An anti-maser for quantum-limited cooling of a microwave cavity

The maser, a microwave (MW) analog of the laser, is a well-established method for generating and amplifying coherent MW irradiation with ultra-low noise. This is accomplished by creating a state of population inversion between two energy levels separated by MW frequency. Thermodynamically, such a state corresponds to a small but negative temperature. The reverse condition, where only the lower energy level is highly populated, corresponds to a very low positive temperature. In this work, we experimentally demonstrate how to generate such a state in condensed matter at moderate cryogenic temperatures. This state is then used to efficiently remove microwave photons from a cavity, continuously cooling it to the quantum limit, well below its ambient temperature. Such an "anti-maser" device could be extremely beneficial for applications that would normally require cooling to millikelvin temperatures to eliminate any MW photons. For instance, superconducting MW quantum circuits (such as qubits and amplifiers) could, with the use of this device, operate efficiently at liquid helium temperatures

Self-diffusion of polystyrene in solution 2. Discussion of experimental results on the basis of the reptation mechanism and entanglements

The expressions for polymer self-diffusion in semidilute solutions, theoretically derived from the reptation mechanism, the blob concept and scaling considerations, are discussed and compared against experimental data from the authors' investigations and the literature. In the nonentangled (from viscoelastic data) semidilute solution, the experimentally observed concentration and molar mass exponents are in fair agreement with those derived theoretically. However, a quantitative estimation shows that the experiments cannot be explained by reptation. Experiments with polymer mixtures also give strong evidence against reptation. It is concluded, that in the nonentangled semidilute solution, the polymer self-diffusion is more complicated than simple reptation. This is also supported by recently observed long-range density fluctuations or cluster formation in this concentration region detected by scattering techniques and NMR-PFGT. In the entangled semidilute solution, the self-diffusion data are in accordance with the reptation mechanism; reptation being within a tube having approximately 20 blobs between entanglements. © 1988 Steinkopff

Poly(methyl methacrylate)/1,2-dichloroethane system: Freezing of conformational mobility in the low-molecular component

The conformational dynamics in 1,2-dichloroethane (DCE)/poly(methyl methacrylate) (PMMA) mixtures has been studied at different concentrations of DCE. The intensities of the infrared absorption bands belonging to the trans and gauche conformers have been measured in the 77-300 K temperature range. Besides, the glass transition temperatures of the mixtures T g were determined by the differential scanning calorimetry. For all the systems under investigation the freezing of the conformational transitions has been found: below a certain temperature T f the trans/gauche ratio becomes temperature independent. The T f value for the lowest volume fraction of DCE (C = 0.01) was found to be close to the temperature of one of the secondary relaxation transitions of pure PMMA (195 K). At this temperature the free volume entities in PMMA should have the volume close to that of the conformationally mobile groups of DCE (∼25 Å 3). The concentration dependence of T f consists of two branches. At low concentrations of the diluent (C < 0.6) T f slowly decreases with the concentration of DCE, reflecting the concentration behaviour of the relaxation transition temperature. At the higher concentrations the freezing of the conformational equilibrium in DCE occurs at the glass transition of the mixtures, and the T f values are close to the T g ones. Copyright © 1996 Elsevier Science Ltd

Autodiffusion and phase separation in aqueous solutions of polyoxypropylene diol

Phase equilibrium in the polyoxypropylene-water system at the lower consolute temperature has been studied by an NMR impulse method and by an interference micro-method. An analysis of the shape of the diffusional attenuations which in this case are complex, and also of the experimentally obtained population values, enabled one to construct the phase diagram in the 250-315° K range. The concentrated polymer phase formed by phase separation consists of polyoxypropylene diol, almost free of water. © 1989

Some properties of polyphenyleneimine

Recently, Nikitina et al. [1] have obtained semi-conducting polymers containing in the main chain aromatic rings separated by imino groups. The present paper is devoted to a detailed study of the physical properties of one of them - polyphenyleneimine. © 1964

Small conformationally mobile molecules as probes for molecular mobility in glassy polymers

A new method for studying molecular mobility in glassy polymers-the method of conformationally inhomogeneous probes-is described. A small quantity of a low-molecular-weight compound (probe) having unidentical conformations with different vibrational spectra is introduced into a polymer. The thermodynamic and activation parameters responsible for the concentrations of the conformers and the rates of conformational transitions are connected with both the intramolecular interactions and the properties of the medium (e.g. polymer). Information about the kinetics and equilibria of the conformers could be obtained by investigating the vibrational spectra. This information may be the key to understanding the molecular mobility and free-volume distribution in polymers. The following compounds were used as probes: 1,2-bromofluoroethane, methyl dichlorophosphate and trans-1,2-dichlorocyclohexane. The polymers poly-styrene, poly(vinyl chloride), poly(methyl methacrylate), poly(vinyl acetate), poly(vinylbutyral), poly-propylene and polybutadiene were investigated. The temperature dependences of the absorption-band intensities of the probes were studied. Freezing of the conformational transitions in the probe molecules was found at temperatures Tf characterizing specific polymer-probe systems. The Tf are close to the temperatures of the relaxation transitions in the pure polymers. The possibilities of the method are discussed. © 1994

Self-diffusion of polystyrene in solution 1. Experimental results of the NMR pulsed field gradient technique

We report self-diffusion measurements for polystyrene dissolved in benzene and chloroform using the NMR pulsed field gradient technique. The observed echo attenuations point to dynamic exchange processes or cluster formation in the semidilute solution. The experimental results are compared with theoretical predictions from the reptation mechanism and the 'blob' theory. There is qualitative agreement, but a more comprehensive analysis of the data and results from experiments with polymer mixtures show that polymer self diffusion in semidilute solutions cannot be explained by the reptation mechanism in its simple form. © 1988 Steinkopff

Conformational equilibria and the glass transition

Solutions of the conformationally inhomogeneous compounds 2-chlorobutane, chlorocyclohexane and trans-1,2-dichlorocyclohexane in glass-forming liquids (Nujol, butyl chloride and some phthalates) were investigated by i.r. absorption spectra. Freezing the conformational equilibrium at the glass transition of the solutions was observed. The method of using conformationally inhomogeneous compounds as a probe for the determination of the glass transition temperature (Tg) is proposed. The necessity of taking into account the glass transition process in interpreting results obtained for the temperature range T < Tg has been shown. The possibilities of the application of the proposed method to polymers have been explored, and Tg of polystyrene has been determined. © 1986

On the generalized concentration and molecular mass dependencies of macromolecular self-diffusion in polymer solutions

Self-diffusion experimental data obtained with the n.m.r. pulsed gradient spin-echo method in polyethylene oxide (PEO), polystyrene (PS), dextran, gelatine, cellulose triacetate (CT), poly(dimethyl siloxane) (PDMS) solutions and melts in a wide range of solvents, with molecular mass (M) and concentration (ø), were analysed to show the existence of common dependencies for Ds(M) and Ds(ø). The general law for Ds(ø) is expressed as f( ø \ ̂o) = Ds(ø) L(ø)Ds(0) and is correct for the solvent quality ranging from θ to 'good'. The existence of the generalized f( ø \ ̂o) was examined for the 17 different polymer-solvent systems. With the use of the generalized function, where Ds(O)=lim Ds \ ̂o,Ds(O)≈M-β, \ ̂≈M- 2-β 3 nearly 100 Ds(ø) dependencies were described. The renormalization function L(ø) accounts for the local dynamic properties of the concentration dependence. © 1988