title: Light-sensitive lamellar phases.
abstract: Light sensitive lamellar (L(alpha)) phases have been generated in glycerol/water mixtures from blends of an inert ABA tri-block co-polymer (dimethylsiloxane-polyethylenoxide, (EO)(15)-(PDMS)(15)-(EO)(15)), and a photodestructible anionic surfactant C(6)PAS (sodium 4-hexylphenylazosulfonate). These L(alpha) systems have been formulated in a 6/4 glycerol/water (v/v) mixed solvent. Rheology, small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS) and dynamic light scattering (DLS) have been used to characterize the change in phase behavior and structure after the incorporated C(6)PAS is selectively degraded by UV light incident on the L(alpha) phases. The ABA co-polymer alone forms weakly structured lamellar mesophases, which are stabilized by thermal fluctuations and characterized by low shear moduli (L(alpha) phase-A). Addition of C(6)PAS (10 mM) introduces charge stabilization, generating more ordered and stiffer L(alpha) systems (L(alpha) phase-B). After UV irradiation (Hg lamp) of the L(alpha)-B phases, and subsequent degradation of the ionic C(6)PAS, the results of rheological and scattering studies are consistent with an irreversible change back to L(alpha) phase-A type systems. These formulations display a novel transition between electrostatically- and thermally-stabilized lamellae, which may be controlled by incident UV light.
authors.affiliation: School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK.
authors.forename: Aihua
authors.initials: A
authors.lastname: Zou
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe
authors.forename: Kevin
authors.initials: K
authors.lastname: Mutch
authors.forename: Paul
authors.initials: P
authors.lastname: Wyatt
authors.forename: Günther
authors.initials: G
authors.lastname: Scherf
authors.forename: Otto
authors.initials: O
authors.lastname: Glatter
authors.forename: Isabelle
authors.initials: I
authors.lastname: Grillo
mesh_terms: D008027:Light; D008567:Membranes, Artificial; D033363:Neutron Diffraction; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry; D012212:Rheology; D012542:Scattering, Radiation; D053838:Scattering, Small Angle; D012833:Siloxanes / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry; D014466:Ultraviolet Rays; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D008567:Membranes, Artificial; D011108:Polymers; D012833:Siloxanes; D013501:Surface-Active Agents