Relaxation solid state

The combined investigations of a series of aryl-aliphatic copolyamides (xTyl -y and MT) by dielectric relaxation, solid-state 13C and 2H NMR, and dynamic mechanical experiments demonstrate the existence of three secondary transitions y, ft and co, in order of increasing temperature. 

The approach developed in this paper, combining on the one side experimental techniques (dynamic mechanical analysis, dielectric relaxation, solid-state 1H, 2H and 13C NMR on nuclei at natural abundance or through specific labelling), and on the other side atomistic modelling, allows one to reach quite a detailed description of the motions involved in the solid-state transitions of amorphous polymers. Bisphenol A polycarbonate, poly(methyl methacrylate) and its maleimide and glutarimide copolymers give perfect illustrations of the level of detail that can be achieved. 

Funke, K., Banhatti, R. D., Braeckner, S., Cramer, C., and Wilmer, D. (2002) Dynamics of mobile ions in crystals, glasses and melts, described by the concept of mismatch and relaxation. Solid State Ionics 154-155, 65-74... 

Figure 21.10 shows the partially relaxed solid-state NMR spectrum of a P(3HB-co-37%3HP) sample measured by Torchia s pulse sequence [56]. 

It is worth noticing that a molecular modelling approach is used to complement the experimental techniques of dynamic mechanical analysis, dielectric relaxation, solid-state and H NMR. 

Sasaki, K., and Maier, J. (2000). Re-analysis of defect equilibria and transport parameters in Y203-stabilized Zr02 using EPR and optical relaxation. Solid State Ionics 134 303-321. Birkby, I., and Stevens, R. (1996). Applications of zirconia ceramics. Key. Eng. Mater. 122-124 327-332. 

Keywords solid-state extrusion, roll-drawing, orientation, crystallinity, mechanical properties, a-relaxation, solid-state deformation, compression ratio, morphology, tie molecules, lamellar orientation, laminate theory, fibrillar structure, rolling. 

Measuring oxygen diffusion and oxygen surface exchange by conductivity relaxation. Solid State Ionics, 136-137, 997-1001. 

E. De Grave, Fe Mossbauer effect in ankerite Study of the electronic relaxation. Solid State Commun. 60, 541-544 (1986)... 

M continually decreases under the influence of spin-spin relaxation which destroys the initial phase coherence of the spin motion within they z-plane. In solid-state TREPR, where large inliomogeneous EPR linewidths due to anisotropic magnetic interactions persist, the long-time behaviour of the spectrometer output, S(t), is given by... 

Different solid-state NMR techniques CPMAS NMR, the second moment of the signal, the spin-lattice relaxation time in the rotating frame T p) were combined to reach the conclusion that in the case of por-phine H2P the double-proton transfer is followed by a 90° rotation within the crystal (see Scheme 2). 

In the preparation and processing of ionomers, plasticizers may be added to reduce viscosity at elevated temperatures and to permit easier processing. These plasticizers have an effect, as well, on the mechanical properties, both in the rubbery state and in the glassy state these effects depend on the composition of the ionomer, the polar or nonpolar nature of the plasticizer and on the concentration. Many studies have been carried out on plasticized ionomers and on the influence of plasticizer on viscoelastic and relaxation behavior and a review of this subject has been given 119]. However, there is still relatively little information on effects of plasticizer type and concentration on specific mechanical properties of ionomers in the glassy state or solid state. 

Solid-state C NMR techniques have been applied to the characterization of the different phases of several polybibenzoates [25,30], including P7MB, PDTMB and PTEB. The last two polymers offer the advantage of the stability of the mesophase at room temperature. The spectra corresponding to the pure mesophase of these samples only exhibited a broad component, while the spectra of the annealed samples were separated into two components crystal and noncrystal. The shapes of the mesophase and the noncrystal components are very similar, and only modest variations in the relaxation times were observed between these two components. The degree of crystallinity of these samples was determined... 

