Stefan Antonius Franciscus Bon

Multilayered Nanocomposite Polymer Colloids Using Emulsion Polymerization Stabilized by Solid Particles

We report a versatile emulsion polymerization process in which solid nanoparticles are used as stabilizer, thereby replacing the role of surfactants, allowing for simple fabrication of armored nanocomposite polymer latexes. Use of a second conventional seeded emulsion polymerization step provides a straightforward route to more complex multilayered nanocomposite polymer colloids.

Colloidosomes as micron-sized polymerisation vessels to create supracolloidal interpenetrating polymer network reinforced capsules

Supracolloidal interpenetrating polymer network reinforced capsules are prepared by using micron-sized colloidosomes of poly(methyl methacrylate--divinylbenzene) microgels as reaction vessels. An interpenetrating polymer network as scaffold is generated radical polymerisation of the interior phase to produce hollow supracolloidal structures with a raspberry core-shell morphology. Their flexibility is tailored by variation of the monomer feed composition.

“Sandwich” Microcontact Printing as a Mild Route Towards Monodisperse Janus Particles with Tailored Bifunctionality

A “sandwich” microcontact printing method is reported. A monolayer of porous epoxy polymer microspheres is transformed into Janus particles with distinct functionality on each face by reaction with amine functional fluorescent dyes, carbohydrates, and magnetic nanoparticles.

An "inside-out" microfluidic approach to monodisperse emulsions stabilized by solid particles

We report a versatile “inside-out” microfluidic approach to producing monodisperse particle-stabilized emulsions, as well as supracolloidal polymer microspheres. This approach addresses the challenges faced in conventional strategies for the preparation of Pickering emulsions, that is, an insufficient control of droplet dimensions and an excess of particles in the continuous media. The proposed method minimizes waste of particles, due to their introduction in the droplet phase, rather than in the continuous medium; allows control over the coverage of droplets with particles by manipulating the concentration of particles or the flow rates of the liquids; and provides a route for an easier analysis of the dynamics of formation and buckling of Pickering emulsions.

Influence of Janus particle shape on their interfacial behavior at liquid-liquid interfaces.

We investigate the self-assembly behavior of Janus particles with different geometries at a liquid-liquid interface. The Janus particles we focus on are characterized by a phase separation along their major axis into two hemicylinders of different wettability. We present a combination of experimental and simulation data together with detailed studies elucidating the mechanisms governing the adsorption process of Janus spheres, Janus cylinders, and Janus discs. Using the pendant drop technique, we monitor the assembly kinetics following changes in the interfacial tension of nanoparticle adsorption. According to the evolution of the interfacial tension and simulation data, we will specify the characteristics of early to late stages of the Janus particle adsorption and discuss the effect of Janus particle shape and geometry. The adsorption is characterized by three adsorption stages which are based on the different assembly kinetics and different adsorption mechanisms depending on the particle shape.

Soft polymer and nano-clay supracolloidal particles in adhesives: synergistic effects on mechanical properties

Numerous synthesis routes toward nanostructured polymer particles have emerged, but few examples demonstrate the essential need for such complex particle structures to achieve any added benefit in a target application. Here, polymer particles having Laponite clay armor were prepared by the Pickering miniemulsion polymerization of n-lauryl acrylate. The resulting “soft–hard” poly(lauryl acrylate) (PLA)–Laponite hybrid particles were blended at various low concentrations with a standard poly(butyl acrylate-co-acrylic acid) (PBA) latex for application as a waterborne pressure-sensitive adhesive (PSA). The tack adhesion properties of the resulting nanocomposite films were compared with the performance of the PBA when blended with either a conventional non-armored PLA latex, with Laponite RD nanosized clay discs, or a mixture of both. A true synergistic effect was discovered showing that the clay-armored supracolloidal structure of the hybrid particles was essential to achieve a superior balance of viscoelastic properties. The addition of small amounts, e.g. 2.7 wt%, of the “soft–hard” clay-armored PLA particles increased the tack adhesion energy considerably more than found for the two individual components or for the sum of their individual contributions. The soft PLA core ensures that the adhesives are not stiffened too much by the nanosized Laponite clay. Slippage at the interface between the nanoclay platelets and the PBA matrix introduces an additional energy dissipation mechanism during deformation. Through the synergistic effect of the clay and PLA in the supracolloidal armored latex structure, the tack adhesion energy is increased by 45 J m−2, which is about 70% greater than found for the PBA adhesive alone.

