Relationship between structural gel and mechanical gel for ABA triblock copolymer in solutions: a molecular dynamics simulation.

Polymer gel exists ubiquitously in our daily life, as in food, cosmetics, drugs, and so on. From the structural point of view, the 3D network can be found in a structural gel. In most experimental work, the gel is identified by the sharp increase in modules; that is, the gel should have similar properties as those of a solid, which is named as mechanical gel. However, not all structural gels have strong mechanical responses. Therefore, studying the relationship between structural gel and mechanical gel is very important. In this work, we investigate the structure and mechanical properties of symmetric ABA copolymers with solvophobic end blocks during the sol-gel transition. Three typical systems with weak, middle, and strong solvophobicities are simulated. It is found that the gelation concentration, gel structure, and mechanical response of structural gel are strongly affected by the solvophobicity of ABA block copolymer. We also find that only the gel formed in strong solvophobic systems has a strong mechanical response. Furthermore, the influence of solvophobicity of A-block on the static and dynamic properties of ABA block copolymers in solutions is also studied to give a molecular understanding of physical gelation.