Interfacial region in blends of linear polymers formed in situ

Blends of linear polyurethane and poly(methyl methacrylate) were obtained by the simultaneous curing of the mixture of two monomers. It was shown that the blends obtained in situ are two-phase systems in which two phases enriched in one of the blend components are separated by an intermediate region, the interphase. From the DSC data the compositions of two phases were estimated. It was observed that introduction of a filler leads to the appearance of an additional temperature transition lying between glass transition temperatures of the two phases. The fraction of the interphase was calculated from the calorimetric data. The introduction of a filler increases this fraction. This may be considered as some improving of compatibility of the two components in the presence of a filler.     

Critical Exponents of Gelation and Conductivity in Polyacrylamide Gels Doped by Multiwalled Carbon Nanotubes

Polyacrylamide (PAM) doped by multiwalled carbon nanotube (MWNT) gels were prepared with different amounts of MWNTs varying in the range between 0.1 and 15 wt%. The PAM–MWNT composite gels were characterized by the steady state fluorescence technique (SSF). The alternative electrical conductivity (AC) of PAM–MWNT composite gels was measured by the dielectric spectroscopy technique. Observations around the gel point, t _gel for PAM–MWNTs composite gels showed that the gel fraction exponent β obeyed the percolation result. The critical exponent r of AC electrical conductivity for the composite PAM–MWNT gel was also measured and found to be about 2.0, which agrees with a random resistor network.     

Critical exponents in the transition to chaos in one-dimensional discrete systems

We report the numerically evaluated critical exponents associated with the scaling of generalized fractal dimensions during the transition from order to chaos. The analysis is carried out in detail in the context of unimodal and bimodal maps representing typical one-dimensional discrete dynamical systems. The behavior of Lyapunov exponents (LE) in the cross over region is also studied for a complete characterization.     

In-situ elastomer composite based on fluorocarbon elastomer/liquid crystalline polymer blend

Blends of fluorocarbon elastomer (FKM) and liquid crystalline polymer (LCP) have been prepared by melt mixing technique. Processing studies indicated the decrease in the viscosity and the state of cure with the addition of 10 wt% LCP, and then increased at a higher rate with the addition of more LCP to the blend. The tensile strength values decreased at lower level of LCP. However, the modulus and tear strength values increased with higher increment of LCP content. From the X-ray diffraction measurements it has been observed that the crystalline structure of the FKM is greatly affected by the addition of LCP. The degradation temperatures from thermogravimetric analysis (TGA) suggested improved thermal stability of the fluorocarbon-LCP blends. From the dynamic mechanical analysis (DMA), it has been found that the glass transition temperature (T _g) of the blends increased with increase in LCP content. For the compositions of 10 wt% and 20 wt% LCP blends, enhancement in storage modulus is found above the glass transition of FKM. Under dynamic conditions the increase of LCP content restricts the matrix flow and hence cracks developed at the interface of the LCP fibrils and matrix.     

Applications of expanded polystyrene (EPS) beads and polyamide-66 in civil engineering,Part One: Lightweight polymeric concrete

EPS concrete is a lightweight material. In this study different sizes of expanded polystyrene (EPS) beads and polyamide-66 yarns were utilized to make a new lightweight concrete. Parts of the results were obtained from our earlier study reported as a novel lightweight concrete essentially having EPS and polyamide-66 yarns. The research showed that largest EPS beads disintegrate along the contact zone and can decrease the adhesion strength. The use of polyamide-66 yarns had a significant influence in crack reduction.     

非晶材料玻璃转变过程中记忆效应的热力学

低温下处于非平衡态的非晶材料升温到玻璃转变以上,要先后发生弛豫和回复最终达到平衡过冷液态,其中弛豫过程中释放的能量在回复过程中以等量的方式获取,表现出明显记忆行为.本文基于氧化物、金属与小分子等多种非晶形成体系,全面探讨了在围绕玻璃转变的一个冷却加热循环过程中的焓弛豫特征,建立了弛豫谱,发现弛豫焓在数值上与熔化焓密切相关.基于弛豫焓与非晶材料动力学Fragility之间的关联,展示了非晶体系在动力学极限(m=175)条件下的玻璃转变热力学基本特征,与热力学二级相变进行了对比.研究深化了对非晶弛豫与玻璃转变热力学的理解.     

