The "single chain" microgels were synthesized successfully from the crosslinkable Poly( N isopropylacrylamide) copolymers. The viscosity properties show that the microgels have an even higher LCST than that ...The "single chain" microgels were synthesized successfully from the crosslinkable Poly( N isopropylacrylamide) copolymers. The viscosity properties show that the microgels have an even higher LCST than that of the corresponding linear copolymers.展开更多
Collapse of a poly（N-isopropylacrylamide） （PNIPAM） chain upon heating and phase diagrams of aqueous PNIPAM solutions with very fiat LCST phase separation line are theoretically studied on the basis of cooperative ...Collapse of a poly（N-isopropylacrylamide） （PNIPAM） chain upon heating and phase diagrams of aqueous PNIPAM solutions with very fiat LCST phase separation line are theoretically studied on the basis of cooperative dehydration （simultaneous dissociation of bound water molecules in a group of correlated sequence）, and compared with the experimental observation of temperature-induced coil-globule transition by light scattering methods. The transition becomes sharper with the cooperativity parameter σ of hydration. Reentrant coil-globule-coil transition in mixed solvent of water and methanol is also studied from the viewpoint of competitive hydrogen bonds between polymer-water and polymer-methanol. The downward shift of the cloud-point curves （LCST cononsolvency） with the mole fraction of methanol due to the competition is calculated and compared with the experimental data. Aqueous solutions of hydophobically-modified PNIPAM carrying short alkyl chains at both chain ends （telechelic PNIPAM） are theoretically and experimentally studied. The LCST of these solutions is found to shift downward along the sol-gel transition curve as a result of end-chain association （association-induced phase separation）, and separate from the coil-globule transition line. Associated structures in the solution, such as flower micelles, mesoglobules and higher fractal assembly, are studied by USANS with theoretical modeling of the scattering function.展开更多
Investigating average thermodynamic quantities is not sufficient to understand conformational transitions of a finite-size polymer. We propose that such transitions are better described in terms of the probability dis...Investigating average thermodynamic quantities is not sufficient to understand conformational transitions of a finite-size polymer. We propose that such transitions are better described in terms of the probability distribution of some finite-size order parameter, and the evolution of this distribution as a control parameter varies. We demonstrate this claim for the coil-globule transition of a linear polymer and its mapping onto a two-state model. In a biological context, polymer models delineate the physical constraints experienced by the genome at different levels of organization,from DNA to chromatin to chromosome. We apply our finite-size approach to the formation of plectonemes in a DNA segment submitted to an applied torque and the ensuing helix-coil transition that can be numerically observed, with a coexistence of the helix and coil states in a range of parameters. Polymer models are also essential to analyze recent in vivo experiments providing the frequency of pairwise contacts between genomic loci. The probability distribution of these contacts yields quantitative information on the conformational fluctuations of chromosome regions. The changes observed in the shape of the distribution when the cell type or the physiological conditions vary may reveal an epigenetic modulation of the conformational constraints experienced by the chromosomes.展开更多
DNA condensation is an important process in many fields including life sciences, polymer physics, and applied technology. In the nucleus, DNA is condensed into chromosomes. In polymer physics, DNA is treated as a semi...DNA condensation is an important process in many fields including life sciences, polymer physics, and applied technology. In the nucleus, DNA is condensed into chromosomes. In polymer physics, DNA is treated as a semi-flexible molecule and a polyelectrolyte. Many agents, including multi-valent cations, surfactants, and neutral poor solvents, can cause DNA condensation, also referred to as coil–globule transition. Moreover, DNA condensation has been used for extraction and gene delivery in applied technology. Many physical theories have been presented to elucidate the mechanism underlying DNA condensation, including the counterion correlation theory, the electrostatic zipper theory, and the hydration force theory. Recently several single-molecule studies have focused on DNA condensation, shedding new light on old concepts. In this document, the multi-field concepts and theories related to DNA condensation are introduced and clarified as well as the advances and considerations of single-molecule DNA condensation experiments are introduced.展开更多
The temperature dependence of the specific refractive index increment d n /d c of aqueous poly( N isopropylacrylamide) solution in the range of 20 ℃ to 35 ℃ were determined by a differential refractometer. The measu...The temperature dependence of the specific refractive index increment d n /d c of aqueous poly( N isopropylacrylamide) solution in the range of 20 ℃ to 35 ℃ were determined by a differential refractometer. The measured d n /d c of the solution decreases regularly and smoothly with increasing temperature until to the specific coil globule transition temperature of PNIPAM (around 32 ℃) and afterwards it increases with increasing temperature on the contrary. This extraordinary phenomenon is successfully explained and treated by a quantitative theory in terms of accompanying solvation desolvation process in the course of coil globule transition of the polymer chain in solution.展开更多
