Understanding nanoparticle aggregation

Nanoparticles form the fundamental building blocks for many exciting applications in various scientific disciplines. However, the problem of the large-scale synthesis of nanoparticles remains challenging. It is necessary to understand the nanoparticle aggregation for the rational design of reactors for high-throughput synthesis of nanoparticles with well-controlled properties. Often, nanoparticle aggregation is modeled using stochastic methods based on scaling arguments and assumptions about the nanoparticle interaction potential. Therefore, a more rigorous approach is desired for understanding nanoparticle aggregation. In this dissertation, a novel framework integrating experiments and multi-scale simulations for studying nanoparticle aggregation is presented. Atomic force microscopy (AFM) was employed to measure the force between polystyrene (PS) micro- and nanoparticles. Specifically, AFM was used to directly measure the force (in air) between a 300 nm PS nanoparticle and a PS film, which was compared with the force measured between a 2 ym PS particle and a PS film. A novel approach based on layer-by-layer assembly to functionalize an AFM probe was developed and applied to the measurement of the force between nanoparticles. The nanoparticle force was deduced from the variation of force between a silica colloidal probe (5-30 ym) functionalized with a monolayer of 300 nm PS particles and a PS film as a function of the diameter of the silica particle. It was shown that continuum models are inadequate to explain the measured forces, which underlines the need for a more rigorous multiscale modeling methodology to understand nanoparticle interaction potential. In principle, nanoparticle interaction potentials can be derived from electronic structure calculations for a molecule using a multiscale modeling approach. To this end, a systematic method of coarse-graining based on force matching was implemented and applied to coarse-grain three common solvent molecules (carbon tetrachloride, benzene and water) to their center of mass. The coarse-grained potentials derived from first principles based effective fragment potential (EFP) were able to reproduce the structural properties that were in reasonable agreement with those obtained using EFP molecular dynamics while achieving a computational speed-up of four orders of magnitude. The nanoparticle interaction potential determines the morphology of corresponding aggregates. On the other hand, the aggregation kinetics are governed by the diffusivity of the aggregates. Therefore, it is essential to relate the aggregate morphology to its mobility in order to study aggregation kinetics. The diffusion of nanoparticle aggregates in the limit of infinite dilution was studied as a function of their mass (N) and fractal dimension (df) using molecular dynamics simulations in the presence of explicit solvent molecules. The diffusion coefficient (Do) for aggregates was found to scale as Do ∼ N-1/df. The ratio of the hydrodynamic radius to the radius of gyration was found to be independent of mass for aggregates of a given fractal dimension, thus enabling an estimate of the diffusion coefficient for a fractal aggregate based on its radius of gyration. The research presented in this work provides a robust framework integrating experiments and multiscale simulations for studying nanoparticle aggregation

Radio-Frequency Sensors for Detection and Analysis of Chemical and Biological Substances

Dielectric spectroscopy (DS) is an important technique for scientific and technological investigations in various areas. DS sensitivity and operating frequency ranges are critical for many applications, including lab-on-chip development where sample volumes are small with a wide range of dynamic processes to probe. In this dissertation, the design and operation considerations of radio-frequency (RF) interferometers that are based on power-dividers (PDs) and quadrature-hybrids (QHs) is presented. The effective quality factor (Qeff) of the sensor is as high as ∼3.8×10^6 with 200 μL of water samples. Such interferometers are proposed to address the sensitivity and frequency tuning challenges of current DS techniques. A high-sensitivity and stable QH-based interferometer is demonstrated by measuring glucose-water solution at a concentration level that is ten times lower than some recent RF sensors and DNA solution at ~3×10^-15 mol/mL that is close to the previously reported lowest result while the sample volume is ~1 nL. Composition analysis of ternary mixture solutions are also demonstrated with a PD-based interferometer. Using a tunable liquid attenuator by accurately changing its liquid volume, the sensitivity of a RF interferometer is tuned automatically. The obtained Qeff of the interferometer is up to 1×10^8 at ~5 GHz, i.e., ~100 times higher than previously reported results. When material-under-test, i.e., methanol-water solution in this work, is used for the tuning, a self-calibration and measurement process is demonstrated from 2 GHz to 7.5 GHz at a methanol concentration level down to 5×10^-5 mole fraction, which is 100 times lower than previously reported results. A microwave scanning technique is reported for the measurement of floating giant unilamellar vesicles (GUV) in a 25 μm wide and 18.8 μm high microfluidic channel. The measurement is conducted at 2.7 GHz and 7.9 GHz, at which a split ring resonator (SRR) operates at odd modes. A 500 nm wide and 100 μm long SRR split gap is used to scan GUVs that are slightly larger than 25 μm in diameter. The smaller fluidic channel induces flattened GUV membrane sections, which make close contact with the SRR gap surface. The used GUVs are synthesized with POPC (16:0-18:1 PC 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), SM (16:0 Egg Sphingomyelin) and cholesterol at different molecular compositions. It is shown that SM and POPC bilayers have different dielectric permittivity values, which also change with measurement frequencies. The obtained membrane permittivity values, such as 73.64-j6.13 for POPC at 2.7 GHz, are more than 10 times larger than previously reported results. The discrepancy is likely due to the measurement of dielectric polarization responses that are parallel with, other than perpendicular to, the membrane surface. POPC and SM-rich GUV surface sections are also clearly identified from scanning measurement results. Further work is needed to enable accurate analysis of membrane composition and dynamics at high spatial resolutions

