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Synthesis and Characterization of Quantum Dots
Published in Li Jun, Wu Nianqiang, Biosensors Based on Nanomaterials and Nanodevices, 2017
The drawback of the ligand exchange method is that the stripping of the original surface ligands from QD surfaces leads to a decrease of the QY after water transfer [57,58]. To avoid ligand stripping and thereby keep the high QY of organometallically prepared QDs, the method of amphiphilic polymer encapsulation has recently been investigated [59–62]. This approach will not disturb the original capping ligands on the QD surface. Instead, multiple hydrophobic chains of the amphiphilic polymer can have numerous interactions with the native hydrophobic ligands on the QD surface, thus helping “fix” the ligands on the surface. On the other hand, the hydrophilic end groups of the amphiphilic polymer endow the QDs with good water-solubility and even biocompatibility, depending on the nature of the end groups. This approach has indeed been successfully applied to UV–visible–emitting QDs, such as CdSe/ZnS and CdSe/CdS, and NIR-emitting QDs, such as PbS and PbS/CdS [59–63]. As an example, water-soluble NIR-emitting PbS QDs were achieved by performing the following procedures: PbS QDs capped with oleylamine were first synthesized by the hot-injection approach in an organic phase [64]. Then, the PbS QDs were mixed with the amphiphilic polymer poly(maleic anhydride-alt-1-octadecene)-co-poly(ethylene glycol) (PMAO–PEG) in chloroform and stirred. After that, air-free water was added to the chloroform solution [61,62]. Chloroform was then gradually removed by evaporation. In this case, the PEG group of the amphiphilic polymer is also expected to improve the biocompatibility and ease of bioconjugation of the QDs.
Hydrodynamic Processes
Published in Robert C. Knox, David A. Sabatini, Larry W. Canter, Subsurface Transport and Fate Processes, 1993
Robert C. Knox, David A. Sabatini, Larry W. Canter
In order to grasp the concepts of advective flow and microscopic dispersion, it is necessary to consider an idealized condition (Figure 2.4). Figure 2.4.a shows a soil column initially (t ≤ t0) saturated with solute free water (concentration of solute = 0). At some time “t0” a tracer solution containing a solute (concentration of solute = C0) is introduced to the top of the soil column. As the solution moves through the column it displaces (flushes out) the solute free water. The effluent concentration of the solute (C) is then monitored over time.
Adaptation of existing methods to incorporate recycled aggregates
Published in François de Larrard, Horacio Colina, Concrete Recycling, 2019
A solution to compensate the increase of free water demand could be to keep the free water content constant (even if the added water increases to compensate the RA absorption) but to increase the superplasticizer content drastically. In that case, the plastic viscosity of the concrete may rise to unacceptable values, and it is worth checking if this solution is economic. However, the cement content may be kept constant for environmental reasons (see Chapters 30 and 33).
Drying of Spent Nuclear Fuel: Considerations and Examples
Published in Nuclear Technology, 2023
Anna d’Entremont, Rebecca Smith, Christoph Rirschl, Keith Waldrop, Darrell Dunn, Robert Einziger, Robert Sindelar
There are three primary forms of water that could remain within the canister following drying: free or unbound bulk water, physisorbed water, and chemisorbed water. Free water encompasses water vapor, liquid water, and ice. Liquid and vapor are the forms expected before drying, but freezing may occur, e.g., during vacuum drying. Physisorbed (adsorbed) water is present on all surfaces, including fuel cladding, canister basket, and other canister internals’ surfaces. Physisorption is a reversible process; the molecules of water and the surface do not chemically change.[3] The amount of physisorbed water on the surface varies depending on the number of monolayers of water, with the outer layers being less strongly bound than the first monolayer.[4] Cracks, open pores, and corrosion products may hinder evaporation during drying and increase the amount of residual physisorbed water by virtue of additional surfaces and capillary action. Chemisorbed water is chemically incorporated as a hydroxide or hydrate in the native oxides of components or in corrosion products that formed on the cladding or other materials internal to the canister.[2]