Between two polymers

Processes that occur at a size scale larger than the individual chain have been studied using microscopy, mainly transmission electron microscopy (TEM), but optical microscopy has been useful to examine craze shapes. The knowledge of the crazing process obtained by TEM has been ably summarised by Kramer and will not be repeated here [2,3]. At an interface between two polymers a craze often forms within one of the materials, typically the one with lower crazing stress. 

Brown, H.R., The relation between the width of an interface between two polymers and its toughness. Macromolecules (2(X)1, in press). 

The above theories are a necessary condition to judge the compatibility between two polymers, but not a sufficient condition. 

Earlier studies [14,15] clearly reveal that there is a reaction between two polymers and that the extent of reaction depends on the blend ratio. As 50 50 ratio has been found to the optimum (from rheological and infrared studies) ratio for interchain crosslinking, the higher heat of reaction for the NBR-rich blend may be attributed to the cyclization of NBR at higher temperatures. There is an inflection point at 50 50 ratio where maximum interchain crosslinking is expected. Higher viscosity, relaxation time, and stored elastic energy are observed in the preheated blends. A maximum 50-60% of Hypalon in NBR is supposed to be an optimum ratio so far as processibility is concerned. 

Binger and Hanna [76] have considered the alignment of 4-n-octyl-2-flurophenyl-4-n-octyloxybiphenyl-4 -carboxylate (MBF) and 8CB at room temperature on the (110) surface of polyethylene and the (100) surface of nylon. They find that alignment of both molecules is dominated by the behaviour of the flexible tails that prefer to align parallel between two polymer chains. This forces the mesogenic core to straddle one or more chains. This is illustrated in Fig. 4 for the specific case of MBF on the (110) surface of... 

Bartlett, P., Henderson, S. I. and Mitchell, S. J. (2001) Measurement of the hydrodynamic forces between two polymer-coated spheres. Philos. Trans. R. Soc. London, Ser.A, 359, 883-895. 

One way to describe the interaction between two polymers is through their interaction parameter, The interaction parameter is a thermodynamic term which encompasses the... 

R is a measure of the energy absorbed by a surface plasmon, K is the equilibrium constant for a reaction between two polymers, A and B... 

One practical example of demixing that might be attributed to a difference in crystallizability is the incompatibility in blends of polymers with different stereochemical compositions. The stereochemical isomers contain both chemical and geometrical similarities, but differ in the tendency of close packing. In this case, both the mixing energy B and the additional mixing entropy due to structural asymmetry between two kinds of monomers are small. However, the stereochemical differences between two polymers will result in a difference in the value of Ep. Under this consideration, most experimental observations on the compatibility of polymer blends with different stereochemical compositions [89-99] are tractable. For more details, we refer the reader to Ref. [86]. 

Bico technology can also be used to form composite fibers that can be broken apart, by using polymers with poor mutual adhesion (e.g. polyolefin and PET). A fiber made with a dozen or more segments, alternating between two polymer... 

In general, the miscibility between two polymers can be predicted by thermal characterization of the blends [36], One of the most simple and effective ways to predict miscibility between two polymers is to consider the behavior of the glass transition temperature in the blend systems, which is known as the Tg method. In miscible blend systems, only a single 7 g intermediate between two components appears in the amorphous state. Therefore, we studied the change of... 

The structure, the thickness, and the interactions generated by the presence of the adsorbed polymer layers have been extensively studied [17], In particular, the force between two polymer-covered mica sheets in various solvency conditions has been probed via the SEA technique [27,28], The force is purely repulsive in a good solvent and becomes attractive as the solvent gets poorer. However, these studies concern only a regime of large interaction compared to the thermal energy and are restricted to interactions between solid surfaces. 

If we assume that crosslinking is primarily caused by the reaction between two polymer radicals, we must still explain how they come sufficiently close together to react. Here we must choose between two alternatives ... 

FIG. 13.15 Examples of the various contributions to the interaction energies between two polymer-coated particles. The curves shown illustrate qualitatively the change in Gibbs free energy due to the overlap of the tails, loops, and so on. (Redrawn with permission from Sato and Ruch 1980.)... 

Whether a polymer is grafted on the surface or simply adsorbed on the surface has a bearing on the force between two polymer-coated surfaces. Adsorption is a reversible process and can be affected by temperature, compression of the polymer layer, and the like. 

We discussed in Section 13.5 how thermodynamic considerations determine the effects of polymer layers on stabilization. In this section we consider a simple case of interaction between two polymer layers to illustrate the ideas introduced above. It will become evident that some, but not all, of the polymer-induced forces discussed in Section 13.6 are encompassed by the arguments presented in this section. Even with some factors omitted, detailed determination of forces is considerably involved, as is evident from the following discussion. 

