Self-consistent field lattice model study on the phase behavior of physically associating polymer solutions

Abstract

The phase behavior of physically associating polymer solutions, where the polymer chain contains a small fraction of "stickers" regularly placed along the backbone, is studied using self-consistent field lattice model. Two inhomogenous morphologies are observed. One is a microfluctuation homogenous (MFH) morphology, where the mean-field values of the local average concentrations of polymers phi(P)(r) and stickers phi(st)(r) slightly fluctuate around their respective bulk average values phi(P) and phi(st) and regularly from site to site. The other is a randomly close-packed micelle (RCPM) morphology. The structure of the micelle in RCPM morphology is similar to that of the "flower micelle" in the telechelic associative polymer system, where stickers are located in the core of the micelle and nonsticky groups in the corona. When phi(P) approximately or> 0.08, if homogenous associating polymer solutions are cooled, MFH morphology appears, and the system entirely changes from homogenous solutions (HS) to MFH morphology; If the solutions are cooled further, RCPM morphology appears. When phi(P) < 0.08, however, RCPM morphology appears immediately. If phi(P) < 0.53, a macroscopic phase separation, where the polymer rich phase is RCPM morphology, occurs. If phi(P) approximately or > 0.53, only RCPM morphology is found in the system. A peak appears in the temperature-dependent specific-heat curve C(V)(chi) at each transition point. For the HS-MFH transition, C(V)(chi) has an abrupt increase and a slow decrease, whereas for the MFH-RCPM transition, both the increase and the decrease in C(V)(chi) are slow. Furthermore, the system with only MFH morphology may be trapped in one of the two energy basins in a experimental time scale. However, the appearance of RCPM morphology means that the system is trapped in one of a series of "deeper" energy basins, and it is very difficult to jump off this deep basin into the one of MFH morphology or one of the other RCPM morphologies through thermal fluctuations.

Effect of distribution of stickers along backbone on temperature-dependent structural properties in associative polymer solutions

“…Nearest neighbor pairs of stickers have attractive interaction −ǫ with ǫ > 0, which is the only non-bonded interaction in the present system. In this simulation, however, instead of directly using the exact expression of the nearest neighbor interaction for stickers, we introduce a local concentration approximation for the non-bonded interaction similar to the references [23,27]. The interaction energy is expressed as:…”

“…When a local concentration approximation for the nonbonded interaction is introduced, the SCFT descriptions of lattice model for PAPSs presented in this work is basically equivalent to that of the "Gaussian thread model" chain for the similar polymer solutions [28]. The related illumination in detail refers to reference [27].…”

Effect of polymer concentration and length of hydrophobic end block on the unimer-micelle transition broadness in amphiphilic ABA symmetric triblock copolymer solutions

“…It is shown that the magnitude of the temperature-dependent range of micelle aggregation does not monotonously change withφ P , which is different from the case of changing N st at fixedφ P . 1 The structural morphology of MFH morphology [17] occurs at a narrow region of ∆χ = 0.1 neighboring the micellar boundary whenφ P > 0.7 (not shown), which is ignored.…”

“…Although self-intersections of a chain are not permitted, the excluded volume effect is sufficiently taken into account [21]. The saddle point is calculated using the pseudo-dynamical evolution process [17]. The calculation is initiated from appropriately random-chosen fields ω + (r ) and ω − (r ), and stopped when the change of free energy F between two successive iterations is reduced to the needed precision.…”

“…In this report, a SCFT lattice model is applied [14][15][16]. In earlier publications, we have used the SCFT lattice model to study the phase behavior of physically associating polymer solutions [5,17,18]. It is established that the temperature-dependent behavior of aggregates is affinitive to chain architecture [5], and the effect of polymer concentration is in a way similar to that of chain architecture [18].…”