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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Developing New Strategies for the Preparation of Micro- and Nano-structured Polymer Materials

Nie, Zhihong 19 January 2009 (has links)
This thesis described the development of new strategies for the preparation of micro- and nano-structured polymer materials. In particular, this thesis focused on: i) the synthesis of polymer particles in microreactors, and ii) the self-assembly of inorganic nanorods. First, this thesis presented the synthesis of polymer particles and capsules with pre-determined sizes and narrow size distributions (CV<2%) in continuous microfluidic reactors. The method includes (i) the emulsification of monomers in a microfluidic flow-focusing device and (ii) in-situ solidification of droplets via photopolymerization. This microfluidic synthesis provides a novel strategy for the control over the shapes, compositions, and morphologies of polymer particles. In particular, we demonstrated the control over particle shapes by producing polymer ellipsoids, disks, rods, hemispheres, plates, and bowls. We produced polymer particles loaded with dyes, liquid crystals, quantum dots, and magnetic nanoparticles. We generated core-shell particles, microcapsules, Janus and three-phasic polymer particles. Control over the number of cores per droplet was achieved by manipulating the flow rates of liquids in the microchannels. We further investigated the hydrodynamic mechanism underlying the emulsification of droplets, which helps in guiding scientists and engineers to utilize this technique. Second, we described the self-assembly of inorganic nanorods by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tethered with hydrophobic polystyrene chains at both ends. We organized metal nanorods in structures with various geometries such as nanorings, nanochains, bundles, bundled nanochains, and nanospheres by tuning solely the quality of solvents. The self-assembly was tunable and reversible. This approach paved the way for the organization of anisotropic nanoparticles by using the strategies that are well-established for the self-assembly of block copolymers. We further described a systematic study of the self-assembly of polymer-tethered gold nanorods as a function of solvent composition in the system and the molecular weight of the polystyrene blocks. We found that the structure of the polymer pom-poms played an important role on the organization of polymer-tethered gold NRs. The 'supramolecular' assembly was governed by the competition between the end-to-end and side-by-side association of NRs and resulted in the controlled variation of the plasmonic properties of NRs, reflected in a 3-D plasmonic graph.
32

Developing New Strategies for the Preparation of Micro- and Nano-structured Polymer Materials

Nie, Zhihong 19 January 2009 (has links)
This thesis described the development of new strategies for the preparation of micro- and nano-structured polymer materials. In particular, this thesis focused on: i) the synthesis of polymer particles in microreactors, and ii) the self-assembly of inorganic nanorods. First, this thesis presented the synthesis of polymer particles and capsules with pre-determined sizes and narrow size distributions (CV<2%) in continuous microfluidic reactors. The method includes (i) the emulsification of monomers in a microfluidic flow-focusing device and (ii) in-situ solidification of droplets via photopolymerization. This microfluidic synthesis provides a novel strategy for the control over the shapes, compositions, and morphologies of polymer particles. In particular, we demonstrated the control over particle shapes by producing polymer ellipsoids, disks, rods, hemispheres, plates, and bowls. We produced polymer particles loaded with dyes, liquid crystals, quantum dots, and magnetic nanoparticles. We generated core-shell particles, microcapsules, Janus and three-phasic polymer particles. Control over the number of cores per droplet was achieved by manipulating the flow rates of liquids in the microchannels. We further investigated the hydrodynamic mechanism underlying the emulsification of droplets, which helps in guiding scientists and engineers to utilize this technique. Second, we described the self-assembly of inorganic nanorods by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tethered with hydrophobic polystyrene chains at both ends. We organized metal nanorods in structures with various geometries such as nanorings, nanochains, bundles, bundled nanochains, and nanospheres by tuning solely the quality of solvents. The self-assembly was tunable and reversible. This approach paved the way for the organization of anisotropic nanoparticles by using the strategies that are well-established for the self-assembly of block copolymers. We further described a systematic study of the self-assembly of polymer-tethered gold nanorods as a function of solvent composition in the system and the molecular weight of the polystyrene blocks. We found that the structure of the polymer pom-poms played an important role on the organization of polymer-tethered gold NRs. The 'supramolecular' assembly was governed by the competition between the end-to-end and side-by-side association of NRs and resulted in the controlled variation of the plasmonic properties of NRs, reflected in a 3-D plasmonic graph.
33

Nanocarrier mediated therapies for the gliomas of the brain.

