Phase Transitions in Swollen Networks

Moerkerke, R.; Koningsveld, R.; Berghmans, Hugo; Dušek, Karel; Šolc, Karel

doi:10.1021/ma00108a043

Cited by 123 publications

(116 citation statements)

References 8 publications

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“…20 However, for polymer gels that undergo discontinuous volume phase transitions, the threephase equilibrium among the pure solvent, the swollen gel, and the collapsed gel requires a stronger quadratic dependence of = 0 + 1 + 2 2 to describe such systems. 19 Experimentally Horkay and co-workers 9,27 found that a that was independent of the polymer concentration could not adequately describe the osmotic pressure data of polyacrylate gels, but that a that was linearly dependent on provided a satisfactory model for these gels.…”

Section: +mentioning

confidence: 99%

Molecular simulation of the swelling of polyelectrolyte gels by monovalent and divalent counterions

Yin

Horkay

Douglas

et al. 2008

The Journal of Chemical Physics

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Permanently crosslinked polyelectrolyte gels are known to undergo discontinuous first-order volume phase transitions, the onset of which may be caused by a number of factors. In this study we examine the volumetric properties of such polyelectrolyte gels in relation to the progressive substitution of monovalent counterions by divalent counterions as the gels are equilibrated in solvents of different dielectric qualities. We compare the results of coarse-grained molecular dynamics simulations of polyelectrolyte gels with previous experimental measurements by others on polyacrylate gels. The simulations show that under equilibrium conditions there is an approximate cancellation between the electrostatic contribution and the counterion excluded-volume contribution to the osmotic pressure in the gel-solvent system; these two contributions to the osmotic pressure have, respectively, energetic and entropic origins. The finding of such a cancellation between the two contributions to the osmotic pressure of the gel-solvent system is consistent with experimental observations that the swelling behavior of polyelectrolyte gels can be described by equations of state for neutral gels. Based on these results, we show and explain that a modified form of the FloryHuggins model for nonionic polymer solutions, which accounts for neither electrostatic effects nor counterion excluded-volume effects, fits both experimental and simulated data for polyelectrolyte gels. The Flory-Huggins interaction parameters obtained from regression to the simulation data are characteristic of ideal polymer solutions, whereas the experimentally obtained interaction parameters, particularly that associated with the third virial coefficient, exhibit a significant departure from ideality, leading us to conclude that further enhancements to the simulation model, such as the inclusion of excess salt, the allowance for size asymmetric electrolytes, or the use of a distance-dependent solvent dielectricity model, may be required. Molecular simulations also reveal that the condensation of divalent counterions onto the polyelectrolyte network backbone occurs preferentially over that of monovalent counterions.

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Section: +mentioning

confidence: 99%

Molecular simulation of the swelling of polyelectrolyte gels by monovalent and divalent counterions

Yin

Horkay

Douglas

et al. 2008

The Journal of Chemical Physics

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“…To an ice-cold solution of glycine ethyl ester, Marchetti et al 18 20 suggested a simple model in manner. The mixture was stirred at room temperwhich the polymer-solvent interaction parameature for 5 h. The precipitated solid (Et 3 NHCl), ter depends not only on the temperature but also which was gradually separated during the reacon the concentration of polymer and fitted it to tion, was filtered off, and the filtrate was evapoInomata's swelling data.…”

Section: Methodsmentioning

confidence: 99%

“…dissolved solution was held in a thermostated waThe elastic contribution, DG el , is expressed as ter bath at 70ЊC. The reaction was initiated by follows 20,23 : adding 200 mL of 1 wt % solution of APS. Simultaneously, 100 mL of 1 wt % solution of Tween20 to DG el prevent aggregation during polymerization.…”

Section: Theoretical Considerationmentioning

confidence: 99%

Swelling behavior of thermosensitiveN-isopropylacrylamide-ethylN-acryloylglycine submicron-sized copolymer gel particles

Choi

Kim

Lee

et al. 1998

J. Appl. Polym. Sci.

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Submicron-sized N-isopropylacrylamide (NIPA) -ethyl N-acryloylglycine (ENAG) copolymer gel particles with various compositions were prepared by precipitation polymerization in water. Their swelling behaviors were determined by photon correlation spectroscopy (PCS). Our results showed that the volume transition temperature of copolymer gel particles decreased with increasing the mole ratio of ENAG. In model development, we modified the extended Flory-Huggins theory as a free energy of mixing term and employed the modified Flory-Rehner theory for the elastic contribution and compared the proposed model with our swelling data. The model predicted fairly well the swelling behaviors of copolymer gel particles.

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“…À30 1C) and vitrification is likely to have no effect on the crystallization of water. 15,16 In noncrystallizable solutions, water is assumed to be bound to polymer chains and a polymer/solvent complex forms. It remains unclear whether this complex is kinetically or thermodynamically controlled.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the heat capacity of poly (vinyl methyl ether)/water mixtures using the stepscan method

Guan

Huang

2010

Polym J

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The heat capacity of poly(vinyl methyl ether) (PVME)/water mixtures was measured over a wide range of temperatures using the stepscan method. The results showed that water exists in different states in the mixtures. The C p values of dry PVME and PVME/ water mixtures with a low water content were obtained by the stepscan method, and the C p of bound water in the mixtures was approximated. The results showed that the C p of bound water in the mixtures with a low water content is higher than that of mixtures with glassy water and ice, and it shows no dependence on water content in the glassy state. Because of the larger conformational contribution to C p , the heat capacity of water in the mixtures in the liquid state increases with water content. Because there is a weak interaction between PVME and water molecules, the structure of water in mixtures is different from that of glassy water. The C p value of unfreezable bound water in the mixtures was calculated without considering the effect of polymer content, and the interaction between PVME and water was obtained; these calculations explained the phase separation observed at high temperature. Polymer Journal (2010) 42, 540-545; doi:10.1038/pj.2010.37; published online 5 May 2010Keywords: DSC; glassy water; phase separation; stepscan INTRODUCTION Water-soluble polymer solutions have recently aroused a great deal of interest among research studies for use in academic and industrial applications. 1,2 Aqueous polymers have numerous applications in scientific and industrial areas, such as food and/or pharmaceutical applications. Aqueous polymer solutions have exhibited peculiar and complicated behaviors, such as depressed melting point and crystallization temperature of water in aqueous polymer solutions and unusual phase behavior. At the same time, some aqueous polymer water solutions exhibit phase separations above the lower critical solution temperature and closed loop phase behavior, which are characteristics of polymer solutions that exhibit hydrogen bonding. 3,4 Poly(vinyl methyl ether) (PVME) is a classical example of a polymer presenting an lower critical solution temperature at a moderate temperature range of around 35 1C, 5,6 above which the solution separates into two phases. It has been shown that, in aqueous solution, the ether functions of repeat units in the PVME molecule form a complex with water molecules. Maeda 7 proposed a formation of a stable molecular complex with 2.7 molecules of water per repeat unit of PVME. At a higher overall water content, a higher degree of hydration was achieved with up to five water molecules per repeat unit of PVME.

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Phase Transitions in Swollen Networks

Cited by 123 publications

References 8 publications

Molecular simulation of the swelling of polyelectrolyte gels by monovalent and divalent counterions

Molecular simulation of the swelling of polyelectrolyte gels by monovalent and divalent counterions

Swelling behavior of thermosensitiveN-isopropylacrylamide-ethylN-acryloylglycine submicron-sized copolymer gel particles

Investigation of the heat capacity of poly (vinyl methyl ether)/water mixtures using the stepscan method

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