Seasonal variability of optical properties in a highly turbid lake (Laguna Chascomús, Argentina)

We study the underwater light field seasonality in a turbid lake, Laguna Chascomús (Buenos Aires, Argentina). We report (1) relationships between optical properties (OPs) and optically active substances (OASs); (2) relationships between inherent (IOPs) and apparent (AOPs) optical properties; and (3) the seasonal variability in OASs and OPs. Light absorption was dominated by the particulate fraction. The contributions of phytoplankton pigments and unpigmented components were similar. The best predictors of total particulate absorption, unpigmented particulate absorption, turbidity and vertical attenuation coefficient were total suspended solids or their ash content. Many OASs and OPs varied seasonally. The concentrations of OASs were higher during spring and summer, resulting in lower transparency and higher turbidity. However, mass-specific absorption coefficients displayed lower values during spring and summer. Thus, the higher light attenuation observed during spring and summer resulted from higher concentrations of relatively less absorptive OASs. Collectively, these results suggest that: (1) light extinction is enhanced during spring and summer; (2) the enhanced light extinction is due to changes in the particulate fraction; (3) the enhanced light extinction is mostly due to an increase in the amount of particulate material; and (4) the increase of particulate matter also enhanced light extinction through increased scattering.     

Nanofluidic osmotic power generators – advanced nanoporous membranes and nanochannels for blue energy harvesting

The increase of energy demand added to the concern for environmental pollution linked to energy generation based on the combustion of fossil fuels has motivated the study and development of new sustainable ways for energy harvesting. Among the different alternatives, the opportunity to generate energy by exploiting the osmotic pressure difference between water sources of different salinities has attracted considerable attention. It is well-known that this objective can be accomplished by employing ion-selective dense membranes. However, so far, the current state of this technology has shown limited performance which hinders its real application. In this context, advanced nanostructured membranes (nanoporous membranes) with high ion flux and selectivity enabling the enhancement of the output power are perceived as a promising strategy to overcome the existing barriers in this technology. While the utilization of nanoporous membranes for osmotic power generation is a relatively new field and therefore, its application for large-scale production is still uncertain, there have been major developments at the laboratory scale in recent years that demonstrate its huge potential. In this review, we introduce a comprehensive analysis of the main fundamental concepts behind osmotic energy generation and how the utilization of nanoporous membranes with tailored ion transport can be a key to the development of high-efficiency blue energy harvesting systems. Also, the document discusses experimental issues related to the different ways to fabricate this new generation of membranes and the different experimental set-ups for the energy-conversion measurements. We highlight the importance of optimizing the experimental variables through the detailed analysis of the influence on the energy capability of geometrical features related to the nanoporous membranes, surface charge density, concentration gradient, temperature, building block integration, and others. Finally, we summarize some representative studies in up-scaled membranes and discuss the main challenges and perspectives of this emerging field.

Advanced nanostructured membranes with high ion flux and selectivity bring new opportunities for generating clean energy by exploiting the osmotic pressure difference between water sources of different salinities.     

Core-shell particles: building blocks for advanced polymer materials

Polymer particles with submicrometer dimensions show promising applications in “bottom-to-top approach” to fabrication of materials with periodic structure, function, and composition. A novel approach to producing such materials is proposed, which employs core-shell particles with specific structures and compositions. We report on the synthesis of core-shell particles using interfacial polymerization and heterocoagulation techniques. The compositions of core-forming material and/or the shell-forming polymers were selectively controlled to be make the cores or the shells rigid or fluid, fluorescent or non-fluorescent, organic or inorganic. Several potential applications of nanocomposite materials obtained from these particles are demonstrated, including three-dimensional optical data storage and optical limiting and switching.     

Thermoreversible gels of polymers in recycled motor oil

A study of the dynamic viscoelastic properties of gels of Ethylene Vinyl Acetate (EVA) and Styrene‐Butadiene‐Styrene (SBS) copolymers in recycled motor oil is presented. Both systems form gels with enhanced elastic moduli, with respect to SBS/aromatic oil gels which have been used to develop synthetic binders. Although the procedure described by Winter is conveniently applied to obtain gel‐sol transition of EVA/oil gels, it is not suitable for SBS/oil gels which do not give rise to a homogeneous liquid when they melt. For EVA/oil gels the relaxation exponent at the gel point is Δ=0.5, which according to Muthukumar's model corresponds to a fractal dimension d_f=2. The variation of the elastic modulus with polymer concentration follows the scaling law G_e‐cⁿ, with n=2.8 for EVA/oil and n=1.3 for SBS/oil. In the case of EVA/oil gels the validity of theoretical models relating fractal dimension to n exponent is discussed.     

Lignosulfonate/silica hybrid nanoparticles as a novel biobased filler in polybenzoxazine matrix

Lignin is an abundant and sustainable resource that exhibits numerous attractive functional properties as a reinforcing agent for benzoxazine-based composites, due to its stiffness, thermal stability, and high carbon content. However, the low quality of lignin particles dispersions associated with the weak particles-matrix interactions reduces the reinforcement capability. In this work, hybrid lignin/silica (NaLS/SiO₂) nanoparticles were obtained from sodium lignosulfonate (NaLS) and tetraethylorthosilicate (TEOS) under basic conditions. The particles were characterized by transmission electron microscopy (TEM) confirming their spherical morphology and narrow nanometric-size distributions. The hybrid particles were incorporated into conventional benzoxazine (BA-a) and a difuran biobased benzoxazine (SA-dfda) to prepare nanocomposites with different mass compositions (3, 5, and 10 wt%). Morphological, mechanical, dynamo-mechanical, and thermal properties of the obtained composites were assessed. All the materials exhibited a homogenous filler dispersion that contributed to improve the reinforcement properties. Hybrid nanoparticles proved to be an interesting alternative as a filler in the benzoxazine matrix to prepare high-performance thermosetting composites.