Simultaneous tailoring of surface topography and chemical structure for controlled wettability

Wettability was controlled in a rational manner by individually and simultaneously manipulating surface topography and surface chemical structure. The first stage of this research involved the adsorption of charged submicrometer polystyrene latex particles to oppositely charged poly(ethylene terephthalate) (PET) film samples to form surfaces with different topographies/roughness; adsorption time, solution pH, solution ionic strength, latex particle size, and substrate charge density are external variables that were controlled. The introduction of discrete functional groups to smooth and rough surfaces through organic transformations was carried out in the second stage. Amine groups (-NH(2)) and alcohol groups (-OH) were introduced onto smooth PET surfaces by amidation with poly(allylamine) and adsorption with poly(vinyl alcohol) (PVOH), respectively. On latex particle adsorbed surfaces, a thin layer of gold was evaporated first to prevent particle redistribution before chemical transformation. Reactions with functionalized thiols and adsorption with PVOH on patterned gold surfaces successfully enhanced surface hydrophobicity and hydrophilicity. Particle size and biomodal particle size distribution affect both hydrophobicity and hydrophilicity. A very hydrophobic surface exhibiting water contact angles of 150 degrees /126 degrees (theta(A)/theta(R)) prepared by adsorption of 1-octadecanethiol and a hydrophilic surface with water contact angles of 18 degrees /8 degrees (theta(A)/theta(R)) prepared by adsorption of PVOH were prepared on gold-coated surfaces containing both 0.35 and 0.1 microm latex particles. The combination of surface topography and surface-chemical functionality permits wettability control over a wide range.     

Latex Fractionation by Sedimentation and Colloidal Crystallization: The Case of Poly(styrene-co-acrylamide)

Poly(styrene-co-acrylamide) (PS-AAM) latex was prepared, fractionated by sedimentation under gravity, and characterized by PCS, infrared spectra, secondary and backscattered electron imaging in the scanning electron microscope, and electron spectroscopy imaging in an analytical transmission electron microscope. Three latex fractions were obtained. The lower fraction was opalescent and its particles were the more uniform, concerning size, chemical composition, and topochemical features. This lower fraction was still further fractionated by zonal centrifugation in a density gradient, yielding two fractions with similar macrocrystal-forming abilities but different sizes and chemical compositions. These results confirm those previously obtained for the PS-HEMA latex. Copyright 2000 Academic Press.     

Rotational spectroscopy and equilibrium structures of S3 and S4

The sulfur molecules thiozone S3 and tetrasulfur S4 have been observed in a supersonic molecular beam in the centimeter-wave band by Fourier transform microwave spectroscopy, and in the millimeter- and submillimeter-wave bands in a low-pressure glow discharge. For S3 over 150 rotational transitions between 10 and 458 GHz were measured, and for S4 a comparable number between 6 and 271 GHz. The spectrum of S3 is reproduced to within the measurement uncertainties by an asymmetric top Hamiltonian with three rotational and 12 centrifugal distortion constants; ten distortion constants, but an additional term to account for very small level shifts caused by interchange tunneling, are required to reproduce to comparable accuracy the spectrum of S4. Empirical equilibrium (r(e)(emp)) structures of S3 and S4 were derived from experimental rotational constants of the normal and sulfur-34 species and vibrational corrections from coupled-cluster theory calculations. Quantum chemical calculations show that interchange tunneling occurs because S4 automerizes through a transition state with D2h symmetry which lies about 500 cm(-1) above the two equivalent C2upsilon minima on the potential energy surface.     

On a question of Zhang

When studying the conjugacy class version of the Huppert’s ρ-σ conjecture, Jiping Zhang raised a number theory question. In this article, we provide examples to show that the question raised by Zhang is not always true in general.     

THE PECULIAR α-AMIDOALKYLATION OF VINYLTRIMETHYLSILANE

Abstract

α-Amidoalkylation of allyttrimethylsilane with methyl-2-chloro-2-(p-chlorobenzoylamino)-ethanoate 1 gave in the presence of Lewis acid racemic methyl-2- (p-chlorobenzoylamino)-4-penteno ate 2. Under the same conditions, vinlytrimethylsilane afforded (±)-trans-2-(p-chlorophenyl)-5,6-dihydro-4-methoxycarbonyl-6-trimethylsilyl-4H-1, 3-oxazine 4 as the major, by n.m.r. data and x-ray crystallography established product.