Silicon Nanocrystal Superlattice Nucleation and Growth.

Colloidal dodecene-passivated silicon (Si) nanocrystals were dispersed in hexane or chloroform and deposited onto substrates as face-centered cubic superlattices by slowly evaporating the solvent. The uniformity of the nanocrystals enables extended order; however, the solvent and the evaporation protocol significantly influence the self-assembly process, determining the morphology of the films, the extent of order, and the superlattice orientation on the substrate. Chloroform yielded superlattices with step-flow growth morphologies and (111)SL, (100)SL, and (110)SL orientations. Hexane led to mostly island morphologies when evaporated at room temperature with exclusively (111)SL orientations. Higher evaporation temperatures led to more extensive step-flow deposition. A model for the surface diffusion of nanocrystals adsorbed on the superlattice surface is developed.

Orientationally Ordered Silicon Nanocrystal Cuboctahedra in Superlattices.

Uniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices.

Potential Impact of Infusion Technique on Drug Delivery.

BACKGROUND: Infusion practices have been modified, especially for antineoplastic drugs, through the use of specific infusion devices with postadministration rinsing (PAR) so as to decrease occupational exposure to drugs. The aim of this study was to highlight how such infusion devices may impact the drug delivery of injectable drugs. MATERIALS AND METHODS: Drug infusions were simulated with a radiotracer (99mTc) for 30 minutes to assess nine different infusion lines: 2 infusion methods without PAR (1 gravity-fed infusion and 1 pump infusion), 2 extension lines to be connected to standard infusion devices to allow PAR, and 5 specific infusion sets allowing a PAR. 99mTc was compounded in 250 or 100 mL of 0.9% NaCl solution. From the continuous recording of drug concentrations at device outlets, the areas under the drug concentration-time curve (AUC) were computed and divided in 2 parts: the AUCadm corresponding to the administration phase and the AUCrin corresponding to the rinsing phase. Their comparison to the initial activity led to compute the drug delivery. Results between groups were compared using a Kruskal-Wallis test (P < 0.05). RESULTS: Using standard infusion devices leads to administer only 91% and 88% when the drug is diluted in 250 and 100 mL, respectively. During the administration phase with the extension lines connected to infusion sets, between 90.8 ± 6.9% and 94.2 ± 1.8% of the drug is infused for 250 mL dilutions and 87.7 ± 2.0% for 100 mL dilutions. For specific infusion sets, the proportion of infused drug varied between 88.6 ± 6.0% and 95.3 ± 1.5% for dilutions in 250 mL and 71.2 ± 3.1% and 90.4 ± 2.8% for dilutions in 100 mL. Rinsing the lines means the remaining drug is administered a rinsing volume ranging between 47.0 ± 6.6 and 92.2 ± 8.9 mL according to the device and drug dilution. CONCLUSIONS: This study shows that drug delivery may differ according to infusion line and dilution volume. Further study is required to assess the impact of these devices on pharmacokinetics.

Bubble Assemblies of Nanocrystals: Superlattices without a Substrate.

A method was developed to create free-standing nanocrystal films in the form of solidified bubbles. Bubbles of octadecanethiol-capped gold nanocrystals were studied by in situ grazing incidence small-angle X-ray scattering (GISAXS) to determine how the absence of an underlying substrate influences a disorder-order transition of a nanocrystal superlattice. We find that the presence of the substrate does not significantly change the nature of the disorder-order transition but does lead to reduced interparticle separation and reduced thermal expansion. Bubble assemblies of silicon and copper selenide nanocrystals are also demonstrated.

Nanocrystal superlattices that exhibit improved order on heating: an example of inverse melting?

Grazing incidence small angle X-ray scattering (GISAXS) measurements reveal that superlattices of 1.7 nm diameter, gold (Au) nanocrystals capped with octadecanethiol become significantly more ordered when heated to moderate temperatures (50-60 °C). This enhancement in order is reversible and the superlattice returns to its initially disordered structure when cooled back to room temperature. Disorder-order transition temperatures were estimated from the GISAXS data using the Hansen-Verlet criterion. Differential scanning calorimetry (DSC) measurements of the superlattices exhibited exotherms (associated with disordering during cooling) and endotherms (associated with ordering during heating) near the transition temperatures. The superlattice transition temperatures also correspond approximately to the melting and solidification points of octadecanethiol. Therefore, it appears that a change in capping ligand packing that occurs upon ligand melting underlies the structural transition of the superlattices. We liken the heat-induced ordering of the superlattices to an inverse melting transition.