摘要:

The liquid‐glass transition of LiI has been investigated by means of the constant‐temperature and constant‐pressure molecular dynamics method. Because LiI is one of the most simple examples of the coulombic system and the most contrasted combination of the cation and anion among all alkaline halides (the mass ratio of I to Li is 18.3 and the ionic size ratio is 3.6), we have expected to see the ionic motion most drastically. We calculated both static and dynamic properties with microscopic analyses for ionic motions. In the vicinity of the glass transition, the mean‐square displacement shows a non‐t‐linear behavior, sometimes called a subdiffusive behavior, and the incoherent scattering function are well fitted by ‘‘stretched exponential’’ function. The non‐Gaussian parameter as a function of time has a large maximum, and the product of the maximum value and the corresponding time increases sharply as approaching the glass transition. All these anomalous characteristic behaviors, as well as those found for the binary soft‐sphere system, are in good agreement with the prediction of the trapping diffusion theory. We discuss the validity of this theory.

ISSN:0094-243X    

DOI:10.1063/1.42437

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We discuss experimental results on molecular motion in polymer melts, obtained by neutron spin echo spectroscopy (NSE). We show that in the short time regime the assumption of entropic restoring forces (Rouse model) describes well the space and time dependence of the pair correlation function of one chain molecule. For longer times we observe systematic deviations from the Rouse model, revealing the presence of a well defined intermediate dynamical length scale beyond which density fluctuations within a given chain are strongly reduced. Its value is found to be in excellent agreement with the entanglement distance obtained from rheological measurements. Measurements of the temperature dependence and polymer volume fraction dependence of the entanglement distance give insight into the molecular origin of entanglement constraints.

ISSN:0094-243X    

DOI:10.1063/1.42438

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Gel electrophoresis (GE) is an important analytical technique in biology and medicine. The technique can be improved based on a better understanding of DNA structure and dynamics in the polymer network.Movement of fluorescence pattern after photobleaching (MOFPAP), together with its modified approaches, can measure stained DNA electrophoretic mobility in less time, permitting determinations of mobility (and probably velocity distribution) changes as a function of time during DNA chain deformations.

ISSN:0094-243X    

DOI:10.1063/1.42439

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Specific heat and thermal conductivity data for a homologous series of base‐catalyzed silica aerogels in the temperature range 0.1–20 K are analyzed in a three regime model. The three regimes, dominated by phonons, fractions and particle modes, respectively, reflect three structural regions as found by SANS measurements. The thermal properties of aerogels are compared to those of dense amorphous quartz and important differences are found.

ISSN:0094-243X    

DOI:10.1063/1.42440

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Quasi elastic light scattering is used to investigate the polyelectrolyte and added salt concentration dependence of the diffusion coefficient of sodium polystyrene sulfonate (NaPSS). Two relaxation times are observed in semi dilute regime at low salt concentration. With polyvalent salts (LaCl3and Th (NO3)4) a precipitation of NaPSS is obtained at constant Cm/Cs(Cmand Csare NaPSS and salt concentrations in mono M). The phase separation usually called ‘‘salting out phenomena’’ was studied and some investigations are made in single homogeneous phase.The dynamics show some interesting behavior of the effective diffusion coefficient as a function of NaPSS and LaCl3: The presence of slow and fast modes at low salt concentration and the existence of a large splitting of the relaxation times. a q2dependence of the fast diffusion coefficient and a q3dependence of the slow mode. a power law Dfast≊Cm+0.65at constant salt concentration.

ISSN:0094-243X    

DOI:10.1063/1.42442

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.42443

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Dielectric constant and loss were studied for the &agr;‐relaxation of isotactic polystyrene (IPS). The decay function for the relaxation was calculated directly from the dielectric loss. It was found that the dielectric relaxation becomes slower as the degree of crystallinity increases. It was also found that the relaxation undergoes a crossover from a stretched exponential decay to a power law decay in the long time region as the relaxation proceeds.

ISSN:0094-243X    

DOI:10.1063/1.42444

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The allyl‐ester is a new thermosetting resin composed on an allyl‐oligomer and a curing agent. The curing time variations of imaginary parts of dielectric constant (&Vegr;‘) exhibited a peak as the case of epoxy resins. The peak was detected when the sound velocities revealed considerable increases. Namely, the peak is thought to occur according to the proceed of vitrification process, suggesting the relation to &agr;‐relaxation process.

ISSN:0094-243X    

DOI:10.1063/1.42445

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The heat‐, and pressure‐induced gelation process of actomyosin was investigated by observing the transmitted light spectra. First, pH and [NaCl] dependences of the characteristic temperature (T’g) related to the gelation were determined at atmospheric pressure. Then, the temperature variations of the transmitted light spectra were monotored after the temperature‐ and pressure‐jump procedures, revealing the growth of the actomyosin assembly during these gelation processes.

ISSN:0094-243X    

DOI:10.1063/1.42469

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Frequency dependence of the dynamic heat capacity, which is the frequency response function characterizing the temperature response to the heat absorption, was measured around the glass transition temperature of atactic polypropylene and the solid‐liquid phase transition temperature of n‐paraffin. It was shown that the measurement of the frequency dependence of the dynamic heat capacity is useful technique to study the dynamic properties of the glass transition and the phase transition.

ISSN:0094-243X    

DOI:10.1063/1.42446

出版商:AIP    

年代:1992

数据来源: AIP