title: On the scattered light by dilute aqueous dispersions of nanogel particles.
abstract: This work deals with the scattered light by nanoparticles formed by a temperature sensitive polymer networks, namely nanogel particles. The scattered light is measured as a function of the scattering angle at temperatures below and above the volume phase transition temperature (VPTT) of nanogel particles. Our experimental results indicate that nanogel particles have a core-shell structure, formed by a uniform highly cross-linked core surrounded by a fuzzy shell where the polymer density decays to zero gradually for swollen configurations and sharply for shrunken states. The theoretical fitting of the experimental curves shows that the scattered light at low angle obeys a decreasing power law with the scattering vector, q(-α). The value of exponent α provides information about the radial dependence of the polymer density at the external shell of the particles for swollen nanogels, and about the degree of roughness of the surface for the case of shrunken nanogels. On the one hand, at low temperatures (below the VPPT), the nanogel particle is in the swollen state and the light scattering data show that its shell structure follows a fractal behaviour, with a polymer density that decays as r(α-3), where r is the distance to the particle centre. On the other hand, above the VPPT the results indicate that nanogel collapses into a core of uniform polymer density and a rough shell, with a fractal surface dimension of 2.5.
authors.affiliation: Grupo de Física de Fluidos y Biocoloides, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain. Electronic address: jcalleja@ugr.es.
authors.forename: J
authors.initials: J
authors.lastname: Callejas-Fernández
authors.affiliation: Department of Materials, Department of Bioengineering, and the Institute for Biomedical Engineering, Imperial College London, London SW7 2AZ, United Kingdom; POLYMAT, Bionanoparticles Group, Departamento de Química Aplicada, UFI/56, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, Apdo. 1072, 20080 Donostia-San Sebastián, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Ramos
authors.affiliation: POLYMAT, Bionanoparticles Group, Departamento de Química Aplicada, UFI/56, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, Apdo. 1072, 20080 Donostia-San Sebastián, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Forcada
authors.affiliation: Grupo de Física de Fluidos y Biocoloides, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Moncho-Jordá
mesh_terms: D006358:Hot Temperature; D008027:Light; D053758:Nanoparticles / Q000737:chemistry*; D012542:Scattering, Radiation
keywords: Core–shell structures; Fractal structures; Light scattering; Nanogels; Poly (N-vinylcaprolactam) nanogels; Polymeric networks