Structural and kinetic modification of aqueous hydroxypropylmethylcellulose(HPMC) induced by electron beam irration

Electron beam was irradiated on 10% and 20% hydroxypropylmethylcellulose (HPMC) aqueous solutions with different doses to make gel films. As increasing dose, the gel fraction of the film increased sharply above a critical dose and then decreased gradually after passing a maximum. The scission/cross-linking ratio and the critical dose were determined using the Charlesby-Rosiak equation as 0.52 and 9 kGy for 10% gel and 0.43 and 14 kGy for 20% gel, respectively. The gel fraction for 20% HPMC film was lower at low dose and higher at high dose than that for 10% film. The behavior of the swelling ratio of the gel film was just opposite to that of the gel fraction. The cross-linking density of the gel estimated from the Flory theory linearly increased with irradiation dose at low dose, passed a maximum around 100 and 160 kGy for 10% and 20% films, respectively, and decreased at high dose. These results suggest the competition of scission and cross-linking induced by indirect effect of irradiation. Dielectric relaxation measurement by time domain reflectometry and RF impedance/material analyzer revealed two characteristic relaxations of chain motions around 100MHz and of orientation of free water around 20GHz. From the dose dependence of the relaxation parameters determined by fitting to a combined equation of Cole-Cole type and KWW type, a coupling of motions of HPMC molecules and water molecules was strongly suggested. The critical dose for gelation was coincident with the dose for the maximum of t h and the minimum of Deh together with the minimum of t m and the maximum of Dem, where t h and Deh denote the relaxation time and the relaxation strength for free water molecular motion and t m and Dem the corresponding ones for HPMC molecular motion. The characteristic behavior was discussed in terms of the increase of affinity between HPMC and water and the constrained molecular motion in the gel network

How does thermodiffusion of aqueous solutions depend on concentration and hydrophobicity?

The thermal diffusion of aqueous solutions of mono-, di-ethylene glycols, poly(ethylene glycol), methanol, and glycerol is investigated systematically as a function of concentration using the Thermal Diffusion Forced Rayleigh Scattering (TDFRS). For all investigated binary mixtures, the Soret coefficient, S T , decays with increasing concentration of the non-aqueous component showing two regions. For aqueous solution of ethylene glycol, at a very low solute content the decay is steep, while it becomes less steep for higher solute concentration. All mixtures show a sign change of S T with concentration. The sign change concentration is discussed with respect to chemical structures of solute molecules and the partition coefficient, log p . It turns out that the number of hydroxyl groups plays an important role. For the investigated aqueous mixtures, we find empirical linear relations between the sign change concentration and the ratio of the number of hydroxyl groups to the number of carbon atoms as well as the partition coefficient, log p

Ludwig-Soret effect of aqueous solutions of ethylene glycol oligomers, crown ethers, and glycerol: Temperature, molecular weight, and hydrogen bond effect

The thermal diffusion, also called the Ludwig-Soret effect, of aqueous solutions of ethylene glycol oligomers, crown ethers, and glycerol are investigated as a function of temperature by Thermal Diffusion Forced Rayleigh Scattering (TDFRS). The Soret coefficient, $S_{\rm{T}}$, and the thermal diffusion coefficient, $D_{\rm{T}}$, show a linear temperature dependence for all studied compounds in the investigated temperature range. The magnitudes and the slopes of $S_{\rm{T}}$ and $D_{\rm{T}}$ vary with the chemical structure of the solute molecules. All studied molecules contain ether and/or hydroxyl groups, which can act as acceptor or donor to form hydrogen bonds, respectively. By introducing the number of donor and acceptor sites of each solute molecule, we can express their hydrogen bond capability. $S_{\rm{T}}$ and $D_{\rm{T}}$ can be described by an empirical equation depending on the difference of donor minus acceptors sites and the molecular weight of the solute molecule

Broadband complex dielectric constants of water and sodium chloride aqueous solutions with different DC conductivities

Broadband dielectric constant measurements in the frequency range between 40 Hz and 50 GHz of pure water, tap water, and sodium chloride aqueous solutions with different DC conductivities up to 5 S/m were conducted. The measurements were done using an impedance analyzer for the frequency range 40 Hz to 110 MHz and a vector network analyzer for 10 MHz to 50 GHz. The results show that the dielectric constant decreases with the increase in DC conductivity and is dependent on the frequency. The dielectric relaxation of water with a constant dielectric loss peak was also observed. The frequency dependence of the conductivity is also large