Dielectric investigation of a binary system of self-organized diols

Dielectric measurements on a binary system of two liquid crystalline diols were carried out. These show a SmA and a cubic phase. In the middle concentration range of the system, a columnar phase is induced. The self assembly of the molecules giving different liquid crystalline phases is clearly seen in the dielectric spectrum, and therefore details of this process may be discussed. All the samples show a high frequency dielectric absorption which is related to the dynamics of the network of hydrogen bonds. In the columnar phase an additional low frequency mechanism is seen which may be caused by the internal dynamics in the columns.     

Functionalization of magnetic nanoparticles with amphiphilic block copolymers: self-assembled thermoresponsive submicrometer particles

For the first time the four block copolymers derived from 1-alkyl[2-(acryloyloxy)ethyl]dimethylammonium bromides with hexyl (ADA) or cetyl (ADHA) groups and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) were synthesized and employed for functionalization of monodisperse iron oxide nanoparticles (NPs). The polyADA (pADA) or polyADHA (pADHA) block consists of long hydrophobic tails (C(6) or C(16)) connected to a positively charged quaternary ammonium group, making this block amphiphilic. The second block was either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). The dependence of the NP coating on the length of the hydrophobic tail in the amphiphilic block, the composition of the hydrophilic block, and the NP sizes have been studied. Unusual self-assembling of iron oxide NPs into well-defined composite submicrometer particles was observed for pADHA-b-pNIPAM in the wide range of concentrations (at the pADHA repeating unit concentrations of 0.065 × 10(-2)-2.91 × 10(-2) mmol/mL per 1 mg/mL NPs) but only two concentrations, 1.62 × 10(-2) and 1.94 × 10(-2) mmol/mL, led to regular spherical particles. The thermoresponsive behavior of these composite particles was tested using ζ-potential and dynamic light scattering measurements, while the morphology of particles was characterized by transmission electron microscopy. Coating of NPs with pADHA-b-pHEA results in the formation of individually coated NPs. The different composite particle morphologies are explained by different properties of pHEA and pNIPAM. It is demonstrated that the composite particles based on pADHA-b-pNIPAM are responsive to a magnetic field and can be recommended as magnetic stoppers in biorelated membrane separations. The incorporation of Pd species in submicrometer particles makes them promising candidates for catalytic applications as magnetically recoverable catalysts with a high magnetic response.     

Separation of a CaCl2-HCl Model Mixture on Neutral Nanoporous Hypercrosslinked Polystyrene under Static and Dynamic Conditions

The distribution of CaCl₂ and HCl (separately and in a mixture) between the aqueous and nanoporous hypercrosslinked polystyrene sorbent phases was studied under static conditions. It was shown that virtually the whole pore volume of the sorbent was accessible to HCl, whereas CaCl₂ was largely excluded from small pores. It was found that the distribution isotherms of the electrolytes between the phases changed significantly in going from the pure electrolytes to their mixture. Under dynamic (chromatographic) conditions, the elution profiles of CaCl₂ and HCl (separately and in a mixture) were studied. It was shown that the components of the mixture competed for the pore space of the sorbent: small HCl molecules were displaced from large pores and the interstitial space into small pores inaccessible to CaCl₂. (This is why the retention of HCl in the chromatography column significantly increased as the concentration of the mixture grew; that is, both the efficiency and selectivity of separation increased as the column became loaded heavier.) It was found that the degree of hydration of ions decreased as the concentration of the solution increased.     

The contraction of granules of nanoporous super-cross-linked polystyrene sorbents as a result of the exclusion of large-sized mineral electrolyte ions from the polymer phase

The deformation of neutral super-cross-linked polystyrene sorbents and ionites based on styrene-divinylbenzene gel-type copolymers brought in contact with concentrated solutions of HCl, H₃PO₄, NaOH, NH₄Cl, (NH₄)₂SO₄, and LiCl electrolytes was studied by dilatometry for separate spherical granules. Considerable contraction of super-cross-linked polystyrene matrices swollen in water was observed in concentrated solutions containing large-sized lithium, sulfate, and phosphate ions. Volume compressive strain correlated with the size of excluded hydrated ions. The contraction effect was caused by the difference in the osmotic pressure of water in thin pores and water in concentrated solutions filling large pores. The exclusion effect ignored earlier should also influence the degree of ion exchange and volume deformation of standard ion-exchange resins brought in contact with solutions of various electrolytes. Original Russian Text ? A.V. Pastukhov, V.A. Davankov, M.P. Tsyurupa, Z.K. Blinnikova, N.E. Kavalerskaya, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 541–549.     

Self‐assembled diols: synthesis,structure and dielectric studies

In single‐, double‐, and triple‐chain amphiphilic diols the CONH group was replaced by CON(CH₃) in order to reduce the number of proton donor groups available for intermolecular hydrogen bonding. The resulting three new liquid crystalline diols were studied by DSC, X‐ray and dielectric measurements, and show the mesophases SmA, Col_H2 or Cub_I2, depending on the number of decyloxy groups in the hydrophobic part of the molecule. The process of self‐assembly to different liquid crystalline phases is well seen in the dielectric spectrum and details of this process are discussed together with results from the X‐ray measurements. All the compounds show a high frequency dielectric absorption caused by the dynamics of the network of hydrogen bonds. An additional low frequency process related to the internal dynamics of the columns is seen only in the columnar phase.