Abstract
Host–guest interaction, being reversible and stimuli-responsive, is ideal to be applied to the design of hydrogels. We created a gelation system based on the host–guest interactions between the adamantyl groups and β-cyclodextrin (β-CD) polymer. N,N,N-trimethyl-1-adamantylammonium hydroxide (TriMAA) cations were attached to the pre-exfoliated α-zirconium phosphate (α-ZrP) nanosheets by ionic bonding through a displacement reaction with the exfoliating agents. The exfoliated α-ZrP nanosheets with adamantyl groups directly or indirectly attached to the surface act as reversible high-functionality crosslinkers within the β-CD polymer. The gelation occurred at a host-to-guest ratio of 1:10 or 1:5 at room temperature within minutes. The agents used to exfoliate α-ZrP can tailor the surface of the resultant α-ZrP nanosheets and the ionic strength of the system, which directly affects the further gelation results. Plus, the exfoliating agent cations may generate a host-and-guest interaction with the β-CD polymer as well. This gelation process without covalent bonding formation should help fellow researchers to better understand the gelation system and host–guest interactions.
Highlights
We proposed a design of a gelation system, making use of abundant host–guest interactions, as shown in Figure 1. α-zirconium phosphate (α-ZrP) microcrystals (Figure 1a) could be exfoliated by propylamine or TXA [36] in an aqueous system into single-layer nanosheets, forming a homogenous colloid dispersion (Figure 1b)
The exfoliated nanosheets could react with trimethyl-1-adamantylammonium hydroxide (TriMAA), a quaternary ammonium hydroxide possessing an adamantyl group
The resulting dispersion of nanosheets with adamantyl groups directly or indirectly attached to the surface led to gelation after being mixed with β-CD polymer (Figure 1d)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Host–guest interaction usually refers to the formation of a complex between two species through special structure relationship and non-covalent bonding only [1]. A representative example is a crown-shaped hollow host molecule to interact with a guest molecule that could fit into the cavity of the host molecule [2]. The inclusion of the guest molecule into the host molecule is usually reversible and stimuli-responsive [3]
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