Viscoelastic properties, NMR

C. J. Lewa and J. D. De Certaines, Viscoelastic property detection by elastic displacement NMR measurements, J. Magn. Reson. Imaging, 1996, 6, 652-656. 

Bulky crosslinks or side-groups in the network chains, e.g., dendritic wedges [73], may also influence molecular mobility and viscoelastic properties of polymer networks. For example, UV curing of difunctional acrylates results in the formation of zip-like network junctions, which may be regarded as extreme cases of bimodal networks [52], Results obtained with the NMR T2 relaxation method agree well with those of mechanical tests... 

The viscoelastic properties of the vulcanizates in the function of temperature were examined by means of the method of resonance-free, forced vibrations, using Rheovibron apparatus DDV-II-C at frequency of 110 Hz. The mobility of macromolecules and their fragments was examined by means of the nuclear magnetic resonance (NMR) method. 

Viscoelastic properties of silica gels were investigated gels based on formamide/(decane + decanol) molar ratio 2.5-3 gave the highest elasticity [63]. Condensation rate monitored with 29si NMR [64]. 

The vast range of supramolecular polymeric materials also extends from the use of small molecules (e.g., double-sided discotics or multifunctional monomers with a discrete tether) to very large molecules (polymeric or dendritic). Another important characteristic of SPs is the timescale upon which the chains exist, which is defined by the rate of association/ dissociation of the monomers. Tme dynamic SPs must be reversible (breaking and recombining) on experimental time-scales (e.g., NMR timescale). A physical model developed by Cates and co-workers predias many viscoelastic properties of SPs as a funaion of the strength of the noncovalent interactions existing between monomers.Although initial studies focused on wormlike micelles, the model has been demonstrated to successfully describe the viscosity behavior of reversible, self-complementary UPy-based SPs. ... 

Finally, other than the techniques discussed in the foregoing, the probe to highlight polymer properties includes viscoelastic properties and NMR. These probes are also combined with STM and AFM and integrated instruments are being developed to elucidate the polymer properties. One of the inventors of STM, Rohrer, had proposed the possibility of such a direction several years ago [86]. 

Green MA, Bilston LE, Sinkus R (2008) In vivo brain viscoelastic properties measured by magnetic resonance elastc raphy. NMR Bio-med 21 755-764... 

In Chapter 4 it was explained that the linear elastic behavior of molten polymers has a strong and detailed dependency on molecular structure. In this chapter, we will review what is known about how molecular structure affects linear viscoelastic properties such as the zero-shear viscosity, the steady-state compliance, and the storage and loss moduli. For linear polymers, linear properties are a rich source of information about molecular structure, rivaling more elaborate techniques such as GPC and NMR. Experiments in the linear regime can also provide information about long-chain branching but are insufficient by themselves and must be supplemented by nonlinear properties, particularly those describing the response to an extensional flow. The experimental techniques and material functions of nonlinear viscoelasticity are described in Chapter 10. 

The challenges involved in the material properties of PPC relate to its thermal features, i.e., its thermal decomposition, and the glass transition temperature (Tg) of about body temperature of the otherwise amorphous polymer. These have implications for processing and application of the material. This review will discuss consecutively the thermal, viscoelastic, and mechanical properties of PPC and the experiences in processing PPC and its composites. The properties of solutions of PPC will also be presented, and the biodegradabUity and biocompatibility discussed. Spectroscopic properties will not be discussed. Further information on NMR data can be found in the following references [2, 10-12]. A t3 pical spectrum is shown in Fig. 2 [13]. 

Rheological properties are particularly sensitive and for some solubilizates, such as a-methylnaphthalene, the solutions may become viscoelastic the appearence of viscoelasticity often depends on subtle effects in chemical structure29). Certain spectroscopic features are strongly influenced. Thus the H and 13C NMR line widths show large increases, the 81 Br quadrupole relaxation may be strongly affected and there may be the appearance of linear dichroism, birefringence and conductance anisotropy for flowing systems. 

The presence of a temporary network structure manifests itself through the first factor in the right hand side of Eq. 17. It comes from the h (t) component of the relaxation function. The second factor results from fast non-isotropic motions of monomeric imits which give rise to the (t r(t) function defined in equations (6) and (9). It must be noticed that the reference temperature Ti = Tg(,xi,2) +50 which appears in NMR properties, is close to the reference temperature Tj introduced from viscoelastic measiurements [11]. The second factor reflects a free volume effect it depends necessarily on an expansion coefficient which is about equal to 10-3K. 

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