Interfacial Electrochemistry-Induced Detachable Adhesives with Ultra-High Bonding Strength and Detaching Efficiency

Abstract

Detachable adhesives with simultaneously high bonding strength and detaching efficiency have remained a great challenge in adhesion science. The existing detachable adhesives (e.g., solid–liquid phase transitions-based adhesives) usually show low initial cohesion and require long detaching time (several minutes or hours for transitions). Herein, by introducing ionic liquids (ILs) and soft polyethylene glycol (PEG) into a rigid epoxy precursor and curing, we demonstrated the adhesives with both high initial bonding strength (>13 MPa) and detaching efficiency (100% detachment within 10 s under a 90 V DC voltage). The high initial bonding strength is due to the imidazolium cations of ILs and their ion–dipole interactions with PEG can promote the curing of epoxy, decrease the glass–transition temperature, increase the interfacial wettability, and transmit external stress. Also, the outstanding detaching efficiency is because the tetrafluoroborate anions of ILs can electrochemically react rapidly under a voltage and generate fluorinated nanoparticles at the bonding interface within 1 minute. The high bonding and electrochemistry-induced detaching mechanism were further characterized. This work opens up a new avenue for the rational design of fast-detachable adhesives with high bonding strength, showing wide potential in many modern fields.

Electrically Detachable Ionic Conductive Epoxy Adhesives with High Bonding Strength

“…Figure G displays the relations between the detaching efficiency (Ψ [60 V,30 s] and Ψ [60 V,60 s] ) and ionic conductivity (σ); it is found that the electrically detaching behavior of IEPs is positively related to the ionic conductivity and it is consistent with our previously published work . It also can be explained that the strong crystallization of PEG2000 significantly limits the ion migrations under an electric field, which hinders the interfacial electrochemical reactions.…”

“…Moreover, a semicircle and a following straight line are observed for all IEP-M 15–10 from the Nyquist plots (Figure B), indicating that the ion conduction of ionic liquids in IEPs is a typical Faradic process . An equivalent circuit was used to simulate the electrochemical impedance spectroscopy (EIS) results (Figure S5), which contains two constant-phase elements (CPE) and three resistors including contact resistance ( R c ), ion transfer resistance ( R b ), and interfacial resistance ( R i ) . According to this model, the ionic conductivity (σ) of IEP- M 15–10 gradually decreases from 7.5 × 10 –5 to 4.04 × 10 –5 S·m –1 with the PEG molecular weight increasing from 200 to 1000 g·mol –1 , while it sharply decreases to 4.62 × 10 –7 S·m –1 when the PEG molecular weight reaches 2000 g·mol –1 .…”

“…32 An equivalent circuit was used to simulate the electrochemical impedance spectroscopy (EIS) results (Figure S5), which contains two constant-phase elements (CPE) and three resistors including contact resistance (R c ), ion transfer resistance (R b ), and interfacial resistance (R i ). 28 According to this model, the ionic conductivity (σ) of IEP-M 15−10 gradually decreases from 7.5 × 10 −5 to 4.04 × 10 −5 S•m −1 with the PEG molecular weight increasing from 200 to 1000 g•mol −1 , while it sharply decreases to 4.62 × 10 −7 S•m −1 when the PEG molecular weight reaches 2000 g•mol −1 . It is because the longer PEG molecules have a stronger crystallization tendency (as mentioned in Figure 1C), and the formation of microcrystalline regions in IEPs restricts the movements of PEG segments and thus limits the motion of ions, which reduces the ionic conductivity of IEP-M 15−10 .…”

“…All IEPs were prepared through a simple one-pot process according to our previously published work. 28 Firstly, the PEG was added into a clean and dry beaker. Because PEG1000 and PEG2000 are solids under ambient condition, they should be heated for about 10 min at 60 °C to obtain a uniform liquid phase.…”

“…Recently, we reported on an electrically detachable adhesive without phase transition designed by building a rapid interfacial electrochemistry reaction at the bonding interfaces, which demonstrated a bonding strength of about 13 MPa and could be completely detached within 1 min. 28 Here, the ionic conductive epoxy adhesives (IEPs) are further investigated by introduction of [BMIM]TFSI and poly(ethylene glycol) The strong interfacial interactions with the bonding substrate, including interlocked forces, van der Waals' forces, and hydrogen bonding interactions, endow the neat EP with a high bonding strength of about 14.9 MPa (Figure 1B). Owing to the strong interactions between the PEG molecules and epoxy chains (Figure S1), the PEG molecules display a toughened effect on EP adhesives (Figures S2 and S3); all IEP-M 5 demonstrate a higher bonding strength compared with neat EP.…”