The refractive index increment, dynamic and static laser light scattering, intrinsic viscosity [η] and Huggins constant （KH） of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 10-60℃. Th...The refractive index increment, dynamic and static laser light scattering, intrinsic viscosity [η] and Huggins constant （KH） of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 10-60℃. The intrinsic viscosity, Rn, Rg, A2, and （〈 S 〉2）^1/2 （calculated from viscosity data） and ＂a＂ values of nylon 12 are found to be higher in m-cresol than in sulphuric acid. All these parameters decrease with the increase in water contents in sulphuric acid. The refractive index increment, KH and activation energy show an opposite trend to that of [η]. The intrinsic viscosity, RH, Rg, A2, and （〈 S 〉2）^1/2 have maximum values around 30-40℃ in sulphuric acid/water system, whereas in m-cresol they fall at about 20℃. It has been concluded that the variation in size, interaction parameter （second virial coefficient）, [η] and KH of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents, selective adsorption, hydrogen bonding and conformational transitions. It has also been concluded that the increase in temperature first enhances the quality of the solvent, encourages hydrogen bonding and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. However, the addition of water to sulphuric acid continuously deteriorates the solvent quality. This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures.展开更多
The chain conformation of polymers in binary solvent mixtures is a key issue in the study of functional soft matter and lies at the heart of various applications such as smart soft materials.Based on a minimal lattice...The chain conformation of polymers in binary solvent mixtures is a key issue in the study of functional soft matter and lies at the heart of various applications such as smart soft materials.Based on a minimal lattice model,we employ Monte Carlo(MC)simulation to systematically investigate the effects of solvent qualities on the conformation of a single homopolymer chain in binary mixed solvents.We also perform calculations using a Flory-type mean-field theory.We focus on how the introduction of a second solvent B affects the dependence of chain conformation on the quality of solvent A.We mainly examine the effects of the composition of solvent B,denoted by x,and the interactions between the two solvents.First,when x is low,the mean-square chain radius of gyration exhibits qualitatively similar behaviors to those in an individual solvent A,with a slight chain contraction when solvent A is very good.Second,in equal-molar mixtures with x=0.5,a homopolymer chain collapses when solvent A is either poor or very good,while expands at intermediate qualities.Lastly,at large x,a chain undergoes a coil-to-globule transition with the increasing quality of solvent A when solvent B is good,but mainly adopts the collapsed conformation when solvent B is poor.Our findings not only improve our understanding on the chain conformation in binary solvent mixtures,but also provide valuable guidance on the rational design of stimuli-responsive polymeric materials.展开更多
The intrinsic viscosity [η], Huggins constant （Ku）, [η]0, α^3 and flow activation energy values of nylon 6 have been measured in wateηm-cresol （0/100-20/80） systems at different temperatures （20-60℃）. It ha...The intrinsic viscosity [η], Huggins constant （Ku）, [η]0, α^3 and flow activation energy values of nylon 6 have been measured in wateηm-cresol （0/100-20/80） systems at different temperatures （20-60℃）. It has been found that the intrinsic viscosity, [η]0 and α^3 increase with the increase in water contents in m-cresol up to 15% and then decrease. They increase with the increase in temperature irrespective of solvent composition. It has been noted that the percent increase of α^3 is the highest at 60℃ and the lowest at 20℃ for a particular solvent system. The intrinsic viscosity data obey Arrhenius equation over the considered conditions. The activation energy and the KH values decrease very sharply with the addition of water, giving a minimum value at 15% of water and then increase slowly. The variation of all the parameters has been explained in terms of variation in thermodynamic quality of solvent with the addition of water to m-cresol and change in temperature, resulting in the change of conformational and orientational properties of polymer molecules. This change of solvent quality also results in variation of selective sorption of solvent over the polymer, such as hydrogen bonding, etc.展开更多
Monte Carlo simulations were used to study the translocation of a flexible polymer through a pore in a membrane, assuming an attractive interaction between the monomers and the membrane on the trans side of the membra...Monte Carlo simulations were used to study the translocation of a flexible polymer through a pore in a membrane, assuming an attractive interaction between the monomers and the membrane on the trans side of the membrane and no interaction on the cis side. For the case T〈Tc （the temperature corresponding to the minimum in the translocation time τ）, the value of τdecreases with increasing temperature, whereas for T〉Tc, τ increases with increasing temperature. The translocation time depends on the absorbed energy uo in a nontrivial way. The value of τ increases initially upon increasing uo before it begins to decrease. The variation of the translocation time with respect to the solvent quality was also studied. It showed that there is a transition, as the solvent quality improves from ＂poor＂ to ＂good＂： when εAB〈εc （the interaction energy corresponding to the minimum in τ）, τdecreases with increasing the value of εAB; when εAB〉εc, τincreases with increasing εAB- When the chain length was changed, it was found that when the absorbed energy uo was greater than uc,τ was proportional to N1.602; for uo〈uc, τ∝N2.248. As the solvent quality improved from ＂poor＂ to ＂good,＂ the translocation probability increased initially before becoming stable.展开更多
文摘The refractive index increment, dynamic and static laser light scattering, intrinsic viscosity [η] and Huggins constant （KH） of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 10-60℃. The intrinsic viscosity, Rn, Rg, A2, and （〈 S 〉2）^1/2 （calculated from viscosity data） and ＂a＂ values of nylon 12 are found to be higher in m-cresol than in sulphuric acid. All these parameters decrease with the increase in water contents in sulphuric acid. The refractive index increment, KH and activation energy show an opposite trend to that of [η]. The intrinsic viscosity, RH, Rg, A2, and （〈 S 〉2）^1/2 have maximum values around 30-40℃ in sulphuric acid/water system, whereas in m-cresol they fall at about 20℃. It has been concluded that the variation in size, interaction parameter （second virial coefficient）, [η] and KH of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents, selective adsorption, hydrogen bonding and conformational transitions. It has also been concluded that the increase in temperature first enhances the quality of the solvent, encourages hydrogen bonding and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. However, the addition of water to sulphuric acid continuously deteriorates the solvent quality. This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures.
