Synthesis and Characterization of Supramolecular Colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

Eindhoven University of Technology

Hollow silica microcoils have been prepared by using functionalized carbon microcoils as hard templates and surfactant or amphiphilic dye aggregates as soft templates. The obtained materials have been characterized by electron and optical microscopy, nitrogen sorption and small angle X-ray scattering. The obtained hollow microcoils resemble the original hard templates in shape and size. Moreover, they have mesoporous walls (pore size ≈ 3 nm) with some domains where pores are ordered in a hexagonal array, originated from surfactant micelles. The obtained silica microcoils also show preferential adsorption of cationic fluorescent dyes. A mechanism for the formation of silica microcoils is proposed.

A combination of hard and soft templating for the fabrication of silica hollow microcoils with nanostructured walls.

A novel approach for the synthesis of silicone capsules using double W/O/W emulsions as templates is introduced. The low viscosity of the silicone precursors enables the use of microfluidic techniques to accurately control the size and morphology of the double emulsion droplets, which after cross-linking result in the desired monodisperse silicone capsules. Their shell thickness can be finely tuned, which in turn allows control over their permeability and mechanical properties; the latter are particularly important in a variety of practical applications where the capsules are subjected to large external forces. The potential of these capsules for controlled release is also demonstrated using a model hydrophilic substance.

Fabrication of novel silicone capsules with tunable mechanical properties by microfluidic techniques.

Multicompartment poly(dimethylsiloxane) particles were produced for the first time using water-in-oil-in-water (W1/O/W2) emulsions as templates. Multiple silicone W1/O/W2 emulsions were successfully prepared by using silicone precursors with a low viscosity. Several formulation parameters were studied to determine their effect on the properties of emulsions and derived particles. It was observed that the mass fraction of the inner aqueous phase (φ(W1)) and the concentration of both the hydrophobic and hydrophilic surfactants played a crucial role in the morphology and stability of the emulsions. Thus, the derived silicone porous particles also showed different characteristics depending on the emulsion formulation because of the templating effect. At low φ(W1) or high concentrations of the hydrophobic surfactant, particles showed smaller pore sizes as a result of more stable inner droplets. On the other hand, high concentrations of the hydrophobic surfactant resulted in an increase in the size of the derived particles, whereas high concentrations of the hydrophilic surfactant caused the opposite effect. In addition, fluorescein was encapsulated into the hydrophobic particles during the synthesis process and released in a controlled manner. The possibility to encapsulate simultaneously but independently two different hydrophilic components inside the same globule was also tested. On the basis of these results, the obtained silicone porous particles are envisioned to have applications in several advanced fields, for instance, as hydrophobic delivery systems.

Preparation of novel silicone multicompartment particles by multiple emulsion templating and their use as encapsulating systems.

In this paper, we report the one-step synthesis of metallic silver nanoparticles (Ag NP) using nonionic surfactant reverse micelle as nanoreactors. Diglycerol monolaurate (C12G2) spontaneously self-assemble into spheroid reverse micelles having size 10-12 nm in cyclohexane under ambient conditions of temperature and pressure. The spheroid C12G2 reverse micelles swell with water. Swollen reverse micelles having size - 20 nm are formed upon incorporation of 1% water. We used C12G2 reverse micelles as nanoreactors for making ordered nanostructure of Ag-NP by replacing water with aqueous silver nitrate solution. The diglycerol moiety of the surfactant reduces silver ions into metallic silver and thereby stabilizes the generated Ag NP. We found that shape and size of the Ag NP is closely related to the structure of nanoreactor. Similar results have been observed in linear chain alkane n-octane. We found bigger Ag NP from the C12G2/octane reverse micelle system as the size of the micelle in this system is bigger than that of the C12G2/cyclohexane system. This simple approach based on in-situ reduction of metal ions (without the need of reducing agent) opens a new possibility for the development of controlled synthesis of nanostructured noble metallic nanoparticles.

In-situ formation of silver nanoparticles using nonionic surfactant reverse micelles as nanoreactors.

Multiple emulsion templating is a versatile strategy for the synthesis of porous particles. The present work addresses the synthesis of multifunctional poly(dimethylsiloxane) porous particles using multiple water-in-oil-in-water emulsions as soft templates with an oil phase constituted by a crosslinkable poly(dimethylsiloxane) (PDMS) oil. Herewith, the impact of the viscosity of PDMS oil (i.e., molecular weight) on the properties of both the emulsion templates and the resulting particles was evaluated. The viscosity of PDMS oil has a strong effect on the size and polydispersity of the emulsion templates as well as on the mechanical properties of the derived particles. The elastic modulus can be tuned by mixing PDMS oils of different viscosities to form bimodal crosslinked networks. Iron oxide nanoparticles can be readily incorporated into the emulsion templates to provide additional functionalities to the silicone particles, such as magnetic separation or magnetic hyperthermia. The synthesized composite magnetic particles were found to be useful as recoverable absorbent materials (e.g., for oil spills) by taking advantage of their high buoyancy and high hydrophobicity.

Multiple emulsions as soft templates for the synthesis of multifunctional silicone porous particles.

The interest in the production of foods enriched with vitamins, in order to prevent diseases related with their deficiency, has recently increased. However, the low stability and the low water solubility of certain vitamins make difficult their incorporation in foodstuff, especially in water-based formulations. This limitation is typically overcome by using encapsulating systems such as cyclodextrins. In this paper the formation of water-soluble inclusion complexes of Vitamin A Palmitate with β-cyclodextrins, without the use of organic solvents, is described. The objective was to increase the water solubility of Vitamin A Palmitate and its stability against different external factors to eventually enrich aqueous-based products. The stability of Vitamin A Palmitate in the complexes towards temperature, oxygen and UV light was investigated. All results showed a notably increase of Vitamin A Palmitate water solubility and stability in front of those variables when encapsulated. The surface activity of the complex suggests its possible use as stabilizer in emulsion formulations.

Vitamin A Palmitate-β-cyclodextrin inclusion complexes: characterization, protection and emulsification properties.

The introduction of super-resolution fluorescence microscopy (SRM) opened an unprecedented vista into nanoscopic length scales, unveiling a new degree of complexity in biological systems in aqueous environments. Regrettably, supramolecular chemistry and material science benefited far less from these recent developments. Here we expand the scope of SRM to photoactivated localization microscopy (PALM) imaging of synthetic nanostructures that are highly dynamic in organic solvents. Furthermore, we characterize the photophysical properties of commonly used photoactivatable dyes in a wide range of solvents, which is made possible by the addition of a tiny amount of an alcohol. As proof-of-principle, we use PALM to image silica beads with radii close to Abbe's diffraction limit. Individual nanoparticles are readily identified and reliably sized in multicolor mixtures of large and small beads. We further use SRM to visualize nm-thin yet μm-long dynamic, supramolecular polymers, which are among the most challenging molecular systems to image.

Neus Vilanova

Laboratory of Macromolecular and Organic Chemistry,
Institute for Complex Molecular Systems

Eindhoven University of Technology

Synthesis and Characterization of Supramolecular Colloids

Neus Vilanova

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Laboratory of Macromolecular and Organic Chemistry,Institute for Complex Molecular Systems

Eindhoven University of Technology

Synthesis and Characterization of Supramolecular Colloids

Laboratory of Macromolecular and Organic Chemistry,
Institute for Complex Molecular Systems