Lithium ion batteries (LIBs) are highly efficient. They have high capacities and long cycle lives with coulombic efficiencies of over 98%. With their immense success, they now find use in many applications, for example, electric vehicles (EVs). The increasing demand puts a lot of pressure on lithium and cobalt reserves as these metal oxides (LiCoO2) form the basic component of LIB electrode. Furthermore, the typical electrolyte in LIBs is flammable rendering these batteries hazardous. Any damage to the cell (like thermal runaway reactions, direct electrode contact) leads to short circuits, sometimes leading to an explosion!

Aluminum ion batteries (AIBs) are cheap and non-flammable alternatives to LIBs. They can be easily recycled. The theoretical energy density of aluminum is higher than lithium and hence, it may exceed the current performance of LIBs. Graphite is the most commonly used cathode in AIBs. Its layered structure helps in insertion/extraction of electrolyte ions (AlxCly) or Al3+ into the cathode. However, most of the AIBs have a low electrode potential and a short cycle life. We will present new high-surface area cathode nanomaterials that will lead to better performing AIBs. Some of the tested cathodes have shown an improved cycle life and a much better electrode potential (~2.0 V).

Recent studies have expanded our understanding of the effects of nanoparticles on hydrogel mechanical properties. However, further studies are needed to validate the generality of the findings, as well as to determine the exact mechanisms behind the enhancements afforded by the incorporation of nanoparticles. In this study, we performed rotational rheological characterizations of chemically crosslinked poly(acrylamide) hydrogels incorporating silica nanoparticles to better understand the role of nanoparticles on the enhanced properties of hydrogel nanocomposites. Our results indicate that the increases in elastic moduli due to the addition of nanoparticles depend strongly on particle size and concentration, as well as the overall concentration of the hydrogel. Moreover, we find that incorporating nanoparticles can lead to enhancements in hydrogel elastic moduli greater than the maxima obtainable through purely chemical crosslinking. Finally, our data indicates a strong role for pseudo-crosslinking mediated by non-covalent interactions between the nanoparticles and hydrogel polymers on the observed reinforcements. Collectively, our results shed further insight into the role of nanoparticles on enhancements of mechanical properties of polymers and may thereby facilitate engineering specific mechanical properties in a wide range of hydrogel nanocomposite systems.

We fabricated Au nanoparticles on the surface of TiO₂ by photo-reduction method. The structural property of film is investigated using transmission electron microscopy technique. The surface plasmon resonance absorption peaks of TiO₂ and Au-TiO₂ were recorded using Shimadzu (UV-2450) UV-visible spectrophotometer. The work function of films was measured by scanning Kelvin probe microscopy (SKP5050) from KP technology, United Kingdom. The nonlinear optical refractive index and nonlinear optical absorption coefficient of Au-TiO₂ nanocomposites were simultaneously measured using z-scan technique.

The nonlinear optical response of Au-TiO₂ nanocomposites is due to pure electronic transfer effects in Au nanoparticles. The observed nonlinearity is due to the dielectric constant of Au, which is due to the surface plasmon resonance and surface polarization between Au nanoparticles and TiO₂. The dielectric constant of Au shows maximum value at 532 nm wavelength (2.33 eV). Surface plasmon resonance effect of Au nanoparticles is directly related to the metal dielectric constant, therefore it is increased. The increase in surface plasmon rsonance of Au-TiO₂ nanocomposites can be observed from UV-visible absorption spectra. The optical nonlinearity depends strongly on the dielectric constant of Au. Therefore, the optical nonlinearity increases with the increase in surface plasmon resonance peak. The absorption peak of surface plasmon resonance at 544 nm is inversely proportional to the work function. Therefore, we can say that the Au dopant decreases the work function that effectively increases the surface plasmon resonance absorption peak at 544 nm, so that the nonlinear response is enhanced. The systematic change in the work function with Au concentration plays a major role in optical nonlinearity. The estimated optical nonlinearity was found to increase from 3.80×10^-6 to 9.69×10^-6 esu with increase in Au concentrations from 0 to 1.0x10^-2 mole. This observed increment in nonlinearity is due to the enhancement of local electric field created by excitation of surface plasmon resonance that affects the work function. Therefore, the surface plasmon resonance and work function help in tuning the optical nonlinearity. The tunable nonlinear optical response of the Au-TiO₂ nanocomposites may find applications in nonlinear optics at wavelength 532 nm and the development of materials for generating the higher order harmonics.

