Dielectric relaxation measurement

Dielectric relaxation measurements of polyethylene grafted with acrylic acid(AA), 2-hydroxyethyl methacrylate (HEMA) and their binary mixture were carried out in a trial to explore the molecular dynamics of the grafted samples [125]. Such measurements provide information about their molecular packing and interaction. It was possible to predict that the binary mixture used yields a random copolymer PE—g—P(AA/HEMA), which is greatly enriched with HEMA. This method of characterization is very interesting and is going to be developed in different polymer/monomer systems. 

The same information may be obtained from purely rotational far infrared spectroscopy (FIR) and depolarized Rayleigh spectra. Dielectric relaxation measurements are also used for the same goal, most successfully in combination with far-infrared data. The absorption coefficient of a periodic electric field... 

While it is not clear how the constant frequency low field dielectric relaxation measurements mentioned above should be applied to reactions in liquids, save for a complete time-dependent theory of liquids, these effects are very significant. At short times (<10ps) the effective Onsager distance may be 20 nm, even in methanol or ethanol, but over the next two or three decades of time reduce to more nearly 2 nm. Such a change can reduce the rate of reaction much more rapidly than that which occurs by decay of the transient time dependence discussed in the previous sub-section. 

Dielectric relaxation measurements define an operational correlation time for the decay of the correlation function (P cosO)). For alcohols, the monomer rotation time, r2, increases from 18ps for n-propanol at 40°C to 44 ps for n-dodecanol at 40°C [83], A small measure of saturation in the dielectric relaxation time of alkyl bromides with increasing chain length has been noted by Pinnow et al. [242] and attributed to chain folding. 

Dielectric relaxation measurements for the adsorbed water have been reported by Jansen (44) the dielectric relaxation time is essentially 3r where r is the rotational jump time of the water molecule. From Figure 5 it can be seen that the dielectric and NMR mobility estimates agree rather well. All is not quite in order, however, for Jensen estimates from relaxation strength that he sees only one-third of the water molecules. 

Here td is the so-called Debye dielectric relaxation time. One could view td as a phenomenological time constant which applies to dielectric relaxation measurements, or alternatively for simple causes, involving dielectric relaxation of weakly interacting dipoles, tD is related to the reorientation time constant of the solvent dipole in the laboratory frame. 

Results of the dielectric relaxation measurements of the pure constituents and of the polyblends in terms of c" as a function of temperature... 

For si and sll, Davidson et al. (1977a, 1981) performed NMR spectroscopy and dielectric relaxation measurements where applicable, in order to estimate the barriers to molecular reorientation for simple hydrates of natural gas components, except carbon dioxide. Substantial barriers to rotation should also affect such properties as hydrate heat capacity. 

In order to assess the orientational stability of the poled state, the temperature dependence of the dipole mobility of the side groups was examined through dielectric relaxation measurements. (13) No low temperature relaxation below Tg was observed in the frequency range studied (100 Hz-100 kHz). In addition, the dielectric constant was approximately equal to the square of the refractive index, indicating that below T only electronic and no significant orientational contributions to the dielectric displacement are present. Thus, it was expected that a given orientational state of the ensemble would be stable at temperatures significantly below Tg. 

Dielectric relaxation measurements have been performed on a series of MGIMx copolymers with x varying from 21 to 76% [75]. 

The efficient mechanism for translative motion of a stem through an orthorhombic crystal discovered by dielectric relaxation measurements has... 

The results corresponding to dielectric relaxation measurements are more explicit than the mechanical ones. Figure 2.68 shows the data corresponding to s and tan 8 for the four first members of the series of poly(itaconate)s. 

This electro-optical effect, commonly observed as transient changes in optical birefringence of a solution following application, removal, or reversal of a biasing electric field E(t), has been used extensively as a probe of dynamics of blopolymer solutions, notably by O Konski, and is a valuable tool because it gives information different in form, but related to, results from conventional dielectric relaxation measurements. The state of the subject to 1975 has been comprehensively presented in two review volumes edited by O Konski (25). The discussion here is confined to an outline of a response theory treatment, to be published in more detail elsewhere, of the quadratic effect. The results are more general than earlier ones obtained from rotational diffusion models and should be a useful basis for further theoretical and experimental developments. 

Schwarz, G. Seelig, J. Kinetic properties and electric field effect of the helix-coil transition of poly(gamma-benzyl 1-glutamate) determined from dielectric relaxation measurements. Biopolymers 1968, 6, 1263-1277. 

A measurement of the Kerr relaxation times in succinoni-trile(SN)as a function of temperature is shown in Fig. 2. The Kerr relaxation times measured show the effect of temperature on the rotational motion of the SN molecules as they undergo a change from the liquid to the plastic crystal phase. The data obtained from the Kerr gate measurement is shown along with a best fit curve from depolarized Rayleigh scattering (dotted line), and a best fit curve from dielectric relaxation measure-... 

Dielectric relaxation measurements on some amines (aniline, N,N-di-methylaniline, benzidine. ..) display two relaxation times a longer one (of the order of 20—30.10-12 sec) attributed to overall molecular reorientation, and a shorter one (of the order of 1.10-12 sec) which may be interpreted as arising from an intramolecular process and has been attributed to nitrogen inversion 19-aa>, although this attribution is not unequivocal (rotation about the N—C bond may also contribute to the observed relaxation). 

Dielectric relaxation measurement in similar to dynamic mechanical measurements, except that it exploits the dipole electrical properties of the blend. It is, therefore. 

We interpret these results by assuming that the high values for the heats of adsorption pertain to specifically active centers, such as lattice holes (7). Dielectric relaxation measurements (4) and KMR studies (2) substantiate such conclusions. 

Proton magnetic resonance, infrared spectroscopy and dielectric relaxation measurements, on ortho- and meta-disubstituted anilines, indicate that (despite what is expected on the basis of the usual steric hindrance arguments) a meta-substituted compound such as 32 results in more hindered rotation of the NH2 group than for orf/zo-substituted compounds such as 33. Solute/solvent and solute/solute intermolecular hydrogen bonding interactions are responsible for this hindered rotation73. 

The transport properties were measured at 25°C using a variety of techniques. An extensive analysis of the dielectric relaxation measurements is provided by Epstein (4). The other methods are conventional and will only be summarized briefly ... 

This is, however, a macroscopic explanation of changes that occur on a molecular level, and is rather superficial. There is clearly a distribution of dielectric relaxation times in the microemulsion. The timescale of the dielectric relaxation measurement (tens of picoseconds) is too short for the phenomenon of fast exchange. It would appear, therefore, that the motional restriction of the water must vary throughout the microemulsion. 

The most powerful technique for studying molecular motions in protein-water systems below 0°C is magnetic resonance. Dielectric relaxation measurements can be used, but these measurements are more suitable at higher temperatures in homogenous solutions (13). Recently, the frequency dependence of the mehcanical properties of biopolymers has been shown to yield considerable kinetic information (14). I will limit discussion to the salient results attainable from these techniques. 

When the blends were examined using dielectric relaxation measurements which probe the dipole relaxation spectrum, values of P were found to be much lower (0.1-0.22). This was interpreted as indicating the development of heterogeneity at the molecular level caused probably by the crystalhzation of the PEEK component. 

In order to construct a more reliable relaxation time map quantitatively, complementary use of other methods like dielectric relaxation measurements and INS measurements with different energy resolutions are still needed. 

In general a polymer will have several different relaxation mechanisms, each of which will behave in a way similar to that just described. Many mechanical and dielectric relaxation measurements were made before the... 

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