In a recent publication on critical opalescence it was shown that, for a binary liquid mixture of critical concentration, measurements of the angular dependence of scattered intensity at small temperature distances above the critical temperature can be related to the range of molecular forces.' This concept has been applied to polymer solutions. The range of molecular forces and the critical temperature of solutions of polystyrene of different molecular weights in cyclohexane have been reported.2 It was found that the range of molecular forces I was strikingly small. Thus, we investigated the critical opalescence of polystyrene in ethylcyclohexane in order to see whether the smallness of 2 is characteristic only of the system polyst yrene-cyclohexane.The scattering formula of solutioiis of critical concentration at small temperature distances above the critical temperature is stated in a simplified form in eq. (1) := C(T/T,)/[(AT/TJ + (81r2/3) (Z2/X2) sin ' ( 0 / 2 ) ](1)
The theoretical justification for using M[η], or a similar quantity, as a universal calibration parameter in GPC is reviewed. The equation based on this parameter is applied to transform the primary calibration curve, obtained by means of polystyrene samples, into calibration curves for poly‐α‐methylstyrene, polypropylene, and linear polyethylene. The Mark–Houwink equations for these polymers, as they are used in the transformation, are discussed. The resulting GPC calibration curves are compared with molecular weights and peak elution volumes of fractionated poly‐α‐methylstyrene and polypropylene. The same comparison is made with samples of polypropylene and polyethylene having very broad molecular weight distributions. The agreement lies within experimental error.
CuSO4 in solutions of NaC103 and Bu4NC103 plotted against the molar concentrations of the added salts. I t can be seen that the curves essentially duplicate those of Figure 1. If anything, assuming constant absorptivity coefficients for CuS04 ion pairs, the demixing effect of Bu4NC103 may be greater than that of Bud- NETS.Spectra were run in 0.02 M CuS04 containing 0.1 M NaBr and 0.1 M Bu&Br. After rough empirical corrections for absorption by the CuBr+ complex, a t 250 mp, the residual absorbance in NaBr was 0.95 arid in Bu4NBr was 1.35. The same demixirig effect is qualitatively evident in this latter system.Up to this point, it has been assumed that the only significant antagonistic interaction is that between the organic cations and the sulfate anions. However, the remaining ions must also play some part, although it is probably less important in the present cases. The anions chlorate and bromide are water structure-breakers, with negative viscosity-B coefficients. l 2 The ethanesulfonate ion may also be a structure-breaker, or a weak structure-former of the organic type. A structurebreaking anion would exert a cooperative effect in the sense that it can provide loose water molecules to be organized around the quaternary ammoninm ion.2 The small differences between the ethanesulfonate and chlorate solutions may reflect differences in their compatibilities with the quaternary ammonium ion. One consequence of this hypothesis is that the demixirig effect would be very much smaller in solutions of CuSOl and Bu4NF, since both sulfate and fluoride ions are strong water-structure formers of the chargooriented type.Acknowledgment. We thank Professor S. Petrucci of this department for assistance and helpful sugges tions.The micellar weight of well-purified sodium dodecyl sulfate (NttDDS) was determined by means of an automatic osmometer in 0.03,0.1, and 0.342 ?il aqueous sodium chloride solutioii at 36.5'. The respective average numbers of monomer molecules in the micelles, N , were 58.9, 82.9, arid 115; in 0.03 .M NaCl at 3l0, N = 63.1.The solvent contained a specified amount of NaDDS in order to repress dissociation of the micelles and to minimize the monomer contribution to the osmotic pressure. The dialytic behavior of YaDDS is discussed, and the tnagnitude of the Staverman reflection coefficient is estimated. Saturation of the aqueous solution with benzene was found to increase N .
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