Stability of polymer solutions

Bouldin M, Kulicke W-M, Kehler H (1988) A prediction of the non-Newtonian viscosity and shear stability of polymer solutions Colloid Polym Sci 266 793... 

The synthesis of polymeric membranes is mostly achieved through the phase inversion process. Phase inversion is one of the most versatile and economical processes used to develop polymeric membranes. In this process, a membrane is prepared from a thermodynamically stable solution, in its most basic form consisting of a polymer and a solvent. This polymer solution is often called the casting solution, and is sometimes also called dope. The casting solution is cast onto a supporting material, which is typically nonwoven, but sometimes also woven, resulting in a thin liquid-cast-polymer film, further referred to as cast film, which is later transformed into a solid membrane. The phase transformation from liquid to solid is induced by disturbing the stability of polymer solution. 

J. F. Joanny, L. Leibler, P. G. de Gennes. Effects of polymer solutions on colloid stability. J Polym Sci Polym Phys Ed 77 1073-1084, 1979. 

Prediction of Viscoelastic Properties and Shear Stability of Polymers in Solution 17... 

Grest, G.S. Normal and Shear Forces Between Polymer Brushes. Vol. 138, pp. 149-184 Grigorescu, G, Kulicke, W.-M.t Prediction of Viscoelastic Properties and Shear Stability of Polymers in Solution. Vol. 152, p, 1-40. 

Suspension Model of Interaction of Asphaltene and Oil This model is based upon the concept that asphaltenes exist as particles suspended in oil. Their suspension is assisted by resins (heavy and mostly aromatic molecules) adsorbed to the surface of asphaltenes and keeping them afloat because of the repulsive forces between resin molecules in the solution and the adsorbed resins on the asphaltene surface (see Figure 4). Stability of such a suspension is considered to be a function of the concentration of resins in solution, the fraction of asphaltene surface sites occupied by resin molecules, and the equilibrium conditions between the resins in solution and on the asphaltene surface. Utilization of this model requires the following (12) 1. Resin chemical potential calculation based on the statistical mechanical theory of polymer solutions. 2. Studies regarding resin adsorption on asphaltene particle surface and... 

In the previous sections, we described the overall features of the heat-induced phase transition of neutral polymers in water and placed the phenomenon within the context of the general understanding of the temperature dependence of polymer solutions. We emphasised one of the characteristic features of thermally responsive polymers in water, namely their increased hydropho-bicity at elevated temperature, which can, in turn, cause coagulation and macroscopic phase separation. We noted also, that in order to circumvent this macroscopic event, polymer chemists have devised a number of routes to enhance the colloidal stability of neutral globules at elevated temperature by adjusting the properties of the particle-water interface. 

The number of polymer particles is the prime determinant of the rate and degree of polymerization since it appears as the first power in both Eqs. 4-5 and 4-7. The formation (and stabilization) of polymer particles by both micellar nucleation and homogeneous nucleation involves the adsorption of surfactant from the micelles, solution, and monomer droplets. The number of polymer particles that can be stabilized is dependent on the total surface area of surfactant present in the system asS, where as is the interfacial surface area occupied by a surfactant molecule and S is the total concentration of surfactant in the system (micelles, solution, monomer droplets). However, N is also directly dependent on the rate of radical generation. The quantitative dependence of N on asS and R,- has been derived as... 

Figure 3. Effect of 2-m.e.v. electron radiation on shear stability of Poltjox solution. 5% aqueous solutions prepared from dry irradiated polymer...

Some factors that influence the stability of polymer chelates should be mentioned. Hojo et a/.61) have reported the effect of the ligand ratio [ligand]/[metal ion] on the formation of the Cu chelate of poly(vinylalcohol)(PVA). Figure 10 shows the relationship between the formation constant of the Cu complex, the viscosity of an aqueous solution of PVA, and the ligand ratio. The viscosity diminishes very sharply at about [PVA]/[Cu] = 32 this corresponds to an increase in the formation constant. A tightly packed conformation of PVA, caused by intra-polymer chelation with Cu, facilitates more and more chelate formation. 

In the final section, we build on the thermodynamic theories of polymer solutions developed in Chapter 3, Section 3.4, to provide an illustration of how a thermodynamic picture of steric stabilization can be built when excluded-volume and elastic contributions determine the interaction between polymer layers. 

A number of chapters have been overhauled so thoroughly that they bear only minor resemblance to their counterparts in the first edition. The thermodynamics of polymer solutions is introduced in connection with osmometry and the drainage and spatial extension of polymer coils is discussed in connection with viscosity. The treatment of contact angle is expanded so that it is presented on a more equal footing with surface tension in the presentation of liquid surfaces. Steric stabilization as a protective mechanism against flocculation is discussed along with the classical DLVO theory. 

The theories of polymer solutions upon which steric-stability theories are based are usually formulated in terms of a portmanteau interaction parameter (for example Flory s X Parameter and the excluded volume integral) which does not preclude electrostatic interactions, particularly under conditions where these are short range. It is thus appropriate to consider whether polyelect-roly te-stabilisation can be understood in the same broad terms as stabilisation by non-ionic polymers. It was this together with the fact that polyelectrolyte solutions containing simple salts show phase-separation behaviour reminiscent of that of non-ionic... 

Generally speaking, the reason for this behavior is simple. It is known that low-molecular-weight surfactants dramatically increase the stability of polymers and are widely used to prevent aggregation in polymer solutions. In the HA model, surfactants , i.e., amphiphilic A groups, are incorporated into the polymer chain, thus ensuring the stabilizing effect. From the tempera-... 

Several attempts have been made to explain theoretically the effects of flow on the phase behavior of polymer solutions [112,115-118,123,124]. This has been done by modification of the mean-field free energy. The key point is to include properly the elastic energy of deformation produced by flow. A more rigorous approach originates from Helfand et al. [125, 126] and Onuki [127, 128] who proposed hydrodynamic theories for the dynamics of concentration fluctuations in the presence of flow coupled with a linear stability analysis. 

The addition of polymers can also destabilize a colloidal solution for two reasons. Firstly, when polymers adsorb on more than one colloid and this phenomenon is called bridging. Secondly, when polyelectrolytes neutralize oppositely charged colloids and thereby reduce the electrostatic repulsion between the colloids. In some cases both a destabilization and a stabilization of a solution is desired. One example is the manufacturing of paints, where it is required that the paint is easy to apply on the wall and that it stays on the wall. This can be achieved with a solvent which stabilizes the solution but rapidly evaporates when the paint is applied and makes it possible for the colloidal particles to coagulate. 

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