Preparation and surface characterization of polymer nanoparticles designed for incorporation into hybrid materials

Fabrication and Characterization of Spectroscopically Encoded Core-shell Nanoparticle-polymer Nanocomposite

Metal nanoparticles are of great importance in the fabrication of new nanocomposite materials. One area of increasing interest is the application of metal nanoparticles (NP) as substrates for surface enhanced Raman scattering (SERS). In this regard, self-assembled monolayers (SAMs) of sulfur containing organic compounds are ideal target for SERS studies due to the strong affinity of sulfur for noble metals. Two types of molecules were synthesized for this study, an organic-soluble and a water-soluble styrene derivative. Self-assembling behaviors of these monomers on gold or silver nanostructured surfaces at room temperature were studied by UV-Vis spectroscopy, dynamic light scattering (DLS), SERS spectroscopy, and scanning electron microscopy (SEM). It was found that the interaction between sulfur compounds and metal NPs is strongly dependent on the NP size and the monomer environment. The hydrophilic NP surface switches to hydrophobic upon binding of sulfur-containing monomers, which leads to the formation of aggregates in aqueous solution for both water-soluble and oil-soluble monomers. The self-assembling behavior of these monomers on the metallic surface was compared with that of the corresponding homopolymers. Due to macromolecular and steric effects, the binding interaction between homopolymer and metal NP is weaker than that between NP and monomers. Surface polymerization of these monomers on metallic surfaces was observed as supported by SERS. Core-shell nanoparticles could also be obtained through seeded emulsion polymerization, but a decrease in SERS activity was observed.

Transmission electron microscope-induced structural evolution in amorphous Fe, Co, and Ni oxide nanoparticles

The high-energy electron beams in transmission electron microscopes (TEM) are known to cause structural changes and damage in some materials. In this paper, we describe unique and reproducible TEM-induced changes to the morphology of amorphous metal oxide (Fe, Co, and Ni) nanoparticles. The studied particles were synthesized via literature methods and fully characterized by X-ray powder diffraction and time-resolved, low-dose TEM. As a result of electron beam irradiation, we observe these particles to transform from initially solid spheres to core/void/shell structures and eventually to hollow nanoparticles. The rate of these transformations depends on the size and composition of the particles but is not unique to the Fe oxide we previously reported. These data suggest that structural analysis of nanoparticles by TEM must consider the impact of the high-energy electron beam and use low-dose imaging.

pH-Responsive polymers: synthesis, properties and applications

pH-Responsive polymers are systems whose solubility, volume, and chain conformation can be manipulated by changes in pH, co-solvent, and electrolytes. This review summarizes recent developments covering synthesis, physicochemical properties, and applications in various disciplines. A variety of synthetic methodologies comprising of emulsion polymerization and living radical polymerization techniques are described, and some of their salient features are highlighted. Several polymeric systems, such as homopolymers, block copolymers, microgels, hydrogels and polymer brushes at interfaces are reviewed, where important characteristics that govern their behavior in solutions are described. Potential applications of these systems in controlled drug delivery, personal and home care, industrial coatings, biological and membrane science, viscosity modifiers, colloid stabilization, and water remediation, are discussed.