Viscosity solvent quality effect

Phillies GDJ (1995) Hydrodynamic scaling of viscosity and viscoelasticity of polymer solutions, including chain architecture and solvent quality effects. Macromolecules 28(24) 8198-8208... 

Effects of Aggregation and Solvent Quality on the Viscosity of Semidilute Poly(vinylbutyral)... 

This study addresses two questions 1) Is polymer aggregation in solutions directly related to solvent quality 2) If not, does solvent quality exert an effect on the viscosity of semidilute solutions separate from the effect of aggregation The copolymer poly(vinylbutyral) (PVB) was chosen for this investigation. PVB is known to aggregate in several solvents (IS). Light scattering and intrinsic viscosity measurements were used to assess solvent quality. Viscosities were measured at one concentration in three solvents and temperatures from 25 to 55 C. 

The intrinsic viscosity [r ] of a polymer increases with rising solvent quality (see Solvent in Chap. 5) due to the increased solvating envelope of the polymer chain. An increased effective volume of the chain leads to an expansion of the polymer coil and therefore to an increased intrinsic viscosity (see Fig. 5.2). The solvent quality can also be seen in the exponent a of the [q]-M-relationship. In the case that the interactions of the solvent molecules with the chain are so small that the coil is not contracted or expanded, theta-conditions are reached and the coil has its unperturbed dimensions in solution. A theta solvent is referred to as a thermodynamically poor solvent. In this solution state a theoretical value for the exponent a=0.5 can be derived (the required Eqs. 8.22 and 8.33 are discussed in detail in A deeper insight into in Chap. 8). This value of a=0.5 is also experimentally observed as shown in Fig. 6.7 for the theta system poIy(styrene) in cyclohexane (T=34.5 C). 

As seen in Figure 12.27a, the effect of solvent quality on viscosity was obtained by Gold, et al, as part of a study of probe diffusion(57). The polymer was 350 kDa polymethylmethacrylate. Good solvents were dimethylformamide (DMF)... 

It has been shown that the expansion of a copolymer coil depends largely on the number of heterocontacts, i.e. contacts between unlike monomers [26, 27]. The larger the number of heterocontacts the higher the expansion of the copolymer coil. As a consequence, the intrinsic viscosity of the copolymer is higher than that of the equivalent homopolymers. The importance of this effect increases as the solvent quality decreases [27]. 

Intrinsic Viscosity. Due to the complicating effects of aggregation and selective adsorption on the A2 values determined by light scattering, another means was sought to characterize the quality of solvents for PVB. The alternate means chosen was intrinsic viscosity measurements. Theory relates the intrinsic viscosity to the polymer chain dimensions through the expression (24)... 

With the least polar solvent, 9 1 MIBK/MEOH, aggregation dominates the viscosity behavior. This solvent is of intermediate quality, between pure MeOH and the 1 1 mixture. Still, the viscosity is greatest using the 9 1 mix at all temperatures, by up to a factor of four. The effect of temperature on the aggregation in the 9 1 MIBK/MeOH solution is so large that the fmj versus 1/T curve becomes significantly nonlinear. An apparent E determined when... 

The difference in replacement of the lEP for 19a (pHiEp = 3.6) and 19b (pHiEP = 2.9) is probably connected with the different hydrophobicity of polycarboxybetaine chains, e.g., the cationic group of 19b is more effectively screened by ethyl substituents, as they are bulkier than the methyl groups of 19a. The effect of organic solvent on the solution behavior of 19b was studied [193]. In saline water, the conformation of 19b is compact due to the screening of the electrostatic repulsion by the neutral salt KCl. Addition of ethanol improves the thermodynamic quality of the solvent with respect to the hydrophobic parts of the macromolecules, and the reduced viscosity increases and has the maximal value at 60-80 vol % of ethanol in a water/ethanol mixture. 

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