Evolution of Surface Morphology of Spin-Coated Poly(methyl methacrylate) Thin Films.

The morphology of sub-micron poly(methyl methacrylate) films coated to glass supports by spin coating from toluene is examined using surface profilometry. Wrinkled surfaces with local quasi-sinusoidal periodicity were seen on the surfaces of films with thicknesses of larger than 75 nm. The surface wrinkles had large aspect ratios with wavelengths in the tens of microns and amplitudes in the tens of nanometers. Wrinkles that formed during spin-coating are attributed to surface perturbations caused by Rayleigh-Bénard-Marangoni convective instabilities. The effects of film thickness, coating solution concentration, and drying rate on the thin film surface morphology are investigated. The results can be used to prepare surfaces with controlled morphology, either smooth or with periodic wrinkles.

A new insight into the mechanism for cytosolic lipid droplet degradation in senescent leaves.

Leaf senescence involves lipid droplet (LD) degradation that produces toxic fatty acids, but little is known about how the toxic metabolites are isolated from the rest of the cellular components. Our ultramicroscopic characterization of cytosolic LD degradation in central vacuole-absent cells and central vacuole-containing cells of senescent watermelon leaves demonstrated two degradation pathways: the small vacuole-associated pathway and the central vacuole-associated pathway. This provided an insight into the subcellular mechanisms for the isolation of the fatty acids derived from LDs. The central vacuole-containing cells, including mesophyll cells and vascular parenchyma cells, adopted the central vacuole-associated pathway, indicated by the presence of LDs in the central vacuole, which is believed to play a crucial role in scavenging toxic metabolites. The central vacuole-absent intermediary cells, where senescence caused the occurrence of numerous small vacuoles, adopted the small vacuole-associated pathway, evidenced by the occurrence of LDs in the small vacuoles. The assembly of organelles, including LDs, small vacuoles, mitochondria and peroxisome-like organelles, occurred in the central vacuole-absent intermediary cell in response to leaf senescence.

Rhodamine 6G Structural Changes in Water/Ethanol Mixed Solvent.

In water rhodamine 6G (Rh6G) tends to form aggregates at higher concentrations while in ethanol the aggregation is minimal. The extent of aggregation can be controlled by changing the water to ethanol ratio. In ethanol the absorption spectra have a low energy peak and a higher energy shoulder, which are assigned to the S1 π-π* transition and vibronic side band, respectively, of Rh6G monomers. In water the same two peaks absorption peaks are observed at low concentrations but at higher concentrations a new peak grows in, which is assigned to an H-dimer. Emission spectra are in agreement with these assignments, but also develop a third peak at higher concentrations that is assigned to emission from excimer aggregates. For the first time, the monomer and dimer average diameters were measured by light scattering to be 1.4 ± 0.2 nm and 3.3 ± 0.6 nm, which form in the ground state, leading to the observed excited states. In a mixed solvent the extent of aggregation can be controlled by selecting the ethanol to water ratio, even at the highest concentrations. Graphical Abstract ᅟ.