It should be mentioned that the value of yInax for the complexes, that are saturated with PEG of relatively high molecular weight (6000), is larger than 1.0 (Ymax = 1.5). Thus there are 1.5 units of PEG per one unit of PMAA instead of 1 per 1 corresponding to the maximum number of the hydrogen bonds between two polymer components. This discrepancy can be explained by the fact that macromolecules of PEG form loops in the complex. The units of loop sections do not participate in the formation of hydrogen bonds. 

An example of photo-crosslinking is the reaction which follows the photodissociation of diazofluorenes, with the loss of molecular nitrogen and formation of a carbene. Two carbenes will then react to form an adduct between two polymer chains (the crosslink). In this case irradiation can be made in the near UV, for instance at 365 nm with a medium-pressure mercury arc lamp (Figure 6.13). 

This repulsion was calculated by different authors [201,202], For a low grafting density (T < 1 /R2g), the repulsive force per unit area in a good solvent and between two polymer coated surfaces is [200]... 

Polymer radicals may recombine upon bimolecular termination. When this cross-linking takes place between two polymer molecules the molecular yield increases. When there are more than one radical on the polymer chain, cross-linking between these two sites will form only a loop (Fig. 9.1), that is, no increase in the molecular weight ensues despite the fact that cross-linking has occurred. In competition to recombination, radicals may disproportionate, when at least... 

Levels of lactate in buttermilk and yoghurt (and blood) were estimated using disposable sensors formed from screen-printed graphite laminated between two polymer sheets [18]. Platinum (deposited by sputter-coating) was the transducing surface. Layers of Nation were added to reduce interference and were surmounted by lactate oxidase in a mixture of polyethyleneimine and poly (carbamoyl) sulphonate hydrogel. The samples were measured in stirred buffer. A good correlation between biosensor results and those obtained with an enzyme kit was claimed but the data had a considerable amount of scatter—if the enzyme kit is taken as the reference method then a more severe analysis of the biosensor results [33] would not have shown them in a... 

In contrast, there are no big differences (although sometimes they can be significant) between two polymers with distinct irregular structures undergoing a step-by-step degradation process. These polymers are difficult or impossible to stabilize and the effect of an eventual stabilization is not so marked as in the case of chain degradation. 

Copolymers have been studied extensively for several decades, partly because of their industrial and biological importance, and partly because of their interesting and sometimes perplexing properties. Many physical and mechanical properties of copolymers, which comprise two or more covalently bonded sequences of chemically distinct monomer species, depend on both the comonomer composition and the arrangement of these comonomers in the polymer chain. There may be significant differences, for example, between two polymer systems with the same chemical composition, but one of which has the comonomers randomly distributed in the chain while the other has long blocks of each monomer type. 

The concept of interpenetrating the polymer network was introduced in the early 1960s [108]. The basic idea is the formation of blends with two different independent polymer networks on the nano scale. The non-miscibility between two polymers is the general rule and an important question is to know if the gelation takes place before or after the phase separation, because the timing for these two phenomena will govern the size of each network domain [109,110]. 

Many theories were developed to describe the distribution of segments between two polymer brushes. On the basis of a lattice... 

Compatibility of polymers implies a semi-quantitative measure can be used to predict whether two or more polymers are compatible. The use of one of the semi-quantitative approaches, solubility parameter, was demonstrated by Hughes and Britt (22). It was concluded (8) that one parameter was insufficient to predict the compatibility. In this paper, we now introduce critical surface tension which is determined from the surface properties of a polymer. Though both of these parameters have been related by Gardon (15), we are inclined to use the latter because we can further describe the wettability between two polymers. For instance, by the use of yc, we can predict equally well that compatibility between polystyrene and polybutadiene can be improved if butadiene is... 

Fuel cell researchers have also investigated other reference electrodes, such as a pseudo-reference electrode constructed by inserting a micro-sized carbon filament between two polymer electrolyte membranes [73], The main advantage of pseudoreference electrodes is their easy implementation, although one disadvantage is that their DC potential is unknown. However, this DC potential may not be that critical because EIS measurements mainly rely on the AC perturbation signal from which the impedance is calculated. 

The value of the maximum strain e m iX depends on the type of micro-elements A and B. Thus the superscript t in the previous equation can be (a) PP, to denote the connection between two polymer micro-elements P or P (b) CC, to denote the connection between two catalyst micro-elements C or C and, finally, (c) PC, to denote the connection between polymer and catalyst microelements. 

The base-base interaction between two polymer chains is well reflected by a hypochromic effect, which can be studied by UV spectroscopy in solution. For a series of compounds, UV measurements were done and the results discussed and compared with those of emission spectroscopy. 

There are two explanations of inereased melt PET thermal stability when organomodified layered silicates are introduced. On the one hand the increased PET thermal stability is connected with barrier properties of layered silicate itself On the other - layered silicate plate can participate as a binding bridge between two polymer macromolecules, which can fix end-groups and decrease their hydrolytic activity. 

There are several different ways of obtaining an estimate of the interaction between two polymers. These include heat of mixing measurements, inverse gas chromatography, solvent vapour absorption, various scattering techniques and viscosity... 

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