Concentration-dependent Line Research Articles

Dynamical properties in dense triblock copolymer micellar system

We present results of analyses of an extensive set of dynamic light scattering (PCS) and viscoelastic (frequency dependent complex moduli) measurements in concentrated aqueous solutions of a triblock copolymer L64 (PEO 13PPO 30PEO 13) micellar system at different temperatures. In particular we study the system dynamical properties in a region of the phase diagram characterized by the existence of a percolation process and a kinetic glass transition. Both the processes, temperature and concentration dependent, are related with adhesive interaction between micelles. The intermediate scattering function (ISF) shows an ergodic to non-ergodic transition on crossing a temperature and concentration dependent line. Viscoelasticity data, determined by means of frequency-dependent complex moduli, satisfy the scaling relations predicted by the scalar elasticity percolation theory and well account for the glass transition process, give indication that percolation and the ergodic non-ergodic transitions take places in separate regions of the phase diagram. Detailed analysis of ISF and rheological data, conducted in terms of the mode coupling theory (MCT) gives evidence of a logarithmic decay on the density fluctuations, which could be attributed to a higher order singularity, followed by a power-law behavior.

Kinetic glass transition in a micellar system with short-range attractive interaction

We show that percolation and structural arrest transitions coexist in different regions of the phase diagram of a copolymer-micellar system and relate them to short-range intermicellar attraction. The intermediate scattering function shows a nonergodic transition along a temperature and concentration dependent line. Analyses show a logarithmic time dependence, attributed to a higher-order glass transition singularity predicted by mode-coupling theory, followed by a power law.

Der Einfluß unmagnetischer Dotierungen auf die ESR-Linienbreite von antiferromagnetischen Verbindungen / The Influence of Non-Magnetic Dopants on the ESR Line Width of Antiferromagnetic Compounds

ESR spectra of doped antiferromagnetic compounds exhibit a concentration-dependent line width ∆B̄(x). We have investigated polycrystalline samples of Cr2O3 doped with Ga2O3 and Al2O3. For temperatures T sufficiently high above the Néel point TN and for concentrations x≦10%, the experimental values of AB show a linear dependence on x. This behaviour deviates from theoretical predictions based on the method of second moments. Starting with other reasonable assumptions, we have developed a statistical model of resonance that describes ∆B(x) as a linear function of x. Moreover this allows us to deduce that as far as antiferromagnetic Cr2O3 is concerned, the dopants Ga2O3 and AI2O3 are distributed homogene­ously throughout the lattice sites.

Low temperature nuclear orientation and NMR of oriented nuclei

Recent developments in nuclear orientation (NO) and radiative detection of NMR (NMR/ON) are reviewed. Details of the hyperfine interaction hamiltonian in cubic ferromagnets and the principles of measurement by these techniques of both magnetic dipole and electric quadrupole terms are outlined. In the experimental survey a full account is given of measurements of the electric quadrupole interaction by frequency modulated and fast passage NMR/ON, with briefer coverage of applications of both techniques to implanted systems, of linewidths, concentration dependent line structure, and Knight shifts in NMR/ON and of NO measurements of electric quadrupole interactions in non-cubic non-magnetic metals. The review incorporates a tabulation of NMR/ON measurements to date.