Zein as a renewable material for the preparation of green nanoparticles for drug delivery

Environmental sustainability is a key challenge driven by the increased consumption of natural resources with limited availability. In this scenario agriculture has emerged as a privileged source of renewable resources, hence more efforts should be addressed to the study of plant-derived materials for medical applications. Zein is a biocompatible, biodegradable and amphiphilic prolamin protein extracted from the endosperm tissue of corn. For these reasons, its applications span from coatings for edible capsules, to the fabrication of bi- and tridimensional scaffolds for tissue engineering, and to develop drug delivery systems. This review aims at describing the properties and main applications of zein with a focus on the most recent and updated state of the art literature on zein based nanoparticles for the controlled delivery of various drugs. The main focus is to analyze the state of the art literature to understand how to implement sustainable methods for the preparation of zein NPs and to propose their exploitation as novel drug delivery systems for multiple applications, including oligonucleotide delivery. Main methods for zein NP preparation are described under an ecofriendly point of view, highlighting their environmental sustainability based on used solvents, waste products and energy consumption

Mueller matrix polarimetry of anisotropic chiral media

[eng] Esta tesis se centra en el estudio de medios quirales mediante polarimetría de matriz de Mueller. Ópticamente los medios quirales se caracterizan por tener actividad óptica, que se manifiesta en procesos dispersivos con la birefringencia circular o en procesos de absorción mediante el cicroismo circular. Nuestro ámbito de estudio han estado los anisótropos no es posible aplicar los métodos convencionales de determinación de la actividad óptica ya que la descripción de la propagación de la luz polarizada se vuelve mucho más compleja ya que el dicroismo y la birefringencia lineales también están presentes. Una parte importante del trabajo han sido el desarrollo teórico necesario para poder obtener los parámetros de dicroismo circular o birefringencia circular a partir de las medidas de la Matriz de Mueller de una muestra anisótropa arbitraria. Otra parte importante del trabajo ha sido la y construcción de un polarímetro de matriz de Mueller de alta resolución basado en el uso de dos moduladores fotoelásticos y es capaz de trabajar en dos modos de funcionamiento: espectroscópico y con resolución espacial. Los desarrollos instrumentales teórico nos han llevado a poder realizar caracterizar muestras de diversa índole. En el ámbito cristalográfico hemos medido espectroscópicamente el tensor de girotropía del cuarzo y hemos mostrado la posibilidad de distinguir dominios quirales en capas delgadas policristalinas. Otro apartado experimental fundamental ha sido la caracterización de procesos de inducción de quiralidad supramolecular mediante efectos hidrodinámicos en soluciones agitadas de nanopartículas orgánicas de formas alargadas

Supramolecular self-assembly with precisely control and potential biological application

Self-assembly is one of the most interesting phenomena in the field of life science. Inspired by life system, taking advantage of non-covalent interaction to construct artificial self-assembly systems with different functions has become a hot topic in interdisciplinary research. This work is devoted to the design and synthesis of new building blocks based on BCPs or amino acid to build 1D chiral and 2D platelet micelles with controllable morphology and exploring the potentially biology and optoelectronics application. In chapter 2 and 3, block copolymers of PPV-b-P2VP were employed as building units for supramolecular self-assembly. By the introduction of chlorine, morphological transformation from rod-like micelles to diamond-like micelles was achieved by the thermally induced nucleation process that lets the kinetically trapped 1D nanostructures to transform as the 2D nanostructures in the thermodynamic state. Then the crystalline groups as TIPS group was introduced into the copolymers, which caused the morphology transition from 2D square to rectangular or rod-like micelles with controllable aspect ratios. These nanomaterials with controllable shapes that possess fluorescent and semiconducting properties could be potential candidates for biological and optoelectronics applications. Chapter 4 and 5 describes the study of amino acid derivatives based on thiophene core with different amino acid arms as building blocks. After supramolecular self-assembly, the helices with controllable chirality and 2D rectangular microsheets were obtained. In addition, by utilizing co- assembly, helicity appearance and inversion were observed for the TDAP-MA system, which was used to provide a feasible detection approach for melamine

