Hydrophobically modified complex coacervates for designing aqueous pressure-sensitive adhesives

Abstract

The rheology of complex coacervates can be elegantly tuned via the design and control of specific non-covalent hydrophobic interactions between the complexed polymer chains.

Effect of Polyelectrolyte Charge Density on the Linear Viscoelastic Behavior and Processing of Complex Coacervate Adhesives

“…This transition from solid-like adhesive debonding to viscoelastic debonding with the formation of fibrils to liquid-like cohesive debonding is reminiscent of traditional PSAs for which the cross-linking density, or cohesiveness, is gradually decreased. , In addition, similar to PSAs, we observe a maximum of W adh in the regime of viscoelastic debonding where the bulk energy dissipation is optimized. In the case of complex coacervates, an identical transition has been reported and obtained by increasing the salt concentration at which the complex coacervates were prepared. ,,, In light of these results, the charge density of one of the polyelectrolytes appears to be an efficient parameter for tuning the adhesive behavior of complex coacervates. Nevertheless, it is worth noting that the maximum work of adhesion obtained here (around 5.5 J m –2 ) remains noticeably lower compared to our previous study, or to the studies performed by Vahdati et al or Dompé et al , (around 16 J m –2 ) where polyelectrolytes with a higher charge density and/or polyelectrolytes modified with a substantial amount of strongly associating hydrophobic units are used.…”

“…This is probably due to a kinetic trapping effect caused by the fast electrostatic complexation at such a low salt concentration upon mixing the oppositely charged polyelectrolytes. The possibility of performing the TSS for each of the coacervates formed with varying charge density of the polyanion indicates that the inclusion of the OEGMA hydrophilic units does not impact the mechanism by which the material relaxes but only the time scale at which it occurs, in a similar fashion as reported for a growing number of complex coacervate systems. ,,− …”

“…The marginally higher dispersities of the copolymers with a higher ratio of OEGMA may result in a broadening of the distribution of relaxation times. However, this effect is relatively limited for complex coacervates with no chain entanglements, where the longest characteristic relaxation time is mainly dictated by the lifetime of electrostatic interactions. , …”

“…Probe-tack measurements were carried out to test the adhesion performance of our complex coacervates following procedures that have been successfully applied for similar systems. ,,,, These nonlinear strain experiments usually provide valuable information about the mode of debonding (adhesive or cohesive failure), the force required to separate the two surfaces and the work of adhesion of PSAs. − First, by visually looking at the debonding mechanism, adhesive failure was observed for cc100 and cc82 made with 0.00 M NaCl (Figure a and Movie S1). The corresponding stress–strain curves presented in Figure b,c also bear the signature of an adhesive debonding process, where a high peak stress is reached (above 100 kPa) in both cases before early detachment from the probe occurs.…”

“…Furthermore, in our recent study, for which a controlled amount of uncharged self-associative hydrophobic units were randomly included within the backbone of the polyanion chains, we showed that increasing the ratio of the hydrophobic groups led to gradual slowdown of the dynamics and a shift to lower frequencies. 22,55 Overall, by putting our work in the perspective of these previous studies, we are able to highlight the efficiency of diluting the charges along one of the polyelectrolyte chains using charge-neutral, nonassociative water-soluble OEGMA units. This enables us to speed up the relaxation dynamics of the formulated complex coacervates while keeping the salt concentration unchanged.…”