The electrical conductivity in the solid state is determined by the product of the carrier concentration and the carrier mobility. In conjugated polymers both entities are material dependent and, i.e., are different for electrons and holes. Electrons or holes placed on a conjugated polymer lead to a relaxation of the surrounding lattice, forming so-called polarons which can be positive or negative. Therefore, the conductivity, o, is the sum of both the conductivity of positive (P+) and negative polarons (P ) ... 

The solid-state NMR technique may also be used in cellulose derivatives to follow the degree of substitution and degradation of the chain e.g. as found for cellulose nitrate 16). Investigations on the composition of copolymers may also been done as examplared by celluloseacetate-butyrate given in Fig. 6, 20). Here, owing to relaxation differences the spectra cannot be used for elementary analyses, but for estimating the relative number of the components. 

The high degree of resolution in the CP/MAS NMR spectra also permits the analysis of the relaxation behaviour of individual carbon atoms. The T1 relaxation is seldom solely determined by a single motion of a single intermolecular interaction. Nevertheless, if the dominant source is known, T1 can provide useful information. As an example the relaxation behaviour of celluloseacetate in both acetone solution and in the solid state will be discussed. The experimental data in Table 2 give chemical shifts and relaxation T1 information for the above system 21 . 

By the comparison of T1 relaxation data in solution and in the solid state it is realised that the relaxation time increases disproportionally when going from solution to... 

Table 2. 13C NMR chemical shifts and relaxation data T1 of cellulose acetate in solid state and a in acetone-d6 soution at 298 K. Spectrometer JEOL FX-200, frequency 50 MHz...

Not only relaxation T1 data, but chemical shifts also give indications regarding the effect of water on cellulose. In Fig. 7 (and Table 3) 22) some data are collected for the solid-state NMR spectra of moist cellulose and for comparison, also of cellulose acetate under similar conditions. 

Fig. 7. A C-13 relaxation time measurement of solid state wetted cellulose acetate (6% by weight water) using the inversion recovery (IR) method at 50.1 MHz and spinning at 3.2 kHz at the magic angle (54.7 deg) with strong proton decoupling during the aquisition time (136.3 ms), (upper part of the Figure). Tau represents the intervals between the 180 deg (12.2 us) inverting and 90 deg (6.1 us) measuring pulse. 2200 scans were collected and the pulse delay time was 10 s, Cf. Table 3 and Ref.281...

Recent reports 54 seem to indicate that the resolution of the notoriously difficult solid-state spectra of coals may be enhanced by such techniques as double exponential multiplication and convolution difference. Differential relaxation behaviour as discussed in connection with intermolecular effects in carbohydrates and low temperature methods may further improve identification. 

Experimental data on nitrogen obtained from spin-lattice relaxation time (Ti) in [71] also show that tj is monotonically reduced with condensation. Furthermore, when a gas turns into a liquid or when a liquid changes to the solid state, no breaks occur (Fig. 1.17). The change in density within the temperature interval under analysis is also shown in Fig. 1.17 for comparison. It cannot be ruled out that condensation of the medium results in increase in rotational relaxation rate primarily due to decrease in free volume. In the rigid sphere model used in [72] for nitrogen, this phenomenon is taken into account by introducing the factor g(ri) into the angular momentum relaxation rate... 

In addition to giving conformational information, solid state NMR relaxation experiments can be used to probe the thermal motion of polymers in the hydrated cell wall (5). The motion of the polymers can give us clues as to the environment of the polymer. When there are both rigid and mobile polymers within a composite material, NMR spin-diffusion experiments can be used to find out how far apart they are. 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

This report has been written in order to demonstrate the nature of spin-state transitions and to review the studies of dynamical properties of spin transition compounds, both in solution and in the solid state. Spin-state transitions are usually rapid and thus relaxation methods for the microsecond and nanosecond range have been applied. The first application of relaxation techniques to the spin equilibrium of an iron(II) complex involved Raman laser temperature-jump measurements in 1973 [28]. The more accurate ultrasonic relaxation method was first applied in 1978 [29]. These studies dealt exclusively with the spin-state dynamics in solution and were recently reviewed by Beattie [30]. A recent addition to the study of spin-state transitions both in solution and the... 

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