Irreversible dimensional change

There are two principally different types of temperature-driven dimensional changes in plastics and plastic-based composites linear shrinkage (which we will further call shrinkage) and expansion-contraction. Shrinkage is both the irreversible process and the result of the process. Expansion-contraction is a reversible process. 

Fig. 5 Typical isotherm of a a hydrophilic and b a hydrophobic surface layer. 0 is the starting point of the rising segment of the isotherm at n = 0, C is the collapse point of the two-dimensional gel structure, B-C is the range of irreversible structural changes when the particles are removed from the interface, B is the point where the nanoparticulate layer breaks up and H denotes the minimal area of the monolayer in a hexagonal arrangement of the particles...

Although irreversible melting is commonly associated with oriented crystalline polymers, the possibility of conducting the transformation under reversible conditions that approach equilibrium cannot be disregarded. In fact, the treatment of this problem as one of phase equilibria lead to important relations between crystallization, deformation, and dimensional changes.(3,4)... 

The a- and p-keratins exist in the oriented crystalline state and possess a high concentration of the cystine residues. They also undergo contraction when subjected to the action of a wide variety of reagents.(70) It is recognized that two distinctly different types of contractile processes can be observed in a-keratin fibers. One of these involves the interaction with reagents known to sever disulfide cross-links. As would be expected, in this case the observed dimensional changes are irreversible. 

Figure 7.13 indicates the relationship between mould temperature and irreversible post-moulding dimensional changes after temperature ageing for a series of LCP variants moulded into couplers. The effect of in-mould annealing is clear for all of the variants, namely a substantial reduction of post-mould dimensional change occurs with increasing mould temperature. Table 7.14 shows environmental test results, and... 

D is a scalar with respect to transformations of the three-dimensional space, but changes sign when t is replaced by —t. In molecular-kinetic theory this property of D is related to the well-known problems of irreversibility and entropy increase, the more so since by the dissipation theorem,... 

An experiment with an irreversible inhibitor should carry with it a control experiment involving the addition of a substrate if the location of the reaction with inhibitor is at the active site, then the addition of a substrate will slow down the rate of inhibition. For example, the reactivity of papain (5 pM) with a 1.71 pM solution of 4-toluenesulphonylamidomethyl chloromethyl ketone suffers a drop of 1.68-fold when the substrate (methyl hippurate) is changed from 12.7 to 21.1 mM. The inhibitor which reacts covalently with the enzyme should carry either a radioactive or spectroscopic tag which would enable the location of the altered amino acid to be determined in the sequence, and hence in the three-dimensional X-ray crystallographic map of the enzyme. An alternative approach is to design an inhibitor with groups (analogous to those attached to the substrate) which force it to bind at the active site (Scheme 11.18). 

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