Publisher's Note: Effect of the salt-induced micellar microstructure on the nonlinear shear flow behavior of ionic cetylpyridinium chloride surfactant solutions [Phys. Rev. E 95, 032603 (2017)].

This corrects the article DOI: 10.1103/PhysRevE.95.032603.

Effect of the salt-induced micellar microstructure on the nonlinear shear flow behavior of ionic cetylpyridinium chloride surfactant solutions.

The shear flow dynamics of linear and branched wormlike micellar systems based on cetylpyridinium chloride and sodium salicylate in brine solution is investigated through rheometric and scattering techniques. In particular, the flow and the structural flow response are explored via velocimetry measurements and rheological and rheometric small-angle neutron scattering (SANS) experiments, respectively. Although all micellar solutions display a similar shear thinning behavior in the nonlinear regime, the experimental results show that shear banding sets in only when the micelle contour length L[over ¯] is sufficiently long, independent of the nature of the micellar connections (either linear or branched micelles). Using rheometric SANS, we observe that the shear banding systems both show very similar orientational ordering as a function of Weissenberg number, while the short branched micelles manifest an unexpected increase of ordering at very low Weissenberg numbers. This suggests the presence of an additional flow-induced relaxation process that is peculiar for branched systems.

The role of the binding salt sodium salicylate in semidilute ionic cetylpyridinium chloride micellar solutions: a rheological and scattering study.

The micellar system based on cetylpyridinium chloride (CPyCl) and sodium salicylate (NaSal) in brine solution is investigated on both macro- and micro-length scales through rheology and scattering measurements. The linear viscoelasticity of the system and its structural parameters are explored by systematically changing the amount of NaSal over an extremely wide range of concentrations, thus producing salt-to-surfactant molar ratios from zero to about 8.5. As a result, the well-known non-monotonic behaviour of the zero-shear rate viscosity as a function of salinity can be connected to micellar morphological changes, whose driving force is represented by the simultaneous binding and screening actions of NaSal. The viscosity behaviour can be seen as a direct consequence of consecutive lengthening/shortening of the contour length, where the micelles attempt to minimize the electrostatic charge density on their surface. Along similar lines, the scattering measurements of the semidilute solutions show that the local stiffness of the micellar chain changes with increasing salt content influencing the elasticity of the resulting network. Within this general view, the branching of the micelles can be seen as a side effect attributable to the main character of the play, namely, the binding salt NaSal, whereas the overall dynamics of the system is driven by the considerable changes in the entanglement density of the micellar network.

Rheology-sensitive response of zeolite-supported anti-inflammatory drug systems.

Drug release from inorganic supports is a challenge for the scientific community for various reasons, related to the low costs of the systems and the possibility of easily regulating the drug release. In the present work, surface-modified zeolite particles are used as carriers for non steroidal antiflammatory drugs (NSAIDs). The release of the drug has been studied in a solution that simulates the intestinal fluid as well as in a gel-like system, based on a surfactant and a binding salt. In the solution case, the quantity of drug released has been tracked via spectrophotometric assay. Release in the gel has been monitored by rheological methods. The molecular conformation of the NSAIDs is fundamental for the interaction with the zeolite surface, whose modified surface has a strong binding energy. It has been proven that the main mechanism for the drug release is anion exchange. It has been found that the NSAIDs, used in their sodic form, can act as binding salts by themselves in the gel-like system, thus changing the viscoelastic response of the overall solution. Drug release kinetics in the solution compare quantitatively well with the released drug in the gel-like fluid, as measured by rheometry.

Series mechanism of enzyme deactivation. Characterization of intermediate forms.

Acid phosphatase (E.C. 3.1.3.2) undergoes complex thermal deactivation phenomena, as revealed by the two-slope pattern of the enzyme logarithmic-specific-activity versus time curves. The native enzyme first decays toward an equilibrium distribution of less, but still active, intermediate structures and these, in turn, undergo a final degradation to a completely inactive form. The effect of the experimental conditions at which the enzyme is kept during the deactivation process on the characteristics of these intermediate enzymatic structures has been investigated. The kinetic parameters of p-nitro-phenyl phosphate hydrolysis, as catalyzed by some of these intermediate forms, have been determined and the results compared to those obtained with the native enzyme.

Acid phosphatase deactivation by a series mechanism.

Acid phosphatase (E.C.3.1.3.2.) thermal deactivation at pH 3.77 has been investigated by monitoring the enzyme activity as a function of time in the hydrolysis of p-nitrophenyl phosphate. The experimental curves obtained show a two-slope behavior in a log (activity)versus-time plot, which indicates that deactivation occurs via a complex mechanism. From the dependence of the kinetic parameters on both deactivation and hydrolysis temperatures, it is inferred that the deactivation mechanism involves intermediate, temperature-dependent, less-active forms of the enzyme. This interpretation is confirmed by the results of additional tests in which the temperature was suddenly changed during the deactivation process.