Glass transition and relaxation processes in supercooled water

Many of water's peculiar physical properties are still not well understood, and one of the most important unresolved questions is its glass transition related dynamics. The consensus has been to accept a glass transition temperature (T(g)) around 136 K, but this value has been questioned and reassigned to about 165 K. We find evidence that the dielectric relaxation process of confined water that has been associated with the long accepted T(g) of water (130-140 K) must be a local process which is not related to the actual glass transition. Rather, our data indicate a glass transition at 160-165 K for bulk water and about 175 K for confined water (depending on the confining system).     

Glass transition in charge carrier transport phenomena of amorphous photoconductive polymers

The critical temperature T_o in Gill's empirical equation for the charge carrier transport was found to have aclose connection with the glass transition temperature T_g for poly-N-vinylcarbazole containing model compound systems. Interpretations of T₀ and μ₀, i.e., the drift mobility at T₀, were presented.     

Glass transition in biomolecules and the liquid-liquid critical point of water

Using molecular dynamics simulations, we investigate the relation between the dynamic transitions of biomolecules (lysozyme and DNA) and the dynamic and thermodynamic properties of hydration water. We find that the dynamic transition of the macromolecules, sometimes called a "protein glass transition," occurs at the temperature of dynamic crossover in the diffusivity of hydration water and also coincides with the maxima of the isobaric specific heat C_{P} and the temperature derivative of the orientational order parameter. We relate these findings to the hypothesis of a liquid-liquid critical point in water. Our simulations are consistent with the possibility that the protein glass transition results from crossing the Widom line, which is defined as the locus of correlation length maxima emanating from the hypothesized second critical point of water.     

Zr-Al-Ni-Cu(Nb,Ti)大块非晶玻璃转变的动力学性质

以Zr-Al-Ni-Cu (Nb,Ti)大块非晶合金差示扫描量热分析实验为基础,利用Lasocka方程、Kissinger方程及Vogel-Fulcher-Tamman(VFT)方程对其玻璃转变的动力学性质从不同方面进行了研究.分析结果表明：玻璃转变表观激活能越小,则晶化转变激活能越大,表现出相反的难易程度,且玻璃转变表观激活能数值远较传统非晶要小,验证了大块非晶合金独特的结构特点及玻璃形成能力(GFA)强的原因.利用VFT方程对玻璃转变弛豫时间与升温速度的VFT曲线 进行了拟合,所算得的玻璃脆性参数m均在30左右,反映了Zr-Al-Ni-Cu (Nb,Ti)非晶合金强 的脆性属性.玻璃转变处Lasocka关系的B值、原子表观激活能及玻璃脆性参数均反映了相同的GFA大小趋势,从不同方面进一步揭示了非晶合金玻璃转变区间的动力学行为与GFA之 间的密切联系,可作为判断非晶合金GFA强弱的重要依据. 关键词： 玻璃转变 玻璃形成能力 表观激活能 玻璃脆性参数     

Zr-Al-Ni-Cu(Nb,Ti)大块非晶玻璃转变的动力学性质

以Zr Al Ni Cu(Nb ,Ti)大块非晶合金差示扫描量热分析实验为基础 ,利用Lasocka方程、Kissinger方程及Vogel Fulcher Tamman(VFT)方程对其玻璃转变的动力学性质从不同方面进行了研究 .分析结果表明 :玻璃转变表观激活能越小 ,则晶化转变激活能越大 ,表现出相反的难易程度 ,且玻璃转变表观激活能数值远较传统非晶要小 ,验证了大块非晶合金独特的结构特点及玻璃形成能力 (GFA)强的原因 .利用VFT方程对玻璃转变弛豫时间与升温速度的VFT曲线进行了拟合 ,所算得的玻璃脆性参数m均在 30左右 ,反映了Zr Al Ni Cu(Nb ,Ti)非晶合金强的脆性属性 .玻璃转变处Lasocka关系的B值、原子表观激活能及玻璃脆性参数均反映了相同的GFA大小趋势 ,从不同方面进一步揭示了非晶合金玻璃转变区间的动力学行为与GFA之间的密切联系 ,可作为判断非晶合金GFA强弱的重要依据     

Polyamorphic transition in amorphous fullerites

Samples of amorphous fullerites have been prepared by mechanoactivation (grinding in a ball mill), and their structure has been studied using neutron diffraction. It has been found that the amorphous fullerites subjected to high-temperature (600–1700°C) annealing undergo a polyamorphic transition from the molecular glass to the atomic glass, which is accompanied by the disappearance of fullerene halos at small scattering angles.     

Explosive transition in amorphous microwire

An amorphous microwire in a glass shell offers a quick thermal response and can be rapidly heated to the crystallization point. When heated by a current pulse with a small amplitude and duration, the wire passes from the amorphous to microcrystalline state. The crystallization of the amorphous state may represent a slow or explosive process depending on the parameters of the pulse. In the latter case, the emission of electromagnetic waves (flash of light) and a sharp rise in the resistance are observed. The rate of propagation of the crystallization front in our experiments has been found to be about 1 m/s.     

