Synthesis, characterization and study of magnetorheological properties of superparamagnetic photonic crystals

Abstract

[Abstract]: In the past decade, responsive photonic crystals (RPCs) have acquired considerable attention. Their unique responsiveness provides a wide range of applications in different fields. RPCs show advantages in anticounterfeiting and information encryption technologies but they are arising as a new trend in biomedicine: detection of different diseases, drug delivery and tumor screening. Among different types of RPCs, colloidal assembled magnetic responsive photonic crystals are the most interesting due to their reversible and tunable response to magnetic fields. The magnetic responsive photonic crystals prepared in this Master’s Final Project, are characterized by their magnetochromism: a reversible and tunable change in their color in response to the application of a magnetic field. Superparamagnetic Fe3O4 colloidal nanocrystal clusters (MCNCs) with a core-shell structure were synthesized. MCNCs were prepared using a modified one-pot solvothermal method where anionic polyelectrolyte poly(4styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) was used as stabilizer to obtain the core. A modified Stöber process was applied for silica coating to complete the nanostructure. The obtained nanoparticles were characterized by powder X-Ray Diffraction (XRD), Infrared Spectoscopy (IR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Dynamic Light Scattering (DLS), and Electrophoretic Light Scattering (ELS). Moreover, magnetization curve and magnetic hyperthermia measurements were performed. The results showed monodisperse magnetic nanoparticles with a superparamagnetic behavior and high heating power. Furthermore, the ordering of the nanoparticles into 3D chain-like structures was observed in the presence of a magnetic field and evenmore this peculiar arrangement can be modified by the applied magnetic field. A rheological study was designed and carried out, showing that the suspension presents a behavior similar to water. This behavior indicates that the obtained nanoparticles exhibit very weak interactions between them at the water suspension.

[Resumo]: Na década pasada os cristais fotónicos de resposta (RPCs) adquiriron unha considerable atención. A súa única capacidade de resposta proporciona un amplo rango de aplicacións en diferentes campos. Os RPCs mostran vantaxes na prevención das falsificacións e nas tecnoloxías de encriptación de información, mais preséntanse coma unha nova tendencia na biomedicina: detección de diferentes enfermidades, administración de fármacos e revisión de tumores. Entre os diferentes tipos de RPCs, os cristais fotónicos de resposta magnética con ensamblado coloidal son os máis interesantes debido á súa resposta reversible e regulable aos campos magnéticos. Os cristais fotónicos de resposta magnética preparados neste Traballo de Fin de Mestrado caracterízanse polo seu magnetocromismo: un cambio reversible e regulable na súa cor en resposta á aplicación dun campo magnético. Sintetizáronse clusters coloidais superparamagnéticos de nanocristais de magnetita (MCNCs) cunha estrutura de tipo “core-shell”. Preparáronse empregando un proceso solvotermal “one-pot” modificado onde o polielectrolito aniónico empregado foi a sal de sodio do ácido poli(4-estirensulfónico-co-maleico) (PSSMA) como estabilizador para ober o núcleo. Un proceso de Stöber modificado aplicouse para obter o recubrimento de sílice que completa a nanoestrutura. S nanopartículas obtidas caracterizáronse mediante Difracción de Raios X (XRD) de po, Espectroscopía Infravermella (IR), Microscopía Electrónica de Transmisión (TEM), Microscopía Electrónica de Varrido (SEM), Análise Termogravimétrica (TGA), Dispersión de Luz Dinámica (DLS) e Dispersión de Luz Electroforética (ELS). Ademais realizáronse medidas da curva de magnetización e de hipertermia magnética. Os resultados mostran nanopartículas magnéticas cun comportamento superparamagnético e un alto poder de quecemento. Ademais, observouse o ordenamento das partículas en estruturas 3D en forma de cadeas en presenza dun campo magnético e amais esta peculiar disposición pode ser modificada polo campo magnético aplicado. Deseñouse e realizouse un estudo reolóxico, que mostra que a suspensión amosa un comportamento similar á auga. Este comportamento indica que as nanopartículas obtidas presentan interaccións moi débiles entre elas na suspensión acuosa.