Freezing and melting of H 2 O and D 2 O in the cylindrical pores of well-characterized MCM-41 silica materials (pore diameters from 2.5 to 4.4 nm) was studied by differential scanning calorimetry (DSC) and 1 H NMR cryoporometry. Well-resolved DSC melting and freezing peaks were obtained for pore diameters down to 3.0 nm, but not in 2.5 nm pores. The pore size dependence of the melting point depression DT m can be represented by the Gibbs-Thomson equation when the existence of a layer of nonfreezing water at the pore walls is taken into account. The DSC measurements also show that the hysteresis connected with the phase transition, and the melting enthalpy of water in the pores, both vanish near a pore diameter D* E 2.8 nm. It is concluded that D* represents a lower limit for firstorder melting/freezing in the pores. The NMR spin echo measurements show that a transition from low to high mobility of water molecules takes place in all MCM-41 materials, including the one with 2.5 nm pores, but the transition revealed by NMR occurs at a higher temperature than indicated by the DSC melting peaks. The disagreement between the NMR and DSC transition temperatures becomes more pronounced as the pore size decreases. This is attributed to the fact that with decreasing pore size an increasing fraction of the water molecules is situated in the first and second molecular layers next to the pore wall, and these molecules have slower dynamics than the molecules in the core of the pore.

Using a benchtop NMR spectrometer, we performed proton multiple-quantum NMR experiments to study the dynamics of well-entangled linear poly(butadiene), poly(isoprene), and poly(dimethylsiloxane) in a broad molecular weight range. The method provides a direct time-domain measurement of the segmental orientation autocorrelation function over many decades, based on time-temperature superposition. The function can be directly compared to theoretical predictions based on the tube model, and the Rouse and the disentanglement times can be evaluated relative to the known entanglement time. We obtain universal results for all three polymers when plotted against the molecular weight normalized by the entanglement molecular weight, with the familiar mass scaling exponents of 2.0 ( 0.2 and 3.2 ( 0.2, respectively. However, the time scaling exponent derived for motions in the constrained-Rouse regime II is not constant at the predicted value of -1/4 but is always larger and also a universal function of molecular weight. This observation was previously explained by constraint-release effects that are active at surprisingly short times and at local scales. We further discuss observations related to contour-length fluctuations, leading to an isotropically mobile fraction of segments that can also be quantified by our method.

We use a benchtop NMR technique to monitor entangled polymer melt dynamics over 5 decades in time covering regimes II-IV of the tube model. We confirm the familiar molar mass scaling exponents of the regime transitions, but we observe a mass-dependent time scaling exponent describing segmental fluctuations in the constrained-Rouse regime II up to high molecular weights. Local chain motions are thus governed by modes that are much less restricted than predicted by the tube model. Diluting protonated chains in deuterated invisible matrix chains, we prove that the exponent is determined by the matrix molecular weight, suggesting constraint-release effects as the origin.

The solvation of CO(2) in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been investigated by (1)H, (13)C, and (15)N NMR spectroscopy at low CO(2) molar fraction (mf) (x(CO(2)) ca. 0.27) corresponding to the reactive regime described in part 1 of this study. It is shown that a carboxylation reaction occurs between CO(2) and Bmim Ac, leading to the formation of a non-negligible amount (~16%) of 1-butyl-3-methylimidazolium-2-carboxylate. It is also found that acetic acid molecules are produced during this reaction and tend to form with elapsed time stable cyclic dimers existing in pure acid. A further series of experiments has been dedicated to characterize the influence of water traces on the carboxylation reaction. It is found that water, even at high ratio (0.15 mf), does not hamper the formation of the carboxylate species but lead to the formation of byproduct involving CO(2). The evolution with temperature of the resonance lines associated with the products of the reactions confirms that they have a different origin. The main byproduct has been assigned to bicarbonate. All these results confirm the existence of a reactive regime in the CO(2)-Bmim Ac system but different from that reported in the literature on the formation of a reversible molecular complex possibly accompanied by a minor chemical reaction. Finally, the reactive scheme interpreting the carboxylation reaction and the formation of acetic acid proposed in the literature is discussed. We found that the triggering of the carboxylation reaction is necessarily connected with the introduction of carbon dioxide in the IL. We argue that a more refined scheme is still needed to understand in details the different steps of the chemical reaction in the dense phase.

The formation of 1-butyl-3-methylimidazolium-2-carboxylate in the mixture of CO(2) with 1-butyl-3-methylimidazolium acetate under mild conditions (298 K, 0.1 MPa) has been put in evidence in the liquid phase using Raman and infrared spectroscopy complemented by DFT calculations and NMR ((1)H, (13)C, (15)N) spectroscopy.