Self-consistent Field Lattice Theory Study On The Clustering And Phase Separation In Physically Associating Polymer Solutions

Physically associating polymers contain both soluble and insoluble monomers. In solutions of these amphiphilic polymers, if the interactions between soluble monomers are relatively stronger, these soluble monomers are called"stickers"; if there are stronger interactions between insoluble monomers, then insoluble monomers are called"stickers". The properties of these solutions are mainly governed by these stickers. Stickers tend to form small aggregates, and these aggregates play a role of junctions between different chains. If the polymer concentration reaches a certain value, an infinite polymer network may be formed, i. e., the polymer gel is formed. Meanwhile, because the interaction between two stickers is related to the thermal energy , so the junctions are reversible and these polymer gels are also reversible.Materials that contain physically associating polymers are ubiquitous in real life, for example in food, enhanced oil recovery and biological tissues. Polymer physical gel has widespread industrial applications. So the study of these solutions are important for both scientific view and application prospect.In recent years, scientists have carried out some researches on the phase behavior of these physically associating polymer solutions, especially on the reversible polymer networks formed in these solutions. Because experimental works are restricted by many facts, theoretical methods and computer simulation methods are developed by researchers. Computer simulation method is the combination of theoretical work and computer. In the past few years, the computing ability of computer has improved greatly, so computer simulation methods have developed well. In the study of physically associating polymer solutions, there are some works using Molecule Dynamics method (MD) and Monte Carlo method (MC). Because there are many work need to be done in the study of physically associating polymer solutions and every method has its own limitations, it is meaningful to study the problem in a new way.In the thesis we study the clustering and phase separation in physically associating polymer solutions using self-consistent field lattice mode. It is proved the method can be applied both in the study of flexible polymer chains and in the study of rigid polymer chains. Compared with analysis works in theory we can obtain the morphologies of the solution using this method, so we can get the information about the solutions in a more intuitiver way; compared with other computer simulation method, it requires a relatively low amount of computation.In our model, stickers are placed regularly in the chain. We only consider the interactions between different stickers. In order to express the problem in an easy way, we use a parameterχthat is related to temperature and the interactions between different stickers. From the morphologies of the solution, we can see, with the value ofχincreasing, polymers gradually separate from the solvents. And the process can be divided into these main steps: no separation, polymer clusters formed because of the clustering of different polymer chains, polymer gel network formed through junctions between a large number of polymer chains, phase separation etc.We take as an order parameter of our solution system, while the value of reflects the separation degree of polymers and solvents. Combining the morphologies we obtain, we find, withχbecoming bigger, polymer clusters start to come up whenΨp is about 0.1, and also in this stateΨp starts to show an evident change. So we take the value ofχin the very state as the sign that clusters begin to appear; WhenΨp reaches its maximum value, andΨpdoes changes with increasingχ, phase separation has taken place in the system. Using the method mentioned above, we determined the clustering line and phase separation line. Our results are consistent with known results.The effect of solvent size on the solution is also considered in this thesis. We consider polymer chain of polymerization forty, with five sticks placed regularly ten monomers apart. Solutions with polymer concentration between 10% and 30% are studied in the thesis. We have got these results: 1 Increasing the solvent size will facilitate the clustering and phase transition of the solutions. 2 If the solvent's polymerization is smaller than five, the bigger of the solvent's polymerization, the smaller of the correspondingχwhen clustering and phase separation takes place. If the solvent's polymerization is bigger or equals five, evident change occurs in the solutions. When the polymerization of the solvent is five, if the polymer concentration in the solution is smaller than 17.5%, there will only be phase separation and no gelation as the value ofχincreases; if the concentration greater or equals 17.5%, with increasingχ, the solutions first separate into polymer rich solutions and polymer poor solutions, and then gelation takes place in the polymer rich solutions. If the solvent's polymerization is ten, the polymer concentration corresponding to 17.5% in solutions with solvent's polymerization five is 27.5%. If the size of the solvent is bigger than ten, there will only be phase separation and no gelation.