Self-concentration

Lodge TP, McLeish TCB (2000) Self-concentrations and effective glass transition temperatures in polymer blends. Macromolecules 33(14) 5278—5284... 

C. Dombrowski, L. Cisneros, S. Chatkaew, R.E. Goldstein, and J.O. Kessler. Self-concentration and large-scale coherence in bacterial dynamics. Phys. Rev. Lett., 93 098103, 2004. 

The sources of these substances contributed to a number of disputes in the literature. Inexpensive commercial HSs are generally of unknown origin and their relation to surface water organics is questionable. IHSS standard and reference material is unaffordable for medium and large scale research. Self-concentrated NOM is specific with respect to its origin and research results can not be compared to other aquifiers, unless the impact of each component is studied and the NOM itself is wcU characterised. 

Up to 1.8 of the initial value, whereas the concentration of the last eluting major component, HCl, increases only insignificantly. The minor component in this system cannot be salted out into the stagnant pore zone, because CaCl2 does not fit into small pores. In addition, the factor of molar volume difference of the two electrolytes acts here cormterproductively. This is the reason for the much lower separation selectivity and smaller extent of the self-concentration of the minor component, Cp = 1.8,... 

The above experiments on a dry column packing with no dilution of the initial sample unambiguously support the notion that any separation by SEC results in redistribution and self-concentration of all components of the initial mixture within the moving zone of the sample. 

Notably, contrary to the selectivity values A and the self-concentrating coefficients for each of the two components, the corresponding process productivity P values are nearly equal. Such values can be found in Table 12.6, showing that the column productivity P can easily amount to 0.3-0.5 bed volumes for the comparable and not too high concentrations of two electrolytes. In extreme cases, more than 5—8 bed volumes of the feed solution can be processed, if traces of small ions (such as Cl or NH ) are to be removed from very concentrated brines. 

We should not lose sight of the following facts on the LM model. First, the concept of self-concentration in the LM model does not apply to mixtures of small molecular glass-formers, and yet the component dynamics are similar... 

Local Dynamics in Miscible Blends 3.4.1 Self-Concentration... 

The self-concentration, never occurring in homopolymer systems, is one of the most unique features of the miscible blends in the length scale of the monomeric units. The Lodge-McLeish model utilizes the self-concentrated volume fraction ( )2Jf and the nominal volume fraction of the segment X to express the effective ( ) of this segment as (Lodge and McLeish, 2000)... 

Combining the above expression of ( )eff with an empirical equation that describes the single T° in hypothetical (or idealized) miscible blends exhibiting no self-concentration, we can express the effective as a function of the nominal volume fraction (t)x. The Fox equation given below is frequently utilized as this empirical equation. 

For quantitative description of the segmental dynamics of the components in the miscible blends, both concentration fluctuation and self-concentration effects should be consistently incorporated in the model. This approach has already been examined by Kumar et al. (1996), Kamath et al. (1999), and Colby and Lipson (2005). In particular, the model by Colby and Lipson adopted the value ( 1 nm) comparable to the Kuhn segment length to reasonably describe the segmental relaxation time and mode distribution for both PI and PVE components in PI/PVE blends. 

Haley, J. C., and T. P. Lodge. 2005. Viscosity predictions for model miscible polymer blends Including self-concentration, double reptation, and tube dilation.. Rheol. 49 1277-1302. 

The rheological properties of miscible blends tmder different temperatures can be obtained from some theoretical models. One such model is the double reptation self-concentration. The DRSC (double reptation self-concentration) model actually includes the temperature dependency and concentration dependency through a complex mixing mle given by the double reptation model and self-concentration model, which helps to exclude the complex contribution from miscible components under different temperatures in the experimental data and only illustrate the effect of the concentration fluctuation and interface formation. This model is applied to study PMMA/SMA (Wei 2011). 

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