: Long-chain alkanethiols, HS(CH2)nX, adsorb from solution onto gold surfaces and form ordered, oriented monolayer films. The properties of the interfaces between the films and liquids are largely independent of chain length when n > 10; in particular, wetting is not directly influenced by the proximity of the underlying gold substrate. The specific interaction of gold with sulfur and other soft nucleophiles and its low reactivity toward most hard acids and bases make it possible to vary the structure of the terminal group, X, widely and thus permit the introduction of a great range of functional groups into a surface. Studies of wettability of these monolayers, and of their composition using X-ray photoelectron spectroscopy (XPS), indicate that the monolayers are oriented with the tail group, X, exposed at the monolayer-air or monolayer- liquid interface. The adsorption of simple n-alkanethiols generates hydrophobic surfaces whose free energy (19 mJ/sq. m) is the lowest of any hydrocarbon surface studied to date. Measurement of contact angles is a useful tool for studying the structure and chemistry of the outermost few angstroms of a surface. This work used contact angles and optical ellipsometry to study the kinetics of adsorption of monolayer films and to examine the experimental conditions necessary for the formation of high-quality films.

/pdf/formation-of-monolayer-films-by-the-spontaneous-assembly-of-1pfzla949c.pdf

Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold

We have used the technique of static field induced second harmonic generation in liquids to determine the second order hyperpolarizability β, and the third order hyperpolarizability γ, for a wide range of conjugated and nonconjugated organic molecules. The adequacy of the Onsager local field formulation was tested as was the accuracy of the bond additivity approximation. The large π‐electron nonlinearities which are possible in substituted benzene molecules were investigated by measuring a large number of benzene derivatives and subtracting out the σ‐electron contributions.

Second and third order hyperpolarizabilities of organic molecules

Capacitance Transient Spectroscopy

The dielectric constant of interfacial water has been predicted to be smaller than that of bulk water (= 80) because the rotational freedom of water dipoles is expected to decrease near surfaces, yet experimental evidence is lacking. We report local capacitance measurements for water confined between two atomically-flat walls separated by various distances down to 1 nm. Our experiments reveal the presence of an interfacial layer with vanishingly small polarization such that its out-of-plane dielectric constant is only approximately 2. The electrically dead layer is found to be two to three molecules thick. These results provide much needed feedback for theories describing water-mediated surface interactions and behavior of interfacial water, and show a way to investigate the dielectric properties of other fluids and solids under extreme confinement.

/pdf/anomalously-low-dielectric-constant-of-confined-water-321x85m052.pdf

Anomalously low dielectric constant of confined water

Since the early 1970s, three major prerequisites have brought the success of the liquid crystal display (LCD) technology to its key role of today. Namely, the discovery of electro-optical field-effects on which the displays are based, the successful search for liquid crystals (LCs) with material properties that meet the complex requirements of electro-optical effects and render the effects applicable in displays, and last but not least, the development of the technological tools required for manufacturing displays. Virtually all of today’s commercial LCDs are based on the twisted nematic (TN) or on various supertwisted nematic (STN) effects whose extensive development and improvement over the past 25 years is still rapidly progressing. Those liquid crystal material properties and electro-optical effects that essentially determine the performance of nematic displays are reviewed. Correlations between molecular functional structural groups, LC material properties, and their electro-optical relevance for TN and STN displays are outlined. Included are dual-frequency addressing phenomena in liquid crystal materials, in situ dielectric heating of displays, and conductivity phenomena that are related and that may either hamper or improve the performance of high-information content LCDs. Moreover, we review some recent developments made in our laboratories on novel electro-optical devices and device-specific functional organic materials, e.g. optical alignment of monomeric and polymeric liquid crystals by linearly polarized light; the generation of photo-patterned multidomain twisted nematic displays with broad field of view; the operation of displays with circularly polarized light, as well as compact and bright cholesteric LCD projection optics whose polarizers, filters, and modulators are all based on liquid crystal elements.

http://web.mit.edu/daigohji/Public/342/LiqCrys_Mats_Displays_1997.pdf

Nora E. Hill

Papers

Dielectric properties and molecular behaviour