Modification of the ω-bromo end group of poly(methacrylate)s prepared by copper(I)-mediated living radical polymerization

Four different approaches to introduce a specific functional group at the ω terminus of poly(methacrylate)s (PMMAs) prepared via copper(I)bromide/pyridinalimine-mediated atom transfer polymerization, under polymerization conditions, are reported. Method 1 involves the homolysis of the ω-CBr bond with a subsequent reaction, via coupling or disproportionation, with an external radical species. The reaction with 2,2,6,6-tetramethylpiperidin-N-oxyl shows a high conversion (>78%) of the ω-bromo PMMA chains into their corresponding macromonomer analogues. Method 2 utilizes monomers that are able to undergo radical addition followed by subsequent fragmentation. Reactions with trimethyl[1-(trimethylsiloxy)phenylethenyloxy]silane and allyl bromide show quantitative and 57% transformation, respectively. Method 3 is the reaction of a monomer that yields a relatively more stable secondary, or primary, carbon–halogen bond. Reactions with divinylbenzene, n-butylacrylate, and ethylene showed quantitative, 62%, and quantitative additions, respectively. Method 4 is the addition of nonhomopropagating monomers, that is, maleic anhydride. This reaction proceeds quantitatively.

Polymer vesicles with a colloidal armor of nanoparticles

The fabrication of polymer vesicles with a colloidal armor made from a variety of nanoparticles is demonstrated. In addition, it is shown that the armored supracolloidal structure can be postmodified through film-formation of soft polymer latex particles on the surface of the polymersome, hereby effectively wrapping the polymersome in a plastic bag, as well as through formation of a hydrogel by disintegrating an assembled polymer latex made from poly(ethyl acrylate-co-methacrylic acid) upon increasing the pH. Furthermore, ordering and packing patterns are briefly addressed with the aid of Monte Carlo simulations, including patterns observed when polymersomes are exposed to a binary mixture of colloids of different size.

Moldable high internal phase emulsion hydrogel objects from non-covalently crosslinked poly(N-isopropylacrylamide) nanogel dispersions.

High Internal Phase Emulsion hydrogels are prepared from waterborne poly(N-isopropylacrylamide) nanogel dispersions which are non-covalently crosslinked through 2-ureido-4[1H] pyrimidinone (UPy) quadruple hydrogen bond groups. The reversible UPy crosslinks allow for the HIPE-hydrogels to be molded into objects which are thermo-responsive in nature.

Stability of Janus nanoparticles at fluid interfaces

Using Monte Carlo simulations the interaction of a nanometre-sized, spherical Janus particle (a particle with two distinct surface regions of different functionality, in this case showing amphiphilic behaviour) with an ideal fluid interface is studied. In common with previous simulations of spherical, isotropic particles, the range of the nanoparticle-interface interaction is significantly larger than the nanoparticle radius due to the broadening of the interface due to capillary waves. For a uniform particle (an isotropic particle with one surface characteristic) the stability of the particle at a liquid interface is decreased as the affinity for one liquid phase is increased relative to the other; for large affinity differences the detachment energies calculated from continuum theory become increasingly accurate. For a symmetric Janus particle (where the two different surface regions are of equal area), the presence of the particle at the interface becomes more stable upon increasing the difference in affinity between the two faces, with each face having a high affinity for the respective liquid phase. In the case studied here, where surface tension between the A-region of the particle with the A-component is identical to the surface tension between the B-region and B-component, the interaction is symmetric with respect to the nanoparticle interface separation. The particle is found to have a large degree of orientational freedom, in sharp contrast to micrometre-sized colloidal particles. Comparison with continuum theory shows that this significantly overestimates the detachment energy, due to its neglect of nanoparticle rotation; simulations of nanoparticles with fixed orientations show a considerably larger detachment energy. As the areas of the surface regions become asymmetric the stability of the Janus nanoparticle is decreased and, in the case of large differences in affinities of the two faces, the difference between detachment energies from simulation and continuum theory diminishes.