Chain fracture

Step 3. The set of fracture properties G(t) are related to the interfaee structure H(t) through suitable deformation mechanisms deduced from the micromechanics of fracture. This is the most difficult part of the problem but the analysis of the fracture process in situ can lead to valuable information on the microscopic deformation mechanisms. SEM, optical and XPS analysis of the fractured interface usually determine the mode of fracture (cohesive, adhesive or mixed) and details of the fracture micromechanics. However, considerable modeling may be required with entanglement and chain fracture mechanisms to realize useful solutions since most of the important events occur within the deformation zone before new fracture surfaces are created. We then obtain a solution to the problem. 

The dissimilarity in the kinetic laws for chain fracture observed under different flow conditions reflect the deficiencies of the present theories which should be able to incorporate both dependences (M 1 and M 2) into its structure, with either... 

An understanding of the mechanism of creep failure of polymer fibres is required for the prediction of lifetimes in technical applications. Coleman has formulated a model yielding a relationship similar to Eq. 104. It is based on the theory of absolute reaction rates as developed by Eyring, which has been applied to a rupture process of intermolecular bonds [54]. Zhurkov has formulated a different version of this theory, which is based on chain fracture [55]. In the preceding sections it has been shown that chain fracture is an unlikely cause for breakage of polymer fibres. 

Odell JA, Keller A. Flow-induced chain fracture of isolated linear macromolecules in solution. J Polym Sci B 1986 24 1889 1916. 

If the number of radiation-induced cross-links exceeds the number of chain fractures, there is a net molecular weight increase if the degree of cross-linking is sufficiently high, an insoluble network is formed. Charlesby (6) gives a detailed treatment of these processes. 

The evidence is that for poly-D,L-alanine cross-linking is the predominant process for poly-a,L-lysine chain fracture is predominant, and for poly-a,L-glutamic acid cross-linking predominates below pH 4 and chain fracture above pH 4. It is possible that under all conditions studied here all three polymers undergo partial cross-linking and chain scission hence, pH could either suppress cross-linking at high pH or suppress chain fracture... 

Under the influence of stresses chemical reactions take place leading to chain fracture. Examples are... 

Mercier H. and Speer K. G. (1998) Transport of bottom water in the Romanche Fracture Zone and the Chain Fracture Zone. J. Phys. Oc. 28, 779-790. 

Although some theories (e.g Knauss ) utilise the full expression of Eq. (7) to describe the forward reaction rate v for chain fracture, it is usual to approximate this rate by... 

The approach taken in this section will be to consider in turn the empirical factors which govern the occurrence of molecular fracture and its consequences. The incidence of main-chain fracture in polymers under tensile stress is dependent on a wide range of variables, including polymer chemical structure, physical structure or morphology, additives, environment, time, temperature, orientation and physical state, as well as the more obvious variables of stress and strain. 

It is helpful to think of main-chain fracture as a competitive response to deformation if the deformation can be accommodated more readily by molecular flow or by crystallographic processes, then main-chain fracture will be less evident. This competitive situation underlies many of the phenomena reported in what follows. 

Since polymers with tetrasubsltuted centers are difficult to synthesize, two main types of positive resists have been dlsclosed. Polymethylmethacrylate r polymethyl Isopropenyl ketone hich undergo side chain elimination and subsequent main chain fracture have been used as positive electron beam resists (cf. 

Main-chain scission has been shown to occur in polyphenylvinylketone under UV irradiation (366 nm). Norrish type-2 scission due to reaction of the first n-II triplet state of the ketone has been shown to occur [422]. Under 7-irradiation, this polymer, which was expected to crosslink according to the Miller rule, was shown to undergo main-chain fracture with a G value of 0.35. Inhibition of the degradation in the presence of napthalene and diphenyldisulphide demonstrates the participation of radicals and excited n-II triplet states in the radiolysis [423]. 

Flow-Induced Chain Scission. If the chains are overstretched, that is, e increases along the plateau in Figure 2, they will eventually break 12, 13). The molecular weight of the fracture products can then be determined by the method just outlined. Thus, through our technique we can both break chains in a controlled manner and analyze the resulting fracture products within the same apparatus, this double capacity enabling a systematic study of the flow-induced chain fracture. The principal results, to be of consequence later, are as follows ... 

Fig. 11 Imposed strain rates plotted against critical molecular weight for chain fracture for PEO. The triangles are for experiments with aqueous PEO solutions performed using the pressure driven flow apparatus and the squares are from experiments carried out in the pump driven flow loop. The circles are for the viscous solvent (water/glycerol 50/50 = 6.4 cP) passed through the flow cell...

The weaker dependence is completely unexpected and contradicts the common view that hydrodynamic friction force drives CST and chain fracture. Nguyen and Kausch [108] ascribed (10) to the intramolecular friction (so-called internal viscosity ) between chain segments in the coiled part in FTF. Unlike the internal viscosity depends on strain rate and could reach much higher values than... 

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