Second virial coefficients characterize the thermodynamic behavior of a dilute polymer solution. They are usually defined via the concentration dependence of the osmotic pressure, π, of a polymer solution:
π/cB = RT[1/Mn + A2cB + A3cB2 + ···] (1)
where:
A2, A3 | second, third osmotic virial coefficient |
CB | (g cm–3) concentration of polymer (B) |
Mn | number-average relative molar mass of the polymer |
R | gas constant |
T | (measuring) temperature |
However, most experimental data are measured by light scattering. Scattering methods enable the determination of A2 via the common relation:
KcB/R(q) = 1/MwPz(q) + 2A2Q(q)cB + ··· (2)
where:
K | a constant that summarizes the optical parameters of a scattering experiment |
Mw | mass-average relative molar mass of the polymer |
Pz(q) | z-average of the scattering function |
q | scattering vector q = (4π/λ)sin½θ |
Q(q) | function for the q-dependence of A2 |
R(q) | excess intensity of the scattered beam at the value q |
λ | wavelength |
θ | scattering angle |
In the dilute concentration region, the virial equation is usually truncated after the second virial coefficient which leads to a linear relationship. A linearized relation over a wider concentration range can be constructed if the Stockmayer-Casassa relation between A2 and A3 is applied:
A3Mn = (A2Mn/2)2 (3)
The values of second virial coefficients depend on the chosen polymer-solvent pair, on temperature and pressure, and on molar mass. In good solvents, a scaling relation can be applied for the molar mass dependence:
A2 = αMw−β (4)
The constants α and β for a number of polymer-solvent pairs are given in the table below. They were newly fitted to experimental data by a nonlinear least-squares fitting procedure. Experimental data were taken from a recent table of experimental A2 values in Ref. 1. The unit of A2 (used to determine the constants α and β) is cm3 mol g–2. The unit for the molar mass is g mol–1.
Polymer | Solvent | T/K | α | β |
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Amylose | dimethylsulfoxide | 298.15 | 0.0086 | 0.235 |
Amylose tris(N-phenyl carbamate) | 2-propanone | 290.15 | 0.0157 | 0.417 |
Cellulose tris(N-phenyl carbamate) | 2-propanone | 290.15 | 0.0023 | 0.177 |
Cellulose tris(N-phenyl carbamate) | tetrahydrofuran | 298.15 | 0.0021 | 0.116 |
Dextran | water | 298.15 | 0.0353 | 0.394 |
Dextran (acid-hydrolyzed) | water | 298.15 | 0.0516 | 0.361 |
2-(Diethylamino)ethyl dextran | water | 293.15 | 0.129 | 0.503 |
Hydroxypropyl cellulose | ethanol | 298.15 | 0.108 | 0.371 |
Poly(N-acryloylmorpholine) | N,N-dimethylformamide | 298.15 | 0.0084 | 0.295 |
Polybutadiene | cyclohexane | 298.15 | 0.0112 | 0.204 |
Polybutadiene | tetrahydrofuran | 296.15 | 0.0235 | 0.257 |
Poly(butyl methacrylate) | 2-butanone | 298.15 | 0.0099 | 0.285 |
Poly(4-tert-butylstyrene) | cyclohexane | 298.15 | 0.0377 | 0.362 |
Poly(4-tert-butylstyrene) | toluene | 310.15 | 0.0129 | 0.293 |
Polycarbonate-bisphenol-A | 1,2-dichloroethane | 298.15 | 0.0372 | 0.319 |
Polycarbonate-bisphenol-A | dichloromethane | 298.15 | 0.0124 | 0.205 |
Polycarbonate-bisphenol-A | tetrahydrofuran | 298.15 | 0.0426 | 0.333 |
Polycarbonate-bisphenol-A | trichloromethane | 298.15 | 0.016 | 0.227 |
Poly(chloroprene) | butyl acetate | 298.15 | 0.0041 | 0.229 |