Intrinsic Effect of Nanoparticles on the Mechanical Rupture of Doubled‐Shell Colloidal Capsule via In Situ TEM Mechanical Testing and STEM Interfacial Analysis

Abstract

The discovery of Pickering emulsion templated assembly enables the design of a hybrid colloidal capsule with engineered properties. However, the underlying mechanisms by which nanoparticles affect the mechanical properties of the shell are poorly understood. Herein, insitu mechanical compression on Transmission Electron Microscope (TEM) and Aberration-Corrected Scanning Transmission Microscope (AC-STEM) were unprecedentedly implemented to study the intrinsic effect of nanoparticles on the mechanical properties of the CaCO 3 -decorated SiO 2 colloidal capsule. The stiff and brittle nature of the colloidal capsule was due to the interfacial chemical bonding between the CaCO 3 nanoparticles and SiO 2 inner shell. Such bonding strengthened the mechanical strength of SiO 2 shell (166 ± 14 nm) from the colloidal capsule compared to the thicker single SiO 2 shell (310 ± 70 nm) from silica hollow sphere. At elevated temperature, this interfacial bonding accelerates the formation of the single calcium silicate shell, causing shell morphology transformation and yielding significantly enhanced mechanical strength by 30.9% and ductility by 94.7%. The superior thermal durability of the heat-treated colloidal capsule holds great potential for the fabrication of the functional additives that can be applied in the wide range of applications at elevated temperatures.

Smart-Responsive Colloidal Capsules as an Emerging Tool to Design a Multifunctional Lubricant Additive

“…The TEM image (Figure b) reveals the hollow interior structure of the obtained colloidal capsules. As demonstrated previously, the colloidal capsule comprises two distinct shell layers (inner SiO 2 and outer densely packed CaCO 3 nanoparticle shells) and they are interconnected by a strong chemical bond . Due to a significant aggregation of the CaCO 3 nanoparticles on the external shell, it was difficult to observe the encapsulated h-BN nanosheets.…”

“…In general, the presence of the only capsule particles at the sliding interfaces (C-L) significantly increased the steady-state friction coefficient (0.45) compared to the dry sliding (D-L) (0.36). Such an occurrence was expected since the colloidal capsules transform their doubled CaCO 3 –SiO 2 hybrid shell structure into a single calcium silicate shell rather than melt at elevated temperatures . The resulted calcium silicate shell hollow sphere with high strength and excellent ductility might enter the sliding contacts and act as third-body abrasive particles.…”

“…While h-BN nanosheets contribute to friction reduction, silica glass, and CaCO 3 nanoparticles will improve the wear resistance and oxidation prevention of the tribofilm on the worn surfaces. Other information about the thermomechanical robustness and the physicochemical properties of the CaCO 3 -decorated SiO 2 double shell can be referred to a previous publication . Here, a significant modification in the synthesis process of the previous publication has been conducted to add the h-BN nanosheets to the water core.…”

“…The resulting microcapsules were washed by acetone, ethanol, and distilled water, respectively. To identify the function of the h-BN nanosheets in lubrication performances, the colloidal capsules without h-BN nanosheets were synthesized, as a reference, under the optimized conditions in the previous publication …”

“…Synthesis of Smart h-BN Nanosheet-Containing Colloidal Capsules. The smart functional colloidal capsules were synthesized based on the method proposed by Pham et al 36 with similar shell materials. In general, stearic acid-coated calcium carbonate nanoparticles (0.5 g) were diluted in toluene (10 mL) by ultrasonication in 10 min (Bandelin Ultraschall 1955, 6 mm tapered tip, 100 W output).…”