Isothermal calorimetric titrations of aqueous solutions of poly(ethylene glycol) (PEG) with sodium dodecyl sulfate (SDS) are known to exhibit a peculiar trend consisting of endothermic and exothermic effects. This behavior was explained with the formation of two different mixed micellar aggregates, one characterized by hydrophobic interactions and the second by ion-dipole association. Present NMR measurements on 13C, 1H, and 23Na nuclei do not support the formation of a number of PEG-SDS aggregates characterized by interactions of different nature. Our data are rather in accordance with the initial formation, at low surfactant concentration, of a polymer-surfactant aggregate in which the polymeric chain assumes a strained conformation in order to bind a small micellar cluster. The subsequent growing of the aggregate with increasing surfactant concentration allows the polymer to relax to a more expanded, energetically favored, conformation. Further calorimetric titrations with a set of PEG samples of different molecular weight (200 to 20000 Daltons) allowed to establish a few points so far unclear. The minimum molecular weights necessary for observing the onset and the settling, respectively, of polymer-surfactant interaction were identified and the characteristic multiple peak curve of the titration of the polymer with molecular weight of 8000 Dalton was found related to the discrete binding of two successive SDS micellar clusters on the same polymeric chain

In this work, a new procedure for the synthesis of the selectively deuterium-labeled chiral liquid crystal (+)-(S)-4-[4‘-(1-methylheptyloxy)] biphenyl 4-(10-undecenyloxy)benzoate (11EB1M7) has been developed, aimed to the study of its structure, orientational ordering, and dynamic behavior by means of 2H NMR. 11EB1M7 was investigated throughout its mesophasic range, formed by a very rich variety of chiral liquid crystalline phases including blue, cholesteric, TGBA*, and smectic C*. Two isotopomers were synthesized by labeling 11EB1M7 on either the phenyl or the biphenyl moiety of the mesogenic core. This allowed structural information (such as the tilt angle of the rigid fragments of the molecule and the angle between their para axes), orientational order parameters, and individual diffusional coefficients for the various overall and internal motions to be obtained from 2H NMR spectra and relaxation measurements by applying suitable data analyses based on several theoretical models.

In this work, two selectively deuterium-labeled isotopomers of the (S)-2-methylbutyl- [4'-(4' '-heptyloxyphenyl)-benzoyl-4-oxy-(S)-2-((S)-2')-benzoyl)-propionyl)]-propionate (ZLL 7/), one labeled on the phenyl ring (ZLL 7/-phe-D2) and the other one on the biphenyl fragment (ZLL 7/-biphe-D2), have been investigated by deuterium NMR (DNMR) spectroscopy and other experimental techniques. These compounds possess the paraelectric SmA, the ferroelectric SmC, the antiferroelectric SmC(A), the re-entrant ferroelectric SmC(re), and the ferroelectric hexatic phases down to room temperature. The orientational ordering properties of the two labeled fragments have been determined by means of DNMR, and the mesophase behavior at two magnetic fields is discussed. In particular, the effect of the magnetic field on the supramolecular structure of the SmC and SmC(re) phases is commented. This study revealed to be useful to understand the structural and conformational properties of the ferroelectric/antiferroelectric/re-entrant/hexatic smectic phases. Mesomorphic properties, spontaneous tilt angle, polarization, and layer spacing have been studied for the labeled materials and compared with those obtained for the nonlabeled compound. The two self-consistent set of data, from optical and DNMR measurements and X-ray results, allow us to associate at the transition from the SmC to the SmC(A) phase a change of the molecular conformation.

Orientational order properties of two fluorinated nematogens, exhibiting a wide nematic range, have been investigated by means of optical methods, dielectric spectroscopy, and 13C NMR. 13C NMR spectra have been recorded by 1H-SPINAL decoupling CP techniques under both static and magic angle spinning conditions. The order parameters of the fluorinated aromatic fragments have been calculated by analyzing the 13C−19F dipolar couplings at different levels of approximations by means of a least-squares fitting procedure using geometrical parameters determined by DFT methods, eventually including empirical corrections for vibrations and anisotropic scalar couplings. The nematic order parameters determined from optical birefringence data, dielectric anisotropy, and NMR have been compared:  their trends with temperature, analyzed by the Haller model and by more sophisticated ones, are very similar, even if the order parameters from optical birefringence are shifted to slightly higher values. The differences among the results obtained by the three methods can be related to the different anisotropic properties monitored, described by tensors whose principal or “long” axes can be located at slightly different places on the molecule. The assumptions and approximations used in each case are discussed in detail.

No abstract