Joy T. Kunjappu

In-situ investigation of adsorbed surfactants and polymers on solids in solution

Abstract Adsorption of monomeric and polymeric organic compounds onto solids is crucial in regulating such processes as flotation, flocculation and stabilization of minerals as well as other solids. The microstructure of the adsorbed species is of prime concern in understanding the complexities of the resultant processes. In this paper, we summarize the results of our recent investigation on the alumina-sodium dodecyl sulfate system by specially developed techniques based on time-resolved resonance Raman, electron spin resonance and luminescence spectroscopies to supplement the results from measurements of bulk properties such as adsorption density, zeta potential and hydrophobicity. Evidence is presented to substantiate the reverse orientation model. Furthermore, the implications of pH dependent conformational changes of polyelectrolytes in solution and in the adsorbed state are brought forth from fluorescence studies with pyrene-tagged polymers, and a model for the polymer conformational features is presented supported by flocculation response measurements.

A unique conformational equilibrium of polyacrylic acid at the solid/liquid interface

Abstract The adsorption of polyacrylic acid onto an alumina surface is shown using fluorescence spectroscopy to be followed by a rearrangement of its macromolecular segments in the adsorbed state. The adsorption of pyrene-labelled polyacrylic acid has been investigated from its solutions and from solutions mixed with unlabelled acid. The excimer efficiency of the emission of the pyrene-labelled polymer species indicates a pH-independent equilibrium conformation of adsorbed polymer chains. While the slow conformational rearrangement may not affect rapid flocculation processes, it could affect slow flocculation as well as deaggregation and reaggregation processes.

Tris(2,2′-bipyridyl)ruthenium(II) chloride as a probe of adsorption characteristic of sodium dodecyl sulfate on alumina

Abstract Analysis of steady-state luminescence emission of tris(2,2′-bipyridyl) ruthenium (II) chloride incorporated in the alumina-sodium dodecyl sulfate hemimicelles (more appropriately called as “solloids”) substantiates the reverse orientation model at high surface coverage suggested earlier to explain the surface aggregation process. The inadequacy of the bilayer model to account for the above process, especially in region II of the adsorption isotherm, is brought forth.

Enhancement and shifts in the excited-state resonance raman spectrum of Ru(bpy)32+ in anionic micelles

Abstract Excited-state resonance Raman and luminescence spectra of Ru(bpy) 3 2+ showed changes in frequencies and intensities in anionic micelles only. The data are interpreted in terms of the localization of the optical electron in a bipyridine ring that is some distance from the negative micellar surface.

Outlook for potential third-generation immersion fluids

In a search for alkane candidates for 193 nm immersion fluids, several alkanes and cycloalkanes were synthesized, purified and screened to ascertain their absorption at 193 nm, refractive index and temperature dispersion coefficient in the context of the actual application. In general, cycloalkanes, and more specifically polycycloalkanes, possess a higher refractive index than do linear alkanes. Decalin, cyclodecane, perhydrophenanthreme (PHP), perhydrofluorene (PHF) and perhydropyrene (PHPY) are examined as potential second and third generation immersion fluids. The use of perhydropyrene, which possesses a high refractive index of 1.7014 at 193 nm, may be limited as an immersion fluid because of high absorption at 193 nm. Mixtures of cycloalkanes can lead to a higher enhancement of the refractive index together with a decrease on the viscosity. Exhaustive purification of the fluids is a critical step in determining the real absorption of the different fluids at 193 nm. Two simple purification processes of these cycloalkanes were developed that led to low absorption fluids in the VUV region. The possibility of forming the oxygen complex in aerated fluids was reduced by purging samples with argon or nitrogen. This easy elimination of the oxygen complex shows the weak bonding nature of this complex.

