title: Thermorheologic properties of aqueous solutions and gels of Tetronic 1508.
abstract: The rheologic properties of aqueous solutions and gels of Tetronic 1508 were investigated as a function of polymer concentration and temperature utilizing rotational viscometry. Below the sol-gel transition temperature the polymer solutions were low in viscosity and exhibited Newtonian rheologic behavior even at concentrations of 20 and 25% (w/w). Upon sol-gel transition, the more concentrated polymer solutions underwent a dramatic four- to five-orders of magnitude increase in viscosity, resulting in the formation of a rigid gel structure. Above the sol-gel transition temperature, the gels displayed pseudoplastic and plastic rheologic properties and the viscosity of the gels remained at a relatively constant value over a wide temperature range. Eventually, the thermal energy of the system exceeded the bonding forces within the gel structure, resulting in a gel-sol transition which was marked by a dramatic decrease in the viscosity of the system. Above the gel-sol transition temperature, the system reverted to a Newtonian fluid with viscosities very similar to those found for the Tetronic 1508 solutions at temperatures below the sol-gel transition temperature. The thermodynamic implications of the gel-sol transition are discussed.
authors.affiliation: Department of Industrial and Physical Pharmacy, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Indiana 47907.
authors.forename: C W
authors.initials: CW
authors.lastname: Spancake
authors.forename: D O
authors.initials: DO
authors.lastname: Kildsig
authors.forename: A K
authors.initials: AK
authors.lastname: Mitra
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005029:Ethylenediamines / Q000737:chemistry*; D005782:Gels; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D012212:Rheology; D012996:Solutions; D013696:Temperature; D013816:Thermodynamics; D014783:Viscosity; D014867:Water
chemical_list: D005029:Ethylenediamines; D005782:Gels; D011108:Polymers; D012996:Solutions; D014867:Water; C012571:tetronic 701; D011092:Polyethylene Glycols