Bragg reflectors are multi-layered systems of sequentially deposited low and high refractive index materials with quarter-wavelength optical thicknesses exhibiting structural colors due to the presence of high reflection band in the visible spectral range. If Bragg reflector is covered with film sensitive to external stimuli then the change in the environment could be easily detected by monitoring the change of Bragg reflector’s transmittance or reflectance spectra.

In the present study as a sensitive material we use linearly branched copolymer containing poly(N,N-dimethyl acrylamide) and Poly(ethylene oxide) blocks deposited in the form of thin films by spin-coating method. The required thickness is pre-optimized through theoretical modelling in order to achieve the highest sensitivity. Two types of Bragg reflectors, having different optical contrast and operating wavelengths are implemented as transducers of humidity changes. The first one consists of sequentially deposited SiO₂ and Nb₂O₅ films prepared by sol-gel and spin-coating methods. The second one comprises alternating dense and porous Nb₂O₅, the last prepared with addition of organic template. Single films and Bragg reflectors are characterized by transmittance measurements at different humidity levels in the range from 5 to 95 % relative humidity (RH). The influence of number of the layers in the stack, the operating wavelength and optical contrast on the sensitivity is studied. The potential and advantages of using top covered Bragg reflector as humidity sensor with simple optical read-out are demonstrated and discussed.

Acknowledgments: The financial support of Bulgarian National Science Fund, grant number DN08-15/14.12.2016 is highly appreciated. R. Georgiev acknowledges World Federation of Scientists for fellowship and project DFNP-17-97/28.07.2017 of the Program for career development of young scientists.

Introduction: The Caco-2 adenocarcinoma cell line has been used extensively for the past couple of decades in nutrient and drug transport studies as an adequate in vitro model of the intestinal mucosa. However, due to the over-expression of tight junction protein complexes, Caco-2 monolayers fail to provide a reliable estimation in terms of in vivo paracellular permeability of small hydrophilic compounds. To address this issue, we co-cultured Caco-2 and HT29-MTX (mucus-secreting cell-line) to ensure a tunable model and emulate the intestinal transport of two classes of nanoparticles.

Methods: We exposed Caco-2/HT29-MTX of different seeding ratios, cultured on Transwell® systems, to non-cytotoxic concentration levels (20 μg/mL) of Si/SiO₂ quantum dots and iron oxide (α-Fe₂O₃) nanoparticles. Transepithelial electric resistance was measured before and after exposure, and monolayer permeability (P_eff) was assessed via the paracellular marker Lucifer Yellow. At regular intervals during the 3-hour transport study, samples were collected from the basolateral compartments for nanoparticle detection and quantitative testing. Cell morphology characterization was done by phalloidin-FITC/DAPI labelling, and Alcian Blue/eosin staining was performed on insert cross-sections in order to compare the intestinal models and evaluate the production of mucins.

Results: Morphological alterations of the Caco-2/HT29-MTX (7:3 ratio) co-cultures were observed at the end of the transport study compared to the controls. The nanoparticle suspensions tested did not diffuse across the intestinal model and were not detected in the receiving compartments, due to their tendency to precipitate at the monolayer surface level and form visible aggregates. Our preliminary results indicated the need for further nanoparticle functionalization in order to appropriately assess intestinal absorption in vitro. The intestinal models used in this study have been shown to adequately screen for prospective candidate carrier-type materials and gauge the transport dynamics of nanoparticles.

Acknowledgements: This work was supported by the project no. 77/2018 NANO-BIO-INT.