Thermodynamics of phase separation in mixtures of associating polymers and homopolymers in solution

Abstract

The phase behavior of mixtures of a hydrophobically modified polymer capable of forming associations and an unmodified polymer of the same chemical composition has been investigated. The associative thickener (AT) consists of polyethylene glycol) (PEG) end-capped at both ends with hydrophobic alkane groups. It is found that mixtures of the AT solution and the unmodified PEG phase separate into two distinct solutions, provided AT molar fractions are <0.65. This is despite the fact that the overall polymer concentration throughout both phases remains the same. However, the viscosities of the two phases were found to be very different. For example, for a 50:50 mixture at an overall concentration of 5 wt %, the viscosity of one phase was found to be 170 Pa s, consistent with the existence of an AT network, whereas the viscosity of the less viscous solution was measured to be 0.004 Pa s, indicating that nearly all the polymer in this phase is of the unmodified type. When the AT to total polymer ratio is >0.65 or when the overall polymer concentration is below 2 %, no phase separation is observed. It is proposed that the phase separation behavior in this type of system is an entropically driven phenomenon. It is shown that by considering the entropy changes due to the association of the end groups, within a Flory-Huggins framework, all of the above features can be accounted for theoretically.

Relationships between Diffusion and Viscoelasticity of Associative Polymer Networks

“…It is well known that the HEUR networks exhibit single viscoelastic relaxation. Due to this mechanical simplicity, the HEUR networks have been employed as a model system of the transient network [1][2][3][4][5][6][7][8] .…”

“…However, there have been experimentally reported that the relaxation time depends both on the concentration and the molecular mass [1][2][3]7) . Tanaka and Edwards proposed the modified model considering the recombination of the chains, to describe the deviation of the experimental results from the prediction of the classical theory [11][12][13] .…”

First-order phase transition during displacement of amphiphilic biomacromolecules from interfaces by surfactant molecules

“…These bonds need to be sufficiently strong to produce a reasonable degree of incompatibility, while still remaining reversible so as not to trap the structure and hinder the lateral movement of the chains [17]. In our previous work using both theoretical calculations and Brownian dynamics simulations [17,27] we had shown the possibility of both bulk and surface phase separation, resulting from the presence of such reversible bonds between one set of molecules but not the other, in systems consisting of a mixture of the two.…”

“…These serve to produce weak reversible bonds, driven by hydrophobic forces, between the modified molecules, but not the unmodified ones. As a result, it is observed that the mixed solution breaks up into two distinct phases, one rich in the associating molecules and the other in unmodified ones [27][28][29][30]. We also suspect that the possible surface phase separation reported for certain mixed protein films occurring at air-water interfaces [31][32][33][34][35] is also the result of a very similar mechanism.…”

Synthesis of perfluorohexyl‐terminated poly(ethylene oxide) using maghnite‐h as clay catalyst

“…Hydrophobically modified PEO can be obtained by different methods including various linkers used to connect the PEO chain with the hydrophobic segment. The syntheses of modified PEO with linkers such as ethers,4 esters,5, 6 urethanes7, 8 or diurethanes9, 10 were reported.…”