Synergistic Voltaglue Adhesive Mechanisms with Alternating Electric Fields

Abstract

Voltage-activated adhesion is a relatively new discovery that relies on direct currents for initiation of crosslinking. 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 fields are 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 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 versus DC, 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 o C shift curing kinetics by +104 % and -22 % with respect to the control ion (Na + ion at 24 o C), suggesting electrolyte migration is the rate limiting step. Li + ion electrolytes and curing at 50 o C improves storage modulus by 110% and 470 % respectively. Further evaluations of electrocured matrices with 19 F NMR, solid-state NMR and infrared spectroscopy provide insights into the probable crosslinking mechanisms.

Precise Control of Diazirine Reduction to Tune the Mechanical Properties of Electrocuring Adhesives

“…Synthesis and structure-property relationships of voltage, current, electrode design, DC/AC signals, cation, and temperature on viscoelastic properties have been previously reported. [22,26,28,[30][31][32] Electric fields are hypothesized to reduce diazirine to a reversible and semi-stable diazirinyl radical (t 1 = 2 = 46 s), that then transitions to a shortlived (6 ns) carbene intermediate. [22,26] The primary evidence supporting this mechanism is diazirine decay, nitrogen gas emission, and rheological viscoelastic transition from viscous to elastic stress deformation (aka gelation) of the high solute (� 50 %) PAMAM-diazirine formulations.…”

“…More evidences of diazirine consumption leading to N 2 gas release were obtained using FT-IR and F-NMR analyses in previous works. [28] High resolution XPS spectra of the N 1s, F 1s and O 1s signals are presented in supporting information as Figure S2. It can be seen that N and O 1s spectra (Figure S2A and S2B) seems to present no significant difference across the different materials.…”

“…Voltaglue cured by electrical stimuli can achieve viscoelastic properties ranging between 1-10 kPa as storage modulus (1 % strain) and an observed 10-100 kPa lap shear adhesion strength. [28] This opens the possibility of it being employed in soft tissue fixation and repair operations. However, the electrochemical reactions involved during the reducing cross-linking process remain speculative and electrochemical evaluations have been limited to cyclic voltammetry correlated to electrorheology tests.…”

Structure–Activity Relationships of Voltaglue Organic Blends

“…Blended formulations may be further optimized with higher voltages or alternating current for faster activation. [ 4,15 ]…”

“…Voltage activation compared to photocuring also appears to have different intermediate pathways to nucleophilic crosslinking. [ 15 ]…”