Numerous studies have been performed on different aspects of the mechanical behavior of polymer nanocomposites; however, the results obtained still lack a comprehensive comparative analysis of the mechanical properties of composites containing nanofillers of different shapes and concentrations and subjected to different static and dynamic loads. Carbon nanofillers were shown to provide the most significant improvement in the elastic properties of polymer composites. In this paper, we present a comparative analysis of the mechanical properties of polystyrene-based nanocomposites filled with carbon allotropes of different shapes: spherical fullerene particles, filamentary multi-walled nanotubes, and graphene platelets, fabricated by the same technology. The influence of shape and concentration of dispersed carbon fillers on mechanical and viscoelastic properties of composites in different stress–strain states was evaluated based on the results of tensile and three-point bending tests, and ultrasonic and dynamic mechanical analysis. Comparison of the static and dynamic elastic properties of nanocomposites allowed us to analyze their variations with frequency. At low concentrations of 0.1 wt% and 0.5 wt% all nanofillers did not provide significant improvement of elastic characteristics of composites. More efficient reinforcement was observed at the concentration of 5 wt%. Among the filler types, some increase in composite rigidity was observed with the addition of filamentary particles. The introduction of the layered filler provided the most pronounced rise in the composite rigidity. The weak frequency dependence of the mechanical loss tangent, which is characteristic of amorphous thermoplastics, was demonstrated for all the samples.

The fluorescence anisotropy of photosensitizers Radachlorin and chlorin e6 was studied using the time-resolved single photon-counting technique under one- and two-photon excitation within the Soret absorption band. A very small negative anisotropy was observed in both photosensitizers under one-photon excitation in the vicinity of the absorption maximum within the wavelength range of 395–405 nm. Meanwhile, two-photon excitation of the photosensitizers in the same spectral range demonstrated high fluorescence anisotropy with the maximum value of about 0.43. The drastic difference of the fluorescence anisotropy parameters at one- and two-photon excitation modes was suggested to be due to the different symmetries of one- and two-photon absorption tensors when two-photon absorption tensor components have comparable values. The variation of excitation wavelengths in the spectral range of 375–425 nm demonstrated nonlinear wavelength dependence of anisotropy of both Radachlorin and chlorin e6, with opposite tendencies at one- and two-photon excitation. The data obtained suggest that one-photon excitation at about 405 nm often utilized in FLIM experiments is not sensitive to fluorescence anisotropy in Radachlorin and chlorin e6 and therefore cannot be used for the determination of anisotropy/rotational diffusion time in these molecules. Meanwhile, two-photon excitation can provide high fluorescence anisotropy and accurate determination of the rotational diffusion time. At the same time, one-photon excitation at about 405 nm can be used for the accurate evaluation of fluorescence lifetimes within the standard FLIM schematic where fluorescence polarization is not taken into account.

We report measurements of linear and nonlinear elastic properties of polystyrene-based nanocomposites with six types of nanofillers, including single and binary mixtures of allotropic carbon nanoparticles. Composite samples were fabricated by the same technology and contained the same filler concentration (5% wt.), which allowed for a direct comparison of their properties. It was shown that the most significant variations of linear and nonlinear elastic properties occur in different nanocomposites. In particular, the most pronounced enhancements of linear elastic moduli (in about 50%) obtained in tensile and flexural tests and in dynamic mechanical analysis were recorded in the sample filled with spherical fullerene nanoparticles. While the most profound rise of absolute values of nonlinear elastic moduli (tens of times) was obtained in the sample filled with the mixture of carbon nanotubes and graphene. The observed tendencies demonstrated the synergistic effect of fillers of different dimensionality on the elastic properties of nanocomposites.

Nonlinear elastic properties of polymers and polymer-based composites are essential for accurate prediction of their response to dynamic loads, which is crucial in a wide range of applications. These properties can be affected by strain rate, temperature, and pressure. The temperature susceptibility of nonlinear elastic moduli of polymers remains poorly understood. We have recently observed a significant frequency dependence of the nonlinear elastic (Murnaghan) moduli of polystyrene. In this paper we expanded this analysis by the temperature dependence. The measurement methodology was based on the acousto-elastic effect, and involved analysis of the dependencies of velocities of longitudinal and shear single-frequency ultrasonic waves in the sample on the applied static pressure. Measurements were performed at different temperatures in the range of 25–65 °C and at different frequencies in the range of 0.7–3 MHz. The temperature susceptibility of the nonlinear moduli l and m was found to be two orders of magnitude larger than that of linear moduli $\lambda$ and $\mu$. At the same time, the observed variations of n modulus with temperature were low and within the measurement tolerance. The observed tendencies can be explained by the shift of nonlinear moduli towards higher frequencies with increasing temperature.

We report an investigation of the in vivo accumulation of Radachlorin photosensitizer in a murine model in several types of normal and tumor tissues based on an FLIM-assisted analysis of fluorescence intensity images, time-resolved fluorescence signals, and phasor plots. Experiments were performed on ex vivo histological samples of normal and tumor tissues. It was shown that the investigation of fluorescence intensity distributions combined with that of time-resolved fluorescence images can be used for qualitative and—under some limitations—quantitative analyses of the relative uptake of this photosensitizer in tissues. The phasor plot representations of time-resolved fluorescence signals were shown to be suitable for identification of the accumulation of predominant photosensitizers in tissues.