The adhesive properties of pyridine-terminated self-assembled monolayers

The atomic force microscopy (AFM) adhesion force behaviour and contact angle titration behaviour of self-assembled monolayers (SAMs) presenting surface pyridine and substituted pyridine moieties has been investigated as a function of pH and electrolyte concentration. The pK(a)s of the pyridine moieties were modified through the incorporation of fluorine, chlorine and bromine substituents in the pyridyl ring. Contact angle titration and AFM adhesion force measurements were performed using aqueous phosphate buffered saline solutions over the pH range 3-9, and at concentrations of 150 mM and 0.1 mM. AFM adhesion force measurements were performed using a clean Si3N4 pyramidal-tipped AFM cantilever. (C) 2009 Elsevier B.V. All rights reserved

BioNanoAdhesion

The objective of this research was to investigate nanoscale adhesion in a number of scientifically interesting systems. To do this, self-assembled monolayers (SAMs) of alkanethiols and dialkyl disulfides have been formed on thermally evaporated gold films, presenting a variety of chemically modified surfaces. Adhesion studies involving atomic force microscopy (AFM), nanoparticles and living cells have been performed employing the SAMs. The wetting behaviour, elemental composition, thickness and surface topography of the SAMs were assessed. Only one of the SAM compounds was found to have not formed a SAM successfully. The compound contained a terminal quaternary pyridinium moiety, and it is believed the SAM formation was unsuccessful due to interaction between the iodide counterion and the gold surface. The contact angle titration behaviour of the SAMs was investigated over the pH range 3-9, employing aqueous buffer solutions at high and low electrolyte concentrations. It was found that both pH and electrolyte concentration had little or no effect on the contact angle titration behaviour of the SAMs. The effect of pH on the adhesion of poly(styrene) nanoparticles presenting a range COOH and NH2 surface chemistries was studied, using SAMs presenting CH3, COOH, OH, and pyridine moieties. Adhesion was generally found to decrease with increasing pH due to increased repulsive forces between surfaces. A range of surface morphologies for the adsorbed nanoparticles was observed. AFM adhesion measurements were performed in aqueous electrolyte solutions over the pH range 3-9, employing aqueous buffer solutions at high and low electrolyte concentrations. Adhesion was found to vary with both pH and electrolyte concentration, with the wetting behaviour of the surfaces, surface charge and contact area between surfaces affecting the measured forces. Finally, the settlement and adhesion of zoospores of the green alga Ulva linza and the diatom Navicula perminuta to eight of the SAMs, with SAM surface chemistry and SAM alkyl chain length the system variables. Adhesion was influenced by the surface chemistry and wetting behaviour of the SAMs. The adhesion of both organisms to methyl-terminated SAMs was found to decrease with increasing SAM alkyl chain length, which was attributed to changes in the phase state and tribology of the SAMs. The adhesion of Navicula perminuta to SAMs was also affected by the surface chemistry of the SAM

A model for nanoparticle gene delivery systems

The objective of this research was to investigate nanoscale adhesion in systems which mimic non-viral gene delivery vectors. Specifically, chemically modified substrates which presented polyanionic surfaces (mimicking DNA) and polycationic surfaces (mimicking a nanoparticle with which to adhere the DNA) were manufactured. To do this, self-assembled monolayers (SAMs) of alkanethiols and dialkyl disulfides have been formed on thermally evaporated gold films, presenting a variety of chemically modified surfaces. The wetting behaviour, elemental composition, thickness and surface topography of the SAMs were assessed. Only one of the SAM compounds was found to have not formed a SAM successfully. The compound contained a terminal quaternary pyridinium moiety, and it is believed the SAM formation was unsuccessful due to interaction between the iodide counterion and the gold surface. The contact angle titration behaviour of the SAMs was investigated over the pH range 3-9, employing aqueous buffer solutions at high and low electrolyte concentrations. It was found that both pH and electrolyte concentration had little or no effect on the contact angle titration behaviour of the SAMs

The first hexagonal columnar discotic liquid crystalline carbazole derivative

Restricted Access.The synthesis of two carbazole derivatives is described by a method in which one and three carbazole moieties are covalently attached to a hexa-alkoxytriphenylene core, respectively. The rst of these materials displays hexagonal columnar liquid crystalline behaviour when doped with trinitro uorenone, at room temperature, as con rmed by the mesophase textures viewed by optical polarizing microscopy and the results from diOEerential scanning calorimetry. These materials may have potential applications in the area of photorefractive materials

Design of potentially photorefractive liquid crystalline materials: Derivatives of 3,6-disubstituted carbazole

The incorporation of photorefractive molecular units, such as carbazole, into anisotropic materials (liquid crystals) may offer many advantages over conventional electrical poling of photorefractive polymers. Thus, a series of symmetric 3,6-disubstituted carbazole derivatives with a bent molecular shape have been synthesized and characterized. The influence of the nature of the symmetric substituents on the carbazole is investigated through comparison of crystal packing and electrostatic potentials