Diffusion in Polymer Solutions: Molecular Weight Distribution by PFG-NMR and Relation to SEC

2016 ◽  
Vol 218 (1) ◽  
pp. 1600440 ◽  
Author(s):  
Xiaoai Guo ◽  
Esther Laryea ◽  
Manfred Wilhelm ◽  
Burkhard Luy ◽  
Hermann Nirschl ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Polymer Solutions ◽  
Pfg Nmr

Truncation theorems for spinodals and critical points of mean-field models for polydisperse polymer solutions

1981 ◽  
Vol 375 (1762) ◽  
pp. 397-408 ◽  
Keyword(s):  
Molecular Weight ◽  
Critical Point ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Polymer Solutions ◽  
Mathematical Proof ◽  
Mean Field ◽  
Combinatorial Theory ◽  
Mean Field Models ◽  
Polydisperse Polymer

An exact truncation theorem is proved for the expansion, in terms of moments of the molecular weight distribution, of the Gibbs spinodal determinants of a wide class of generalized mean-field Flory-Huggins models for polydisperse polymer solutions. A similar truncation theorem for the critical-point determinants is derived on the assumption that an expansion in a finite number of moments exists. These truncations have been exploited elsewhere through the relative economy they confer on computations involved in the testing and refinement of such theoretical models by fitting them to experimental data. A much simplified general and explicit expression is found for the relevant spinodal determinants of the mean-field models. If the relevant free energy of mixing is assumed to depend on the moments M 0 , M 1 , . . . , M n of the molecular weight distribution, this expression shows the spinodal to be a function of M 0 , M 1 , . . , M 2 n +1 . The critical point is a function of M 0 , M 1 , . . . , M 3 n +2 . The truncations at M 2 n +1 and M 3 n +2 betoken a collapse to a small subspace of the formal Hilbert-space representation of the composition space of the solution. The mathematical proof follows the pathway of the classical routes to the rigorous theory of function spaces opened up by von Koch and Fredholm, and the spinodal expression bears the imprint of a classical solution of Stieltje’s moment problem. In addition, modern operational methods of combinatorial theory are relevant to future extensions of the present work. Theoreticians may, therefore, be interested to come to the aid of experimentalists struggling with the analysis of data of much practical import.

Extraction and Partial Purification of Protease from Bilimbi (Averrhoa bilimbi L.)

2013 ◽  
Vol 10 (2) ◽  
pp. 29
Author(s):  
Normah Ismail ◽  
Nur' Ain Mohamad Kharoe
Keyword(s):  
Molecular Weight ◽  
Protein Content ◽  
Ammonium Sulfate ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Protease Activity ◽  
Protein Concentration ◽  
Temperature Stability ◽  
Partial Purification ◽  
Ammonium Sulfate Precipitation

Unripe and ripe bilimbi (Averrhoa bilimbi L.) were ground and the extracted juices were partially purified by ammonium sulfate precipitation at the concentrations of 40 and 60% (w/v). The collected proteases were analysed for pH, temperature stability, storage stability, molecular weight distribution, protein concentration and protein content. Protein content of bilimbi fruit was 0.89 g. Protease activity of both the unripe and ripe fruit were optimum at pH 4 and 40°C when the juice were purified at 40 and 60% ammonium sulfate precipitation. A decreased in protease activity was observed during the seven days of storage at 4°C. Molecular weight distribution indicated that the proteases protein bands fall between IO to 220 kDa. Protein bands were observed at 25, 50 and 160 kDa in both the unripe and ripe bilimbi proteases purified with 40% ammonium sulfate, however, the bands were more intense in those from unripe bilimbi. No protein bands were seen in proteases purified with 60% ammonium sulfate. Protein concentration was higher for proteases extracted with 40% ammonium sulfate at both ripening stages. Thus, purification using 40% ammonium sulfate precipitation could be a successful method to partially purify proteases from bilimbi especially from the unripe stage. 

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