Amplification of the index of refraction of aqueous immersion fluids with crown ethers

There is a current need for high refractive index RI materials that can be used in aqueous systems for improving 193-nm immersion photolithography. Although heavy metal salts such as Ca 2+ and Ba 2+ have the potential to substantially increase the RI of aqueous solutions, the water solubility of these salts with common anions is often too low to achieve concentrations that significantly increase the RI to the desired values. We therefore investigate the use of crown ethers to enhance the solubility of these cations. Most of crown ethers are soluble in water, are inexpensive materials, and are available commercially. 15-crown-5-ether and 12-crown-4-ether are liquids at room temperature and therefore can be used as neat immersion fluids without dilution in water. Saturation of crown ethers with inorganic salts do not lead to any increase in the refractive index due to their low solubility in such an apolar medium. Thus, the use of inorganic salts as refractive index enhancement agents does not seem to be a desirable proposition in the present case. Instead, the use of crown ethers or their derivatives can be an alternative system, since these compounds have properties such as density, viscosity, and boiling point similar to aqueous media.

Recent trends in bilayer formation of synthetic amphiphiles

The property of synthetic dialkyl amphiphiles to form vesicular structures can be exploited in a variety of situations, such as mimicking biological membranes, drug delivery, studies related to artificial photosynthesis, aggregates on solids, etc. The stability and thermotropic behavior of liposomes from natural lipids could be improved by synthetically modifying the alkyl chains of the lipids or by using totally synthetic structures. This article, which highlights the important milestones in the development of vesicular structures from synthetic amphiphiles, encompasses a brief description of investigations reporting the introduction of totally synthetic dialkyl amphiphiles, mixtures of monoalkyl cationic and anionic amphiphiles, hyperextended alkyl amphiphiles, and so on. Furthermore, most of the relevant work in the last decade relating to bilayer formation from synthetic amphiphiles is documented here.

Methods for the synthesis and purification of polycycloalkane candidates for photolithography immersion fluids at 193 nm: requirements for removal of oxygen

Cycloalkanes are candidates for immersion fluids because of their potential for low absorption in the 193-nm region and for a high refractive index RI. We have developed an empirical correlation be- tween refractive index and density of alkanes, which allows a prediction of the best candidates for immersion fluids based on the alkane struc- ture. In particular, the correlation reveals that polycycloalkanes such as perhydrophenanthrene PHPh and perhydrodropyrene PHPy, which have a higher RI than linear or cyclic alkanes, will be excellent candi- dates for immersion fluids at 193 nm. Therefore, PHPh and PHPy were synthesized by exhaustive hydrogenation of phenanthrene and pyrene. However, methods for the purification of the synthesized and commercial alkanes such as cyclodecane CYD, cyclohexane CYX, pentane PNT, and decalin DEC are required in order to determine the actual absorption of candidates at 193 nm. The presence of an absorbing im- purity at 193 nm can cause the premature elimination of otherwise ex- cellent potential candidates. A rather subtle impurity is molecular oxygen, which does not itself absorb at 193 nm, but which forms complexes with alkanes that do absorb at 193 nm. In this case, the impurity is readily eliminated by simple purging with nitrogen or argon gas.

Amplification of the index of refraction of aqueous immersion fluids with crown ethers: a progress report

There is a current need for high refractive index (RI) materials that can be used in aqueous systems for improving 193 nm immersion photolighography. Although heavy metal salts such as Ca2+ and Ba2+ have the potential to substantially increase the RI of aqueous solutions, the water solubility of these salts with common anions is often too low to achieve concentrations that significantly increase the RI to the desired values. We have therefore investigated the use of crown ethers to enhance the solubility of these cations. Most of the crown ethers are soluble in water, environmentally benign and commercial and inexpensive materials. Details of the preliminary studies on the proposed model system are presented in this paper. 15-crown-5-ether and 12-crown-4-ether are liquids at room temperature and therefore can be used as neat liquids as immersion fluids without dilution in water. Saturation of crown ethers with inorganic salts do not lead to any increase of the refractive index due to the low solubility of those in such an apolar media. Thus, the use of inorganic salt as refractive index enhancement agent does not seem to be a desirable proposition in the present case. Instead, the use of crown ethers or their derivates can be alternative system since these compounds have properties, such as density, viscosity and boiling point, similar to aqueous media.