The conformation of poly(ethyl methacrylate) chains in silica–latex nanocomposites has been studied under zero average contrast conditions (ZAC) using small-angle neutron scattering (SANS). Samples have been prepared by drying colloidal suspensions of silica and polymer nanoparticles (NPs) followed by thermal annealing, for two different silica NPs (radius of 5 and 15 nm) and two chain molecular weights (17 and 100 kg/mol). By appropriate mixing of hydrogenated and deuterated polymer, chain scattering contrast is introduced, and in principle silica scattering suppressed. The silica structure consisting mostly of small fractal aggregates is characterized by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) on the same samples. The measurement of the chain structure by SANS, however, is perturbed by unwanted silica contributions, as often reported in the literature. Here, the contribution of contrast-matched silica is evidenced as a function of system parameters, namely chain mass, silica size, and volume fraction, and a model rationalizing these contributions for the first time is proposed. On the basis of a statistical analysis, a nanometer-thick polymer shell surrounding silica NPs is shown to create contrast, which is presumably maintained by the reduced mobility of polymer close to interfaces or attractive polymer–silica interactions. This shell is proven to be quantitatively important only for the smallest silica NPs. Finally, the pure polymer scattering can be isolated, and the polymer radius of gyration is found to be independent of filler content and NP size.

We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Yoshiya Iwata, Ryan G. Banal, Shuhei Ichikawa, Mitsuru Funato, and Yoichi Kawakami, Journal of Applied Physics 117, 075701 (2015). Our results indicate that low temperature internal quantum efficiencies sit in the 50 % range and we measure that adding an AlGaN layer increases the internal quantum efficiency from 50% up to 57 % with respect to the GaN-InGaN case. More dramatic, it almost doubles from 2.5 % up to 4.3 % at room temperature.

We consider the possibility to produce a bouncing universe in the framework of scalar-tensor gravity models in which the scalar field potential may be negative, and even unbounded from below. We find a set of viable solutions with nonzero measure in the space of initial conditions passing a bounce, even in the presence of a radiation component, and approaching a constant gravitational coupling afterwards. Hence we have a model with a minimal modification of gravity in order to produce a bounce in the early universe with gravity tending dynamically to general relativity (GR) after the bounce.

Regenerative medicine brings promising applications for mesenchymal stem cells, such as dentalpulp stem cells (DPSCs). Confocal Raman microscopy, a noninvasive technique, is used to study osteogenicdifferentiation of DPSCs. Integrated Raman intensities in the 2800 to 3000 cm−1 region (C-H stretching) and the960cm−1 peak (ν1) were collected (to image cells and phosphate, respectively), and the ratio of two peaks1660 over 1690 cm−1 (amide I bands) to measure the collagen cross-linking has been calculated. Raman spectra of DPSCs after 21 days differentiation reveal several phosphate peaks: ν1 (first stretching mode) at 960 cm−1, ν2 at 430 cm−1, and ν4 at 585 cm−1 and collagen cross-linking can also be calculated. Confocal Raman microscopy enables monitoring osteogenic differentiation in vitro and can be a credible tool for clinical stem cell based research.

Formation of dodecagonal quasicrystalline structures on spherical substrates

We propose a simple and original way to prepare surfactant-free SWNT/hydrosoluble polymer composites with high concentrations of individual SWNT. We first disperse single-walled carbon nanotubes (SWNT) in aqueous suspensions using bile salts (BS), and we mix them with a solution of hydrosoluble polymer, poly(vinylpyrrolidone) (PVP) or poly(vinyl alcohol) (PVA). We measure the yield using visible–NIR absorption spectroscopy, and we probe both the chemical environment of the nanotubes and the effectiveness of individualization from coupled Raman/photoluminescence studies. We evidence a direct exchange of BS molecules and PVA chains at the surface of SWNT. By contrast, no direct exchange is observed with PVP. On the other hand, we show that a simple dialysis process leads to the preparation of aqueous suspensions of SWNT covered by PVP or PVA with high yields and an effective individualization of the nanotubes.

The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories, suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation–dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials.