Polímeros sensores: mejora de sus prestaciones mediante métodos físicos y químicos

Esta memoria de tesis doctoral presenta el estudio, síntesis y caracterización de materiales poliméricos, así como la mejora de sus propiedades mediante el empleo de métodos físicos y químicos. Los polímeros son materiales muy versátiles con innumerables aplicaciones en sociedad actual que van desde embalaje, adhesivos o construcción hasta electrónica, biomedicina o aeronáutica. En este trabajo se aborda el empleo de polímeros en forma de películas finas (filmes) con aplicaciones sensoras a diferentes sustancias de interés. Además, se profundiza en la mejora de sus propiedades como sensores aspirando a alcanzar detecciones más rápidas, sensibles y específicas. Las mejoras se han llevado a cabo desde un punto de vista químico, estabilizando las moléculas sensoras y haciendo que la respuesta sensora fuera dual y, desde un punto de vista físico modificando la estructura de los filmes haciéndolos porosos. De esta manera se han obtenido resultados prometedores en lo referente a los materiales poliméricos sensores

Microcellular polymer films based on cross-linked 1-vinyl-2-pyrrolidone and methyl methacrylate

A series of cross-linked copolymer films based on 1-vinyl-2-pyrrolidone and methyl methacrylate were produced using different poly(ethylene glycol) dimethacrylates as cross-linking agents. The average molecular mass of the cross-linking agent was varied, then allowing the foaming process using supercritical CO2 (ScCO2), obtaining microcellular films with different cellular structures as a function of the molecular mass of the cross-linking agent. The chemical structure, swelling behavior, CO2 uptake and cellular morphology of the materials were studied. Finally, the influence of the different cross-linking agents in the mechanical properties was also evaluated by measuring the tensile properties of the microcellular films.Fondo Europeo de Desarrollo Regional (FEDER) and the Spanish Agencia Estatal de Investigación (AEI) (MAT2017-84501-R

Easy and inexpensive method for the visual and electronic detection of oxidants in air by using vinylic films with embedded aniline

Conventional nonconductive vinylic films with dispersed aniline change their color and become conductive in the presence of specific oxidant gases, namely, chlorine and hydrogen peroxide. The color change arises from the polymerization of the aniline to yield the conjugated polymer polyaniline, which at the same time renders the flexible vinylic films conductive. We present a simple and straightforward method using both colorimetric and electrical responses to detect and quantify the presence of oxidants (Cl2 and H2O2) in the air. Using RGB analysis (red, green and blue parameters defining the colors in digital pictures on a computer display) based on different pictures taken with a smartphone of discs extracted from the films and by measuring the UV–vis spectral variation in the presence of different concentrations of Cl2 and H2O2, we obtained limits of detection and quantification between 15 and 200 ppbv for H2O2 and between 37 and 583 ppbv for Cl2. Additionally, the electrical response was measured using a fabricated device to visually detect the electrical conductivity activation of the sensor in the presence of oxidant atmospheres, detecting a rapid decrease in resistivity (three orders of magnitude) when the polymerization of aniline began, changing the film from non-conductive to conductive.FEDER (Fondo Europeo de Desarrollo Regional) and the Spanish Agencia Estatal de Investigación (AEI) (MAT2017-84501-R

Sensory polymeric foams as a tool for improving sensing performance of sensory polymers

Microcellular sensory polymers prepared from solid sensory polymeric films were tested in an aqueous Hg(II) detection process to analyze their sensory behavior. First, solid acrylic-based polymeric films of 100 µm thickness were obtained via radical copolymerization process. Secondly, dithizone sensoring motifs were anchored in a simple five-step route, obtaining handleable colorimetric sensory films. To create the microporous structure, films were foamed in a ScCO2 batch process, carried out at 350 bar and 60 °C, resulting in homogeneous morphologies with cell sizes around 5 µm. The comparative behavior of the solid and foamed sensory films was tested in the detection of mercury in pure water media at 2.2 pH, resulting in a reduction of the response time (RT) around 25% and limits of detection and quantification (LOD and LOQ) four times lower when using foamed films, due to the increase of the specific surface associated to the microcellular structure.Fondo Europeo de Desarrollo Regional) and both the Spanish Agencia Estatal de Investigación (MAT2017-84501-R) and the Consejeria de Educación-Junta de Castilla y León (BU306P18