The phase behaviour of a single polyethylene chain is studied by using molecular dynamics simulations. A free chain and a chain with fixing one end are considered here, since the atomic force microscope （AFM） tip ca...The phase behaviour of a single polyethylene chain is studied by using molecular dynamics simulations. A free chain and a chain with fixing one end are considered here, since the atomic force microscope （AFM） tip can play a significant role in polymer crystallization in experiment. For a free chain, it is confirmed in our calculation that the polymer chain exhibits an extended coil state at high temperatures, collapses into a condensed state at low temperatures, i.e. the coil-to-globule transition that is determined by a high temperature shoulder of the heat capacity curve, and an additional liquid-to-solid transition that is described by a low temperature peak of the same heat curve. These results accord with previous studies of square-well chains and Lennard-Jones homopolymers. However, when one of the end monomers of the same chain is fixed the results become very different, and the chain cannot reach an extended coil-like state as a free chain does at high temperatures, i.e. there exists no coil-to-globule-like transition. These results may provide some insights into the influence of AFM tip when it is used to study the phase behaviour of polymer chains. If the interaction force between AFM tip and polymer monomers is strong, some monomers or one of them can be seen as being fixed by the tip, which is similar to our simulation model, and it is also found that AFM tip could induce polymer crystallization.展开更多
It has been an established practice to estimate the Θ-temperature of a polymer solution from thedisappearance of the interchain interactions (A_2 = 0) Recently, in studies of the temperature dependence ofthe chain co...It has been an established practice to estimate the Θ-temperature of a polymer solution from thedisappearance of the interchain interactions (A_2 = 0) Recently, in studies of the temperature dependence ofthe chain conformation in solution, we found that the change of the chain conformation clearly underwentthree different stages which could be viewed as the 'gas'. 'liquid' and 'solid' states in terms of the freedomof the 'blobs' on the chain. The transition temperature between the first and second stages corresponds nicelyto the Θ-temperature determined by the conventional method. It reveals, for the first time, that the Θ-temperature can be deduced from the conformation change of a single polymer chain in solution, which isimportant not only in conception, but also in practice.展开更多
Coil-to-globule transitions are fundamental problems existing in polymer science for several decades;however, some features are still unclear, such as the effect of chain monomer interaction. Herein, we use Monte Carl...Coil-to-globule transitions are fundamental problems existing in polymer science for several decades;however, some features are still unclear, such as the effect of chain monomer interaction. Herein, we use Monte Carlo simulation to study the coil-to-globule transition of simple compact polymer chains. We first consider the finite-size effects for a given monomer interaction, where the short chain exhibits a one-step collapse while long chains demonstrate a two-step collapse, indicated by the specific heat. More interestingly, with the decrease of chain monomer interaction, the critical temperatures marked by the peaks of heat capacity shift to low values. A closer examination from the energy, mean-squared radius of gyration and shape factor also suggests the lower temperature of coil-to-globule transition.展开更多
In this paper, we present the coil-to-globule(CG) transitions of homopolymers and multiblock copolymers with different topology and stiffness by using molecular dynamics with integrated tempering sampling method. The ...In this paper, we present the coil-to-globule(CG) transitions of homopolymers and multiblock copolymers with different topology and stiffness by using molecular dynamics with integrated tempering sampling method. The sampling method was a novel enhanced method that efficiently sampled the energy space with low computational costs. The method proved to be efficient and precise to study the structural transitions of polymer chains with complex topological constraint, which may not be easily done by using conventional Monte Carlo method. The topological constraint affects the globule shape of the polymer chain, thus further influencing the CG transition. We found that increasing the topological constraint generally decreased CG transition temperature for homopolymers. For semiflexible chains, an additional first-order like symmetry-broken transition emerged. For block copolymers, the topological constraint did not obviously change the transition temperature, but greatly reduced the energy signal of the CG transition.展开更多
文摘The "single chain" microgels were synthesized successfully from the crosslinkable Poly( N isopropylacrylamide) copolymers. The viscosity properties show that the microgels have an even higher LCST than that of the corresponding linear copolymers.