基金financially supported by the National Natural Science Foundation of China(Nos.22473024,22073016 and 21803011)the award of Shanghai Dongfang Scholar。
文摘The chain conformation of polymers in binary solvent mixtures is a key issue in the study of functional soft matter and lies at the heart of various applications such as smart soft materials.Based on a minimal lattice model,we employ Monte Carlo(MC)simulation to systematically investigate the effects of solvent qualities on the conformation of a single homopolymer chain in binary mixed solvents.We also perform calculations using a Flory-type mean-field theory.We focus on how the introduction of a second solvent B affects the dependence of chain conformation on the quality of solvent A.We mainly examine the effects of the composition of solvent B,denoted by x,and the interactions between the two solvents.First,when x is low,the mean-square chain radius of gyration exhibits qualitatively similar behaviors to those in an individual solvent A,with a slight chain contraction when solvent A is very good.Second,in equal-molar mixtures with x=0.5,a homopolymer chain collapses when solvent A is either poor or very good,while expands at intermediate qualities.Lastly,at large x,a chain undergoes a coil-to-globule transition with the increasing quality of solvent A when solvent B is good,but mainly adopts the collapsed conformation when solvent B is poor.Our findings not only improve our understanding on the chain conformation in binary solvent mixtures,but also provide valuable guidance on the rational design of stimuli-responsive polymeric materials.
文摘The intrinsic viscosity [η], Huggins constant （Ku）, [η]0, α^3 and flow activation energy values of nylon 6 have been measured in wateηm-cresol （0/100-20/80） systems at different temperatures （20-60℃）. It has been found that the intrinsic viscosity, [η]0 and α^3 increase with the increase in water contents in m-cresol up to 15% and then decrease. They increase with the increase in temperature irrespective of solvent composition. It has been noted that the percent increase of α^3 is the highest at 60℃ and the lowest at 20℃ for a particular solvent system. The intrinsic viscosity data obey Arrhenius equation over the considered conditions. The activation energy and the KH values decrease very sharply with the addition of water, giving a minimum value at 15% of water and then increase slowly. The variation of all the parameters has been explained in terms of variation in thermodynamic quality of solvent with the addition of water to m-cresol and change in temperature, resulting in the change of conformational and orientational properties of polymer molecules. This change of solvent quality also results in variation of selective sorption of solvent over the polymer, such as hydrogen bonding, etc.
基金This work was supported by the Outstanding Youth Fund （No.20525416）, the National Natural Science Foundation of China （No.20490220, No.20374050, and No.90403022）, and the National Basic Research Program of China （No.2005CB623800）.
文摘Monte Carlo simulations were used to study the translocation of a flexible polymer through a pore in a membrane, assuming an attractive interaction between the monomers and the membrane on the trans side of the membrane and no interaction on the cis side. For the case T〈Tc （the temperature corresponding to the minimum in the translocation time τ）, the value of τdecreases with increasing temperature, whereas for T〉Tc, τ increases with increasing temperature. The translocation time depends on the absorbed energy uo in a nontrivial way. The value of τ increases initially upon increasing uo before it begins to decrease. The variation of the translocation time with respect to the solvent quality was also studied. It showed that there is a transition, as the solvent quality improves from ＂poor＂ to ＂good＂： when εAB〈εc （the interaction energy corresponding to the minimum in τ）, τdecreases with increasing the value of εAB; when εAB〉εc, τincreases with increasing εAB- When the chain length was changed, it was found that when the absorbed energy uo was greater than uc,τ was proportional to N1.602; for uo〈uc, τ∝N2.248. As the solvent quality improved from ＂poor＂ to ＂good,＂ the translocation probability increased initially before becoming stable.