Agarwal, Abhiruchi 21 January 2011 (has links)
Existing methods of treating glioma are not effective for eradicating the disease. Therefore, new and innovative methods of treatment alone or in combination with existing therapies are necessary. Delivery of therapeutic agents through delivery carriers such as liposomes diminishes the harmful effects of the agent in healthy tissues and allows increased accumulation in the tumor. In addition, targeted chemotherapy using liposomes provides the opportunity for further increase in drug accumulation in tumor. However, the current targeting strategies suffer accelerated plasma clearance and are not advantageous in improving efficacy. The search for new tumor targets, novel ligands, new strategies for targeting, and particle stabilization will advance our ability to improve delivery at the tumor level while decreasing toxicity to normal tissues. The global objective of this thesis was to improve the status of current liposomal therapy to achieve higher efficacy in tumors. Here, we show a novel mechanism to increase targeting to tumor while uncompromising on the long circulation of stealth liposomes. Long circulation is essential for passive accumulation of the nanocarriers due to EPR effect, in order to see benefits of targeting. Using phage display technique, a variety of tumor specific peptides were identified for use as targeting moieties. One potential advantage of the approach proposed here is the rapid identification of patient tumor specific peptide that evades the RES. This could lead to the development of a nanocarrier system with high avidity and selectivity for tumors. Therefore, tumor accumulation of the targeted formulations will be higher than that of non‐targeted liposomes due to increased drug retention at the tumor site and uncompromised blood residence time.In addition, it has been shown that the distribution of nanocarriers, spatially within the tumor, is limited that might further hinder the distribution of the encapsulated drug, thereby limiting efficacy. It is necessary to release the drug from within the nanocarrier to promote increased efficacy. Here, we were able to address the problem of drug diffusion within the tumor interstitium using a combination therapy employing a remotely triggered thermosensitive liposomal chemotherapeutic. We fabricated a thermosensitive liposomal nanocarrier that maintained its stability at physiological temperature to minimize toxicity to healthy cells. We, then, showed a remote triggering mechanism mediated by gold nanorods heated via NIR can help in achieving precise control over the desired site for drug release. These strategies enabled increased drug availability at the tumor site and contributed to tumor retardation. Additionally, we show that the synergistic therapy employing gold nanorods and thermosensitive liposomes may have great potential to be translated to the clinic.
34

GOLD NANOSPHERES AND GOLD NANORODS AS LOCALIZED SURFACE PLASMON RESONANCE SENSORS

Matcheswala, Akil Mannan 01 January 2010 (has links)
A novel localized surface plasmon resonance (LSPR) sensor that differentiates between background refractive index changes and surface-binding of a target analyte (e.g. a target molecule, protein, or bacterium) is presented. Standard, single channel LSPR sensors cannot differentiate these two effects as their design allows only one mode to be coupled. This novel technique uses two surface plasmon modes to simultaneously measure surface binding and solution refractive index changes. This increases the sensitivity of the sensor. Different channels or modes can be created in sensors with the introduction of gold nanospheres or gold nanorods that act as receptor mechanisms. Once immobilization was achieved on gold nanospheres, the technique was optimized to achieve the same immobilization for gold nanorods to get the expected dual mode spectrum. Intricate fabrication methods are illustrated with using chemically terminated self assembled monolayers. Then the fabrication process advances from chemically silanized nanoparticles, on to specific and systematic patterns generated with the use of Electron Beam Lithography. Comparisons are made within the different methods used, and guidelines are set to create possible room for improvement. Some methods implemented failed, but there was a lot to learn from these unsuccessful outcomes. Finally, the applications of the dual mode sensor are introduced, and current venues where the sensors can be used in chemical and biological settings are discussed.
35

