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A new and simplified version of the circuitry for the transient hot-wire method is presented. The circuitry provides a wide range of currents allowing probe wires of various diameters to be used in order to match the thermal properties of the specimen to be investigated. The analysis of the temperature increase during the heat pulse is based on the exact solution for a heated wire immersed in a medium. Data are corrected for varying power. The method was tested by computer simulations and by measurements of the thermal conductivity (λ) and the heat capacity per unit volume (ρcp ) of glycerol at room temperature and atmospheric pressure, and for CsCl and NaCl at room temperature and at pressures up to 2 GPa. The results on glycerol and CsCl are in excellent agreement with previous works. The inaccuracy in λ and ρcp is estimated as 1%–2% and 3%–5%, respectively, but the standard deviation of the measurements is as low as 0.2% for λ and 1% for ρcp. The improved procedure makes it possible to detect systematic errors caused by reflection of the heat pulse from the walls of the high-pressure cell. This error, which reveals itself by a curvature of the residual, defined as the difference between fitted function and data, was demonstrated in the case of NaCl. A theoretical estimate of the influence of perturbations due to reflection was also carried out and it was found that the error mainly affects the value of ρcp.

The molecular motion in water of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer with the nominal composition EO 97 PO 68 EO 97 (F127) was investigated with the aid of pulsed field gradient nuclear magnetic resonance (PFG NMR). The signal decays in the PFG experiments have been recorded for 1 wt % F127 in the temperature range from 288 to 313 K and in the concentration range 0.1-35 wt % at 298 K. Below the critical micellization temperature (cmt) or the critical micellization concentration (cmc), the PFG signal decays approximately linearly when the intensities are plotted on a logarithmic scale versus the experimentally relevant parameter. At the cmt or cmc, the signal decays are curved. The NMR data were processed using inverse Laplace transformation to obtain the distribution of self-diffusion coefficients, P(D). At 288 K for a 1 wt % solution, a narrow distribution was observed, while at 302 K a bimodal distribution was observed. This observation can be explained by the polydispersity of the polymer. It implies that, at a given temperature, only the more hydrophobic compound of F127 takes part in the aggregation process, while the more hydrophilic components diffuse as free nonassociated polymer. Increasing the temperature to 313 K resulted in a monomodal distribution, suggesting that all the polymers are aggregated. It is suggested that an ideal mixing model for the Pluronic micelles can explain the self-diffusion data. The NMR self-diffusion raw data were also analyzed with the COmponent REsolved (CORE; Stilbs, P.; Paulsen, K. ReV. Sci. Instrum. 1996, 67, 4380-4386) algorithm, resulting in spectra for free block copolymer and micellized block copolymer. With an increase in temperature, the intensity of the peaks for free block copolymer is reduced, whereas the intensity of the peaks for aggregated block copolymer increases. The ratios between the size of the PEO and PPO blocks (mEO/nPO) show a marked increase in free polymer compared to the ratio observed in micellized polymer when the temperature is increased. The effect of added salts to a 1 wt % F127 solution at 303 K was investigated to determine how the populations of free and micellized surfactant were changed on account of the ions present. Finally, the diffusion behavior of Pluronic F68 (EO 76 PO 29 EO 76 ) at 35 wt % has been investigated from 298 to 313 K. Both the diffusion time and the time of the gradient have been varied. The data show that the diffusion is Gaussian in the temperature range.

An extensive study of the diffusion behavior of the C〈 17 〉E〈 84 〉/water system is presented. The surfactant, when mixed with water, forms a micellar phase below ≈13 wt % and a cubic phase between ≈20−60 wt % (at 25 °C). In addition to the pulsed field gradient (PFG) NMR technique (used to determine the self-diffusion coefficients), the system has been investigated by small-angle X-ray scattering (SAXS), cryo-transmission electron microscopy (cryo-TEM), and time-resolved fluorescence quenching (TRFQ). The self-diffusion coefficient (D) and the transverse relaxation time (T 2) of the surfactant molecules decrease significantly when going from the micellar to the cubic phase. The results of the PFG NMR, SAXS, cryo-TEM, and TRFQ experiments show that the cubic phase is composed of discrete aggregates. On the basis of the rapid transverse 1H NMR relaxation in the cubic phase, it is argued that the micellar building blocks of the cubic phase are nonspherical. Furthermore, the SAXS data for four different concentrations of the surfactant (25, 35, 45, and 55 wt %) in the cubic phase can be indexed to the space group Im3m. If the data from the NMR and the SAXS measurements are combined, a lifetime of the surfactant monomers in the micelles of 8 and 7 ms was obtained at 25 and 35 wt % C〈 17 〉E〈 84 〉, respectively.

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