Mixing unfavorable

Most polymers are not compatible with one another unless specific favorable interactions are present. This is because the favorable entropy of mixing is too small to overcome the unfavorable enthalpy of mixing, thus making the free energy of mixing unfavorable (2). A few pairs of immiscible and miscible polymers, respectively, are shown in Table 22.1. 

Remember that the hump which causes the instability with respect to phase separation arises from an unfavorable AH considerations of configurational entropy alone favor mixing. Since AS is multiplied by T in the evaluation of AGj, we anticipate that as the temperature increases, curves like that shown in Fig. 8.2b will gradually smooth out and eventually pass over to the form shown in Fig. 8.2a. The temperature at which the wiggles in the curve finally vanish will be a critical temperature for this particular phase separation. We shall presently turn to the Flory-Huggins theory for some mathematical descriptions of this critical point. The following example reminds us of a similar problem encountered elsewhere in physical chemistry. 

The contaminant removal and temperature effectiveness in the mixing strategy are equal to 1. In practical installations incomplete mixing in the room and unfavorable temperature gradient and location of the exhaust openings in relation to air supply may, however, cause short-circuiting of the supply air into the exhaust openings and the efficiency may remain below 1. 

Thus, the tendency is that in the absence of any adjacent substituent on either side of an amide bond, the 12-membered turn is favored, the 10-membered being formed when the amide bond is flanked by substituted carbons. The reduced 12/ 10-hehx population or rearrangement to the 3i4-hehx observed upon N-terminal deprotection of mixed /9-peptides can be explained in terms of unfavorable... 

The data from Louvain-la-Neuve suggest that mixed neutron-photon therapy is particularly efficient in patients with unfavorable prognostic factors, such as PSA >20 ng/mL [35]. 

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