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Synergistic Voltaglue Adhesive Mechanisms with Alternating Electric Fields

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posted on 04.03.2020, 13:34 by Manisha Singh, Cheong See Yin, Samuel J. Page, Yuqing Liu, Gautama Wicaksono, Rajashekhar Pujar, Shyam Kumar Choudhary, Giridhar U. Kulkarni, Jun Chen, John V. Hanna, Richard D. Webster, Terry W. J. Steele
Voltage-activated adhesion is a relatively new discovery that relies on direct currents for initiation of cross-linking. Previous investigations have found that direct currents are linearly correlated to the migration rates of electrocuring, but this is limited by high voltages exceeding 100 V with instances of incomplete curing of voltage-activated adhesives on semiconducting substrates. Practical applications of electrocuring would benefit from lower voltages to mitigate high-voltage risks, especially with regard to potential medical applications. Alternative electrocuring strategies based on alternating current (AC), electrolyte ionic radius, and temperature are evaluated herein. Square-waveform AC electric field is hypothesized to initiate a two-sided curing progression of voltage-activated adhesive (PAMAM-g-diazirine, aka Voltaglue), where initiation occurs at the cathode terminal. Structure–activity relationships of Voltaglue as a function of AC frequency at currents of 1–3 mA are evaluated against direct currents, migration rate, storage modulus, and lap-shear adhesion on ex vivo tissue mimics. Numerous improvements in electrocuring are observed with AC stimulation vs direct current, including a 35% decrease in maximum voltage, 180% improvement in kinetic rates, and 100% increase in lap-shear adhesion at 2 mA. Li+ ion electrolytes and curing at 4 °C shifts curing kinetics by +104% and −22% respectively, with respect to the control ion (Na+ ion at 24 °C), suggesting that electrolyte migration is the rate-limiting step. Li+ ion electrolytes and curing at 50 °C improve storage modulus by 110% and 470%, respectively. Further evaluations of electrocured matrices with 19F NMR, solid-state NMR, and infrared spectroscopy provide insights into the probable cross-linking mechanisms.