A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit...A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.展开更多
It has been found recently that an ultrasmall nanoparticle whose size is smaller than the thickness of a cell membrane has unique roles in biomedical applications including the development of next generation of drugs ...It has been found recently that an ultrasmall nanoparticle whose size is smaller than the thickness of a cell membrane has unique roles in biomedical applications including the development of next generation of drugs or advanced nanoscale cargo carriers.However,the effect of physical properties of an ultrasmall nanoparticle on its adhesion to a bilayer membrane,which is a key step for Nano-Bio interaction as well as the biomedical applications,is still largely unknown.By using molecular dynamics,we find that both size and shape of an ultrasmall nanoparticle strongly affect its adhesion states on a bilayer membrane(e.g.,adhesion,separation or entwined by polymer chains).Interestingly,our simulations show that with decreasing particle size,the effect of particle shape becomes even more evident for the adhesion behavior.It is indicated that the competition between nanoparticle-polymer binding and polymer chain deformation,both of which are influenced by particle size and shape,determines the final adhesion states of an ultrasmall nanoparticle.Our results are helpful for the full understanding of interaction mechanism between nanoparticles and cell membranes and the practical applications of such ultrasmall nanoparticles.展开更多
Gas wells often encounter blockages in gas recovery channels owing to fluid accumulation during the later stages of extraction,which adversely affects subsequent recovery efforts.These undesirable conditions(e.g.,high...Gas wells often encounter blockages in gas recovery channels owing to fluid accumulation during the later stages of extraction,which adversely affects subsequent recovery efforts.These undesirable conditions(e.g.,high condensate content,high temperature,and high salinity)often affect foaming agent performance.In this study,surfactants were screened using an airflow method that closely resembles field treatment method.Notably,alcohol ether sulfates(AE_(n)S)with various polyoxyethylene(EO)units demonstrated exceptional performance in terms of liquid unloading efficiency and foam stability.At 80℃,the unloading efficiency of AE_(n)S with two EO units(AE_(2)S)in a high NaCl mass concentration(up to 200 g/L)and high condensate volume fraction(up to 20%)reached 84%.The dynamic surface tension and interfacial tension measured at the same temperature were used to analyze the influence of the diffusion rate and interfacial characteristics on the AE_(n)S foam,while the viscosity and liquid film thickness measurements reflected the mechanical strength and liquid-carrying capacity.In addition,transmission electron microscopy(TEM)revealed that AE_(2)S formed“dendritic”micellar aggregates at a high NaCl mass concentration,which significantly enhanced the viscosity and stability of the foam.The interactions among AE_(n)S,NaCl,and H2O were analyzed using molecular dynamics,and it was confirmed from a molecular mechanics perspective that a stable structure can form among the three,contributing to the foam stability.These findings demonstrate the significant potential of the AE_(2)S foam for gas well deliquification.展开更多
文摘A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.
基金the financial support of the project from the National Basic Research Program of China(No.2012CB821500)the National Natural Science Foundation of China(Nos.91027040,31061160496,21374074,11104192 and 21106114)the support of the Natural Science Foundation of Jiangsu Province of China(Nos.BK20131194 and BK2012177)
文摘It has been found recently that an ultrasmall nanoparticle whose size is smaller than the thickness of a cell membrane has unique roles in biomedical applications including the development of next generation of drugs or advanced nanoscale cargo carriers.However,the effect of physical properties of an ultrasmall nanoparticle on its adhesion to a bilayer membrane,which is a key step for Nano-Bio interaction as well as the biomedical applications,is still largely unknown.By using molecular dynamics,we find that both size and shape of an ultrasmall nanoparticle strongly affect its adhesion states on a bilayer membrane(e.g.,adhesion,separation or entwined by polymer chains).Interestingly,our simulations show that with decreasing particle size,the effect of particle shape becomes even more evident for the adhesion behavior.It is indicated that the competition between nanoparticle-polymer binding and polymer chain deformation,both of which are influenced by particle size and shape,determines the final adhesion states of an ultrasmall nanoparticle.Our results are helpful for the full understanding of interaction mechanism between nanoparticles and cell membranes and the practical applications of such ultrasmall nanoparticles.
文摘Gas wells often encounter blockages in gas recovery channels owing to fluid accumulation during the later stages of extraction,which adversely affects subsequent recovery efforts.These undesirable conditions(e.g.,high condensate content,high temperature,and high salinity)often affect foaming agent performance.In this study,surfactants were screened using an airflow method that closely resembles field treatment method.Notably,alcohol ether sulfates(AE_(n)S)with various polyoxyethylene(EO)units demonstrated exceptional performance in terms of liquid unloading efficiency and foam stability.At 80℃,the unloading efficiency of AE_(n)S with two EO units(AE_(2)S)in a high NaCl mass concentration(up to 200 g/L)and high condensate volume fraction(up to 20%)reached 84%.The dynamic surface tension and interfacial tension measured at the same temperature were used to analyze the influence of the diffusion rate and interfacial characteristics on the AE_(n)S foam,while the viscosity and liquid film thickness measurements reflected the mechanical strength and liquid-carrying capacity.In addition,transmission electron microscopy(TEM)revealed that AE_(2)S formed“dendritic”micellar aggregates at a high NaCl mass concentration,which significantly enhanced the viscosity and stability of the foam.The interactions among AE_(n)S,NaCl,and H2O were analyzed using molecular dynamics,and it was confirmed from a molecular mechanics perspective that a stable structure can form among the three,contributing to the foam stability.These findings demonstrate the significant potential of the AE_(2)S foam for gas well deliquification.
