Influence of geometries on the assembly of snowman-shaped Janus nanoparticles

The self-assembly of micro/nanoparticles into suprastructures is a promising way to develop reconfigurable materials and to gain insights into the fundamental question of how matter organizes itself. The geometry of particles, especially those deviating from perfectly spherical shapes, is of significant importance in colloidal assembly because it influences the particle "recognition", determines the particle packing, and ultimately dictates the formation of assembled suprastructures. In order to organize particles into desired structures, it is of vital importance to understand the relationship between the shape of the colloidal building blocks and the assembled suprastructures. This fundamental issue is an enduring topic in the assembly of molecular surfactants, but it remained elusive in colloidal assembly. To address this issue, we use snowman-shaped Janus nanoparticles (JNPs) as a model to systematically study the effect of colloidal geometries on their assembled suprastructures. Ten types of JNPs with identical chemical compositions but with different geometries were synthesized. Specifically, the synthesized JNPs differ in their lobe size ratios, phase separation degrees, and overall sizes. We show that by altering these parameters, both finite suprastructures, such as capsules with different curvatures, and nonfinite suprastructures, including free-standing single-layered or double-layered JNPs sheets, can be obtained via self-assembly. All these different types of suprastructures are constituted by highly oriented and hexagonally packed JNPs. These findings demonstrate the significance of geometries in colloidal assembly, such that slightly changing the building block geometries could result in a large variety of very different assembled structures, without altering the chemistry of the particles

Polarity reversal in homologous series of surfactant-free Janus nanoparticles : toward the next generation of amphiphiles

The ability to finely tune the amphiphilic balance of Janus nanoparticles (JNPs) could represent a step forward toward creating the next generation of solid-state amphiphiles with significant potential for applications. The inherent amphiphilicity of JNPs stemming from an intrinsic polarity contrast between two surface regions is well-acknowledged, but remained difficult to demonstrate experimentally in the absence of surfactants and stabilizers. We have designed two homologous series of surfactant-free polymeric JNPs starting from polystyrene (PS) seed nanoparticles (NPs) on which we grew Janus lobes of different sizes via seed polymerization and phase separation of the 3-(triethoxysilyl)propyl-methacrylate (3-TSPM) monomer. The two series differ only by the radical initiator used in the seed polymerization: polar ionic ammonium persulfate (APS) vs nonpolar oil-soluble 2,2'-azobis(2-methylpropionitrile) (AIBN). To compare the two series, we employed them in the emulsification of water with heptane or molten paraffin wax. A polarity reversal of the JNPs within AIBN-JNP series could be observed from the catastrophic and transitional emulsion phase inversions and occurred when the more polar lobe was larger than the nonpolar seed PS lobe. Furthermore, the AIBN-JNPs appeared to be amphiphilic and adopt preferred orientation within the monolayer at the oil/water interface. We therefore demonstrated that in the absence of surfactants the amphiphilicity of the JNPs depends not only on the relative size of the lobes, but also on the surface polarity contrast, which can be tuned by changing the nature of radical initiator

Modeling the interfacial energy of surfactant-free amphiphilic Janus nanoparticles from phase inversion in Pickering emulsions

Determining the interfacial energy of nanoparticles is very challenging via traditional methods that first require measuring the contact angle of several liquids of a sessile drop on pellets or capillary rise in powder beds. In this work, we propose an alternative way to model the interfacial energy of nanoparticles directly from emulsion phase inversion data in Pickering emulsions. This could establish itself as a universal and facile way to determine the polarity of nanoparticles relative to a series of standard particles without the need to measure contact angles. Pickering emulsions of several oils in water were generated with a series of snowman-like Janus nanoparticles (JNPs), whose polarity gradually increased with the size of the more polar lobe. Depending on the oil to water ratio and the JNPs lobe size, oil-in-water (o/w) or water-in-oil (w/o) Pickering emulsions were obtained and the affinity of the JNPs to either water or oil can be inferred from the evolution of the emulsion phase inversion curves with these parameters. We further demonstrate that by adopting a simple model for the work of adhesion of JNPs with the water and oil phases, one can quantitatively calculate the relative interfacial energy change of the JNPs with the liquid. In addition, a knowledge of the interfacial energy of nanoparticles is useful for employing these in suspension polymerization to create surface nanostructured materials. The o/w and w/o Pickering emulsions obtained from monomers, such as styrene, could be polymerized, resulting in colloidosomes or hollow-like materials. The hollow materials exhibited a rather high volume storage capacity for the aqueous phase for extended periods of time, which could be released upon microwaving, making them ideal for use in long-term storage applications of various water-soluble actives

Morphological Design and Synthesis of Nanoparticles

Nanoparticles are particles with dimensions measured in nanometers, and exist at a scale where the physical, chemical, and biological properties of materials can differ significantly from those at a larger scale [...