Filling dependence of correlation exponents and metal-Mott insulator transition in strongly correlated electron systems

Using a universal relation between electron filling factor and ground state energy,this paper studies the dependence of correlation exponents on the electron filling factor of one-dimensional extended Hubbard model in a strong coupling regime,and demonstrates that in contrast to the usual Hubbard model(gc = 1/2),the dimensionless coupling strength parameter g c heavily depends on the electron filling,and it has a "particle-hole" symmetry about electron quarter filling point.As increasing the nearest neighbouring repulsive interaction,the single particle spectral weight is transferred from low energy to high energy regimes.Moreover,at electron quarter filling,there is a metal-Mott insulator transition at the strong coupling point gc = 1/4,and this transition is a continuous phase transition.     

Renormalisation group calculation of the critical exponents of the special transition in semi-infinite systems

Renormalisation group calculations of the correlation function exponents η^sp_⊥ and η^sp_∥ of the special transition in semi-infinite φ⁴ systems to second order in ?=4?d are presented.     

Critical dynamics and multifractal exponents at the Anderson transition in 3d disordered systems

We investigate the dynamics of electrons in the vicinity of the Anderson transition in d = 3 dimensions. Using the exact eigenstates from a numerical diagonalization, a number of quantities related to the critical behavior of the diffusion function are obtained. The relation η = d ? D₂ between the correlation dimension D₂ of the multifractal eigenstates and the exponent η which enters into correlation functions is verified. Numerically, we have η ≈? 1.3. Implications of critical dynamics for experiments are predicted. We investigate the long-time behavior of the motion of a wave packet. Furthermore, electron-electron and electron-phonon scattering rates are calculated. For the latter, we predict a change of the temperature dependence for low T due to η. The electron-electron scattering rate is found to be linear in T and depends on the dimensionless conductance at the critical point.     

Universal properties of the transition from quasi-periodicity to chaos in dissipative systems

An exact renormalization group transformation is developed for dissipative systems which describes how the transition to chaos may occur in a continuous and universal manner if the frequency ratio in the quasi-periodic regime is held at a fixed irrational value. Our approach is a natural extension of K.A.M. theory to strong coupling. Most of our analysis is for analytic circle maps. We have found a strong coupling fixed point where invertibility is lost, which describes the universal features of the transition to chaos. We find numerically that any two such critical maps with the same winding number are C¹ conjugate. It follows that the low frequency peaks in an experimental spectrum are universal and we determine how their envelope scales with frequency.When the winding number has a periodic continued fraction, our renormalization transform has a fixed point and spectra are self similar in addition. For a set of non-periodic winding numbers with full measure our renormalization transformation yields an ergodic trajectory in a sub-space of all critical maps. Physically one finds singular and universal spectra that do not scale.     

Spinor behaviour of a double quantum transition in three-level systems

4π rotational symmetry (spinor behaviour) of a two-level subsystem, connected by a double quantum transition is demonstrated in the case of a spin-1 nucleus (deuterium).     

Phase transition in spin systems with various types of fluctuations

Various types ordering processes in systems with large fluctuation are overviewed. Generally, the so-called order–disorder phase transition takes place in competition between the interaction causing the system be ordered and the entropy causing a random disturbance. Nature of the phase transition strongly depends on the type of fluctuation which is determined by the structure of the order parameter of the system. As to the critical property of phase transitions, the concept “universality of the critical phenomena” is well established. However, we still find variety of features of ordering processes. In this article, we study effects of various mechanisms which bring large fluctuation in the system, e.g., continuous symmetry of the spin in low dimensions, contradictions among interactions (frustration), randomness of the lattice, quantum fluctuations, and a long range interaction in off-lattice systems.     

New criterion in predicting glass forming ability of various glass-forming systems

It has been confirmed that glass-forming ability (GFA) of supercooled liquids is related to not only liquid phase stability but also the crystallization resistance. In this paper, it is found that the liquid region interval ($T_{\rm l}-T_{\rm g})$ characterized by the normalized parameter of $T_{\rm g}$/$T_{\rm l}$ could reflect the stability of glass-forming liquids at the equilibrium state, whilst the normalization of supercooled liquid region $\Delta T_{\rm x}$=($T_{\rm x}-T_{\rm g})$, i.e. $\Delta T_{\rm x}$/$T_{\rm x}$ (wherein $T_{\rm l}$ is the liquidus temperature, $T_{\rm g}$ the glass transition temperature, and $T_{\rm x}$ the onset crystallization temperature) could indicate the crystallization resistance during glass formation. Thus, a new parameter, defined as $\xi =T_{\rm g}$/$T_{\rm l}+\Delta T_{\rm x}$/$T_{\rm x}$ is established to predict the GFA of supercooled liquids. In comparison with other commonly used criteria, this parameter demonstrates a better statistical correlation with the GFA for various glass-forming systems including metallic glasses, oxide glasses and cryoprotectants.     