Polymer films containing chemically anchored diazonium salts with long-term stability as colorimetric sensors

We have prepared polymeric films as easy-to-handle sensory materials for the colorimetric detection and quantification of phenol derivatives (phenols) in water. Phenols in water resources result from their presence in pesticides and fungicides, among other goods, and are harmful ecotoxins. Colorless polymeric films with pendant diazonium groups attached to the acrylic polymer structure were designed and prepared for use as sensory matrices to detect phenol-derived species in water. Upon dipping the sensory films into aqueous media, the material swells, and if phenols are present, they react with the diazonium groups of the polymer to render a highly colored azo group, giving rise to the recognition phenomenon. The color development can be visually followed for a qualitative determination of phenols. Additionally, quantitative analysis can be performed by two different techniques: a) by using a UV–vis spectrophotometer (limit of detection of 0.12 ppm for 2-phenylphenol) and/or b) by using a smartphone with subsequent RGB analysis (limit of detection of 30 ppb for 2-phenylphenol)Fondo Europeo de Desarrollo Regional (FEDER) and the Spanish Agencia Estatal de Investigación (AEI) (MAT2017-84501-R

Porous aromatic polyamides the easy and green way

We prepared microporous aramid films through a simple, inexpensive and green way, using ionic liquids (IL) as porosity promoters. Commercial poly(m-phenylene isophthalamide) (MPIA) films with different IL proportions were prepared, and then microporous films were obtained by removing the IL in distilled water. Microporous films presented density values between 0.34 and 0.71 g⋅cm−3 (around five times lower to commercial MPIA), with a homogeneous and controlled cellular morphology dependent on the proportion of the IL, showing cell sizes in the microcellular range (radii between 1 and 8 µm). Thermal, mechanical and electrical properties (specifically ionic conductivity) of the aramid films were analyzed to evaluate the influence of the IL proportion. Finally, it was observed that the MPIA/IL system presented a reversible thermally induced phase-separation process around 60 °C, which was characterized through AFM-Raman images and spectra, together with the variation of the ionic conductivity.FEDER (Fondo Europeo de Desarrollo Regional) and both the Spanish Agencia Estatal de Investigación (MAT2017-84501-R) and the Consejería de Educación-Junta de Castilla y León (BU306P18

Microcellular foamed aromatic polyamides (aramids). Structure, thermal and mechanical properties

We have deeply diminished the density of high performance aromatic polyamides or aramids. Thus, we have prepared microcellular films that at the same time maintain the outstanding thermal and mechanical properties characteristic of these high performance materials. Two different cellular aramids were produced, based on commercial poly(m-phenylene isophthalamide), one of them with an additional azide group. Microcellular structures have been obtained by adding ionic liquids combined to ScCO2 foaming process, with cell sizes between 0.6 and 4.7 µm and cell densities between 109 and 1011 cells cm3. The density was lowered for the commercial poly(m-phenylene isophthalamide) (Nomex® and Teijin Conex®) from 1.43 to 0.62 g cm−3 and from 1.48 to 0.31 g cm3 for the aramid containing the azide group. Foams present the following thermal and mechanical properties: 5% weight loss observed at T > 400 °C and relative Young modulus and tensile strength of 1.2 GPa (g cm−3)−1 and 60 MPa (g cm−3)−1, respectively.FEDER (Fondo Europeo de Desarrollo Regional) and the Spanish Agencia Estatal de Investigación (MAT2017-84501-R