基金supported by a Grant-in-Aid for Scientific Research on Priority Areas"Soft Matter Physics"from the Ministry of Education,Culture,Sports,Science and Technology of Japan,and partly supported by a Grant-in-Aid for Scientific Research(B) from the Japan Society for the Promotion of Science under grant number 19350057
文摘Collapse of a poly（N-isopropylacrylamide） （PNIPAM） chain upon heating and phase diagrams of aqueous PNIPAM solutions with very fiat LCST phase separation line are theoretically studied on the basis of cooperative dehydration （simultaneous dissociation of bound water molecules in a group of correlated sequence）, and compared with the experimental observation of temperature-induced coil-globule transition by light scattering methods. The transition becomes sharper with the cooperativity parameter σ of hydration. Reentrant coil-globule-coil transition in mixed solvent of water and methanol is also studied from the viewpoint of competitive hydrogen bonds between polymer-water and polymer-methanol. The downward shift of the cloud-point curves （LCST cononsolvency） with the mole fraction of methanol due to the competition is calculated and compared with the experimental data. Aqueous solutions of hydophobically-modified PNIPAM carrying short alkyl chains at both chain ends （telechelic PNIPAM） are theoretically and experimentally studied. The LCST of these solutions is found to shift downward along the sol-gel transition curve as a result of end-chain association （association-induced phase separation）, and separate from the coil-globule transition line. Associated structures in the solution, such as flower micelles, mesoglobules and higher fractal assembly, are studied by USANS with theoretical modeling of the scattering function.
基金the program "Small Systems Nonequilibrium Fluctuations,Dynamics and Stochastics,and Anomalous Behavior" of the Kavli Institute for Theoretical Physics China at the Chinese Academy of Sciences(KITPC),held in Bejing in July 2013funded by the French Institut de la Recherche M'edicale,under Grant MICROMEGAS PC201104+1 种基金the French Institut National du Cancer,under Grant INCa-5960the French Agence Nationale de la Recherche under Grant No.ANR-13-BSV5-0010-03.UPMC belongs to Sorbonne Universit'es
文摘Investigating average thermodynamic quantities is not sufficient to understand conformational transitions of a finite-size polymer. We propose that such transitions are better described in terms of the probability distribution of some finite-size order parameter, and the evolution of this distribution as a control parameter varies. We demonstrate this claim for the coil-globule transition of a linear polymer and its mapping onto a two-state model. In a biological context, polymer models delineate the physical constraints experienced by the genome at different levels of organization,from DNA to chromatin to chromosome. We apply our finite-size approach to the formation of plectonemes in a DNA segment submitted to an applied torque and the ensuing helix-coil transition that can be numerically observed, with a coexistence of the helix and coil states in a range of parameters. Polymer models are also essential to analyze recent in vivo experiments providing the frequency of pairwise contacts between genomic loci. The probability distribution of these contacts yields quantitative information on the conformational fluctuations of chromosome regions. The changes observed in the shape of the distribution when the cell type or the physiological conditions vary may reveal an epigenetic modulation of the conformational constraints experienced by the chromosomes.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21204065 and 20934004)the Natural Science Foundation of Zhejiang Province,China(Grant No.Y4110357)
文摘DNA condensation is an important process in many fields including life sciences, polymer physics, and applied technology. In the nucleus, DNA is condensed into chromosomes. In polymer physics, DNA is treated as a semi-flexible molecule and a polyelectrolyte. Many agents, including multi-valent cations, surfactants, and neutral poor solvents, can cause DNA condensation, also referred to as coil–globule transition. Moreover, DNA condensation has been used for extraction and gene delivery in applied technology. Many physical theories have been presented to elucidate the mechanism underlying DNA condensation, including the counterion correlation theory, the electrostatic zipper theory, and the hydration force theory. Recently several single-molecule studies have focused on DNA condensation, shedding new light on old concepts. In this document, the multi-field concepts and theories related to DNA condensation are introduced and clarified as well as the advances and considerations of single-molecule DNA condensation experiments are introduced.
