The adsorption kinetics and adsorption isotherm of a polystyrene (PS)-poly(ethy1ene oxide) (PEO) diblock copolymer onto a silicon wafer from toluene solution was measured in situ by ellipsometry. Both blocks are in good solvent conditions but the small PEO block is adsorbed while the much larger PS block dangles in solution. Thus, PS-PEO behaves like an end-adsorbed chain. The adsorption kinetics shows two processes on a clearly seperated time scale. In the beginning, the time behavior of the adsorbed amount can be described as a diffusion-controlled process leading to a surface coverage with small interaction between molecules. A still denser surface coverage is achieved by the penetration of chains through the existing monolayer combined with the conformational rearrangement to a more brushy conformation. Experiments with different molecular weights indicate that the repulsion between the nonadsorbing PS blocks determines the maximal adsorbed amount. The adsorbed monolayer can be rapidly and completely displaced by PEO oligomer with a length comparable to the PEO block in the block copolymer. Models of the adsorption process are discussed in detail.

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A surface with photocontrollable wetting behavior is introduced. A monolayer of a polymeric material containing 4‘-[trifluormethoxy-4,4‘-dibenzoazo] dyes in the side chains has been transferred on quartz slides and silicon wafer. The azobenzene chromophore possesses two distinct isomers, cis and trans. Transition between these states can be triggered by illumination with light of two different wavelengths. It will be demonstrated that with the use of light and a mask, fine cis−trans patterns on the order of micrometers can be written in the monolayer. The corresponding interface exhibits different wetting behavior. This is visualized by a surface decoration with water droplets. The formation of water microdroplets on the patterned monolayer can be controlled by light. Writing and erasing of patterns is completely reversible. The system has potential for studying wetting behavior on microstructured surfaces.

A versatile modular setup is described which incorporates ellipsometry, surface plasmon spectroscopy, waveguide modes, their corresponding imaging techniques and Brewster angle microscopy in a single instrument. The important design criteria are discussed with special emphasis given to the requirements imposed by imaging under an oblique angle of incidence. Several experimental examples demonstrate the power of the instrument. Imaging nullellipsometry of a patterned monolayer on a highly reflecting support demonstrates a lateral resolution of approximately 1 μm and an accuracy in the thickness determination in the sub-nm region. The localization of the evanescent field of a surface plasmon was exploited to characterize adsorption layers in turbid and thus highly scattering solutions. An example of how an anisotropic sample can be characterized with the aid of waveguide modes is provided.

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We have compared the structural and photoisomerization properties of self-assembled monolayers (SAMs) comprising either the trans or cis isomers of azobenzene terminated dithiolane with in-chain amide unit, viz., 4-(phenyldiazenyl)phenyl-4-(1,2-dithiolane-3-yl)-butylcarboxamide ( 1). These films were prepared on Au(111) from solutions of both isomers. Structure and composition of the SAMs were studied by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The photoresponse of the films was monitored in real time by ellipsometry. SAMs fabricated from the trans isomer were found to be densely packed and highly ordered. These films did not show any discernible photoresponse upon irradiation with UV light, which, under favorable conditions, triggers the trans- cis isomerization. In contrast, films prepared from solutions containing predominantly the cis isomer were loosely packed and mostly disordered but exhibited reversible photoreactivity. The results confirm that steric effects, i.e., available free volume, play a dominant role for the photoresponse of aliphatic SAMs bearing the photoactive azobenzene group. The crystal structure of 1 ( trans isomer) exhibits a row-like aggregation of neighboring molecules by weak hydrogen bonds and can be taken as a model for the arrangement of 1 in the monolayer films. Further, in addition to the surface coordination behavior, we have also mimicked the chemisorption of the 1,2-dithiolane moiety onto the gold substrate in molecular coordination chemistry in oxidative addition reactions with the zero-valent platinum complex [Pt(PPh 3) 4].

Thiocyanate (SCN(-)) is a highly chaotropic anion of considerable biological significance, which interacts quite strongly with lipid interfaces. In most cases it is not exactly known if this interaction involves direct binding to lipid groups, or some type of indirect association or partitioning. Since thiocyanate is a linear ion, with a considerable dipole moment and nonspherical polarizability tensor, one should also consider its capability to adopt different or preferential orientations at lipid interfaces. In the present work, the interaction of thiocyanate anions with zwitterionic phospholipid monolayers in the liquid expanded (LE) phase is examined using surface pressure-area per molecule (pi-A(L)) isotherms and vibrational sum frequency generation (VSFG) spectroscopy. Both dipalmitoyl phosphatidylcholine (DPPC) and dimyristoyl phosphatidylethanolamine (DMPE) lipids, which form stable monolayers, have been used in this investigation, since their headgroups may be expected to interact with the electrolyte solution in different ways. The pi-A(L) isotherms of both lipids indicate a strong expansion of the monolayers when in contact with SCN(-) solutions. From the C-H stretch region of the VSFG spectra it can be deduced that the presence of the anion perturbs the conformation of the lipid chains significantly. The interfacial water structure is also perturbed in a complex way. Two distinct thiocyanate populations are detected in the CN stretch spectral region, proving that SCN(-) associates with zwitterionic phospholipids. Although this is a preliminary investigation of this complex system and more work is necessary to clarify certain points made in the discussion, a potential identification of the two SCN(-) populations and a molecular-level explanation for the observed effects of the SCN(-) on the VSFG spectra of the lipids is provided.