Passive RFID sensors for remote sensing provide cost-effective, lightweight and energy efficient devices, with the additional bonus of readily available reader systems for accurate measuring. Passive gas sensors have a wide range of applications in the automotive, medical and commercial industries. Our particular interest is in the detection and monitoring of food degradation during transit; utilising RFID sensors which are sensitive to substrate swelling deformation upon gas exposure. We present polydimethylsiloxane (PDMS) elastomers and related polysiloxanes as suitable substrates. Their thermal durability, low cost and swelling in solvents makes them ideal. PDMS elastomers were synthesised by a Sn (II) catalysed condensation reaction. Absorption capacity measurements quantified the swelling extent of PDMS in solvent vapour. The total Hansen solubility parameter, δ (MPa1/2) of the solvent influences PDMS swelling [1]. Solvents with a δ similar to that of PDMS (16.5 MPa1/2) [2] tend to cause the largest swelling. We found diethyl ether (15.5 MPa1/2) vapour swelled PDMS the most with volume and weight increases of 155.0% ±21.9 and 173.5% ±21.6 respectively. Whereas methanol (29.4 MPa1/2) vapour swelled PDMS the least with volume and weight increases of 2.5% ±0.5 and 3.4% ±0.8. To tailor substrate gas selectivity, polyphenylmethylsiloxane (PPMS) and polycyanopropylmethylsiloxane (PCPMS) have been added to PDMS at varying weight percentages before cross-linking. Adding polar functionalised polysiloxanes increases the δ of the subsequent elastomers and increases polymer swelling in polar gases. The absorption rate of PDMS elastomers and substrates with increased porosity has also been explored. Macroporous PDMS sponges with interconnected pores were synthesised through a casting technique using sugar templates [3]. The initial absorption rate of PDMS sponges was approximately twice as fast as standard PDMS, with an area increase of 48% compared to 21% after 30 minutes of diethyl ether exposure. RFID sensors incorporating PDMS components have been constructed and a corrlation between substrate swelling and RFID response has been demonstrated. 1. J. N. Lee et al., Analytical Chemistry, 2003, 75, 6544-6554 2. T. Uragami et al., Materials Science and Applications, 2011, 2, 169-179 3. S. J. Choi et al., ACS Applied Materials & Interfaces, 2001, 3(12), 4552-4556

Swellable polysiloxane elastomers as substrates for passive radio frequency identification (RFID) gas sensors

249th National Meeting (2015)

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