) and poly(styrene sulphonate) have been analysed [163, 164]. In addition, compositional separations have been achieved for polystyrene-poly(methyl methacrylate) mixes [165] and comparisons between TFFF and SEC have been made [166]. 

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