The measured capacitance increased linearly with respect to temperature

The measured capacitance increased linearly with respect to temperature: from 657 to 688 pF upon increasing the temperature from 25 to 45 °C. The phenomenon of capacitance and permittivity increases may be related to the PNIPAM backbone chain collapsing as the temperature increased 33,34. PNIPAM contains both hydrophobic and hydrophilic groups that form hydrogen bonds with water molecules 26. Increasing the temperature disrupts the hydrogen bonds between the water molecules and the hydrophobic moieties of PNIPAM, leading to a conformational change from a linear to a globular state 35-37. This transformation from linear to globular occurs with a shrinking of volume that also affects the thickness of a PNIPAM film 38,39. Our results confirmed that the enhanced sensing sensitivity of the OTFT sensor was governed by changes in the structure of the PNIPAM dielectric, as well as the improved thermal transport properties of the pentacene semiconductor.


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