title: Thermodynamic interactions in double-network hydrogels.
abstract: Double-network hydrogels (DN-gels) prepared from the combination of a moderately cross-linked anionic polyelectrolyte (PE) and an uncross-linked linear polymer solution (NP) exhibit mechanical properties such as fracture toughness that are intriguingly superior to that of their individual constituents. The scheme of double-network preparation, however, is not equally successful for all polyelectrolyte/neutral polymer pairs. A successful example is the combination of poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS) cross-linked network and linear polyacrylamide (PAAm), which results in DN-gels with fracture strength under compression approaching that of articular cartilage ( approximately 20 MPa). Small-angle neutron scattering was used to determine the thermodynamic interaction parameters for PAMPS and PAAm in water as a first step to elucidate the molecular origin responsible for this superior property. Measurements on PAMPS/PAAm DN-gels and their solution blend counterparts indicate that the two polymers interact favorably with each other while in water. This favorable PAMPS/PAAm interaction given by the condition chi(PE-NP) < chi(PE-water) <chi(NP-water), where chi is the Flory-Huggins interaction parameter, is consistent with some of the salient features of the DN structure revealed by SANS, and it may also contribute to the ultimate mechanical properties of DN-gels.
authors.affiliation: Polymers Division, National Institute of Standards and Technology, Gaithersburg Maryland, USA.
authors.forename: Taiki
authors.initials: T
authors.lastname: Tominaga
authors.forename: Vijay R
authors.initials: VR
authors.lastname: Tirumala
authors.forename: Sanghun
authors.initials: S
authors.lastname: Lee
authors.forename: Eric K
authors.initials: EK
authors.lastname: Lin
authors.forename: Jian Ping
authors.initials: JP
authors.lastname: Gong
authors.forename: Wen-Li
authors.initials: WL
authors.lastname: Wu
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry; D005782:Gels / Q000737:chemistry; D020100:Hydrogels / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D053838:Scattering, Small Angle; D012996:Solutions / Q000737:chemistry; D013451:Sulfonic Acids / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D000838:Anions; D004573:Electrolytes; D005782:Gels; D020100:Hydrogels; D011108:Polymers; D012996:Solutions; D013451:Sulfonic Acids; D014867:Water; D000099166:Polyacrylamides; C077118:poly(2-acrylamido-2-methyl-1-propanesulfonic acid)