title: Physicochemical properties of methylcellulose and dodecyltrimethylammonium bromide in aqueous medium.
abstract: Interactions between uncharged polymers and cationic surfactants are considered weaker than interactions with the anionic analogues. This work describes the binding occurring between methylcellulose (MC) and the cationic surfactant DTAB in aqueous medium. In the absence of salt, MC-DTAB exhibits a maximum in hydrodynamic radius, R(h,slow), with the increase in the surfactant concentration. Otherwise, in presence of salt the MC-DTAB system shows only a linear increase of R(h,slow). CAC is lower than the CMC, which is taken as an evidence of binding between the cationic surfactant and neutral polymer that induces the aggregation process. Static light scattering, rheology and micro-DSC results highlight the hydrophobic MC-DTAB association. Salt-out and the salt-in effects were observed in presence of DTAB, with a clear transition at concentration values close to the CMC, as judged from rheological and micro DSC measurements. Indeed, DTAB affects both the pattern of the sol-gel transition and the gel strength.
authors.affiliation: Departamento de Física, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, 97105-900 Santa Maria-RS, Brazil. mvilletti@smail.ufsm.br
authors.forename: Marcos A
authors.initials: MA
authors.lastname: Villetti
authors.forename: Clara I D
authors.initials: CI
authors.lastname: Bica
authors.forename: Irene T S
authors.initials: IT
authors.lastname: Garcia
authors.forename: Fabiano V
authors.initials: FV
authors.lastname: Pereira
authors.forename: Francieli I
authors.initials: FI
authors.lastname: Ziembowicz
authors.forename: Carmen L
authors.initials: CL
authors.lastname: Kloster
authors.forename: Cristiano
authors.initials: C
authors.lastname: Giacomelli
mesh_terms: D002152:Calorimetry, Differential Scanning; D005782:Gels / Q000737:chemistry; D057446:Hydrodynamics; D057927:Hydrophobic and Hydrophilic Interactions; D008747:Methylcellulose / Q000737:chemistry*; D044367:Phase Transition; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D005782:Gels; D000644:Quaternary Ammonium Compounds; D014867:Water; D008747:Methylcellulose; C022806:dodecyltrimethylammonium