Thermodynamics of Polydimethylsiloxane‐Solutions III. Experimental Results and Theoretical Calculations of Solvent Activities

Abstract

Solvent activities of seven organic solvents in mixtures with PDMS (Polydimethylsiloxane) of different molecular weights have been measured at 298.15 and 313.15 K using the vapor sorption technique. The results have been used for testing the thermodynamic consistency of an extended version of Flory's theory. In this theoretical approach a more detailed expression of the combinatorial entropy is used and found to be superior to the common Flory‐Huggins expression.

Solvent quality as reflected in concentration- and temperature-dependent Flory-Huggins interaction parameters

“…As already reported in the literature,15, 16 TL represents a good solvent for PDMS. It is, according to the χ values shown in Figure 5, which all lie well below 0.5 in the dilute range, considerably better than the theta solvent (cf.…”

Correlation of solvent activities in polymer solutions: a comparison of models

“…The systems chosen were PS/cyclohexane [25,26,[28][29][30], PS/toluene [17,25,26,28,30,33,35], PDMS/benzene [17][18][19] and PEG/water [38][39][40].…”

“…In general the models investigated provide a good predictive description of the systems studied. Table 5 Average absolute deviations (%) obtained with predictive models studied as a function of the polymer molecular weight for the PDMS/benzene system [17][18][19] The interaction parameters presented were fitted to the data on the top row. Table 6 Average absolute deviations (%) obtained with predictive models studied as a function of the polymer molecular weight for the PEG/water system [38][39][40] Fig.…”

The g interaction parameter of polymer-solvent systems

“…Equations 13 and 14 show that the g interaction parameter is the reduced residual chemical potential (a) of the polymer, in the limit 2 = 0, and (b) of the solvent, in the limit 2 = 1. Determining g°T he empirical value of g°c an be obtained from the experimental result of the parameter (measured through the activity of the solvent) by means of eq 13 gy°= J0 Xv du2 (15) gf°= f0 d</>2 (16) These two g°parameters are related, so that knowledge of in both scales of concentration and integration over the two variables (u2 and 2) is not needed. If is known in one of the scales and g°i s calculated by integration over…”

“…The parameter g°c an thus be calculated theoretically by means of eq 20 and this theoretical g°b e compared with the empirical g°(determined from the experimental through eq 16), if the values of s2/slt X12, and Q12 are known for the system. For some of the systems studied in the present work, the values of s2/s1, X12, and Q12 are available in the literature.…”