Synthesis of cation-exchanged laponite suspensions by laser ablation of microsized-metal particles in liquid

Laser ablation in the liquid technique has been used to synthesize cation-exchanged laponite suspensions. In summary, laser ablation of the microsize-metal powder (Co, Al, and Cu) dispersed in an aqueous solution containing deionized water laponite crystals was carried out using laser beam generated by a single-mode, Q-switched Nd–Yag laser operating at 532 nm with a pulse duration of 5.5 ns and 10 Hz repetition rate. Laser fluence was 0.265 J/cm2 for all tests. For all samples, the mass fraction of laponite was 1%. General observations of the prepared samples indicated that an aqueous suspension of 1 wt% laponite retained its free flowing liquid phase characteristics even after aging for several weeks. When bivalent cationic metals (Cu, Co, Al) were ablated in it for about 1 h, even with a small amount of the metal (0.025% and 0.050%) were generated, the suspension became highly viscous and behaved as a shear-thinning and thixotropic material. That is, the suspension gelled strongly when it was allowed to rest. The gels, however, could easily be reverted to a low viscosity liquid with simple shaking. Information from TEM and XRD analysis indicated that such a sol–gel transformation might be due to the charge exchange between the cationic species produced during the laser ablation and the sodium ions in the interlayers of the clay sheets.

Research Highlights
► Laser ablation in the liquid technique has been used to synthesize cation-exchanged laponite suspensions.
► When cation metals are ablated in water containing dispersed laponite crystals, the ablated metal ions can be absorbed on the basal plane surface of the laponite platelets by exchanging with the dissolving Na+ via two possible routes:
► one route is the intercalation of the ablated ions into the interlayer separation of the laponite platelets and the other is the adsorption of the ablated ions on the negatively charged sites of the surface of the basal plane.
► As a result from such an ion exchange, the negative charges on the laponite faces are partically balanced, weakening the electrostatic repulsive forces between the dispersed laponite disks.
► As a result, the formation of a space-filled structure due to both the van der Waals and electrostatic bonds between the positively charged edges and negatively charged faces is developed. Thus, a sol–gel transition can be induced.