Thermopower of some amorphous transition metal-alloys

Measurements of the thermopower for amorphous alloys are reported in the temperature range 77K to 320K. The alloys examined are Cu₅₀Ti₅₀, Pd₈₀Si₂₀, Pd₃₀Zr₇₀ and Cu₄₀Zr₆₀. The data are compared with values of similar systems, as far as available. In addition we analyse the temperature coefficient of the thermopower, applying a model, based on the Ziman formulation of the transport properties.     

Reentrant coil-to-globule-to-coil transition of a single linear homopolymer chain in a water/methanol mixture

Both water and methanol are good solvents for poly( N-isopropylacrylamide) (PNIPAM) at room temperature, but strangely not a mixture of them. Using narrowly distributed linear PNIPAM chains (M(w) = 2.6x10(7) g/mol and M(w)/M(n)<1.1), we have, for the first time, observed a coil-to-globule-to-coil transition of a single PNIPAM chain when methanol was gradually added into water. This novel reentrant transition leads to insight into the complexation between methanol and water. We also found that the chain was crumpled in its globule state and the globule still contained approximately 80% of solvent in its hydrodynamic volume.     

Glass transition of Langmuir-Blodgett polymer films

The dielectric dispersion of vinylidene fluoride-trifluoroethylene copolymer P(VDF/TrFE) (70/30) films obtained by the Langmuir-Blodgett technique was investigated in the low-temperature range from 20 to −100°C. The thickness of the explored films was 40 nm. A glass-transition range from −25 to −40°C was detected; this indicates the presence of an amorphous phase in the LB films.     

Structural transition in compressed amorphous sulfur

Properties of amorphous sulfur (a-S) were investigated by synchrotron x-ray diffraction up to 100 GPa between 40 and 175 K. Measurements of the structure factor yielded the radial distribution function and the densities of two amorphous forms. a-S undergoes a structural transition above 65 GPa, accompanied by density discontinuity of 7%. These results indicate the amorphous-amorphous transition, from a low-density to a high-density form, and open up the possibility for the direct measurements of density of liquid-amorphous materials at extreme conditions.     

Glass transition and enthalpy relaxation of polyphosphate compounds

The glass transition behaviour of polyphosphate compounds such as di- and tri- polyphosphates used as food additives and ATP, ADP existing in biosystems, were investigated by using DSC. From the DSC heating curves of the frozen solutions, the glass transition temperatures of the maximum freeze concentrated solutions, Tg', were determined. It was found that Tg's for polyphosphates are relatively high. The lyophilized tripolyphosphates, ATP and ADP also showed the glass transition at a relatively high temperature, depending on the moisture content. In addition, the enthalpy relaxation behaviour of glassy ATP and ADP was examined and analyzed by using the Kohlrausch-Williams-Watts (KWW) and the Vogel-Fulcher-Tammann (VFT) equations. Judging from the parameters of the KWW and VFT equations, the amorphous states of ATP and ADP were suggested to be more fragile than trehalose and sucrose.     

Magnetic phases of amorphous transition metal-metalloid alloys

Hysteresis loop and ac susceptibility measurements were performed on three series of amorphous alloys: (A_wB_1-w)₇₅P₁₆B₆Al₃, where (A, B) are (Fe, Ni), (Co, Ni) and (Fe, Mn). Upon cooling, low w alloys undergo paramagne t to spin glass transitions. Alloys with higher w first experience a Curie transition to a ferromagnetic state, and then a spin freezing transition to a spin glass state. the T dependence of the width of the ac hysteresis loop is used to determine the spin freezing transition temperature. A magnetic phase diagram is presented for each alloy series and the value of w required for ferromagnetism, w_C, is determined. When measured in the presence of small constant fields, the ac susceptibility of alloys with w just above w_C has maxima near both transition temperatures. The field and temperature dependences of the peaks are explained by scaling arguments, used to determine the critical exponent δ for the Curie transition, and suggest that a similar scaling law holds for the ferromagnet to spin glass transition.     

Superconducting properties of amorphous transition metal alloys

We have co-sputtered amorphous films of several Mo and W-based superconducting alloys. Measurements of T_c, ($\text{d}\text{H}{}_{\mathrm{c2}}\text{d}\text{T}$)_Tc and the normal state resistivity near T_c were made on a number of these alloys. Our results and other data from the literature are studied to examine the correlation between T_c and the dressed density of states at the Fermi level.     

Electronic structure of amorphous transition metal alloys

The electrical resistivity, the Hall coefficient and the magnetic susceptibility of amorphous alloys (Metglass 2826A, Allied Chemical) have been measured above room temperature. The experimental data show strong similarities with liquid alloys.     

Ferromagnetic-spin glass transition in amorphous and crystalline Fe-Cr

Through a direct comparison of experimental results in amorphous and crystalline forms of Fe-Cr alloys we examine the effect of topological and compositional disorder on magnetic properties. Both types of disorder result in a decrease in the Curie temperature, the magnetic moment at T = 0 and the exchange stiffness constant. These results are discussed in the framework of several models.