Charge-induced conformational changes of dendrimers

We study the effect of chargeable monomers on the conformation of dendrimers of low generation by computer simulations, employing bare Coulomb interactions. The presence of the latter leads to an increase in size of the dendrimer due to a combined effect of electrostatic repulsion and the presence of counterions within the dendrimer, and also enhances a shell-like structure for the monomers of different generations. In the resulting structures the bond-length between monomers, especially near the center, will increase to facilitate a more effective usage of space in the outer-regions of the dendrimer.Comment: 7 pages, 12 figure

The influence of tertiary butyl hydrazine as a co-reactant on the atomic layer deposition of silver

Ultra-thin conformal silver films are the focus of development for applications such as anti-microbial surfaces, optical components and electronic devices. In this study, metallic silver films have been deposited using direct liquid injection thermal atomic layer deposition (ALD) using (hfac)Ag(1,5-COD) ((hexafluoroacetylacetonato)silver(I)(1,5-cyclooctadiene)) as the metal source and tertiary butyl hydrazine (TBH) as a co-reactant. The process provides a 23 °C wide ‘self-limiting’ ALD temperature window between 105 and 128 °C, which is significantly wider than is achievable using alcohol as a co-reactant. A mass deposition rate of ∼20 ng/cm2/cycle (∼0.18 Å/cycle) is observed under self-limiting growth conditions. The resulting films are crystalline metallic silver with a near planar film-like morphology which are electrically conductive. By extending the temperature range of the ALD window by the use of TBH as a co-reactant, it is envisaged that the process will be exploitable in a range of new low temperature applications

A modified box model including charge regulation for protein adsorption in a spherical polyelectrolyte brush

Recent experiments showed significant adsorption of bovine serum albumin (BSA) in spherical polyelectrolyte brushes (SPB) consisting of polyacrylic acid, even for pH values above the isoelectric point of the protein, when both protein and polyion are negatively charged. To describe these experimental findings theoretically, we have constructed a spherical box model for an annealed brush consisting of a weak polyelectrolyte that includes the adsorption of BSA. At equilibrium the chemical potential of BSA in solution equals that at each location in the brush, while the net force on the polyions (including osmotic, stretching, and excluded volume terms) is zero at each location. Protein adsorption is predicted above the isoelectric point and -in agreement with experimental data- is a strong function of ionic strength and pH. Adsorption of protein in the brush is possible because the pH in the brush is below the isoelectric point and protein reverses its charge from negative to positive when it adsorbs

Photo-gravures of Niagara Falls. --

On cover: Niagara Falls

Spherical Polymer Brushes

This chapter is devoted to spherical polymer brush particles bearing a densely packed layer of polymer chains on their surface, which exhibit well defined core shell morphologies. The survey on recent experimental and theoretical developments has demonstrated that spherical polymer brushes present a number of fundamental questions of high interest. In this review we have discussed, by drawing on selected examples of recent research, how spherical polymer brushes are paving the way from synthesis of designed system, characterization to advanced applications. Special attention has been paid to future perspectives of polymer brushes grafted to spherical supports that go beyond simple stabilization of particles through a surrounding brush layer. Possible applications, such as for the preparation of catalytically active metal nanoparticles and the immobilization of proteins, have been discussed in full detail. All results herein demonstrate that such particles may serve as carriers for catalytically active nanostructures, namely for metal nanoparticles and enzymes. In addition, applications in other fields including smart stabilizers for emulsions and as novel retention aids in papermaking industry have been discussed as well. Here interesting developments in nanotechnology are to be expected which make use of the strong responsiveness of the surface layer under external trigger

Nanoparticle assembly by confinement in wrinkles: Experiment and simulations

We created hierarchically ordered structures of nanoparticles on smooth planar hydrophilic substrates by drying colloidal dispersions in confinement under macroscopic stamps with microscopically wrinkled surfaces. Experiments were carried out with model nanoparticle suspensions that possess high colloidal stability and monodispersity. The structures ranged from single parallel lines of particles to arrays of dense prismatic ridges. The type of observed structure could be controlled by the particle concentration in the initial dispersion. Confinement between two crossed stamps led to interconnected meshes of particles. The precise morphology could be predicted in all cases by Monte Carlo computer simulations of confined hard spheres. Our findings open up possibilities for versatile nanoparticle assembly on surfaces. © 2010 The Royal Society of Chemistry