New criterion in predicting glass forming ability of various glass-forming systems

It has been confirmed that glass-forming ability （GFA） of supercooled liquids is related to not only liquid phase stability but also the crystallization resistance. In this paper, it is found that the liquid region interval （T1 - Tg） characterized by the normalized parameter of Tg/T1 could reflect the stability of glass-forming liquids at the equilibrium state, whilst the normalization of supercooled liquid region △Tx=（Tx - Tg）, i.e. △Tx/Tx （wherein T1 is the liquidus temperature, Tg the glass transition temperature, and Tx the onset crystallization temperature） could indicate the crystallization resistance during glass formation. Thus, a new parameter, defined as ζ = Tg/T1＋△Tx/Tx is established to predict the GFA of supercooled liquids. In comparison with other commonly used criteria, this parameter demonstrates a better statistical correlation with the GFA for various glass-forming systems including metallic glasses, oxide glasses and cryoprotectants.     

Studying of the critical exponents around the glass transition in bulk polymerization of ethyl methacrylate by using fluorescence techniques

The glass transition during bulk polymerization was studied in free-radical crosslinking copolymerization (FCC) of ethyl methacrylate (EMA), using both the steady-state fluorescence (SSF) and the fast transient fluorescence (FTRF) techniques. Pyrene (Py) was used as a fluorescence probe. Changes in the viscosity of the pregel solutions due to gel formation dramatically enhance the fluorescent yield of Py molecules. The reaction time at which the Py intensity and lifetime exhibit a sudden increase corresponds to the reaction time at which the rate of polymerization becomes maximum resulting from the gel effect. This effect is used to study the gelation of EMA, as a function of time, at various crosslinker concentrations and different temperatures. The results were interpreted in the view of percolation theory. The gel fraction, β and weight average degree of polymerization, γ exponents β?=?0.37?±?0.01, γ?=?1.71?±?0.04 and β?=?0.36?±?0.002, γ?=?1.687?±?0.01 are found in agreement with percolation results for SSF and FTRF measurements, respectively.     

Optimization of the alkali treatment process of date palm fibres for polymeric composites

The global interest in environmentally friendly material over the past few years has led to the development of new research areas in the field of renewable materials and biocomposites. Within this scope, several researches have been conducted to modify natural fibres aiming at an improved compatibility with polymeric matrices. In this study, fibres from the spadix stem of the date palm tree were treated with sodium hydroxide over different times. The effect of the alkali treatment on the structure, thermal and mechanical behaviour of the fibres was verified through chemical analysis, FTIR spectroscopy, TGA, and tensile testing. Comparing the different alkalisation parameters, promising results are obtained with a 2% sodium hydroxide solution over a treatment time of 2 h.     

Plasma-polymerized organosilicones as engineered interlayers in glass fiber/polyester composites

The plasma polymerization technique was used to surface modify glass fibers in order to form a strong but tough link between the glass fiber and the polyester matrix, and enable an efficient stress transfer from the polymer matrix to the fiber. Plasma polymer films of hexamethyldisiloxane, vinyltriethoxysilane, and tetravinylsilane in a mixture with oxygen gas were engineered as compatible interlayers for the glass fiber/polyester composite. The interlayers of controlled physico-chemical properties were tailored using the deposition conditions with regard to the elemental composition, chemical structure, and Young's modulus in order to improve adhesion bonding at the interlayer/glass and polyester/interlayer interfaces and tune the cross-linking of the plasma polymer. The optimized interlayer enabled a 6.5-fold increase of the short-beam strength compared to the untreated fibers. The short-beam strength of GF/polyester composite with the pp-TVS/O₂ interlayer was 32% higher than that with industrial sizing developed for fiber-reinforced composites with a polyester matrix.     

Lyapunov exponents of stochastic dynamical systems

It is shown that stochastic equations can have stable solutions. In particular, there exists stochastic dynamics for which the motion is both ergodic and stable, so that all trajectories merge with time. We discuss this in the context of Monte Carlo-type dynamics, and study the convergence of nearby trajectories as the number of degrees of freedom goes to infinity and as a critical point is approached. A connection with critical slowdown is suggested.