Intensification of heat exchanger performance utilizing nanofluids

Heat exchangers are widely utilized in different thermal systems for diverse industrial aspects. The selection of HEx depends on the thermal efficiency, operating load, size, flexibility in operation, compatibility with working fluids, better temperature and flow controls, and comparatively low capital and maintenance costs. Heat transfer intensification of heat exchangers can be fulfilled using passive, active, or combined approaches. Utilizing nanofluids as working fluids for heat exchangers have evolved recently. The performance of heat exchangers employed different nanofluids depends mainly on the characteristics and improvement of thermophysical properties. Regarding the unique behavior of different nanofluids, researchers have attended noteworthy progress. The current study reviews and summarizes the recent implementations carried out on utilizing nanofluids in different types of heat exchangers, including plate heat exchangers, double-pipe heat exchangers, shell and tube heat exchangers, and cross-flow heat exchangers. The results showed that nanofluids with enhanced thermal conductivity, although accompanied by a considerable decrease in the heat capacity and raising viscosity, has resulted in performance enhancement of different heat exchangers types. So, the performance evaluation criterion that combines the thermal enhancement and increases the pumping power for any type of heat exchangers is requisite to evaluate the overall performance properly. The challenges and opportunities for future work of heat transfer and fluid flow for different types of heat exchangers utilizing nanofluids are discussed and presented

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (gabs and glum) and on the application of ECD and CPL to derive structural information on aggregated states

The promise of nanofluids: A bibliometric journey through advanced heat transfer fluids in heat exchanger tubes

© 2024 The Author(s). Published by Elsevier B.V. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Thermal management is a critical challenge in advanced systems such as electric vehicles (EVs), electronic components, and photoelectric modules. Thermal alleviation is carried out through the cooling systems in which the coolant and the heat exchangers are the key components. The study examines recent literature on nanofluids and heat exchanger tubes along with state-of-the-art concepts being tested for heat transfer intensification. The performance of nanofluids in several common heat transfer tubes’ geometries/configurations and the effectiveness of novel heat transfer augmentation mechanisms are presented. Promising results have been reported, showing improved heat transfer parameters with the use of nanofluids and intensification mechanisms like turbulators, fins, grooves, and variations in temperature and flow velocity. These mechanisms enhance dispersion stability, achieve a more uniform temperature distribution, and reduce the boundary layer thickness, resulting in lower tube wall temperatures. Moreover, introducing flow pulsations and magnetic effects further enhances particle mobility and heat exchange. However, there are limitations, such as increased frictional losses and pressure drop due to magnetic effects. The combination of nanofluids, novel heat exchanger tube geometries, and turbulators holds great promise for highly efficient cooling systems in the future. The study also presents a bibliometric analysis that offers valuable insights into the impact and visibility of research in the integration of nanofluids into heat transfer systems. These insights aid in identifying emerging trends and advancing the field towards more efficient and compact systems, paving the way for future advancements.Peer reviewe

Hydrodynamics of colloidal ellipsoids and helices under shear flow and active deformation

