Self-assembly Behavior Of Quaternary Ammonium Surfactant And Polyacrylamide Mixtures In Aqueous Solution:A Coarse-grained Simulations Study

The mixing of surfactant and polymer can produce synergistic effect,which makes the richer aggregation morphology formed by the self-assembly and have better properties.These configurations have wide applications in many areas,such as drug delivery,tertiary oil recovery,surface modifications,fracturing fluid,and sewage treatment.In this paper,the self-assembly behavior of single-chain and Gemini quaternary ammonium surfactant dodecyltrimethylammonium bromide(DTAB,12-S-12)and polymer(HPAM)mixtures were investigated by the method of coarse-grained dynamics simulation.We investigate the evolution process of self-assembly configuration of surfactant/polymer mixture systems in the molecular level,revealing the transformation mechanism of aggregate configuration.In the DTAB/HPAM mixture systems,it is found that the aggregates change from sphere to rod structure with the increase of DTAB concentration.The simulation results show that the steric hindrance of surfactant micelles adsorbed polymer chain will have an important influence on the self-assembled morphology of the aggregates.In addition,the increase of the hydrolysis degree of HPAM promotes the morphology transformation from spherical to rod like structures of DTAB/HPAM aggregates.The main reasons are that as the hydrolysis degree of HPAM increases,electrostatic attraction interaction between the DTAB headgroup and the HPAM polar group(-COO~-)enhanced,and the HPAM chain is extended.These are beneficial to the formation of rod-like aggregate in the mixture system.In the 12-S-12/HPAM mixture systems,the morphology of aggregates changed from spherical to rod-like with the increase of surfactant concentration,and branched structures formed in 12-18-12 system at higher surfactant concentrations.Results shows the morphology of aggregate in mixtures undergo change from long rod-like and then short rod-like and then long rod-like with the increase of spacer length of Gemini surfactant 12-S-12.The main reasons were that the electrostatic equilibrium distance of surfactants headgroups,the hydrophobicity of the spacer and the ability of surfactant headgroup to attract Br~-ions were different with different lengths of spacer group.In addition,the simulation results show that polymer chains become the connected node of branching structure.This indicates that the polymer with opposite charges in the system can promote the formation of branched aggregate.