Pulse NMR Measurements

The new interface model and the concept for the carbon black reinforcement proposed by the author fundamentally combine the structure of the carbon gel (bound mbber) with the mechanical behavior of the filled system, based on the stress analysis (FEM). As shown in Figure 18.6, the new model has a double-layer stmcture of bound rubber, consisting of the inner polymer layer of the glassy state (glassy hard or GH layer) and the outer polymer layer (sticky hard or SH layer). Molecular motion is strictly constrained in the GH layer and considerably constrained in the SH layer compared with unfilled rubber vulcanizate. Figure 18.7 is the more detailed representation to show molecular packing in both layers according to their molecular mobility estimated from the pulsed-NMR measurement. 

This conclusion is supported by the experimental result " given by the pulsed-NMR measurement that the spin-spin relaxation time T2 is considerably shorter for the gel than that for the matrix mbber vulcanizate, which of course, indicates that the modulus is considerably higher for the gel than for the matrix mbber. More quantitatively, Maebayashi et al. measured the acoustic velocity of carbon gel by acoustic analysis and concluded that the compression modulus of the gel is about twice that of matrix mbber. Thus, at present, we can conclude that the SH layer, of course without cross-linking, is about two times harder than matrix cross-linked mbber in the filled system. 

Ripmeester and Davidson make first pulsed NMR measurements... 

We dispersed each sample (1.5 g) in 10 mL of 0.01 Af phosphate (pH 7) and submitted the dispersion to pulsed NMR measurement. T2 was obtained from the following equation... 

An ESR study using an oil-soluble free radical probe to observe rotational correlation time, tc, of oil see Table VII), and pulsed NMR measurements indicate that the molecules of the emulsifying surfactants surround an oil particle to form a ternary oil-surfactant-water complex see Figure 6). 

T, T2, and the Correlation Time Chemical Exchange 166 Pulse NMR Measurements 170 Applications 173... 

For the examples discussed so far, continuous wave (cw) ESR was utilized, where the magnetic field is swept during the measurement. In the pulsed free induction decay attenuation method [47, 48], the sample in the applied steady field is subjected to a powerful microwave pulse which causes the tipping of the magnetization vector. This method is analogous to pulsed NMR measurements. After the pulse, the... 

Since the sensitivity of pulse NMR is very high and H Ti values for usual polymers are less than 1 s due to the spin diffusion, rapid measurements with short repetition times are possible. This gives us the real time measurement of nonequilibrium phenomena such as crystallization in the polymer. The crystallization process of polymers has been studied by an optical microscope, dilatometry and X-ray diffraction. These methods only gives static information about the crystallization process. The pulse NMR measurements provide both the fraction and the molecular mobility of each phase. Figures 7.19 and 7.20 show the temperature change of the fractions and T2 values of crystalline, interfacial and amorphous components for poly(e-caprolactone)... 

L. J. Burnett and J. F. Harmon, "Self-diffusion in viscous liquids Pulse NMR measurements," J. Chem. Phys. 57,... 

Nearly all NMR instiunicnts produced today are of the F r type, and the use ot ( VV instruments is largely limited to special routine applicatiotts, such as the determination of the extent of hydrogenation in petroleum process streams and the determination of water in oils, food products, and agricultural materials, Despite this predominance of pulsed instruments in the tnarketplace, we find it convenient lo base our ini lial devolopmeni of NMR theory on C W experiments and move from there to a discussion of pulsed NMR measurements. 

In pulsed NMR measurements, nuclei in a strong magnetic (ield arc subjected periodically to very brief pulses of intense RF radiation as shown in f igure (9-5. The waveform in part (a) of the figure illustrates the pulse train, pulse width, and lime interval between pulses. 1 he expanded view of one of the pulses shows that each pulse is actually a packet of RF radiation. The waveforms arc intended to be illuslraiive and are not drawn to scale. The packet of radiation omsisis of many more cycles than are depicted. I hc length of the pulses 7 is usually less than 10 ps. and the frequency of the radiation is on the order of 10 to 10 MHz. the... 

A variety of compounds have been mixed with oil shale and coals as internal standards to determine the percentage of carbons observed in CP and single-pulse NMR measurements.""In some cases, the spinner material, Delrin, has been used as an internal standard." An excellent reference material is tetrakis (trimethyl silyl) silane (TKS). Furthermore, treatment with samarium (II) iodide selectively reduces the free radical content which can lead to an increase in the percentage of observable carbon. For example, treatment of Wyodak sub-bituminous (x>al with samarium (II) iodide has been shown to increase the percentage of observable carbons by 27%, leading to an increase in the carbon aromaticity of around 10% from 0.66 to 0.73. 

Pulsed NMR measurements have been made as a function of temperature to study the pyrolysis behaviour of oil shales. The method is sometimes referred to as NMR Thermal Scanning. To overcome receiver dead time, a 9O-T-9O90 pulse sequence is used to form the solid echo . The echo signal is then decomposed into a rigid (short relaxation time) and a mobile (longer relaxation time) component. These data are then related to various properties of the system. Parameters that can be extracted from the NMR data relate to the hydrogen content, phase structure, molecular mobility, and free radical content. By measuring the temperature dependence of these parameters... 

Figure 3. Block diagram of the real time pulsed NMR measurement system controlled by a microcomputer.

Figure 4. Probe head for the pulsed NMR measurement at high temperatures up to 330 C.

For dried Artemia cysts as a model system for desiccation tolerant species it has been found out by pulsed NMR measurements that the mobility of water protons unexpectedly increased below a certain residual water content The increased mobility was explained by the existence of intrinsic protective substances such as trehalose and glycerol in the cyst that replace water at the surface of biomolecules and therefore increase molecular mobility. 

The protective effect is dependent on the process conditions. Especially the product temperature during secondary drying seems to be a critical parameter for survival. As the protective effect only occurs for low residual water contents when structural water is already removed, the water replacement mechanism may play a role in protecting cells from desiccation damage. In order to further investigate the mechanism of protection, pulsed NMR measurements were carried out to measure proton mobility of samples with and without added protectant. 

MHz pulsed NMR measurements were made of solid krypton samples containing a natural abundance (11.55%) of Kr and isotopically enriched (73.1%) Kr between 37.2 and 115.6K. The coefficient of atomic self-diffusion in solid krypton was given by ... 

In this section, we first provide a quantum description of NMR applicable to both CW and pulsed NMR measurements. Then, we lake a classical approach to NMR and show how it provides a useful picture of CW-NMR, Finally, we complete this section with a discussion of Fourier transform measurements based again on a classical picture. 

By combining several pulses and performing pulsed NMR measurements, spin-lattice relaxation time (Tj) and spin-spin relaxation time (T2) can be obtained. The NMR parameters can provide information on gel solvents and tiie microscopic molecular movement of polymers. When the relaxation is dominated by dipole-dipole interaction, the correlation time Xg of molecular motion from the relaxation time is based on the Bloembergen-Purcell-Pound (BPP) tiieory [90]. Examples of the structure and dynamics of polymer gels are described in what follows. 

Tanaka H, Nishi T. Study of crystallization process of polymer from melt by a real-time pulsed NMR measurement. J Chem Phys 1986 85 6197. 

Yamanobe T, Kakiage M, Miyazaki N, Morita S, Uehara H. Development and Applications of in situ Pulse NMR measurement System for Drawing of Polymeric Materials. Jpn J Polym SciTech2012 69 235. 

The SET readout permitted pulsed EPR and then pulsed NMR measurements on a single phosphorous dopant. This readout technology removed a key blockage in the silicon qubit field, and revealed encouraging spin coherence times for the electron and nuclear spins. 

---