pH Reversible Encapsulation of Oppositely Charged Colloids Mediated by Polyelectrolytes

Abstract

We report the first example of reversible encapsulation of micron-sized particles by oppositely charged submicron smaller colloids. The reversibility of this encapsulation process is regulated by pH-responsive poly(acrylic acid) (PAA) present in solution. The competitive adsorption between the small colloids and the poly(acrylic acid) on the surface of the large colloids plays a key role in the encapsulation behavior of the system. pH offers an experimental knob to tune the electrostatic interactions between the two oppositely charged particle species via regulation of the charge density of the poly(acrylic acid). This results in an increased surface coverage of the large colloids by the smaller colloids when decreasing pH. Furthermore, the poly(acrylic acid) also acts as a steric barrier limiting the strength of the attractive forces between the oppositely charged particle species, thereby enabling detachment of the smaller colloids. Finally, based on the pH tunability of the encapsulation behavior and the ability of the small colloids to detach, reversible encapsulation is achieved by cycling pH in the presence of the PAA polyelectrolytes. The role of polyelectrolytes revealed in this work provides a new and facile strategy to control heteroaggregation behavior between oppositely charged colloids, paving the way to prepare sophisticated hierarchical assemblies.

Reconfigurable assembly of charged polymer-modified Janus and non-Janus particles: from half-raspberries to colloidal clusters and chains

“…The surface coverage of a large positively charged colloid by smaller negatively charged colloids could be increased when decreasing the pH. 38 …”

“…The surface coverage of a large positively charged colloid by smaller negatively charged colloids could be increased when decreasing the pH. 38 Contrary, reversibility of structures made of 200-PAA-HP or 450-PAA-HP and 1000-PDMAEMA/PNIPAM-JP could not be observed at all ( Fig. 4 and 6a).…”

“…Nevertheless, there are only few examples of reversible selfassembly of non-Janus 12,14,27,[33][34][35][36][37][38][39][40][41][42][43][44] and Janus particles 15,25,34,45 discussed in the literature. The reported colloidal building blocks exhibit either a purely so (organic), 14 purely hard (inorganic), or hybrid (so/hard) character.…”