[en] STUDY OF INTERACTIONS OF THE ANTIBIOTIC NORFLOXACIN AND ITS COPPER-PHENANTHROLINE COMPLEX WITH DRUG DELIVERY SYSTEMS / [pt] ESTUDO DE INTERAÇÕES DO ANTIBIÓTICO NORFLOXACINA E DO SEU COMPLEXO DE COBRE-FENANTROLINA COM SISTEMAS DE DISTRIBUIÇÃO CONTROLADA DE MEDICAMENTOS

GLEICE CONCEICAO MENDONCA GERMANO 10 January 2019 (has links)
[pt] Os sistemas de administração controlada de medicamentos (drug delivery) permitem a introdução de uma substância terapêutica no organismo e melhoram sua eficácia e segurança, controlando a taxa, o tempo e o local de liberação, o que diminui os efeitos colaterais.Nesse trabalho nos dedicamos a estudar dois possíveis sistemas de administração de fármacos: lipossomos associados a surfactantes, já bastante utilizados em farmacologia, e nanobastões de ouro, cujas propriedades únicas têm sido avaliadas em aplicações biomédicas. Os lipossomos têm-se destacado devido a sua estabilidade e baixa toxicidade, os surfactantes são tensoativos muito usados tanto em farmacologia como para estabilizar soluções coloidais de nanopartículas. Já os nanobastões de ouro têm perspectivas promissoras para utilização em entrega de fármacos devido a suas propriedades óticas e biocompatibilidade. Estudamos, por meio de espectrofotometria de fluorescência e de absorção UV-visível, a associação entre esses sistemas e uma classe de fármacos denominada fluorquinolonas, que são antibióticos de amplo espectro bacteriano. A norfloxacina (NFX), pertencente à segunda geração de fluorquinolonas, foi escolhida para esse trabalho por ser naturalmente fluorescente, o que facilita a análise das interações sem a introdução de sondas extrínsecas ao sistema. Segundo a literatura, a associação da NFX com íons metálicos produz modificações nas propriedades desse fármaco, como solubilidade e biodisponibilidade. Essas mudanças têm sido avaliadas como uma possível solução ao problema de resistência bacteriana a antibióticos. Esse trabalho foi dividido em duas partes: na primeira, estudamos a formação dos complexos ternários de NFX com cobre-fenantrolina em presença de lipossomos associados a surfactantes que modificam a distribuição de carga elétrica superficial desses sistemas; na segunda parte estudamos a associação de NFX a nanobastões de ouro estabilizados por diferentes surfactantes. / [en] Drug delivery systems allow the introduction of a therapeutic substance into the body and improve its effectiveness and safety by controlling the rate, time and place of release, which reduces side effects. In this work, we study two possible drug delivery systems: liposomes associated with surfactants, which are already widely used in pharmacology, and gold nanorods, whose unique properties have been evaluated in biomedical applications. Liposomes have been remarkable because of their stability and low toxicity, and surfactants are widely used both in pharmacology and to stabilize colloidal solutions of nanoparticles. On the other hand, gold nanorods have promising perspectives for use in drug delivery due to their optical properties and biocompatibility.We study the association between these systems and a class of drugs called fluoroquinolones, which are broadspectrum bacterial antibiotics, using fluorescence spectrophotometry and UVvisible absorption. Norfloxacin (NFX), a second generation fluoroquinolone, was chosen because it is naturally fluorescent, which facilitates the analysis of interactions without the introduction of extrinsic probes into the system. According to the literature, the association of NFX with metal ions produces changes in the properties of this drug, such as solubility and bioavailability. These changes have been evaluated as a possible solution to the problem of bacterial resistance to antibiotics. This work was divided in two parts: first, we studied the formation of the ternary complexes of NFX with copper-phenanthroline in the presence of liposomes associated to surfactants that modify the distribution of surface electric charge of the systems; in the second part, we studied the association of NFX to gold nanorods stabilized by different surfactants.
36

Síntese, dinâmica de formação, caracterização e propriedades ópticas de nanobastões de ouro dispersos em meio aquoso e matrizes orgânicas / Synthesis, characterization, dynamic formation and optical properties of gold nanorods dispersed in aqueous phase and organic matrices

