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Transition from glass- to gel-like states in clay at a liquid interface

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus

The effect of salt on Laponite nanoparticles structure at the interface.Concentration profiles across the interface after dilution of the water phase for (a) system without salt and (c) system with salt (0.1 M NaCl). Figures b and d show proposed schematic (not to scale) representation of the particle structure for the system without and with salt, respectively. For the system without salt (b), a repulsive “Wigner” colloidal glass is formed at the interface. For the system with salt (d), a particle network is formed at the interface, leading to a gel state. In the schematic representation, each thick line represents a Laponite disk, while the ellipsoids around them represent the range of electrostatic repulsions.
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f2: The effect of salt on Laponite nanoparticles structure at the interface.Concentration profiles across the interface after dilution of the water phase for (a) system without salt and (c) system with salt (0.1 M NaCl). Figures b and d show proposed schematic (not to scale) representation of the particle structure for the system without and with salt, respectively. For the system without salt (b), a repulsive “Wigner” colloidal glass is formed at the interface. For the system with salt (d), a particle network is formed at the interface, leading to a gel state. In the schematic representation, each thick line represents a Laponite disk, while the ellipsoids around them represent the range of electrostatic repulsions.

Mentions: The result for the diluted system with no salinity (Debye screening length, 311 nm32) is shown in Fig. 2a. The Laponite concentration in the interface is lower than in the bulk phase. The dilution of the water phase did not affect the relative distribution of clay particles between the bulk and the interface (the non-normalized intensity of Laponite peak across the interface for the diluted and original Laponite concentration in the water phase are shown in Supplementary Figure 4d,c). Based on the images shown in Fig. 1a, we propose that without salt, the Laponite distribution in the bulk and interface could be represented as sketched in Fig. 2b. Long-range electrostatic repulsions dominate and so the Laponite nanoparticles state is “Wigner” colloidal glass33. The behaviour of the system with salt (0.1 M NaCl) is completely different. The concentration profile before the dilution step is similar to that of the system without salt (see Supplementary Figure 4a). However, after dilution, the Laponite signal at the interface becomes stronger than that of the bulk, as shown in Fig. 2c and Supplementary Figure 4b. Together with the interconnected Laponite signal distributed through the water phase in the interface region shown in Fig. 1b, this is strong evidence that Laponite particles are trapped at the interface and that a particle network is formed forming a stabilizing layer of Laponite with the thickness of about 4 μm. Attractive interactions play a dominant role, a percolated network forms, as sketched in Fig. 2d, which gives the system its elasticity33.


Transition from glass- to gel-like states in clay at a liquid interface
The effect of salt on Laponite nanoparticles structure at the interface.Concentration profiles across the interface after dilution of the water phase for (a) system without salt and (c) system with salt (0.1 M NaCl). Figures b and d show proposed schematic (not to scale) representation of the particle structure for the system without and with salt, respectively. For the system without salt (b), a repulsive “Wigner” colloidal glass is formed at the interface. For the system with salt (d), a particle network is formed at the interface, leading to a gel state. In the schematic representation, each thick line represents a Laponite disk, while the ellipsoids around them represent the range of electrostatic repulsions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121648&req=5

f2: The effect of salt on Laponite nanoparticles structure at the interface.Concentration profiles across the interface after dilution of the water phase for (a) system without salt and (c) system with salt (0.1 M NaCl). Figures b and d show proposed schematic (not to scale) representation of the particle structure for the system without and with salt, respectively. For the system without salt (b), a repulsive “Wigner” colloidal glass is formed at the interface. For the system with salt (d), a particle network is formed at the interface, leading to a gel state. In the schematic representation, each thick line represents a Laponite disk, while the ellipsoids around them represent the range of electrostatic repulsions.
Mentions: The result for the diluted system with no salinity (Debye screening length, 311 nm32) is shown in Fig. 2a. The Laponite concentration in the interface is lower than in the bulk phase. The dilution of the water phase did not affect the relative distribution of clay particles between the bulk and the interface (the non-normalized intensity of Laponite peak across the interface for the diluted and original Laponite concentration in the water phase are shown in Supplementary Figure 4d,c). Based on the images shown in Fig. 1a, we propose that without salt, the Laponite distribution in the bulk and interface could be represented as sketched in Fig. 2b. Long-range electrostatic repulsions dominate and so the Laponite nanoparticles state is “Wigner” colloidal glass33. The behaviour of the system with salt (0.1 M NaCl) is completely different. The concentration profile before the dilution step is similar to that of the system without salt (see Supplementary Figure 4a). However, after dilution, the Laponite signal at the interface becomes stronger than that of the bulk, as shown in Fig. 2c and Supplementary Figure 4b. Together with the interconnected Laponite signal distributed through the water phase in the interface region shown in Fig. 1b, this is strong evidence that Laponite particles are trapped at the interface and that a particle network is formed forming a stabilizing layer of Laponite with the thickness of about 4 μm. Attractive interactions play a dominant role, a percolated network forms, as sketched in Fig. 2d, which gives the system its elasticity33.

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus