Polycaprolactone and polycaprolactone/chitosan nanofibres functionalised with the pH-sensitive dye Nitrazine Yellow

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Dye modification of nanofibrous silicon oxide membranes for colorimetric HCl and NH3 sensing

Colorimetric sensors for monitoring and visual reporting of acidic environments both in water and air are highly valuable in various fields, such as safety and technical textiles. Until now sol-gel-based colorimetric sensors are usually nonflexible bulk glass or thin-film sensors. Large-area, flexible sensors usable in strong acidic environments are not available. Therefore, in this study organically modified silicon oxide nanofibrous membranes are produced by combining electrospinning and sol-gel technology. Two pH-indicator dyes are immobilized in the nanofibrous membranes: methyl yellow via doping, methyl red via both doping, and covalent bonding. This resulted in sensor materials with a fast response time and high sensitivity for pH-change in water. The covalent bond between dye and the sol-gel network showed to be essential to obtain a reusable pH-sensor in aqueous environment. Also a high sensitivity is obtained for sensing of HCl and NH3 vapors, including a memory function allowing visual read-out up to 20 min after exposure. These fast and reversible, large-area flexible nanofibrous colorimetric sensors are highly interesting for use in multiple applications such as protective clothing and equipment. Moreover, the sensitivity to biogenic amines is demonstrated, offering potential for control and monitoring of food quality

Plasma dye coating as straightforward and widely applicable procedure for dye immobilization on polymeric materials

Here, we introduce a novel concept for the fabrication of colored materials with significantly reduced dye leaching through covalent immobilization of the desired dye using plasmagenerated surface radicals. This plasma dye coating (PDC) procedure immobilizes a preadsorbed layer of a dye functionalized with a radical sensitive group on the surface through radical addition caused by a short plasma treatment. The non-specific nature of the plasmagenerated surface radicals allows for a wide variety of dyes including azobenzenes and sulfonphthaleins, functionalized with radical sensitive groups to avoid significant dye degradation, to be combined with various materials including PP, PE, PA6, cellulose, and PTFE. The wide applicability, low consumption of dye, relatively short procedure time, and the possibility of continuous PDC using an atmospheric plasma reactor make this procedure economically interesting for various applications ranging from simple coloring of a material to the fabrication of chromic sensor fabrics as demonstrated by preparing a range of halochromic materials

Nanostructured hydrogels by blend electrospinning of polycaprolactone/gelatin nanofibers

Nanofibrous membranes based on polycaprolactone (PCL) have a large potential for use in biomedical applications but are limited by the hydrophobicity of PCL. Blend electrospinning of PCL with other biomedical suited materials, such as gelatin (Gt) allows for the design of better and new materials. This study investigates the possibility of blend electrospinning PCL/Gt nanofibrous membranes which can be used to design a range of novel materials better suited for biomedical applications. The electrospinnability and stability of PCL/Gt blend nanofibers from a non-toxic acid solvent system are investigated. The solvent system developed in this work allows good electrospinnable emulsions for the whole PCL/Gt composition range. Uniform bead-free nanofibers can easily be produced, and the resulting fiber diameter can be tuned by altering the total polymer concentration. Addition of small amounts of water stabilizes the electrospinning emulsions, allowing the electrospinning of large and homogeneous nanofibrous structures over a prolonged period. The resulting blend nanofibrous membranes are analyzed for their composition, morphology, and homogeneity. Cold-gelling experiments on these novel membranes show the possibility of obtaining water-stable PCL/Gt nanofibrous membranes, as well as nanostructured hydrogels reinforced with nanofibers. Both material classes provide a high potential for designing new material applications

Electrospinning and morphology characterization of polymer blend nanofibers

This PhD explores the potential of blend electrospinning for the production of nanofibers containing a synthetic component, a natural component and/or well-immobilized pH-sensitive dye molecules for biomedical and colorimetric sensor applications. Within this investigation, focus is given to process stability and scalability using a solvent system with limited toxicity, namely acetic acid/formic acid, and subsequent analysis of the obtained nanofibers. A few model systems were selected, with polyamide-6 and polycaprolactone representing well-processable synthetic polymers, gelatin and chitosan representing the two major biopolymer classes and a few azo dyes representing the vast range of applicable pH-indicators

Nanofibre-based sensors for visual and optical monitoring

Sensors supplying a change in optical properties, easily detectable with the naked eye (visual) or inexpensive equipment such as compact spectrometers (optical), are a very powerful tool to visualise a wide range of parameters, including temperature, light, pH and concentration of chemical substances. Most of these sensors rely on indicator compounds showing a change in optical absorbance (colour) or fluorescence under the influence of a certain parameter. Halochromic dyes, for instance, change colour with pH. Since the use of nanofibres improves sensor sensitivity and response time due to their large surface area to volume ratio, the incorporation of indicator compounds into nanofibres is one of the current challenges in sensor design. This chapter discusses the production of colorimetric and fluorescent nanofibrous membranes for visual and optical monitoring (Sects. 7.3 and 7.4), supplemented by some fundamental information on those sensing systems (Sect. 7.2) and some interesting applications (Sect. 7.5)