Ana Maria Percebom

Zwitterionic surfactants have been used as foaming agents in Enhanced Oil Recovery due to their foamability, tolerance to reservoir conditions, low toxicity, and low adsorption on reservoir rocks. However, in the case of back-production, the impact of zwitterionic surfactants on water-in-crude oil (W/O) emulsions and produced water remains unclear, representing a knowledge gap in the field. The present study evaluated the effect of three commercial zwitterionic surfactants, at concentrations ranging from 50 to 1000 ppm, on water-oil separation using a Brazilian Pre-Salt crude oil. Emulsion formation, separation kinetics, and water quality were assessed through bottle tests, droplet size microscopy, and oil-in-water content analysis. At the lowest concentration (50 ppm), these surfactants promoted coalescence and sedimentation of W/O emulsions faster than traditional nonionic and anionic surfactants. Separation kinetics increased as surfactant concentration increased up to 200 ppm, but concentrations above 500 ppm induced the formation of multiple emulsions (W/O/W). After 72 h, these emulsions separated, and the aqueous phase still contained residual oil droplets, indicating potential challenges associated with the disposal or reuse of produced water. Surfactant hydrophobicity, reduction in interfacial tension, and critical micelle concentration were critical properties influencing the observed effects. The surfactant with higher hydrophobicity induced a more significant and rapid reduction in interfacial tension, resulting in faster W/O separation at low concentrations but compromising water quality at high concentrations. These results indicate that careful selection and monitoring of surfactants during EOR operations can optimize oil recovery efficiency while minimizing operational and environmental risks upstream.

Gold and platinum bimetallic nanoparticles, Au@PtNPs, have gained attention due to their plasmonic properties. The controlled synthesis of Au@PtNPs involves complex parameters, and the resulting synergy between Au and Pt introduces possibilities for tailoring their properties. This study explores the effects of key-parameters of synthesis (gold core diameters, reaction time, and Pt concentration) on the final properties of Au@PtNPs. Gold nanoparticles of varying diameters were synthesized and used as cores for the reduction of hexachloroplatinic acid, forming a surrounding shell of Pt nanoparticles. The parameters were systematically tuned to understand their impact on morphology, dimension, stability, and plasmonic properties of Au@PtNPs. Increasing Pt precursor concentration resulted in thicker and denser Pt shells, broadening the localized surface plasmon resonance (LSPR) band and improving Au@PtNPs stability. These properties are essential for applications such as photothermal treatment. The synthesis achieved satisfactory products within just 1 h of Pt4+ reduction at mild temperature without using surfactants. Only limited changes in plasmonic properties were observed after 4 h of synthesis, suggesting an optimal reaction period. Manipulating Au core diameter provided LSPR band control, with smaller cores exhibiting greater broadening towards the infrared region. This systematic exploration provided valuable insights for understanding key-parameters governing the synthesis and properties of Au@PtNPs.

Combining direct targeting, enhanced cellular uptake, photothermal transduction capacity, and biocompatibility in the same system is a challenge to make the application of nanoparticles in biomedicine real. This study involves the functionalization of gold nanoparticles (AuNPs) in a few steps with strategic macromolecules to provide characteristics that are key to theragnostic agents. Polyethylene glycol (PEG) is hydrophilic and can improve nanoparticle stability and circulation lifetime. Polylactic acid (PLA) is a biodegradable hydrophobic polymer important to guarantee the interaction and uptake through the cellular membranes. Folate provides specific targeting because tumors usually overexpress folate receptor proteins. Single, double, and triple functionalization of spherical and rodlike AuNPs with these ligands provided different aggregation, stability, and plasmonic properties. Triple functionalization ensured simultaneous nanoparticle stability in an aqueous medium and enhanced cellular uptake. Infrared irradiation increased the temperature of gold nanorods more than of gold nanospheres due to the longitudinal surface plasmon resonance band. The results suggest that this functionalization strategy can be used to tune the desired properties for applications of gold nanoparticles, such as imaging and photothermal therapy in biomedicine research.

