Asymmetrically Modified Silica Particles:  A Simple Particulate Surfactant for Stabilization of Oil Droplets in Water

Abstract

Spherical silica particles that are able to assemble at a phase boundary of a dual-phase mixture of water and an immiscible organic solvent were prepared by a partial modification of their surface hydroxyl groups with an alkylsilylation agent. Scanning electron microscopic observation of these particles in which their remaining surface hydroxyl groups had been selectively modified with colloidal gold particles revealed that each particle has an asymmetric surface structure: one side of the surface is hydrophilic and the other is hydrophobic. We found that these particles could form a micellar structure in water in the presence of an organic solution of a toluene/polystyrene mixture. The micellar structure was evidenced by formation of golf-ball-like polystyrene particles with dimples imprinting morphologies of the hydrophobic part of modified silica particles.

Fabrication, Assembly, and Application of Patchy Particles

“…Temporary masking and demasking of colloids using gels, waxes or elastomers has been a successful strategy in liquid-phase techniques for producing Janus particles. [10,11,17,21,55,56] Though a variety of other techniques have been developed for producing Janus particles, [57][58][59][60][61] very few of them can be extended or modified to produce patchy particles.…”

“…[10,11,17] In cases where a solid template is implemented, the particle positions at the interface are manually adjusted. On the other hand, particles have a tendency to move to and stabilize liquid-liquid and air-liquid interfaces, as initially discovered by Pickering.…”

“…A wide variety of anisotropic particles with diverse anisotropy in size, shape [1][2][3][4][5][6][7] and chemical functionality [8][9][10][11][12][13][14][15][16][17][18][19][20] has been explored. Within such a large diversity of anisotropic particles, significant attention has been given lately to the study of surface-anisotropic particles, that is, particles exhibiting multiple surface functionalities, while often having an isotropic polymer core.…”

“…A lot of progress has been made regarding the large-scale fabrication and characterization of Janus particles, as well as toward testing and exploring their applications. [11,14,17,[24][25][26] Undoubtedly, Janus particles present an interesting approach to new materials with dual distinguishable properties. However, not restricting the anisotropic surface coverage to a 50:50 ratio has led to the discovery of a new class of so-called ''patchy particles'': particles with precisely controlled dual…”

Heterodimeric particle assemblies: Preparation of anisotropically connected spherical silica particles via surface-bound gold nanoparticles

“…One is that only particles of side-to-side bilateral characters are obtained, and the other is that the amount of anisotropic particles obtained by an operation is limited to the area of interfaces and, therefore, a large-scale apparatus is required for the mass production of 35 anisotropically modified particles. A three-dimensional method that can introduce anisotropy to a large number of particles has been reported by Ikeda et al 11 They used a small amount of water to make dry silica particles aggregated through capillary force and modified only the outer 40 surfaces of the particle aggregates to produce "phase boundary catalyst particles" having both hydrophilic and hydrophobic surfaces on each particle. Although this method provides a way for fabrication of anisotropically modified particles in relatively large amount when compared with the above-mentioned two-45 dimensional methods, the thus-obtained particles have still only side-to-side bilateral characters and no further extension to the other modes of anisotropic modification is expected.…”