Pickering Emulsions Stabilized by Halloysite Nanotubes: From General Aspects to Technological Applications

Abstract

Besides surfactants, which decrease the interfacial tension between two immiscible liquids, also interfacially active particles can successfully stabilize an emulsion system by attaching at the liquid–liquid interface. The preparation of the resulting Pickering emulsions has been so far investigated starting from the study of the interactions arising between the dispersed droplets and the stabilizers, till the application of these systems in a wide range of different fields. This work is intended to provide an overall overview about the development of Pickering emulsions by considering the most general aspects and scanning the diverse types of solid stabilizers. Among them, Halloysite nanotubes play a major role as naturally derived clay with emulsifying capability owing to their cheap, abundant, green and biocompatible properties. Therefore, the design of Halloysite stabilized Pickering emulsions is the main content of this review, which will survey the role of nanotubes in providing colloidal stability and will comprehensively sum up the use of these particles in technological and industrial purposes: from environmental to catalytic, from health to cultural heritage related applications.

Hydrophobic Halloysite Nanotubes via Ball Milling for Stable Pickering Emulsions: Implications for Food Preservation

“…Previous studies , suggested that the wettability of nanomaterials determined the type of water–oil emulsion (W/O or O/W). In addition, the surface charge of the adsorbed particles is also an essential parameter to control the stability of Pickering emulsion.…”

“…During the preparation and application of Pickering emulsions, wettability, size, surface properties, and concentration of emulsifier particles play a critical role . It has been demonstrated that HNTs can be successfully used in the preparation of Pickering emulsions. , There have been considerable studies on loading chemicals into the lumen of HNTs or grafting them on the outer surface to prepare functional Pickering emulsions for different applications . However, HNTs have good water dispersion ability, which is contrary to the moderate wettability required by emulsifier particles.…”

Synergies in antimicrobial treatment by a levofloxacin-loaded halloysite and gold nanoparticles with a conjugation to a cell-penetrating peptide

“…[13][14][15] Among all clay-based species, halloysite nanotubes (HNTs), one of the most well-known clay materials, are particularly preferred for drug delivery due to their unique morphology. [16][17][18] According to the literature, the rod-shaped morphology (also needles and tubes) of drug carriers signicantly affects the cell adhesion, internalization, and uptake processes. 19,20 As a result, more of the administered nanocargo is taken by the living cells during a short contact time, resulting in more efficacy.…”

Printable Hydrogels Based on Alginate and Halloysite Nanotubes

“…The difference in charge is a direct consequence of the chemical composition [ 21 , 22 ]. Halloysite is composed of a layer of a Si-centred tetrahedra overlapped to a layer of an Al-centred octahedra in a kaolinite-like structure [ 23 ]. Then, this kaolinite sheet rolls up to confer the nanoclay and its peculiar morphology and charge separation, bearing Si-O-Si groups outside and Al-OH groups in the inner lumen [ 23 ].…”

“…Halloysite is composed of a layer of a Si-centred tetrahedra overlapped to a layer of an Al-centred octahedra in a kaolinite-like structure [ 23 ]. Then, this kaolinite sheet rolls up to confer the nanoclay and its peculiar morphology and charge separation, bearing Si-O-Si groups outside and Al-OH groups in the inner lumen [ 23 ]. The dimensions of the nanotubes depend on the natural deposit, but generally, the length is in the 0.5–2 µm range, the external diameter is 50–200 nm and the internal diameter is 15–50 nm, respectively [ 24 ].…”