title: Effect of temperature on alpha olefin sulfonate induced softening of gelatin hydrogels.
abstract: Dynamic light scattering (DLS) and oscillatory rheology experiments were performed to study temperature dependence (T=10-25 degrees C) of the interactions in hydrogels of gelatin with AOS (alpha olefin sulfonate, anionic surfactant) for surfactant concentrations in the range 25-100 mM, chosen larger than cmc (approximately 8mM). The network mesh size (xi) values deduced from fastmode diffusivity (D(f)) data obtained from dynamic structure factor measurements, S(q, t) approximately exp(-D(f)q(2)t) (for t<or=1 ms and q being the scattering wave vector), of micelle-bound gelatin gels was analyzed within the framework of Flory-Rhener theory of cross-linking, which revealed a temperature dependence, xi approximately (0.5-chi)(1/5)exp(-DeltaG(Total)/RT) where chi is the Flory-Huggins interaction parameter, the free-energy of the gel-surfactant complex is DeltaG(Total) and R is universal gas constant. The low-frequency isochronal storage, G' and loss, G'' modulii revealed a transition from the rigid to a softened gel state occurring at surfactant concentration close to 55 mM, independent of temperature. The free-energy of interaction between gel and surfactant deduced from Arrhenius plots obtained from temperature dependent rheology, and light scattering data support this observation.
authors.affiliation: School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Mazin Ahmad
authors.initials: MA
authors.lastname: Abed
authors.forename: H B
authors.initials: HB
authors.lastname: Bohidar
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D005780:Gelatin / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry*; D012212:Rheology; D013451:Sulfonic Acids / Q000737:chemistry*
chemical_list: D000475:Alkenes; D020100:Hydrogels; D013451:Sulfonic Acids; D005780:Gelatin