Abstract
Colloidal clay in water suspensions are known to exhibit a multitude of bulk phases depending on initial colloidal concentration and ionic strength, and examples of this include repulsive Wigner colloidal glasses at low ionic strength and attractive gels at higher ionic strength due to screened electrostatic forces by the electrolyte. From confocal Raman microscopy combined with elasticity measurements, we infer that clay trapped at quasi two-dimensional interfaces between oil and water also exhibit confined glass-like or gel-like states. The results can be important for the preparation of particles stabilized colloidal emulsions or colloidal capsules, and a better understanding of this phenomenon may lead to new emulsion or encapsulation technologies.
Highlights
® In the present work we have used Laponite RD synthetic clay colloidal suspensions as the aqueous phase with varying concentrations of clay particles and different salinities (0 and 0.1 M of NaCl)
The crossing point and squares defined by lines separated by 460 nm can be clearly seen in the Raman image (Supplementary Figure 1a) as bright spots whose size is dependent on the chosen intensity threshold, as confirmed by the on line and diagonal cross-section profiles shown in Supplementary Figure 1b
Confocal Raman microscopy was used to reveal the Pickering interfacial films, and images scanning a horizontal plane of 13 × 10 μm[2] crossing the interface between an oil drop dispersed in different water phases were obtained, as displayed in Fig. 1, revealing the presence not of individual clay platelets but rather of tactoids, aggregated laponite particles
Summary
® In the present work we have used Laponite RD synthetic clay colloidal suspensions as the aqueous phase with varying concentrations of clay particles (from 0% to 1.5% by weight) and different salinities (0 and 0.1 M of NaCl). Our observations indicate that the Laponite and salt concentration were so high that a continuous particle structure is not formed in the bulk (the bulk suspension is in the Flocculation region of the phase diagram1), a two-dimensional trapped particle network can be formed at the interface, leading to the strong enhancement of the elastic behavior. We attribute this to Laponite flocs being trapped at the drop interfaces, and that the flocs form a connected two dimensional network with voids. The ability to tune the mechanical behavior of interfaces opens the possibility of controlling the dynamics of interface breakup and coalescence during flow, which can lead to more stable emulsions without the use of surfactants, changes in the phase diagram of emulsions and design complex dispersions of soft capsules with elastic shells with different applications such as in biomedical and oil industries
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