Colloidal suspensions widely exit in our daily life, in the form of food, medicaments, biological materials, or cosmetics, among other examples. Hydrodynamic interactions in colloids suspensions at non-equilibrium give rise to many intriguing phenomena, where the shape of colloidal particles plays an important role. For instance, colloidal ellipsoids tumble and kayak in shear flow. Flexible polymers deform, or multicomponent systems in various phases. Besides the tumbling of elongated colloids, further characteristics are expected in shear flow when the particles are chiral, like a helical structures which display a drift in the vorticity direction. Furthermore, the helix may generate locomotion, when external actuation is able to deform its shape in non-reciprocal ways. Artificial systems have been recently synthesized showing that it is possible to generate net motion by smoothly deforming their helical body, as a response to changing temperature. We combine a theoretical approach based on the Smoluchowski equation and flow- dichroism experiments to measure hydrodynamic aspect ratios and polydispersity of nano particles, which is not feasible with standard methods similar to light scattering. A mesoscale hydrodynamics simulations are used to study the transport of helix in shear flow and swimming of deformable helix at low Reynolds numbers. The particle-based approach of multi-particle collision dynamics also enables simulations of colloids at non- equilibrium where thermal fluctuations are not negligible. The first part of tis thesis investigates the validity of flow dichroism as a characteriza- tion tool by employing dispersions of prolate and oblate quantum dots (QDs). Flow dichroism quantifies the tumbling motion of QDs in shear flow by optical means, which provides a characteristic signature of the particle shape, hydrodynamic friction, and size distribution. Particle size, shape, polydispersity, and shear rate have an important ef- fect on the temporal evolution of the flow-induced alignment which we discuss in detail on the basis of numerical solutions of the Smoluchowski equation describing the QDs motion in the basis of the probability of the orientation of colloids in shear flow. This combination of flow dichroism and the Smoluchowski equation approach is not only use- ful for determining shape and anisotropic of colloidal QDs, but also for other nanoscale systems. The second part of this thesis discusses the transport of a deformable helical polymer in a uniform shear flow. The rigidity of the helix essentially affects its configuration under shear stress. The deformable structure still keep helicity while it is compressed and stretched periodically (breathing), and tumble simultaneously in the shear flow below certain shear stress, above which the helix performs noticeable chaotic motion. The tumbling motion follows Jefferys theory for rigid rod-like particles, although with an effective aspect ratio value which depends on flexibility and chirality parameters. The lateral drift shows to be a hydrodynamic effect with a maximum impact between rod and tube limits, obtained by changing the geometry of rigid helix. The flexibility also plays an important role on the lateral drift because its geometry and chirality keep changing. Finally, we investigate the transport of a perfectly deforming helix interacting with a viscous fluid by hydrodynamic simulations. Maintaining the helical structure and a single handedness along its entire length, we first discuss how the deformation periods, helix configuration, and fluid viscosity impact the net rotational swimming stroke and identify its principle direction of motion. We then explore how the presence of confinement in a planar slit influences the rotation speed, trajectory, and position of the deformable helix. Interestingly the active helix shows to consistently migrate to the channel center while passive helix and helix with reciprocal deformation do not show significant migration in any direction. These results including second part provide important criteria to consider in the design and optimization of helical machines at the nanoscale, and in the understanding of some biological functions, for example of flagellated structures. In summary, non-equilibrium dynamics of anisotropic colloids are studied, which include rods and helices in shear flow, and actuated helices. These results show the importance of shape anisotropy in hydrodynamics of colloidal suspensions, which has significant potential in practical applications and solution of some fundamental questions

Orientation Dynamics of Chiral Liquid Crystalline Dispersions During Processing

Lyotropic chiral nematic liquid crystalline dispersions are a unique state of matter that can be exploited to create materials with directionally dependent optical properties. Because of their unique ability to undergo a phase transition and self-assemble into a helical microstructures, chiral nematic dispersions remain a model system in which fluid phase processing can be studied. They also have great potential for industrial applications since they are capable of being processed into thin films that rotate circularly polarized light for optical sensing, security encryption, and decorative coating applications. However, many challenges remain due to complex rheological behavior and consistency in mesogen properties during preparation. In this dissertation, various aspects of processing liquid crystalline dispersions are investigated. Both external processing parameters and material parameters are explored and compared to their experimental counterparts. Confinement effects were discovered to greatly influence the orientation of the chiral microstructure in initially shear aligned dispersions. Chiral strength also altered the orientation of helical microstructures and the number of defects present in these initially shear aligned dispersions. The most uniform homeotropic helical microstructures were achieved at low chiral strength values and the tightest confinement applied by the shear apparatus. Surface anchoring, concentration, speed of drying and chiral strength were also studied in chiral liquid crystalline dispersions as they were made into optically active thin films. For these purposes, large uniform areas of planar microstructures are desired for selective reflection applications. It was determined experimentally that biphasic dispersions formed the most uniform planar configurations when dried slowly in humid environments when placed between two anchoring surfaces. The computational work in this thesis also confirmed these results. The model was also able to show that the number of defects in the films was highly sensitive to the value of chiral strength, which generated more defects at larger values. This work serves as a basis for comparison between lab-scale experiments and their respective theoretical simulations, and paves the way for future collaborative efforts to develop thin films for practical applications

