Equations for calculating the specific refractive index increment, ∂n/∂c, for polymer/solvent systems have been developed starting with either the Gladstone-Dale equation or the Lorentz-Lorenz equation for the refractive index of a dielectric medium. The resulting equations can be used to estimate ∂n/∂c as a function of polymer concentration, temperature, solvent composition, and, for copolymers, monomer composition. Simplifying assumptions have been made to generalize these equations and make them more usable: 1) molar refractions are treated as constants, 2) the density of the polymer solution, in the limit of low polymer concentration, can be approximated via the additivity of volumes approach; the densities of polymer-free solvents and solvent mixtures are not necessarily subject to this approximation, 3) the mass density of solvents and solvent mixtures can be estimated by any one of several models developed specifically for this purpose; we will consider the Rackett equation, the COSTALD equation, and the standard assumption of mass and volume additivity, and 4) the mass density of a copolymer can be obtained from a weight fraction average of the mass densities of the homopolymers from which it is comprised. Comparisons to experimental data show that (∂n/∂c)_GD and (∂n/∂c)_LL both yield average absolute deviations of approximately 0.009 ml/gm.

从介电介质折射率的Gladstone-Dale方程或Lorentz-Lorenz方程开始，已经开发出了用于计算聚合物/溶剂系统的特定折射率增量∂n/∂c的方程。所得方程可用于估算作为聚合物浓度，温度，溶剂组成以及共聚物的单体组成的函数的ηn/∂c。为了简化这些方程式并使它们更有用，已经做出了简化的假设：1）摩尔折射被视为​​常数，2）在低聚合物浓度的限制下，聚合物溶液的密度可以通过体积加和法来近似; 不含聚合物的溶剂和溶剂混合物的密度不一定要采用这种近似方法，3）可以通过专门为此目的开发的几种模型中的任何一种来估计溶剂和溶剂混合物的质量密度；我们将考虑Rackett方程，COSTALD方程以及质量和体积加和的标准假设，以及4）共聚物的质量密度可以从组成该共聚物的均聚物的质量密度的重量分数平均值中获得。与实验数据的比较表明（∂n/∂c）_GD和（∂n/∂c）_LL均产生约0.009 ml / gm的平均绝对偏差。