Organic & Hybrid Photonic Crystals for Controlling Light-Matter Interaction Processes

Organic & Hybrid Photonic Crystals for Controlling Light-Matter Interaction Processe

Growth and Characterization of some amino acid doped nlo materials crystals

The recent advances in science and technology have brought a great demand of various crystals with numerous applications. A field of multidisciplinary nature in science and technology has been emerged, known as crystal growth, which deals with the crysta

Organic & Hybrid Photonic Crystals for Controlling Light-Matter Interaction Processes

Organic & Hybrid Photonic Crystals for Controlling Light-Matter Interaction Processe

Carbon Nanodots from an In Silico Perspective

Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications

Nekovalentní interakce v základních biologických procesech

Charles University in Prague Faculty of Science Department of Physical and Macromolecular Chemistry Non-covalent interactions in fundamental biological processes Doctoral Thesis Abstract Mgr. Vojtěch Klusák Supervisor: Mgr. Lubomír Rulíšek, CSc. Institute of Organic Chemistry and Biochemistry AS CR Center for Biomolecules and Complex Molecular Systems Praha 2010 2 3 Universita Karlova v Praze Přírodovědecká fakulta Katedra fyzikální a makromolekulární chemie Nekovalentní interakce v základních biologických procesech Souhrn disertační práce Mgr. Vojtěch Klusák Školitel: Mgr. Lubomír Rulíšek, CSc. Ústav organické chemie a biochemie AV ČR Centrum biomolekul a komplexních molekulárních systémů Praha 2010 4 5 Introduction Understanding inter- and intra-molecular interactions is the key for our insight into the properties of the biomolecular systems which, in turn, maintain and govern virtually all the processes in biology. Attempts to draw the structure-function relationship at the atomistic or electronic level bring us quite often beyond experimental resolution and capabilities. Modern tools of computational chemistry enable us to focus with satisfactory degree of reliability on the details of the studied process, gather additional (often complementary) information and ascribe particular structural features to...Charles University in Prague Faculty of Science Department of Physical and Macromolecular Chemistry Non-covalent interactions in fundamental biological processes Doctoral Thesis Abstract Mgr. Vojtěch Klusák Supervisor: Mgr. Lubomír Rulíšek, CSc. Institute of Organic Chemistry and Biochemistry AS CR Center for Biomolecules and Complex Molecular Systems Praha 2010 10 Úvod Klíčem k pochopení vlastností a chování biomolekul je porozumění jejich vzájemným interakcím, ať už jde o interakce mezi nimi jako celky či mezi jejich jednotlivými částmi, (např. funkčními skupinami) .Snaha o pochopení vztahu mezi strukturou a funkcí na úrovni atomů či elektronů nás často dovádí za hranice možností či rozlišení experimentálních metod. Moderní nástroje výpočetní chemie nám však často s dostatečnou mírou přesnosti a spolehlivosti umožňují popsat tyto detaily studovaných procesů a doplnit tak naše znalosti a přiřadit k měřitelným veličinám určité strukturní vlastnosti. Za normálních podmínek, za kterých se biomolekuly při buněčných procesech přeskupují a seskupují (například při sbalování proteinů, formování a přeskupování membrán, při buněčné signalizaci) nedochází ke vzniku a zániku kovalentních vazeb. Takovéto procesy jsou z velké míry řízeny nekovalentními interakcemi. Tyto interakce jsou sice poměrně slabé, jejich celkový...Department of Physical and Macromolecular ChemistryKatedra fyzikální a makromol. chemieFaculty of SciencePřírodovědecká fakult

Electrostatically gated nanofluidic membranes: Technological developments and use of electrochemically polarizable materials

Solid-state nanoporous membranes able to control ionic flows at the molecular level could have important applications in fields of research such as water filtration, nanomedicine, energy production, drug delivery, and bio-chemical analysis. The ability to dynamically control the surface charge and the electrical potential inside nanopores extends the range of applications from passive to active devices, such as nanofluidic transistors. In the first part of the thesis a new wafer-scale manufacturing method for solid-state nanoporous membranes based on casting of sacrificial templates is proposed. This way it is possible to individually define the position and geometry of every nanopore by design, independently from the materials used, whichmake this fabrication strategy adapted to the manufacturing of both passive and active nanofluidic devices. In the second part of the thesis this technology was used to fabricate electrostatically gated nanofluidic membranes with nanopores integrating polarizable electrodes made of amorphous carbon inside the nanochannels. Those membranes demonstrated the ability to modulate the ionic conductivity of the nanopores via the variation of the surface charge of the nanochannels with a sensitivity two-three orders of magnitude larger compared to nanochannels gated through metal-oxide electrodes