Chemical analysis and aqueous solution properties of Charged Amphiphilic Block Copolymers PBA-b-PAA synthesized by MADIX

We have linked the structural and dynamic properties in aqueous solution of amphiphilic charged diblock copolymers poly(butyl acrylate)-b-poly(acrylic acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the physico-chemical characteristics of the samples. Despite product imperfections, the samples self-assemble in melt and aqueous solutions as predicted by monodisperse microphase separation theory. However, the PBA core are abnormally large; the swelling of PBA cores is not due to AA (the Flory parameter chiPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA homopolymers (content determined by Liquid Chromatography at the Point of Exclusion and Adsorption Transition LC-PEAT). Beside the dominant population of micelles detected by scattering experiments, capillary electrophoresis CE analysis permitted detection of two other populations, one of h-PAA, and the other of free PBA-b-PAA chains, that have very short PBA blocks and never self-assemble. Despite the presence of these free unimers, the self-assembly in solution was found out of equilibrium: the aggregation state is history dependant and no unimer exchange between micelles occurs over months (time-evolution SANS). The high PBA/water interfacial tension, measured at 20 mN/m, prohibits unimer exchange between micelles. PBA-b-PAA solution systems are neither at thermal equilibrium nor completely frozen systems: internal fractionation of individual aggregates can occur.Comment: 32 pages, 16 figures and 4 tables submitted to Journal of Interface and Colloidal Scienc

Adsorption of mono- and multivalent cat- and anions on DNA molecules

Adsorption of monovalent and multivalent cat- and anions on a deoxyribose nucleic acid (DNA) molecule from a salt solution is investigated by computer simulation. The ions are modelled as charged hard spheres, the DNA molecule as a point charge pattern following the double-helical phosphate strands. The geometrical shape of the DNA molecules is modelled on different levels ranging from a simple cylindrical shape to structured models which include the major and minor grooves between the phosphate strands. The densities of the ions adsorbed on the phosphate strands, in the major and in the minor grooves are calculated. First, we find that the adsorption pattern on the DNA surface depends strongly on its geometrical shape: counterions adsorb preferentially along the phosphate strands for a cylindrical model shape, but in the minor groove for a geometrically structured model. Second, we find that an addition of monovalent salt ions results in an increase of the charge density in the minor groove while the total charge density of ions adsorbed in the major groove stays unchanged. The adsorbed ion densities are highly structured along the minor groove while they are almost smeared along the major groove. Furthermore, for a fixed amount of added salt, the major groove cationic charge is independent on the counterion valency. For increasing salt concentration the major groove is neutralized while the total charge adsorbed in the minor groove is constant. DNA overcharging is detected for multivalent salt. Simulations for a larger ion radii, which mimic the effect of the ion hydration, indicate an increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure

Quantitative In Situ Attenuated Total Internal Reflection Fourier Transform Infrared Study of the Isotherms of Poly(sodium 4-styrene sulfonate) Adsorption to a TiO2 Surface over a Range of Cetylpyridinium Bromide Monohydrate Concentration

Quantitative in situ attenuated total internal reflection Fourier transform infrared (ATR FTIR) spectroscopy has been used to study the isotherm of poly(sodium 4-styrene sulfonate), PSS, adsorption to a TiO2 surface in aqueous solution at a pH of 3.5. The effect of adding surfactant cetylpyridinium bromide monohydrate (CPBM) on the adsorption isotherm of PSS was investigated at CPBM concentrations of 3.60 × 10−7, 1.02 × 10−5, and 1.04 × 10−4 M. The use of in situ ATR FTIR allowed for the calculation of the concentration of both PSS and CPBM at the TiO2/water interface over the entire course of all experiments. It was found that the addition of a small amount of CPBM, 3.60 × 10−7 M, to PSS solutions resulted in 23 ± 3% less PSS accumulating at the TiO2/water interface compared to isotherm studies with no CPBM present. The mole ratio of CPBM to PSS varies from 4 ± 1 to 1 to 20 ± 4 to 1 in a stepwise manner as the solution concentration of PSS is increased for solutions with a CPBM concentration of 3.60 × 10−7. The addition of CPBM at concentrations of 1.02 × 10−5 and 1.04 × 10−4 M showed distinct differences in the behavior of the PSS isotherm, but at the highest solution PSS concentrations, the amount of PSS at the TiO2/water interface compared to that of PSS solutions with no CPBM added is indistinguishable within the experimental uncertainties. For these higher concentrations of CPBM, both PSS and CPBM appear to come to the TiO2 surface as aggregates and the mole ratio of CPBM to PSS at the TiO2/water interface decreases as the concentration of PSS is increased. For a CPBM concentration of 1.02 × 10−5 M, the mole ratio of CPBM to PSS changes from 139 ± 29 to 1 to 33 ± 7 to 1 as the solution PSS concentration is increased. For a CPBM concentration of 1.04 × 10−4 M, the mole ratio of CPBM to PSS changes from 630 ± 130 to 1 to 110 ± 21 to 1 as the solution PSS concentration is increased. Despite the large differences in the CPBM to PSS mole ratios, the amount of PSS that adsorbs to the surface is statistically indistinguishable for CPBM concentrations of 0, 1.02 × 10−5, and 1.04 × 10−4 M, indicating that the structure of the PSS molecules in each of the systems does not significantly change in the presence of CPBM

Self-assembly of alkali-soluble [60]fullerene containing poly(methacrylic acid) in aqueous solution

Well-defined stimuli-responsive alkali-soluble poly(methacrylic acid)-block-[60]fullerene (PMAA-b60) was synthesized via atom transfer radical polymerization (ATRP), and its aggregation behavior in aqueous solution was examined using potentiometric and conductometric titrations, static and dynamic light scattering, and transmission electron microscopic (TEM) techniques. PMAA-b-C60 shows pH-responsive and water-soluble properties at high pH. In dilute solution, the micelles and large secondary aggregates, which are independent of polymer concentration, coexist in solution. The Rh of micelles increases from 6 to 10 nm with increasing degree of neutralization and remains constant at 10 nm with the addition of salt. However, the Rh, of large aggregates increases from 91 to 153 nm with increasing degree of neutralization and decreases from 153 to 105 nm with increasing NaCl concentration. TEM studies revealed that the large aggregates comprise of individual micelles and possess microstructure similar to large compound micelles (LCM).Palaniswamy Ravi, Sheng Dai, Chung How Tan and Kam Chiu Ta