Silva, Monique Gabriella Angelo da 12 April 2010 (has links)
In this work, different colloidal gold nanorods were prepared dispersed in different liquid matrices. All gold nanorods were prepared from the acid tethrachloroauric (HAuCl4) in the presence of a reducing agent, using the seed mediated method. The cetyltrimethylammonium bromide (CTAB) was employed as director growth agent. The variable concentration of CTAB in the medium was evaluated in order to verify the selectivity in the formation of nanorods. In addition, we performed a kinetic study to obtain information about the formation mechanism of these particles. Colloid containing gold nanorods in organic matrices such as castor oil and hexafluorophosphate ionic liquid butylmethylilimidazolium (BMIM.PF6) were prepared in order to obtain colloid systems with different physico-chemical characteristics, however among same particles. These new colloids were obtained using the transfer technique of particles, which were synthesized in aqueous medium and then dispersed, after separation, for the desired organic matrix. All colloids were characterized by absorption spectroscopy at ultraviolet and visible (UV-Vis) and nanoparticles characterized by Transmission Electron Microscopy (TEM) / Neste trabalho, diferentes colóides contendo nanobastões de ouro dispersos em diferentes matrizes líquidas foram preparados a partir do ácido tetracloroáurico (HAuCl4), em presença de um agente redutor adequado, através do método mediado por sementes. O brometo de cetiltrimetilamônio (CTAB) foi empregado como agente direcionador de crescimento. A variável concentração de CTAB no meio foi avaliada com o objetivo de verificar a seletividade na formação de nanobastões. Além disso, foi realizado um estudo cinético para obter informações sobre o mecanismo de formação dessas partículas. Coloides contendo nanobastões de ouro em matrizes orgânicas como óleo de mamona e o líquido iônico hexafluorofosfato de butilmetilimidazólio (BMIM.PF6) foram preparados a fim de obter sistemas coloidais com diferentes características fisico-químicas porém com as mesmas partículas. Esses novos colóides foram obtidos através da técnica de transferência de partículas, as quais foram sintetizadas em meio aquoso e posteriormente dispersas, após separação, para a matriz orgânica desejada. Todos os colóides preparados foram caracterizados por Espectroscopia de absorção na região do ultravioleta e visível (UV-Vis) e as nanopartículas caracterizadas por Microscopia na eletrônica de transmissão (MET)
37

Charakterizace nanostrukturovaných elektrod pro elektrochemické biosenzory / Characterization of nanostructured electrodes for electrochemical biosensors

Kynclová, Hana January 2012 (has links)
Nowadays it is attached to a major effort to study applications of nanoparticles in biosensors technology. We studied the effect of gold nanoparticles on the surface of the electrodes by Electrochemical Impedance Spectroscopy method and Cyclic Voltammetry. For impedance measurements was proposed substitute electrical model and cyclic voltammetry method was used to determine the electroactive surface of electrodes.
38

Nanomaterial-decorated micromotors for enhanced photoacoustic imaging

Aziz, Azaam, Nauber, Richard, Sánchez Iglesias, Ana, Tang, Min, Ma, Libo, Liz-Marzán, Luis M., Schmidt, Oliver G., Medina-Sánchez, Mariana 13 November 2023 (has links)
Micro-and nanorobots have the potential to perform non-invasive drug delivery, sensing, and surgery in living organisms, with the aid of diverse medical imaging techniques. To perform such actions, microrobots require high spatiotemporal resolution tracking with real-time closed-loop feedback. To that end, photoacoustic imaging has appeared as a promising technique for imaging microrobots in deep tissue with higher molecular specificity and contrast. Here, we present different strategies to track magnetically-driven micromotors with improved contrast and specificity using dedicated contrast agents (Au nanorods and nanostars). Furthermore, we discuss the possibility of improving the light absorption properties of the employed nanomaterials considering possible light scattering and coupling to the underlying metal-oxide layers on the micromotor’s surface. For that, 2D COMSOL simulation and experimental results were correlated, confirming that an increased spacing between the Au-nanostructures and the increase of thickness of the underlying oxide layer lead to enhanced light absorption and preservation of the characteristic absorption peak. These characteristics are important when visualizing the micromotors in a complex in vivo environment, to distinguish them from the light absorption properties of the surrounding natural chromophores.
39

