Increase In Degree Of Ionization Research Articles

SURFACE PROPERTIES AND MICELLIZATION OF SODIUM ALKYLSULPHATES IN THE PRESENCE OF LOW-MOLECULAR ALCOHOLS

The process of micellization of sodium alkyl sulfates (SAS : sodium decyl- (SDS) and dodecylsulfate (SDDS)) of formation in aqueous solution without or with alcohols including propanol-1, propanol-2 and butanol-1 and their adsorption behavior at air-liquid interface were investigated with both the tensiometry and the conductometry at 298 K. The effect of chain length of alcohol on micellar and interfacial properties were discussed. Some parameters including surface excess concentration (Γmax), minimum area per surfactant molecule (Smin) at air-liquid interface, degree of ionization of micelle, and standard free energy of adsorption and micellization, etc. are estimated. It was experimentally established that the introduction of 0.5-1.0 mol/dm3 of alcohols into surfactant solutions contributes to the process of micellar formation of SAS and increases the stability of the micellar phase, as evidenced by the observed synergistic effect on the critical micelle concentration (CMC). The addition of different alcohols changes the values of Γmax, Smin, CMC of SDS and SDDS and induces an increase in degree of ionization (β) of micelle relative to that in pure water. When alcohols are introduced into SDS and SDDS solutions, the degree of ionization of micelles at a constant length of the alkyl radical of surfactant moderately increases with increasing alcohol content in the solution and ranges from 0.50-0.73 and 0.38-0.75, respectively. Also, the effect of alcohol was discussed. The obtained thermodynamic parameters were used to confirm these behaviors of interfacial adsorption or micellization. An increase in chain length of alcohol promotes the micellization process. The CMC values decrease with increasing length of the alkyl radical of alcohols. Propanol-1, compared to propanol-2, somewhat reduces the value of SDS and SDDS CMC to a greater extent. Standard free energy of micellization ∆G0mic, also confirms the micellization behavior. Standard free energy of adsorption (∆G0адс) indicates that an increase in the chain length of alcohol in aqueous solution is favorable to the adsorption of SDS and SDDS at air-liquid interface. A comparison of the values of the standard free energy of adsorption and micelle formation in sodium alkyl sulfates – alcohols – water systems showed that adsorption is the most thermodynamically advantageous process in the studies systems, and the packing of surfactant “molecules” in micelles is less dense, compared to packing in a mixed adsorption layer.

Chain conformation and dynamics in spin-assisted weak polyelectrolyte multilayers.

We report on the effect of the deposition technique on film layering, stability, and chain mobility in weak polyelectrolyte layer-by-layer (LbL) films. Ellipsometry and neutron reflectometry (NR) showed that shear forces arising during spin-assisted assembly lead to smaller amounts of adsorbed polyelectrolytes within LbL films, result in a higher degree of internal film order, and dramatically improve stability of assemblies in salt solutions as compared to dip-assisted LbL assemblies. The underlying flattening of polyelectrolyte chains in spin-assisted LbL films was also revealed as an increase in ionization degree of the assembled weak polyelectrolytes. As demonstrated by fluorescence recovery after photobleaching (FRAP), strong binding between spin-deposited polyelectrolytes results in a significant slowdown of chain diffusion in salt solutions as compared to dip-deposited films. Moreover, salt-induced chain intermixing in the direction perpendicular to the substrate is largely inhibited in spin-deposited films, resulting in only subdiffusional (<2 Å) chain displacements even after 200 h exposure to 1 M NaCl solutions. This persistence of polyelectrolyte layering has important ramifications for multistage drug delivery and optical applications of LbL assemblies.

Experimental study of unconfined surface wave discharges at atmospheric pressure by optical emission spectroscopy

A surface wave discharge (SWD) in argon at atmospheric pressure generated by a surfatron device was studied by optical emission spectroscopy (OES). Two distinct situations were investigated; (i) a discharge plasma in open air and (ii) a discharge plasma totally confined in a quartz tube. The electron density ne, electron temperature Te and gas temperature Tg were investigated as a function of applied power and gas flow rate. The self-absorbing method was used to estimate the population of the metastable state Ar(1s5). These physical quantities were determined through optical measurements along the plasma axis of symmetry. The profile of the electron density presented a maximum value under certain conditions, in contrast with typical electron density profiles of SWDs which are usually monotonically decreasing. A correlation between the electron density and the metastable state Ar(1s5) was found in one of these cases, suggesting that stepwise ionization from metastable states and non-local kinetics play an important role on the unexpected increase in ionization degree along the discharge.

Separation of the effects of pH and polymer concentration on the swelling pressure and elastic modulus of a pH-responsive hydrogel

The elastic shear modulus G and swelling pressure ω are studied for a basic, pH-responsive hydrogel synthesized by crosslinking copolymerization of co-monomers hydroxypropyl methacrylate and N, N-dimethylaminoethyl methacrylate with crosslinker tetraethylene glycol dimethacrylate. Under normal conditions of use as a “smart” material, hydrogel swelling ratio Q and pH vary simultaneously, but here G and ω values are presented as a function of pH with Q held constant and vice versa. At fixed pH, G decreases with increase in Q in a power law dependence, as predicted by the Flory–Rehner model. However, at fixed Q, G increases with decrease in pH (i.e., increase in degree of ionization). The pH effect is more pronounced than the volume effect, thus the hydrogel stiffens as it swells in response to pH change. At high pH, ω values of the uncharged hydrogel obey the Flory–Rehner model, whereas explicit ionic contributions can be identified at lower pH values.

The stellar content, metallicity and ionization structure of HII regions

Observations of infrared ne-structure lines provide direct information on the metallicity and ionization structure of H ii regions and indirectly on the hardness of the radiation eld ionizing these nebulae. We have an- alyzed a sample of Galactic and Magellanic Cloud H ii regions observed by the Infrared Space Observatory (ISO) to examine the interplay between stellar content, metallicity and the ionization structure of H ii regions. The observed (S iv) 10.5/(S iii) 18.7 ma nd (Neiii) 15.5/(Ne ii) 12.8 m line ratios are shown to be highly correlated over more than two orders of magnitude. We have compared the observed line ratios to the results of photoion- ization models using dierent stellar energy distributions. The derived characteristics of the ionizing star depend critically on the adopted stellar model as well as the (stellar) metallicity. We have compared the stellar eective temperatures derived from these model studies for a few well-studied H ii regions with published direct spec- troscopic determinations of the spectral type of the ionizing stars. This comparison supports our interpretation that stellar and nebular metallicity influences the observed infrared ionic line ratios. We can explain the observed increase in degree of ionization, as traced by the (S iv)/(S iii )a nd (Neiii)/(Ne ii) line ratios, by the hardening of the radiation eld due to the decrease of metallicity. The implications of our results for the determination of the ages of starbursts in starburst galaxies are assessed.