Crescimento natural de nano-estruturas de captação de luz a partir de microalgas para soluções energéticas bioinspiradas

Dissertação de mestrado em Physics Engineering, Devices, Microsystems and NanotechnologiesLight, the most widely available source of energy, enables the development of devices that are under constant studying of optimization and improvement. Nowadays, due to the miniaturization of components, nanoscale technologies are at an all-time high. Photonic crystals, nanostructures characterized by defined periodic wavelength-scale patterns, e.g. pore lattices filled with a different refractive index than that of the bulk material, have the ability to ma nipulate light at ease. This periodicity induces a periodic dielectric function that gives rise to the so-called photonic bandgaps, a set of wavelengths/energies and crystallographic directions for which propagation within the photonic crystal is forbidden. Photonic crystals are commonly produced in cleanrooms involving precise nanofabrication techniques. The demand for a high reproducibility of such structures can, in a long term, become cost-unfriendly, not to mention the environmentally hazardous methods some techniques may require. Recent researches confirmed that natural photonic crystals exist in the silicon dioxide exosqueletons of diatoms, abundant microalgae that precipitate silicid acid from water. This Thesis focuses on the study of a specific part of those exosqueletons: the girdles. The highly ordered lattices these structures exhibit create photonic bandgaps with preserved and well defined photonic properties, paving the way for their utilization as environmentally friendly photonic materials. This Thesis shows, through theoretical and experimental studies, the preparation and modification of these photonic structures by tailoring the refractive index contrast with the deposition of higher refractive index materials, aiming to fine tuning of the photonic properties, thus presenting diatom biomass as a highly available photonic crystal with well preserved photonic properties. Potential applications are not restricted to devices that rely on light, but also involving sensing by colorimetry or refractive index change detection.Luz, a maior fonte de energia disponível, permite o desenvolvimento de dispositivos que se encontram sob estudo constante em termos de otimização e aprimoramento. Nos dias de hoje, devido à miniaturização de componentes, tecnologias à nano-escala têm se destacado cada vez mais. Cristais fotónicos, nano-estruturas caracterizadas por padrões periódicos definidos à escala do comprimento de onda, por exemplo redes de poros preenchidas com um índice de refração diferente do material que compõe a estrutura, são capazes de facilmente manipular a luz. Esta periodicidade induz uma função dielétrica periódica que dá origem aos hiatos fotónicos, um intervalo de comprimentos de onda/energias e direções cristalográficas nos quais a propagação de luz no cristal fotónico é proíbida. Cristais fotónicos são regularmente produzidos em ambiente de sala limpa envolvendo técnicas de nanofabricação precisas. A exigência de elevada reprodutibilidade de tais estruturas pode, a longo prazo, tornar-se um processo dispendioso, para não falar dos métodos perigosos para o ambiente que algumas técnicas possam requerir. Pesquisas recentes confirmaram a existência de cristais fotónicos naturais nos exoesqueletos de dióxido de silício de diatomáceas, microalgas abundantes que precipitam ácido silícico da água. Esta Tese foca-se no estudo de uma parte específica destes exoesqueletos: as girdles. As redes altamente ordenadas que estas estruturas exibem criam hiatos fotónicos com propriedades bem definidas e preservadas, abrindo caminho para a sua utilização como materiais fotónicos amigos do ambiente. Esta Tese demonstra, com recurso a estudos teóricos e experimentais, a preparação e modificação destas estruturas periódicas através da modulação do contraste de índice de refração com deposição de materiais de elevado índice de refração, com o objetivo de modificar as propriedades fotónicas, e assim apresentar a biomassa proveniente de diatomáceas como cristais fotónicos altamente disponíveis e com propriedades fotónicas altamente preservadas. As possíveis aplicações não se restringem apenas a dispositivos que trabalhem diretamente com luz, mas também envolvendo deteção por colorimetría a deteção de mudanças no índice de refração