DNA-Templated Nanofabrication of Metal-Semiconductor Heterojunctions and Their Electrical Characterization

Pang, Chao 28 May 2024 (has links) (PDF)
Bottom-up nanofabrication, although still in its early stages with formidable challenges, is considered a potential alternative method to address the limitations of traditional top-down techniques by offering benefits including process simplification, cost reduction, and environmental friendliness. DNA-templated nanofabrication, one of the most powerful bottom-up methods, presents an innovative way to create advanced nanoelectronics. In this approach, nanomaterials with specific electronic, photonic, or other functions are precisely and programmably positioned on DNA nanostructures from a disordered collection of smaller parts. These self-assembled structures offer significant potential for improving many fields such as biosensing, drug delivery and electronic device manufacturing. This dissertation reports the successful fabrication of semiconductor-metal Schottky contacts using a DNA origami scaffold. The scaffold, consisting of DNA strands organized into a specific bar-shaped architecture, facilitates the competitive arrangement of gold and cadmium sulfide nanorods, forming heterojunctions, and addressing previous limitations in semiconductor nanomaterial availability. Electrical characterization reveals nonlinear Schottky barrier properties, with electrical conductivity ranging from 1.1 to 3.7 — 104 S/m, marking a several million-fold increase over prior work. This research establishes the feasibility of using cadmium sulfide prepared as a n-type semiconductor material and an innovative self-assembly approach for making nanoscale Schottky contacts, paving the way for the future development of DNA-based nanoscale logic gate circuits.
40

Insights into Self-Assembly Mechanisms of Polymer-Grafted Gold Nanoparticles in Colloidal Solution

