Orientational Order and Dynamics of Nematic Multipodes Based on Carbosilazane Cores Using Optical and Dielectric Spectroscopy

Abstract

The birefringence, refractive indices, and dielectric measurements have been carried out for the double- and triple-branched multipodes based on the carbosilazane cores. The orientational order parameters have been obtained using both the optical and the dielectric measurements. The dielectric response is identified to arise from the dipoles of the carboxyl and the alkoxy groups in the ortho position of the benzene ring. Results are analyzed in the framework of the mean-field theory. At least three molecular modes are resolved in the dielectric relaxation spectra in the nematic phase. The lower frequency process is retarded, and the other two processes are accelerated significantly with respect to the relaxation rate in the isotropic phase. The acceleration effect is even much stronger than the retardation effect. The acceleration factors are also found to be much higher than those for the low molar mass nematic liquid crystals. These results show that the anisotropy of the macromolecule plays a significant role in determining the nematic potential which governs the relaxation dynamics. The results on the relaxation dynamics show that the mesogens are decoupled from the core of the macromolecules.

Self- or Induced Organization of [60]Fullerene Hexakisadducts

“…The design and selection of the molecular building blocks to reach nematic orderings close to or just above room temperature is challenging as shown in the literature reporting systems containing multivalent cores ranging from soft and flexible such as carbosilazane [86][87][88], siloxane [89][90][91][92], and silsesquioxane [93][94][95][96][97][98], to hard such as gold nanoparticles [99][100][101][102][103][104][105][106][107][108][109]. These systems are technologically relevant too, as the nematic phase allows often the control of the macroscopic alignment in thin films, important for potential technological applications.…”

Colloidal soft matter as drug delivery system

“…Finally other techniques can be successfully applied: rheology is used to monitor the intrinsic viscosity variation,385, 386 DSC detects glass transition temperature, which depends on the molecular weight, entanglement and chain‐end composition of polymers,387, 388 while dielectric spectroscopy gives information on the molecular dynamics processes 389–391…”

New Insights into the Dynamics of Poly(amidoamine) Dendrimers with Amino Surface Groups from Segmental Relaxation and Ionic Conductivity

“…In this regard, broadband dielectric spectroscopy (BDS) is one of the most effective techniques because it is capable of exploring orientational/dipolar and translational motions on a broad range of length scales and in a wide temperature/pressure range due to its coverage of an extremely broad range of frequency and temperature/pressure . Nonetheless, although the family member of dendrimers keeps exploding and the glassy dynamics of dendrimers are still much less understood relative to linear polymers, only a few limited families of bulk dendrimers have been investigated with BDS so far, including but not limited to carbosilane dendrimers, , ARB dendrimers, poly­(ether amide) dendrimers, PMMH dendrimers, , carbosilazane dendrimers, PAMAM dendrimers, bis-MPA polyester dendrimers, − and PPI dendrimers, , and most of them were carried out about two decades ago. According to these studies, the molecular dynamics of dendrimers seem to be straightforward and not much different from linear polymers, which are typically characterized by a segmental relaxation signifying glass transition and several secondary relaxations arising from motions of different subunits like terminal groups.…”