ABSTRACT
Solution studies have proposed that crystal nucleation can take more complex pathways than previously expected in classical nucleation theory, such as formation of prenucleation clusters or densified amorphous/liquid phases. These findings show that it is possible to separate fluctuations in the different order parameters governing crystal nucleation, that is, density and structure. However, a direct observation of the multipathways from aqueous solutions remains a great challenge because heterogeneous nucleation sites, such as container walls, can prevent these paths. Here, we demonstrate the existence of multiple pathways of nucleation in highly supersaturated aqueous KH2PO4 (KDP) solution using the combination of a containerless device (electrostatic levitation), and in situ micro-Raman and synchrotron X-ray scattering. Specifically, we find that, at an unprecedentedly deep level of supersaturation, a high-concentration KDP solution first transforms into a metastable crystal before reaching stability at room temperature. However, a low-concentration solution, with different local structures, directly transforms into the stable crystal phase. These apparent multiple pathways of crystallization depend on the degree of supersaturation.
ABSTRACT
We report an alternate light scattering approach to measure intermediate scattering function and structures of colloidal suspension by using two-pulse speckle contrast correlation analysis. By systematically controlling time-delays between two laser pulses incident on the sample, we are able to monitor transient evolution of coherent diffraction pattern, from which particle dynamics at different length and time scales are obtained simultaneously. Our result demonstrates the feasibility of utilizing a megapixel detector to achieve sufficient data statistics in a short amount of time while enabling microsecond time-resolution. Ultimately, this method provides means to measure high-speed dynamics well beyond the time response limit of a large area two-dimensional (2D) detector.
ABSTRACT
We studied CdSe Quantum dot-Liposome Complexes (QLCs), which are GUVs (Giant Unilamellar Vesicles) incorporated with quantum dots (QDs) loaded into the DOPC lipid bilayer. QLCs were prepared by employing the electroswelling method combined with spin coating techniques. Hexadecylamine (HDA) coated CdSe QDs of five different sizes from blue- (radius ~2.05 nm) to red-emission (~3.5 nm) were used to examine what size of QDs can be loaded into the DOPC lipid bilayer. Blue (radius ~2.05 nm), green (~2.25 nm), and yellow (~2.65 nm)-emission QDs were successfully inserted in the lipid bilayer. However, we did not observe any QLCs for the orange-emission QDs (~3.0-3.15 nm) and red-emission ones (~3.5 nm). This QD size dependence of the incorporation into the lipid bilayer is partly supporting the predictions in our published theoretical work. DOPC lipids showed a much smaller QLC yield than that of asolectin which is a mixture of many different kinds of lipids. Our model explains this large difference in the population qualitatively. The existence of QDs in the lipid bilayer at a nanometer scale was confirmed by employing laser-scanning confocal microscopy, Cryo-TEM, and negative staining and sectioning TEM.
Subject(s)
Lipid Bilayers/chemistry , Quantum Dots , Unilamellar Liposomes/chemistry , Amines/chemistry , Hydrocarbons , Liposomes/chemistry , Microscopy, Electron, TransmissionABSTRACT
We developed a statistical mechanical theory that describes the adsorption of nanoparticles (NPs) at liquid-vapor surfaces. This theory accounts for the surface to bulk NP thermodynamic equilibrium, as well as the NP mechanical equilibrium, wettability, and line tension at liquid-vapor surfaces. The theory is tested by examining the adsorption of 5 nm diameter dodecanethiol-ligated gold NPs at the liquid-vapor surface of a homologous series of n-alkane solvents, from n-nonane to n-octadecane, where the NP wettability decreases with an increasing n-alkane chain length.