Although nanoparticles (NPs) are known to increase foam stability, foam stabilisation is not observed in all surfactant/NP combinations. The present study evaluates the stability of CO₂ foams containing surfactant/NP mixtures with attractive or repulsive electrostatic interactions at the low pH imposed by CO₂ in the presence of a high-salinity brine. Three ionic surfactants and two oxide NPs (SiO₂ and Al₂O₃) were used in combinations of similar or opposite charges. Surface tension, viscosity, ζ-potential and hydrodynamic size experiments allowed the analysis of CO₂ foam stability based on the impact of surfactant–NP interactions on bulk and interfacial properties. All oppositely charged systems improved the foam half-life; however, a higher NP concentration was required to observe a significant effect when more efficient surfactants were present. Both bulk viscosity and rigidity of the interfacial films drastically increased in these systems, reducing foam drainage. The mixture of SiO₂ with a zwitterionic surfactant showed the greatest increase in CO₂ foam stability owing to the synergy of these effects, mediated by attractive interactions. This study showed that the use of NPs should be tailored to the surfactant of choice to achieve an interplay of interfacial and rheological properties able to reduce foam drainage in applications involving CO₂ foam in brine.

Understanding of the temperature-induced phase transition of poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) random copolymers with varied composition remains largely incomplete. Upon heating they can form either macroscopically phase-separated aggregates or micelles. We examined the effect of polymer architecture by rationally designing and synthesizing various POEGMA copolymer structures via atom transfer radical polymerization using OEGMA monomers of different EO lengths. Micelle formation occurred for copolymers with a small fraction of long side chains counterbalanced by an appropriate number of short side chains, while macroscopic phase separation occurred for other copolymer compositions. In some copolymer compositions and architectures, micelle formation followed by macroscopic phase separation occurred, and the temperature of these phase transitions could be tailored accordingly. This new strategy allows the control over the microstructure and specific transition temperatures enabling, for instance, the preparation of nanocarriers for encapsulating hydrophobic compounds.

Small-angle X-ray scattering (SAXS) is an accurate nondestructive method that requires a minimum of sample preparation and is employed to study porosity, morphology and hierarchical structures. Zeolites and silica are among the porous materials that are widely investigated by SAXS. However, studies of covalent organic frameworks (COFs) are still scarce. In the present study, SAXS was employed to investigate meso- and microporous COFs, affording insightful information about their nanostructure textural properties. SAXS is especially useful when combined with other characterization techniques, such as powder X-ray diffraction and N₂ adsorption isotherms, emerging as an efficient tool to further characterize COFs. For microporous COFs, SAXS was used mainly to obtain quantitative values of surface roughness as a function of fractal parameters, in all cases indicating surface fractals of the large-scale scattering object, namely the `grain'. Mesoporous COF studies allowed elucidation of their hexagonal structure on the basis of their structure peaks; however, the main result lies in the distinction between the pore and the grain, which are described as a hierarchical structure by the Beaucage model and evaluated according to their fractality. These COFs generally exhibit pores with mass fractal features and grains with surface fractal features when they are submitted to post-functionalization, which may be due to the poor diffusivity of the functionalizing agents into the pores. In addition, a proposed aggregation description of the porous scattering objects was envisioned, based on small-angle scattering premises, which was confirmed for a microporous COF by high-resolution transmission electron microscopy.

Through charge-driven interfacial complexation, we produced millimetre-sized spheroidal hydrogels (SH) with a core-shell structure allowing long term stability in aqueous media. The SH were fabricated by extruding, drop-wise, a cationic cellulose nanofibril (CCNF) dispersion into an oppositely charged polyacrylic acid (PAA) bath. The SH have a solid-like CCNF-PAA shell, acting as a semi-permeable membrane, and a liquid-like CCNF suspension in the core. Swelling behaviour of the SH was dependent on the osmotic pressure of the ageing media. Swelling could be supressed by increasing the ionic strength of the media as this enhanced interfibrillar interactions and thus strengthened the outer gel membrane. We further validated a potential application of SH as re-usable matrixes for glucose oxidase (GOx) entrapment, where the SH work as “microreactors” from which substrate and product are freely able to migrate, through the SH shell whilst avoiding enzyme leakage.