文摘The temperature dependence of the specific refractive index increment d n /d c of aqueous poly( N isopropylacrylamide) solution in the range of 20 ℃ to 35 ℃ were determined by a differential refractometer. The measured d n /d c of the solution decreases regularly and smoothly with increasing temperature until to the specific coil globule transition temperature of PNIPAM (around 32 ℃) and afterwards it increases with increasing temperature on the contrary. This extraordinary phenomenon is successfully explained and treated by a quantitative theory in terms of accompanying solvation desolvation process in the course of coil globule transition of the polymer chain in solution.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 20574052 and 20774066)the Program for New Century Excellent Talents in University (Grant No NCET-05-0538)the Natural Science Foundation of Zhejiang Province (Grant No R404047)
文摘The phase behaviour of a single polyethylene chain is studied by using molecular dynamics simulations. A free chain and a chain with fixing one end are considered here, since the atomic force microscope （AFM） tip can play a significant role in polymer crystallization in experiment. For a free chain, it is confirmed in our calculation that the polymer chain exhibits an extended coil state at high temperatures, collapses into a condensed state at low temperatures, i.e. the coil-to-globule transition that is determined by a high temperature shoulder of the heat capacity curve, and an additional liquid-to-solid transition that is described by a low temperature peak of the same heat curve. These results accord with previous studies of square-well chains and Lennard-Jones homopolymers. However, when one of the end monomers of the same chain is fixed the results become very different, and the chain cannot reach an extended coil-like state as a free chain does at high temperatures, i.e. there exists no coil-to-globule-like transition. These results may provide some insights into the influence of AFM tip when it is used to study the phase behaviour of polymer chains. If the interaction force between AFM tip and polymer monomers is strong, some monomers or one of them can be seen as being fixed by the tip, which is similar to our simulation model, and it is also found that AFM tip could induce polymer crystallization.
基金The support of the National Distinguished Young Investigator Fund(1996,29625410)is gratefully acknowledged
文摘It has been an established practice to estimate the Θ-temperature of a polymer solution from thedisappearance of the interchain interactions (A_2 = 0) Recently, in studies of the temperature dependence ofthe chain conformation in solution, we found that the change of the chain conformation clearly underwentthree different stages which could be viewed as the 'gas'. 'liquid' and 'solid' states in terms of the freedomof the 'blobs' on the chain. The transition temperature between the first and second stages corresponds nicelyto the Θ-temperature determined by the conventional method. It reveals, for the first time, that the Θ-temperature can be deduced from the conformation change of a single polymer chain in solution, which isimportant not only in conception, but also in practice.
基金supported by the National Natural Science Foundation of China(No.21574066 and No.21204093)
文摘Coil-to-globule transitions are fundamental problems existing in polymer science for several decades;however, some features are still unclear, such as the effect of chain monomer interaction. Herein, we use Monte Carlo simulation to study the coil-to-globule transition of simple compact polymer chains. We first consider the finite-size effects for a given monomer interaction, where the short chain exhibits a one-step collapse while long chains demonstrate a two-step collapse, indicated by the specific heat. More interestingly, with the decrease of chain monomer interaction, the critical temperatures marked by the peaks of heat capacity shift to low values. A closer examination from the energy, mean-squared radius of gyration and shape factor also suggests the lower temperature of coil-to-globule transition.
基金supported by the National Basic Research Program of China(2012CB821500)the National Natural Science Foundation of China(21025416)Jilin Province Science and Technology Development Plan(20140519004JH)
文摘In this paper, we present the coil-to-globule(CG) transitions of homopolymers and multiblock copolymers with different topology and stiffness by using molecular dynamics with integrated tempering sampling method. The sampling method was a novel enhanced method that efficiently sampled the energy space with low computational costs. The method proved to be efficient and precise to study the structural transitions of polymer chains with complex topological constraint, which may not be easily done by using conventional Monte Carlo method. The topological constraint affects the globule shape of the polymer chain, thus further influencing the CG transition. We found that increasing the topological constraint generally decreased CG transition temperature for homopolymers. For semiflexible chains, an additional first-order like symmetry-broken transition emerged. For block copolymers, the topological constraint did not obviously change the transition temperature, but greatly reduced the energy signal of the CG transition.
