Microscopic composition maps of poly(styrene-co-2-hydroxyethyl methacrylate) colloidal crystals and interconnected colloidal arrays.

Colloidal crystalline films were prepared from poly(styrene-co-2-hydroxyethyl methacrylate) (PS-HEMA) latex particles by evaporative deposition. The hexagonally ordered surfaces of the colloidal crystals (CCs) were transformed with styrene vapor at room temperature to interconnected colloidal arrays (ICAs) that have a honeycomb-like ridge of polymer surrounding hexagonally ordered dimples in the surface. When the styrene vapor temperatures were increased systematically to 45 degrees C, the regularity of ICA structure decreased and finally disappeared. Images from transmission electron microscopy (TEM) and from atomic force microscopy (AFM) show that the surfaces of the PS-HEMA particles and the ICAs have raspberry textures. Monolayer CCs and ICAs fabricated on TEM grids were analyzed by energy dispersive spectroscopy (EDS) to determine the elemental compositions of the different regions of the textured surfaces. Carbon, oxygen, and sulfur were distributed all over the surface of the CC. While carbon was distributed over the entire surface of the ICA, oxygen, sulfur, sodium, and potassium were concentrated mainly on the ridges of the honeycomb and not in the dimples of the ICA. The results are discussed in terms of a mechanism of transformation of the CC to the ICA in which styrene monomer swells the polystyrene-rich regions of the particles, and the swollen polystyrene rises to the surface. The polyHEMA-rich regions of the particles maintain the hexagonal periodicity, and liquid styrene evaporates to leave a more polystyrene-rich textured surface.

Surface heterogeneity of polystyrene latex particles determined by dynamic force microscopy.

Atomic force microscopy (AFM) was employed to characterize the surface chemistry distribution on individual polystyrene latex particles. The particles were obtained by surfactant-free emulsion polymerization and contained hydrophilic quaternary ammonium chloride, sodium sulfonate, or hydroxyethyl groups. The phase shift in dynamic force mode AFM is sensitive to charge/chemical interactions between an oscillating atomic force microscope tip and a sample surface. In this work, the phase imaging technique distinguished phase domains of 50-100 nm on the surfaces of dried latex particles in ambient air. The domains are attributed to the separation of ion-rich and ion-poor components of the polymer on the particle surface.

Monitoring the transformation of colloidal crystals by styrene vapor using atomic force microscopy.

The stages of transformation of a colloidal crystalline film of latex spheres to a new periodic structure were imaged by atomic force microscopy. Colloidal crystalline films were prepared with 320 nm diameter poly(styrene-co-2-hydroxyethyl methacrylate) (PSt/HEMA) spheres. The hexagonally ordered surfaces of the colloidal crystalline films were transformed with styrene vapor at room temperature to a new morphology having holes in the surface and the same periodicity as the original films. The surfaces of colloidal crystals and the transformed films have a raspberry-like texture superposed on the 320 nm hexagonal periodicity. Both height images and phase images reveal that the latex spheres shrink and the transformation proceeds by an order-disorder-order sequence. The final structure is an interconnected colloidal array with smaller polystyrene particles dispersed in a continuous PSt/HEMA matrix.

Polymer brushes on single-walled carbon nanotubes by atom transfer radical polymerization of n-butyl methacrylate.

Polymer brushes with single-walled carbon nanotubes (SWNT) as backbones were synthesized by grafting n-butyl methacrylate (nBMA) from the ends and sidewalls of SWNT via atom transfer radical polymerization (ATRP). Carboxylic acid groups on SWNT were formed by nitric acid oxidation. The ATRP initiators were covalently attached to the SWNT by esterification of 2-hydroxyethyl 2'-bromopropionate with carboxylic acid groups. Methyl 2-bromopropionate (MBP) was added as free initiator during the brush preparation to control growth of the brushes and to monitor the polymerization kinetics. Size-exclusion chromatography (SEC) results show that the molecular weight of free poly(n-butyl methacrylate) (PnBMA) increased linearly with nBMA monomer conversion. PnBMA cleaved from the SWNT after high conversion had the same molecular weight as PnBMA produced in solution. Thermogravimetric analyses (TGA) show that the amount of PnBMA grown from the SWNT increased linearly with the molecular weight of the free PnBMA. The most highly PnBMA-functionalized SWNT dissolve in 1,2-dichlorobenzene, chloroform, and tetrahydrofuran, and solubility increases with the amount of PnBMA bound to SWNT. Near-infrared and Raman spectra indicate that the side walls of the SWNT were lightly functionalized by the nitric acid treatment and that the degree of functionalization of the SWNT did not change significantly during the formation of initiator or during the polymerization. Atomic force microscopy (AFM) images show contour lengths of the SWNT brushes on a mica surface from 200 nm to 2.0 microm and an average height of the backbone of 2-3 nm, indicating that the bundles of original SWNT were broken into individual tubes by functionalization and polymerization.