Atomistic Molecular Dynamic Simulation of Dilute Poly(acrylic acid) Solution: Effects of Simulation Size Sensitivity and Ionic Strength

Abstract

Physical properties of polyelectrolytes have been shown to be significantly related to their chain conformations. Atomistic simulation has been used as an effective method for studying polymer chain structures, but few has focused on the effects of chain length and tacticity in the presence of monovalent salts. This paper investigated the microscopic conformation behaviours of polyacrylic acid (PAA) with different chain sizes, tacticity and sodium chloride concentrations. The hydrogen behaviours and corresponding radial distribution functions were obtained. The results showed that the increase of salt concentrations led to the collapse of PAA chains, especially for longer chains. It was found that the effects of salt were mainly attributed to the shielding screening effect by sodium ions rather than the hydrogen bonding effect. Two different structure were form by iso-PAA and syn-PAA, respectively, which due to the deprotonation patterns along the PAA chain.

Molecular dynamics insight into viscosity reduction of hydrolysed polyacrylamide by using carbon quantum dots

“…Based on our previous work, 39 the conformation of polyacrylic acid (PAA) with different ionization could be successfully captured by Gromos53a6 force field 54 and the concomitant results are agreed well with others'. 38 The only difference between HPAM and PAA is that the carboxyl groups are replaced by amide groups, which are both non-charged that show slight effects on the intra-repulsion along polymer chain.…”

“…The HPAM chain with 40 monomers this is quite similar with our previous investigations. 39 Although the small oligomers could reflect properties of long chain polymer and the interaction between molecules are quite similar (this could also be implied from the RDFs of pure HPAM water shown later), the long chain polymer owns more clear trends of the macro physical properties such as the radius of gyration. Another reason could be ascribed to that compared with the 2 nm CQD, the full length of the HPAM chain with 30 monomers is too short.…”

“…This is attributed to the non-charged amide group along the polymer chain. Based on our previous studies, 39 the charged carboxylate functional group results in the electronic repulsions within the polymer backbone. Therefore, for a HPAM molecule with 40% hydrolysis, the polymer chain exhibits partially coiled state.…”

Effects of salinity on the onset of elastic turbulence in swirling flow and curvilinear microchannels

“…In addition, the transition from laminar to elastic turbulence was accompanied by a coil-stretch transition observed by Gerashchenko [55]. HPAM could have different morphologies under different salt concentrations, as revealed recently by experiments and simulations [56][57][58]. However, how such variations of initial configurations would affect the elastic turbulence is still unclear.…”

Effects of rheological properties on heat transfer enhancements by elastic instability in von-Karman swirling flow

“…Specially, with functional groups modification, the polymer rheology is affected by many water chemistry elements. The hydrolysed polyacrylamide (HPAM), which is capable of inducing elastic turbulence in porous media for enhancing oil recovery (EOR) [45][46][47], is sensitive to the surrounding ion effects due to the charged carboxylate groups [48]. The presence of different ions, typified by the salinity effect, is prevail in most of oil reservoirs and shall have large impacts on the polymer rheological properties [49], whose effects on the heat transfer have not been investigated as well.…”