No abstract

the presence of a bi-refringent meiotic spindle in human oocytes by using the Polscope can predict a higher embryonic developmental competence. However, the relative position of the spindle within the oocyte doesn't appear to influence the developmental potential of embryos.

We report studies of reactive wetting employing droplets of a nonpolar liquid (decahydronaphthalene) on chemically patterned surfaces. The drops contain an n alkylamine that adsorbs onto surfaces exposing carboxylic acid groups and produces surfaces exposing methyl groups. The change in surface energy that occurs concurrent with the formation of an oriented monomolecular film of alkylamine during this process is sufficient to produce a self-propelled movement of decahydronaphthalene drops on the surface. We employed patterning to direct the movement of the drops on the surface, thereby allowing measurements of the relationships between the macroscopic fluidic behavior of the droplets and microscopic adsorption events. Specifically, we examined the effects of the unbalanced surface-tension force and the influences of adsorbate concentration on drop movement. In this latter case, both kinetic and thermodynamic arguments can be applied to describe the system. We compared the predictions from these two approaches by analyzing data from the present system and those reported by F. Domingues Dos Santos and T. Ondarcuhu [Phys. Rev. Lett. 75(16), 2972 (1975)] that exhibited opposite trends in behavior. The present analysis provides insight into the influence of chemical reaction kinetics on adsorption-mediated drop movement (i.e., reactive wetting).

We developed a new chemical strategy to enhance the stability of lead selenide nanocrystals (PbSe NCs) against oxidation through the surface passivation by P-O- moieties. In the synthesis of PbSe NCs, tris(diethylamino)phosphine (TDP) selenide (Se) was used as a Se precursor, and the resulting PbSe NCs withstood long-term air exposure while showing nearly no sign of oxidation. Nuclear magnetic resonance (NMR) spectroscopy reveals that TDP derivatives passivate the surface of PbSe NC. Through a series of ligand cleavage reactions, we found that the TDP derivatives are bound on NC surface through the P-O- moiety. Based on such understanding, it turned out that direct addition of various PAs during the synthesis of PbSe NCs also results in the NCs whose absorption spectrum remains nearly intact after air exposure for weeks. The P-O- moieties render the NCs stable in the operation of field effect transistors, suggesting that our findings can enable the use of air stable PbSe NCs in wider array of optoelectronic applications.

We report synthesis of PbSe nanorods (NRs) and PbSe/ CdSe axial heterojunction NRs via direct Cd-to-Pb cation exchange in CdSe NRs. Use of suited ligand−cation combinations enables the cation exchange while keeping the nanomaterial morphology intact. For example, solvation of Cd 2+ using oleylamine (OLA) allows for the cation exchange process, which would not be possible by using oleic acid instead of OLA. A mild cation exchange process, such as mixing Pb-oleate and OLA with CdSe NRs at 130 or 150°C, results in anisotropic replacement of CdSe into PbSe along the ⟨0001⟩ direction of wurtzite CdSe, and a partial conversion leads to the formation of heterostructure NRs containing axial CdSe/PbSe heterojunctions. While the cation exchange proceeds at both tips of CdSe NRs, exchange appears to be faster on (0001̅ ) planes. Binding energy calculation based on density functional theory reveals that OLA binds strongly to the (0001̅ ) facet of CdSe NRs, leading to asymmetric cation exchange. This protocol to convert CdSe nanocrystals directly into PbSe broadens the design range of CdSe/PbSe heterojunction nanomaterials potentially with various morphologies because template CdSe nanocrystals can be prepared in different shapes via colloidal synthesis.