Subject entanglements

Finishing of Wool. Wool (qv) competes for markets where warmth, wrinkle recovery, and abiUty to set in creases are important. Wool problems relate to shrinkage, particularly to its tendency to felt. This is caused by scaly stmcture, which tends toward fiber entanglement when wet and subjected to mechanical action. In order to compensate for this tendency, wool needs to be set and also made shrinkproof if it is to be laundered. 

The combined effects of a divalent Ca counterion and thermal treatment can be seen from studies of PMMA-based ionomers [16]. In thin films of Ca-salts of this ionomer cast from methylene chloride, and having an ion content of only 0.8 mol%, the only observed deformation was a series of long, localized crazes, similar to those seen in the PMMA homopolymer. When the ionomer samples were subject to an additional heat treatment (8 h at 100°C), the induced crazes were shorter in length and shear deformation zones were present. This behavior implies that the heat treatment enhanced the formation of ionic aggregates and increased the entanglement strand density. The deformation pattern attained is rather similar to that of Na salts having an ion content of about 6 mol% hence, substitution of divalent Ca for monovalent Na permits comparable deformation modes, including some shear, to be obtained at much lower ion contents. 

The nature of the bonds between cellulosic fibres in paper has been the subject of some controversy over many years. The early and now largely discredited view was that paper derived its strength merely from mechanical entanglement of the fibres. However, experiments in which paper is formed from non-aqueous solvents produce sheets with very poor strength properties and have thus tended to disprove this conjecture. In the mid-1950s deuteration experiments were carried out which demonstrated that of the order of 0.4-2% of all hydroxy groups are additionally bonded in paper as compared with the unbonded fibres. This observation led to the view that... 

The chain tension arises in a physical way at timescales short enough for the tube constraints to be effectively permanent, each chain end is subject to random Brownian motion at the scale of an entanglement strand such that it may make a random choice of exploration of possible paths into the surrounding melt. One of these choices corresponds to retracing the chain back along its tube (thus shortening the primitive path), but far more choices correspond to extending the primitive path. The net effect is the chain tension sustained by the free ends. 

Starting from simple statistical considerations concerning the coupling between similar or dissimilar chains, a model was constructed for the architecture of a class of IPN where interaction among phases occurs on a molecular level. It was shown(Equation 13) that the contributions to the modulus due to crosslinks are subject to linear additivity, while a square root additivity rule holds for the contributions due to entanglements. 

Lack of steady flow of a liquid-bearing colloidal solution requires the existence of a space-filling, three-dimensional structure. As we might select a perfect crystal as a csuionical solid, or liquid argon as a prototypical liquid, we csui choose the covalently crosslinked network, without any entanglements, to represent the ideal gel state. Then an appropriate time scale for reversible gels would be the lifetime of a typical crosslink bond if subjected to conditions that would cause flow in a pure... 

The first principle that can be accepted in the composition of mixed bodies is a mineral spirit, which being distributed everywhere, produces various things according to the different matrices or pores of the earth in which it may be entangled but as this is somewhat metaphysical, and as it is not subject to the senses, it is well to establish the sensible principles of it. I will report those in common use. 

Analysis of networks in terms of molecular structure relies heavily on the kinetic theory of rubber elasticity. Although the theory is very well established in broad outline, there remain some troublesome questions that plague its use in quantitative applications of the kind required here. The following section reviews these problems as they relate to the subject of entanglement. 

Fig. 25 Viscoelastic behavior of a semi-dilute solution of DNA. Elastic modulus (G, filled symbols) and viscous modulus (G", open symbols) are plotted, together with their ratio G"IG = tan 5 (solid curve), for a 93 mg/mL DNA solution subjected to a heating-cooling cycle. The entanglement of DNA helices and, at high temperature, of single strands causes the almost monotonous increase of the dynamic moduli. Reproduced with permission from [110]...

---