Small Angle Neutron Scattering Studies on Viscoelastic Detergents

Abstract

Small angle neutron scattering experiments (SANS) on solutions of cetylpyridiniumsalicylate (CPS) in D2O over a large concentration range show a characteristic scattering maximum due to mutual interactions between the rodlike micelles. From the scattering rates structure factors S(Q), pair correlation functions g(r) and corresponding mean potentials W(r) are derived. Furthermore it is shown, that the length L of the scatterers decreases in a concentration range from 20 mM to 160 mM CPS. To study the influence of interaction on the rods, increasing amount of salt (NaCl and NaSal) was added to a 5 mM solution of CPS. As one would expect, the scattering maximum decreases, while the length of the micelles increases. It is shown, that the rods remain rather stiff when small amounts of salt are added. In the case of 32 mM NaCl it was also possible to fit the data with a persistence length model showing that the rods may become flexible when large amounts of salt are added. A persistence length of 8000 – 12000 Å was evaluated for these conditions.

Aqueous Two-Phase Systems of the Aqueous Mixtures of Cationic–Anionic Surfactants

“…The rheological properties of the oil-like phases of ASTP-A are very peculiar; it is obviously viscoelastic and trimethylammonium bromide-salicylic acid (CTAB-SA) are interpreted in terms of a network of overlapping rodlike negative thixotropic although its viscosity is low. Table 4 shows the apparent viscosity of the oil-like phase of ASTP-micelles (16)(17)(18). Therefore, we suggested that the upper phases of ASTP-C and the water-like phases of ASTP-A A, which shows that the solution is negative thixotropic.…”

Small-angle neutron scattering investigation of correlations in charged macromolecular and supramolecular solutions

“…of CPS in D20 at 298 K is 0"15 mM. Hoffmann, Kalus, Thurn & Ibel (1983) observed that the rod length of micelles continues to increase for CPS concentration c (mM) from the c.m.c, up to about c*= 10 mM, at which concentration the rod length begins to be equal to the interparticle spacing. We shall call c* the overlap concentration.…”

“…SANS intensity distributions of these saltfree micellar solutions show a strong correlation peak which indicates a high degree of nearest-neighbour ordering of the rods. Furthermore, by addition of NaC1 (0.5-32 mM) to a 5 mM solution of CPS, L can be increased to several thousand fingstr6m (Hoffmann, Kalus, Thurn & Ibel, 1983). In a brief report Hayter & Penfold (1984) described a SANS experiment with a mixed surfactant system SDS/TDPS (tetradecylpyridinium salicylate) in aqueous solutions.…”

Growth of linear charged micelles

“…(12) which converges for nonzero a. Equations (l), (7) and (15) lead to an anomalous growth law [13] (n + 1) log L = constant + ~/KQ (16) The effect of counterions condensing nonuniformly is remarkable: it changes the sign of eq. (10). This comes about because the effective elec-trostatic potential does not change along the understand.…”