Vazirieh Lenjani, Shayan 20 August 2024 (has links)
This thesis aims to shed light on the mechanisms governing the self-assembly of polymer-functionalized gold nanoparticles (AuNPs) in colloidal solutions, with the ultimate goal of enhancing control over the directed assembly of these hybrid nanomaterials (HNMs) for potential sensor applications. State-of-the-art analytical methods were employed to investigate the nano/microscopic forces involved in the self-assembly process. The first step involved the development of a method using energy-filtered transmission electron microscopy (EFTEM) to quantify the polymer grafting density (PGD) for polystyrene (PS)-grafted isotropic and anisotropic AuNPs (nanospheres (NSs) and nanorods (NRs)). This method addressed the lack of techniques capable of quantifying polymer loads for individual nanoparticles. The analysis results, in agreement with values from thermogravimetric (TGA) measurements, revealed no preferential polymer load at the surfaces with higher curvature (tips of AuNRs) for functionalized NRs with a measured PGD of  0.05 chain nm–2. This observation led to discovery of a novel aspect of the self-assembly of anisotropic PS-grafted AuNPs: By reducing the solvent quality for PS brushes through the addition of 20% v/v water to the dimethylformamide (DMF) solution, preferential tip-to-tip assembly of AuNRs occurred, even for species coated with a homogeneous PS layer. The origin and influence of surface charges and electrostatic forces on the preferential tip-to-tip assembly of AuNRs was then examined with Zeta-potential and kelvin probe atomic force microscopy (KPAFM) and through control experiments involving the addition of NaCl electrolyte to the colloidal solution. Changes in assembly rates and modes were monitored by observing shifts in longitudinal/transversal localized surface plasmon resonance (LSPR) peaks in the vis/NIR spectroscopy. The self-assembly kinetics of similar PS-grafted AuNR systems were further studied using a combination of time-resolved vis/NIR spectroscopy, finite-difference time-domain (FDTD) simulations, and additional data from transmission electron microscopy (TEM) analysis. The results indicated faster assembly rates and lower energy barriers for nanorods grafted with thicker PS shells compared to those coated with thinner shells, emphasizing the role of electrostatic repulsive forces in preventing assembly when the polymer spacing between nanorods is smaller. Coarse-grained molecular dynamic (MD) simulations supported the explanation emphasizing on the impact of electrostatic forces on the preferential tip-to-tip self-assembly of PS@AuNRs, as well as the effect of PS layer thickness on the energy barrier for such assemblies. The knowledge gained was applied to design co-assembled structures using blocks of nanorods coated with two distinct molecular weights (12 and 50 kDa), revealing a narcissistic self-assembly signature arising from different assembly rates of each block. Another model system involving gold nanospheres (AuNSs) grafted with thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) brushes was employed in a separate research project to study the assembly/disassembly mechanism of brush-coated nanoparticles. The assembly/disassembly was triggered by changing the solvent conditions for the polymer brushes, through heating/cooling the colloidal solution above/below the lower critical solution temperature (LCST) of the 30 kDa PNIPAM brush (32 °C). Clusters with different sizes and geometries were successfully formed in aqueous solution by varying the ionic strength of solution through changing the concentrations of NaCl electrolyte. No cluster were formed at 40 °C in systems with little to no electrolyte, underlining the role of repulsive electrostatic forces in solution-based self-assembly of colloidal NPs. Moreover, transition from single NPs to 1D/2D assemblies and then growing globular structures with increasing electrolyte concentrations was observed by increasing the electrolyte concentration at temperatures above the LCST. This transition was tracked using polarized angle-dependent dynamic light scattering (DLS) and TEM analysis. Additionally, real-time micrographs and videos of self-assembly in the presence of electrolyte and upon an increase in solution temperature to 40 °C were recorded via in-situ liquid-phase TEM. To the best of author’s knowledge, the employed approaches have not been previously reported to gain deep insights into the assembly of thermo-responsive HNMs in solution and points out to potentials for future analytical studies. Based on the obtained results, scattering measurements in glass fiber nanochannels are planned to provide further insights into the assembly/disassembly process for single clusters. / Das Ziel dieser Arbeit ist es, die Mechanismen der Selbstassemblierung von polymerfunktionalisierten Goldnanopartikeln (AuNPs) in kolloidalen Lösungen zu untersuchen. Dies soll dazu beitragen, die Kontrolle über die gezielte Anordnung dieser hybriden Nanomaterialien (HNMs) für potenzielle Sensoranwendungen zu verbessern. Hierzu