Plasmons are resonant excitations in metallic films and nanoparticles. For small enough static distances of metal nanoparticles, additional plasmon-coupled modes appear as a collective excitation between the nanoparticles. Here we show, by combining poly(N-isopropylacrylamide) micro- and nanospheres and Au nanoparticles, how to design a system that allows controllably and reversibly switching on and off, and tuning the plasmon-coupled mode.

Remarkable properties have emerged recently for aqueous foams, including ultrastability and responsiveness. Responsive aqueous foams refer to foams for which the stability can be switched between stable and unstable states with a change in environment or with external stimuli. Responsive foams have been obtained from various foam stabilizers, such as surfactants, proteins, polymers, and particles, and with various stimuli. Different strategies have been developed to design this type of soft material. We briefly review the two main approaches used to obtain responsive foams. The first approach is based on the responsiveness of the interfacial layer surrounding the gas bubbles, which leads to responsive foams. The second approach is based on modifications that occur in the aqueous phase inside the foam liquid channels to tune the foam stability. We will highlight the most sophisticated approaches, which use light, temperature, and magnetic fields and lead to switchable foam stability.

Nanoparticles can be efficient foaming agents. Yet, the detailed mechanisms of foam stabilization by these particles remain unclear. In most cases, the foamability and foam stability of a system have to be determined empirically. We used a multiscale approach to reveal how the microscopic properties of the nanoparticle dispersion are translated into their foaming behavior at the macroscopic scale. As a model system we used silica nanoparticles that were hydrophobized by the in situ adsorption of short-chain alkylamines of chain length C5 to C8. We used fluorescence spectroscopy and electrophoretic mobility measurements to characterize the bulk behavior of the nanoparticles with adsorbed amines. The interfacial behavior was probed by compressing particle monolayers while monitoring the surface tension. The macroscopic foamability and foam stability were evaluated. There are strong correlations between the system properties at all length scales. The most prominent effects are observed at a critical bulk concentration of amines at which the nanoparticles start to aggregate due to hydrophobic interactions. Our study shows how the foam properties are related to the features of the bulk dispersions and to the ordering of particles at the air/water interface. The present results help to understand the surfactant concentration dependent stages of foaming behavior of in situ hydrophobized nanoparticles.

fatty acids · foams · interfaces · self-assemblyOwing to their high surface/volume ratio, stable foams are well suited for the decontamination of surfaces, for example. At the end of the cleaning process, the foam should be destabilized in a controlled way in order to end up with a small volume of contaminated liquid which is easier to handle. While there are already several examples of ultrastable foams in literature, reports of foams with switchable stability are rare. In this context the work of Fameau et al.[1] presents a milestone in the triggering of foam stability by external stimuli.In the production of foams the amount and stability depend on the complex interplay between the foamability at the beginning of the foaming process and the subsequent drainage, which is highly related to surface and bulk rheological properties. When the drainage is slow, the stability is governed by gas diffusion and surface forces across the lamellae which affect the coalescence (lamella rupture) and coarsening (gas exchange between bubbles as a result of differences in Laplace pressure). Hence, in order to gain full understanding of the system, information about the bulk structure, surface tension and surface viscoelasticity, foam lamella behavior, and the macroscopic foam is essential.[2]

The present study describes the temporary evolution of size and morphology of thermosensitive and biocompatible microgel particles based on ethylene glycol (EG). P-MeO 2 MA-co-OEGMA particles were synthesized by precipitation polymerization. The growth of the microgel particles was analyzed at different reaction times using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The scattering data show the increase of particle size and swelling capability during the polymerization process. After 60 min further continuation of the polymerization reaction causes no further change of neither external nor internal particle properties. SANS measurements reveal the formation of a dense core, mainly consisting of cross-linker at an early polymerization state. This is followed by the growth of a loosely packed polymer shell. Nanodomains, observed during the volume phase transition (VPT), as well as a second correlation-length of the network fluctuations arise with progressing polymerization reaction related to the buildup of the shell.