Interpenetrated PNIPAM−Polythiophene Microgels for Nitro Aromatic Compound Detection

• Published in: Langmuir Vol. 25; no. 16; pp. 9579 - 9584
• Main Authors: Laurenti, M, López-Cabarcos, E, García-Blanco, F, Frick, B, Rubio-Retama, J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 18.08.2009
• Subjects: Acrylic Resins - chemistry; Chemistry; Colloidal state and disperse state; Exact sciences and technology; Fluorescence; Gels - chemical synthesis; Gels - chemistry; General and physical chemistry; Hydrocarbons, Aromatic - chemistry; Materials: Nano-and Mesostructured Materials, Polymers, Gels, Liquid Crystals, Composites; Microchemistry; Molecular Structure; Phase Transition; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Surface physical chemistry; Temperature; Critical property; Nitro compound; Five membered ring; Photoluminescence; Reuse; Fluorescence; Polymer; Thiophene; Phase transitions; Wavelength; Sulfonate; Acrylamide; Sulfur heterocycle; Acids; Neutron scattering; Monodispersed particle; Aromatic compound; Critical temperature; Diameter; Low temperature
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la900864a

In this work, we present a facile and reproducible method to obtain thermally responsive, monodisperse, fluorescent microgels with diameters smaller than 700 nm based on poly(N-isopropyl acrylamide) (PNIPAM) interpenetrated with poly(thiophene-ethyl buthyl sulfonate) (PTEBS). Changing the temperature and inducing the microgel volume phase transition, it is possible to modify the photoluminescence (PL) properties of the microgels. Thus, when the temperature was below the low critical solution temperature (LCST) of PNIPAM, the PL intensity was higher than that above the LCST. Time-resolved fluorescence measurements indicate that, in the swollen state, the increment of cross-linking increases the fluorescence decay time of PTEBS. By contrast, in the collapsed state, variations in the decay time were attributed to higher rigidity of the PNIPAM−PTEBS system, which was confirmed by neutron scattering measurements. Moreover, the shift in the wavelength of the fluorescence emission peak observed above the LCST indicates that the collapsed PNIPAM matrix was able to interact with the PTEBS chains hindering the formation of π−π interactions. This property is envisaged for developing a picric acid microsensor based on the formation of π−π interactions with the π-conjugated polymer, thus quenching its PL emission. Above the LCST of PNIPAM−PTEBS microgels, the interactions would be broken and the initial PL emission would be recovered. This property could render reusable microsensors for detection of nitro aromatic compounds.