kamen moderne Analysemethoden zum Einsatz, um die bei diesem Selbstassemblierungsprozess wirkenden nano-/mikroskopischen Kräfte zu erforschen. Im ersten Schritt wurde eine Methode entwickelt, die auf energiegefilterter Transmissionselektronenmikroskopie (EFTEM) basiert. Diese Methode ermöglichte die Quantifizierung der Polymerpfropfdichte (PGD) für isotrope und anisotrope AuNPs (Nanokugeln (NS) und Nanostäbchen (NR)), die mit Polystyrol (PS) gepfropft wurden. Mit dieser Methode konnte die Polymerbeladung erstmals auf der Ebene einzelner Nanopartikel quantifiziert werden. Die Analyseergebnisse, die mit den Werten thermogravimetrischer Messungen (TGA) übereinstimmen, zeigten, dass bei funktionalisierten Nanopartikeln mit einer PGD von 0,05 Ketten/nm¬2 keine bevorzugte Polymerbeladung an den Oberflächen mit höherer Krümmung (Spitzen der AuNRs) vorhanden ist. Diese Beobachtung führte zur Entdeckung eines neuen Aspekts der Selbstassemblierung von anisotropen PS-gepfropften AuNPs: Durch die Verringerung der Lösungsmittelqualität für PS-Bürsten durch Zugabe von 20 % v/v Wasser zur Dimethylformamid (DMF)-Lösung kam es zu einer bevorzugten Spitze-zu-Spitze-Anordnung von AuNRs, sogar für Nanostäbe, die von einer homogenen PS-Schicht umgeben waren. Der Ursprung und der Einfluss von Oberflächenladungen und elektrostatischen Kräften auf die bevorzugte Spitze-zu-Spitze-Anordnung von AuNRs wurden dann mit Zeta-Potential und Kelvin-Sonden-Atomkraftmikroskopie (KPAFM) sowie durch Kontrollexperimente unter Zugabe von NaCl-Elektrolyt zur kolloidalen Lösung untersucht. Änderungen der Assemblierungsgeschwindigkeit und -Modi wurden durch Beobachtung von Verschiebungen der longitudinalen/transversalen Moden der lokalisierten Oberflächenplasmonenresonanz (LSPR) in der vis/NIR-Spektroskopie verfolgt. Die Selbstassemblierungskinetik ähnlicher PS-gepfropfter AuNR-Systeme wurde mit einer Kombination aus zeitaufgelöster vis/NIR-Spektroskopie, Finite-Differenzen-Zeitbereichssimulationen (FDTD) und zusätzlichen Daten aus der TEM-Analyse weiter untersucht. Die Ergebnisse deuten auf schnellere Assemblierungsgeschwindigkeiten und niedrigere Energiebarrieren für solche Nanostäbchen hin, die mit dickeren PS-Hüllen gepfropft sind, im Vergleich zu solchen, die mit dünneren Hüllen beschichtet sind. Dies unterstreicht die Rolle der elektrostatischen Abstoßungskräfte bei der Verhinderung der Selbstanordnung, wenn der Polymerabstand zwischen den Nanostäbchen kleiner ist. Vergröberte molekulardynamische (MD)-Simulationen unterstützten die Erklärung, wobei der Einfluss elektrostatischer Kräfte auf die bevorzugte Spitze-zu-Spitze-Anordnung von PS@AuNRs sowie die Auswirkung der PS-Schichtdicke auf die Energiebarriere für solche Assemblierungen hervorgehoben wurde. Die gewonnenen Erkenntnisse wurden für das Design von ko-assemblierten Strukturen unter Verwendung von Nanostäbchenblöcken verwendet, die mit zwei unterschiedlichen Molekulargewichten (12 und 50 kDa) beschichtet sind. Dabei wurde eine narzisstische Selbstassemblierungssignatur aufgedeckt, die sich aus unterschiedlichen Assemblierungsraten der einzelnen Blöcke ergibt. Ein weiteres Modellsystem mit Goldnanokugeln (AuNS), die mit thermoresponsiven Poly(N-Isopropylacrylamid)-Bürsten (PNIPAM) gepfropft wurden, wurde in einem anderen Forschungsprojekt verwendet, um den Mechanismus der Assemblierung/ des Zerfalls von bürstenbeschichteten Nanopartikeln zu untersuchen. Die Assemblatbildung/-Zerfall wurde durch Änderung der Lösungsmittelbedingungen für die Polymerbürsten ausgelöst, indem die kolloidale Lösung über/unter die untere kritische Lösungstemperatur (LCST) der 30 kDa PNIPAM-Bürste (32 °C) erhitzt/abgekühlt wurde. Cluster mit unterschiedlichen Größen und Geometrien wurden erfolgreich in wässriger Lösung gebildet, indem die Ionenstärke der Lösung durch Änderung der Konzentrationen des NaCl-Elektrolyten variiert wurde. Bei 40 °C wurden in Systemen mit wenig oder gar keinem Elektrolyten keine Cluster gebildet, was die Rolle der abstoßenden elektrostatischen Kräfte bei der lösungsbasierten Selbstassemblierung kolloidaler NPs unterstreicht. Der Übergang von einzelnen NPs zu 1D/2D anisotropen Assemblaten und dann zu wachsenden kugelförmigen Strukturen wurde beobachtet, indem die Elektrolytkonzentration bei Temperaturen oberhalb der LCST geändert wurde. Dieser Übergang wurde mittels polarisierter, winkelabhängiger dynamischer Lichtstreuung (DLS) und TEM-Analyse verfolgt. Echtzeit-Elektronenmikroskopie der Selbstassemblierung in Anwesenheit des Elektrolyten und bei einer Erhöhung der Lösungstemperatur auf 40 °C wurden mittels In-situ-TEM in einer Flüssigkeitszelle realisiert. Nach bestem Wissen des Autors wurde bisher noch nicht über die angewandten Ansätze berichtet, um tiefe Einblicke in den Aufbau thermoresponsiver HNMs in Lösung zu gewinnen, und sie weisen auf Potenziale für zukünftige analytische Studien hin. Geplante Messungen der Bildung/Deformation einzelner Cluster in optischen Fasern sind geplant, um weitere Einblicke in den Assemblierungsprozess zu erhalten.

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