Pickering Emulsion Polymerization Technology

Ministry of Research, Innovation and Digitization of Romania, CNCS/CCCDI-UEFISCDI, project number PN-III-P4-PCE-2021-0306 (Contract Nr. PCE62/2022)

Self-assembly of Janus nanoparticles into transformable suprastructures

One of the greatest challenges in colloidal self-assembly is to obtain multiple distinct but transformable suprastructures from the same particles in monophasic solvent. Here, we combined deformable and rigid lobes in snowman-shaped amphiphilic Janus nanoparticles (JNPs). These JNPs exhibited excellent ability to self-assemble into micelles, worms, mini-capsules, giant- and elongated-vesicles. This rich suprastructural diversity was obtained by kinetic manipulation of the self-assembly conditions. The suprastructures consist of four to thousands of highly oriented JNPs with dimensions ranging from 500-nanometer to 30-μm. Moreover, the suprastructures can be transformed into one another or dissembled into individual particles. These features make colloidal assembly highly comparable to that of amphiphilic molecules, however, key differences were discovered

Semiconductive materials with tunable electrical resistance and surface polarity obtained by asymmetric functionalization of Janus nanoparticles

Janus nanoparticles (JNPs) can offer significant potential for synthesis of multifunctional materials, due to their inherent property contrast between the lobes. Asymmetric surface chemical modifications on JNPs can be performed such that each lobe can carry different surface and/or bulk‐like properties, which could be combined in surprising ways. In this work, it is shown that snowman‐type polymeric JNPs can be used to make conductive materials with tunable resistance and surface polarity. By changing the relative size between a conductive and an electrically insulating lobe, the bulk powder conductivity within a series of JNPs by a factor of 10 without changing the intrinsic conductivity of the polymer can be tuned. In the same time, the surface polarity of the powder material decreased by a factor of 5. The possibility to synthesize multifunctional materials from JNPs building blocks that enable the coupling of a bulk‐like property with a surface functionality is therefore demonstrated

Les tribunaux criminels français de Tunisie / Paul Médam,...

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Growth of nano-/microcolloidal architectures from janus seeds by ATRP

In the natural world, seeds grow into plants, and the seed diversity ensures significant vegetation heterogeneity. Here, we show the growth of colloidal structures from starting seed nanoparticles by controlled radical polymerization, which resembles the natural processes of plant growth from seeds. Specifically, nano-/microsized architectures with a surprising diversity can be “grown” from snowman-type Janus nanoparticle seeds (JNPS) by atom transfer radical polymerization (ATRP) technique. The current approach aims at concentrating ATRP initiators asymmetrically in the bulk of one JNPS lobe. After the initiating of the polymerization, the addition of monomers promotes JNPS growth into asymmetric nano-/microcolloidal architectures. Depending on the types of the JNPS and on the growth conditions, the grown architectures could adopt dish-, basket-, cocoon-, flower-, helmet-, mushroom-, dumpling-, and pumpkin-like geometries. Additionally, the surfaces of these grown architectures could be controlled to have smooth-, island-, and grouped-island-like nanostructures. This method, providing an alternative approach for synthesizing anisotropic colloids with complex geometries and tunable surface morphologies, enriches the variety of colloidal particle synthetic families

A Diversity of Asymmetric Nano-/Microcolloidal Architectures Grown by ATRP from Janus Seeds

The fabrication of colloids has witnessed significant progress during the last decade, however, fabrication of anisotropic colloidal particles with complex geometries still represents a challenging task. Here, we present nano-/micro-sized colloidal architectures which 'grow' directly from nanoparticle seeds by controlled radical polymerization, resembling the growth of plants from seeds in the natural world. Specifically, we use the atom transfer radical polymerization (ATRP) technique to grow colloidal architectures from snowman-shaped Janus nanoparticle seeds (JNPS). The key to this synthetic approach is the asymmetric placement of the ATRP initiators in the bulk of one JNPS lobe. By starting the polymerization, monomers continuously add to the initiator containing the JNPS lobe, which subsequently grows into a larger colloidal structure. By controlling growth conditions mainly through the interaction strength between the monomer and JNPS, a variety of colloidal architectures result, for example, dish-, basket, cocoon-, flower-, helmet- mushroom-, dumpling and pumpkin-like geometries. Furthermore, each of these grown architectures have different surface morphologies, including smooth-, island- and grouped island nanostructures. The present work provides an alternative method to the synthesis of anisotropic particles with complex geometries and tunable surface morphologies, thus enriching the toolbox for the colloid synthesis