Phase transition temperatures three methods

TABLE 5.5 Phase Transition Temperatures (°C) Obtained by Three Methods (a) Neutron Diffraction ... 

Stabilization of the Cellular State. The increase in surface area corresponding to the formation of many ceUs in the plastic phase is accompanied by an increase in the free energy of the system hence the foamed state is inherently unstable. Methods of stabilizing this foamed state can be classified as chemical, eg, the polymerization of a fluid resin into a three-dimensional thermoset polymer, or physical, eg, the cooling of an expanded thermoplastic polymer to a temperature below its second-order transition temperature or its crystalline melting point to prevent polymer flow. 

In order to compare calculated and experimentally observed phase portraits it is necessary to know very exactly all the coefficients of the describing nonlinear differential Equation 14.3. Therefore, different methods of determination of the nonlinear coefficient in the Duffing equation have been compared. In the paraelectric phase the value of the nonlinear dielectric coefficient B is determined by measuring the shift of the resonance frequency in dependence on the amplitude of the excitation ( [1], [5]). In the ferroelectric phase three different methods are used in order to determine B. Firstly, the coefficient B is calculated in the framework of the Landau theory from the coefficient of the high temperature phase (e.g. [4]). This means B = const, and B has the same values above and below the phase transition. Secondly, the shift of the resonance frequency of the resonator in the ferroelectric phase as a function of the driving field is used in order to determine the coefficient B. The amplitude of the exciting field is smaller than the coercive field and does not produce polarization reversal during the measurements of the shift of the resonance frequency. In the third method the coefficient B was determined by the values of the spontaneous polarization... 

The introduction in the early 1980s of the concept of in situ gel systems demonstrated that a considerable prolongation in duration of action could be obtained. In situ gelling systems have unique properties, which can make a liquid change phase to a gel or sohd phase in the culde-sac upon its instillation into the eye. Three methods have been employed to induce phase transition on the eye surface change in pH and temperature as well as activation by ions. 

Finally, all three electronic characterisation methods indicate deviations from the expected Hoestery-Letson behaviour at temperatures between 360 K and 400 K where the structural phase transition was identified by X-ray diffraction. The deviation of the //(r)-characteristic from the expected trapping-and-release behaviour starts at a lower temperature for the in-plane FET transport than for the SCLC or TOF transport along the surface normal. Moreover, the temperature interval where the in-plane transport is affected by structural changes amounts to at least 60 K and appears to be much broader than that for the out-of-plane transport. 

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