| Polyacrylamide（PAM）and its derivatives are a class of important functional polymers.Its structural units contain amide groups and tend to form hydrogen bonds,making it have good water solubility and high chemical activity.It is found that the polyelectrolyte properties of PAM and its derivatives endow it with some functions such as flocculation,drag reduction and dispersibility in aqueous solutions,which play an important role in some fields such as oil exploitation,water treatment and biomedicine and so on.However,the mechanism of these functions is still unclear.The macroscopic properties of these polymers can be understood more intuitively by studying the microstructures of PAM and its derivatives.Therefore,it is expected to provide a reference for the research and application of PAM-based functional polymer materials by the study on PAM and its derived polymers at the single molecular level.In this paper,the single-molecule force spectroscopy（SMFS）is used to study the PAM and its derivatives at the single-molecular level.First,the effects of the environments on the intramolecular hydrogen bond of non-ionic polyacrylamide（NPAM）have been studied and the intramolecular hydrogen bond strength of NPAM has been calculated.Secondly,the hydrolysis of NPAM in aqueous solution and the effects of the side chains of its basic hydrolysate,anionic polyacrylamide（APAM）,on the conformation of its main chain have been studied.Finally,the interactions between APAM-modified hydrogenated styrene-ethylene/butylene-styrene copolymer（SEBS）membranes（APAM-SEBS membrane substrate）and different proteins at physiological p H have been studied.Based on the above researches,the following conclusions are drawn in this paper:（1）In this paper,the single-molecule force spectroscopy has been used to study the hydrogen bond interactions of NPAM chains in vacuum and non-polar organic solvent nonane.Due to the exclusion of solvent molecules in the vacuum environment,intramolecular hydrogen bonds of NPAM are formed in vacuum.In nonpolar organic solvents,the intramolecular hydrogen bonds are significantly weakened or completely disappeared due to the influence of the solvent molecules.These hydrogen bond interactions directly affect the single-chain elasticity of NPAM.By integrating the area difference between the force-distance curves of NPAM in vacuum and nonane and the fitting curve of free-rotating chain（QM-FRC）model,it is found that the intramolecular hydrogen bond strengths of NPAM in vacuum and nonane are 2.034 kcal/mol and 0.462kcal/mol,respectively.The calculation results show that the intramolecular hydrogen bond strength of NPAM in nonane is much smaller than that in vacuum,indicating that the solvent environment has a great effect on the formation of intramolecular hydrogen bonds of NPAM.（2）Single-chain elasticity of non-ionic polyacrylamide（NPAM）and its hydrolysate APAM in different liquid environments has been studied by single-molecule force spectroscopy.The single-chain elasticity of NPAM in aqueous solutions with different p H values is described by using the single-chain elastic modulus parameter（K0）in the free-linked chain（M-FJC）model.The experimental results show that K0 increased with the increase of p H of the solution,proving that the degree of hydrolysis of NPAM in alkaline solution is p H-dependent.Due to the positive correlation between K0 and the net charge of the polymer chain,the increase of K0indicates that the net charge of the NPAM chain is increased,and the electrostatic repulsion between the structural units is enhanced,so that the polymer chain assumes a highly extended conformation.On this basis,the conformations of APAM in different p H solutions has been studied.The single molecular force spectrum data shows that APAM is a flexible chain in acidic aqueous solution and showed a relatively extended conformation in basic aqueous solution,thus elucidating the swelling mechanism of hydrogel network constructed by APAM chains at the molecular level.In-depth study at the single-molecule level is expected to elucidate the drag reduction mechanism of this type of polymers.（3）We have successfully prepared APAM-modified SEBS membrane（APAM-SEBS membrane substrate）by the UV-graft polymerization and the alkaline hydrolysis reaction,and studied the interactions between the APAM-SEBS membrane substrates and three different proteins in physiological acid-base environments.The calculation results show that the APAM-SEBS membrane substrates have different adsorption capacities for different proteins.It is shown that protein adsorption on the substrate surface of APAM-SEBS film is not only related to the surface charges of the materials,but also related to the charges carried by proteins and the shapes of proteins. |
