Coated magnetite nanoparticles with a 6−8 nm average diameter were prepared. The surfactants used
to stabilize the nanoparticles and disperse them in organic solvents were oleic acid (OA), lauric acid ,
dodecyl phosphonate, hexadecyl phosphonate, and dihexadecyl phosphate. Transmission electron microscopy
analyses of the aggregation of the coated particles suggest that carboxylate surfactants provide the particles
with better isolation and dispersibility as compared with phosphonate surfactants. However, Fourier
transform infrared spectra of the phosphonate and phosphate coated particles suggest that these surfactants
cover the surface of the nanoparticles in islands of high packing density. The thermogravimetric and
differential scanning calorimetry measurements suggest that there is a quasi-bilayer of these surfactants
covering the surface of the nanoparticles, with varying amounts of surfactant in the outer layer and with
the second layer weakly bound to the primary layer through hydrophobic interactions between the alkyl
chains. The desorption temperatures of the alkyl phosphonates and phosphate are higher than those of
the carboxylate coated particles. The enthalpy of binding of the ligands suggests strong P−O−Fe bonding
on the surface. Nevertheless, regardless of binding strength, the OA coated particles are better dispersed
in organic solvents. Their higher hydrophobicity is likely due to different interactions among the oleyl
chains and/or a smaller tendency to form bilayer structures.
FTIR-ATR measurements permit detailed structural analysis and in situ titration of carboxylate-terminated self-assembled monolayers. Both monomeric and dimeric/oligomeric acid groups are seen, and their acid-base behavior is directly monitored. Monomers that are hydrogen bonded only to surrounding water molecules have a pKa = 4.9, while the pKa for the aggregated molecules is 9.3.
Liquid-phase deposition (LPD) from aqueous solution, under mild conditions of temperature (e55 °C) and pH (2.88-3.88), can produce thin (0.1-1.0 µm), adherent titania (TiO 2 ) films. This paper reports a systematic study of LPD TiO 2 films on variously prepared silicon wafer substrates, including (to our knowledge for the first time with LPD) several types of sulfonated surfaces (including sulfonated self-assembled monolayers and sulfonated polyelectrolyte multilayers). The growth rate and crystallinity of these films could be controlled by careful manipulation of solution parameters and surface functionality of the substrate.
Siloxane-anchored, self-assembled monolayers (SAMs) on single crystal Si were prepared with a variety of surface functional groups using a single commercially available surfactant (1-bromo-11-(trichlorosilyl)undecane) followed by in situ transformations. Polar (thioacetate and thiol), nonpolar (methyl), acidic (sulfonic and carboxylic), basic (various amines), and ionic (alkylammonium) surface functionalities were prepared. For primary amine and sulfonate surfaces, the degree of surface charge as a function of pH was determined ex situ using X-ray photoelectron spectroscopy (XPS). Sulfonate SAMs exhibited much higher effective pKa (approximately 2) than dilute sulfonic acid (-5 to -6), and amine SAMs exhibited much lower pKa (approximately 3) than dilute organic amines (approximately 10). This is attributed to the stabilization of nonionized groups by adjacent ionized groups in the SAM. Zeta potentials of these SAMs as a function of pH were consistent with the XPS results and indicated that ionizable SAM surfaces can generate surface potentials much higher than those of nonionic SAMs (thioacetate, methyl) and typical oxide surfaces.
A new low-modulus β Ti−Nb alloy with low elastic modulus and excellent corrosion resistance is
currently under consideration as a surgical implant material. The usefulness of such materials can be
dramatically enhanced if their surface structure and surface chemistry can be controlled. This control is
achieved in two stages. Electropolishing and anodic oxidation of the Ti45Nb alloy provide a surface
with a uniform oxide layer that is a mixture of TiO2 and Nb2O5. The impact of each of these two steps
on the morphology of the surface and on the thickness and chemistry of the oxide layer has been assessed.
In addition, as a first step toward controlling the surface chemistry of this material, a self-assembled
monolayer (SAM) based on hexadecylphosphonic acid (HDPA) is attached to the anodized surface. The
SAM is characterized based on its wetting properties and by Fourier transform infrared (FTIR) and X-ray
photoelectron spectroscopy (XPS) analysis. Using variable angle XPS analysis, detailed information is
obtained about the orientation and structure of the SAM, its thickness, and the chemistry of its interaction
with the metal oxide surface of the alloy. Further support for the creation of a true monolayer film is
obtained from FTIR measurements on a model oxide surface analogous to that of the alloy. This is the
first report of SAM attachment to this alloy and opens the possibility of monolayer control of its
biocompatibility.
Self-assembled monolayers (SAMs) bearing sulfonate (-SO3H) surface functional groups, on single-crystal Si wafers, were used as substrates for the deposition of TiO2 thin films from aqueous solutions. Polycrystalline TiO2 thin films over 50 nm thick formed in 2 h by hydrolysis of TiCl4 in aqueous HCI solutions at 80 °C. The films were pore-free, showed excellent adherence and uniformity, and consisted of anatase crystallites 2–4 nm in diameter. Annealing at temperatures up to 600 °C caused coarsening of the anatase grains, but no loss of adherence or structural integrity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.