The number of hydrated water molecules per poly(N-isopropylacrylamide) monomer unit in homogeneous aqueous solution was determined to be 11 exactly and anew below the lower critical solution temperature of 32 degrees C employing high-frequency dielectric relaxation techniques.

The factor governing the stability of micelles and hence controlling the rheological behavior of aqueous solutions of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (NaSal) was investigated.The solutions containing fully entangling threadlike micelles of CTAB-NaSal complexes may be modeled by a Maxwell model with a single relaxation time. Concentrations Cs* of free salicylate ions in the systems were estimated by carrying out XH NMR measurement on deuterium oxide solutions with varying CTAB (CD) and NaSal (Cs) concentrations. The results of NMR measurement suggested that the threadlike micelles existed in the form of a 1:1 complex between CTAB and NaSal. Thus, the relation Cs* = Cs -CD was obtained in the range Ds > CD. On the other hand, we confirmed that the relaxation time rm is influenced only by Cs* independently of Cd, and thus the factor controlling rm is Cg*. Furthermore, consideration on the basis of a quasi-network model led to an idea that the free salicylate ions are behaving as a catalyst for a disentangling reaction.

Viscoelastic properties of aqueous solutions of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (Nasal) were examined by varying the CTAB, CD, and Nasal, CS, concentrations. The results were compared with those of flexible-chain polymer solutions. With increasing salt-to-detergent ratio, C&D-l, up to a certain critical value close to 1 for the solutions of a given CD, the rheological behavior changed from that of low molecular weight polymer solutions in which the polymer chains are not entangling to behavior similar to that of high molecular weight polymer solutions in which polymer chains are fully entangling. These results suggest that threadlike micelles composed of CTAB/NaSal complexes began to form as C8Cp-l increased, resulting in an entanglement network exhibiting pronounced viscoelasticity. However, at high CSCD-~ above the critical value, their behavior can be represented by a Maxwell model with a constant plateau compliance JNO and a single relaxation time 7,. Interestingly, JNo waa proportional to CD-2.2 but independent of CSCD-', but the relaxation time 7 , decreased with increasing CSCD-l. The complex dependence of 7 , of all the solutions at high CSCD-~ may be reduced to a single composite function of CSC~-'/~. These results suggest that relaxation of the entanglement network took place by chemical processes involving actual breakdown and re-formation of the threadlike micelles.

The number of hydrated water molecules per N-isopropylacrylamide in homogeneous aqueous solution was determined to be a constant with a value of 5-6 below and above the lower critical solution temperature, LCST (32 degrees C), of its polymer, poly(N-isopropylacrylamide), by high-frequency dielectric relaxation techniques.

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The dynamic behaviors of ionic liquid samples consisting of a series of 1-alkyl-3-methylimidazolium cations and various counteranionic species are investigated systematically over a wide frequency range from 1 MHz to 20 GHz at room temperature using dielectric relaxation (DR) and nuclear magnetic resonance (NMR) spectroscopies. DR spectra for the ionic liquids are reasonably deconvoluted into two or three relaxation modes. The slowest relaxation times are strongly dependent upon sample viscosity and cation size, whereas the relaxation times of other modes are almost independent of these factors. We attribute the two slower relaxation modes to the rotational relaxation modes of the dipolar cations because the correlation times of the cations evaluated using longitudinal relaxation time (T(1) (13)C NMR) measurements corresponded to the dielectric relaxation times. On the other hand, the fastest relaxation mode is presumably related to the inter-ion motions of ion-pairs formed between cationic and anionic species. In the case of the ionic liquid bis(trifluoromethanesulfonyl)imide, the system shows marked dielectric relaxation behavior due to rotational motion of dipolar anionic species in addition to the relaxation modes attributed to the dipolar cations.

Viscoelastic properties were examined in aqueous solutions of cetyltrimethylammonium bromide (CTAB) complexed salicylic acid (HSal), coded as CTAB:HSal/W (W represents water), as a function of the detergent, CD, and acid, CA, concentrations. Effects of adding NaBr were also examined. The results were compared with those of CTAB:NaSal/W containing sodium salicylate (NaSal) instead of HSal. In the solutions of CD > 1.0 X 10~2 mol Lr1 and CACD-1 > 0.5, the CTAhHSal complex formed fully entangling threadlike micelles. NMR spectroscopy conducted on the D20 solutions with a similar range of CD and CA suggested that besides free HSal of concentration CA* existing in the aqueous medium, HSal molecules immobilized in the micelles appear to exist in at least two different states through complexation with CTA+. One is the state equivalent to that occupied by Sal" in CTAB:NaSal micelles, and the other is a more nonpolar environment.