Conformation and adsorption behavior of associative polymer for enhanced oil recovery using single molecule force spectroscopy

Hydrophobically associating polyacrylamide (HAPAM) is considered as a promising candidate as a mobility control agent in enhanced oil recovery because of its excellent thickening ability and adsorption capacity. Previous studies have shown that the adsorption capability of HAPAM is higher than that of traditional polyacrylamide, but the reasons are still unclear. In order to uncover why HAPAM can establish a higher resistance factor, the conformations and adsorption behavior of HAPAM on the silica surface were studied by single molecule force spectroscopy (SMFS). For comparison, the partially hydrolytic polyacrylamide (HPAM) was also studied by SMFS under identical conditions. Two types of force profiles with plateau were obtained; indicating that train-like structure was predominant when HPAM was adsorbed on the substrate. For HAPAM, besides the above two types of force profiles, three types of representative force profiles demonstrating single-molecule characteristics were observed. The SMFS results show a strong attachment of the hydrophobic microblock to the silica surface with an adhesion force of 200-280pN in contrast to a weaker adhesion force of only 79.5 pN for HPAM chains on the silica surface. The adhesion force of HAPAM is higher than that of HPAM, so the desorption of HAPAM from silica surface is more difficult than HAPM, leading to the higher retention capacity of HAPAM than that of HPAM.