Volatile organic compound assaying is crucial for health and environmental safety. Developing selective and sensitive volatile organic compound assays is of ultimate importance when it comes to avoiding long term exposure to toxic volatile organic compounds. A number of volatile organic compound assay techniques have been developed, but optical and electrical based transduction stand out owing to their superior sensing functionalities.
Polydiacetylene, as a conjugated polymer, has been investigated for solvatochromic volatile organic compound assay because of its alternating structure and outstanding optical attributes.
Polydiacetylene changes color from blue to red with conformational alternations in its backbone, which may be initiated by external stimuli including, pH change, mechanical stress, and temperature. Unfortunately, the color change of polydiacetylene upon exposure to volatile organic compounds in the vapor phase is not as immediate as compared to when the corresponding solvents are added.
Researchers led by professor Bo Liedberg at Nanyang Technological University in Singapore developed a rational strategy to enhance the volatile organic compound response in the vapor phase through the incorporation of matrix polymers including polyethylene glycol, poly(4-vinylpyridine), polyacrylic acid, and polyvinylpyrrolidone with diacetylene. The matrix polymers were expected to condense the volatile organic compounds in the vapor phase, therefore, concentrating them in the vicinity of the Polydiacetylene enabling solvatochromic responses. Their work is now published in Journal of Material Chemistry.
The authors prepared polydiacetylene membrane by drop casting approach. They dissolved diacetylene monomer, matrix polymer and 10,12-docosadiynedioic acid in dichloromethane or ethanol. Drop casting of the resulting viscous solution onto cellulose membrane yielded a white diacetylene membrane upon evaporation of the organic solvent.
For control experiments, the authors prepared diacetylene membranes without the matrix polymers. The membranes were then exposed to UV for about 5 seconds for a polymerization that would yield blue polydiacetylene matrix polymer for the volatile organic compound assay.
The volatile organic compound atmosphere was then generated by dropping volatile organic compound solvents in a sealed chamber. The researchers then recorded the response time from closing the chamber to the time a color change was detected.
It was observed that for the polydiacetylene embedded membrane without the polymer matrix, there was no evident color change for volatile organic compounds concentrations lower than 0.4%. Solvatochromic responses of low magnitudes were however realized for 2% of toluene, chloroform, and dichloromethane.
For the polydiacetylene incorporated with polyacrylic acid, the researchers observed that all the tested volatile organic compounds led to indistinguishable solvatochromic responses even at high solvent concentrations. Polydiacetylene incorporate with polyvinylpyrrolidone and poly(4-vinylpyridine) indicated distinguishable responses to ethanol, chloroform and dichloromethane for concentrations in the order of 0.4%.
The addition of polyethylene glycol to the polydiacetylene membrane was observed to improve the solvatochromic response owing to its capacity to absorb volatile organic compound vapors. The response was observed to be saturated at 0.4% of dichloromethane and 0.08% of chloroform vapors. A higher solvatochromic response to toluene vapor was observed.
Mixing two matrix polymers with the polydiacetylene enabled the authors to tune the solvatochromic response, therefore, indicating a possibility of developing solvatochromic sensors with improved selectivity. Generally, the results of the proposed approach give some hope in the development of solvatochromic sensor arrays for identification and classification of volatile organic compounds.
Meng-Che Tu, Jamal Ahmed Cheema, Umit Hakan Yildiz, Alagappan Palaniappan and Bo Liedberg. Vapor phase solvatochromic responses of polydiacetylene embedded matrix polymers. J. Mater. Chem. C, 2017, 5, 1803—1809.Show Affiliations
Meng-Che Tu,1,2 Jamal Ahmed Cheema,1,2 Umit Hakan Yildiz,3 Alagappan Palaniappan*1,2 and Bo Liedberg*1,2,4
1Center for Biomimetic Sensor Science, Nanyang Technological University, Singapore 637553, Singapore
2School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
3Department of Chemistry, Izmir Institute of Technology, Izmir, Turkey.
4Nanyang Institute of Technology in Health and Medicine, Interdisciplinary Graduate School, Nanyang Technological University, Singapore 637553, Singapore.
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