Viscosity of dilute and moderately concentrated polymer solutions

The viscosit ies of solut ions of t hree polysty rene fractions in t hree solve nts of v ar y ing solvent power were m easured at t wo temperat ures.The relat ive vi scosit ies of the syst em s investigated ranged from 1.03 to 43.The appli cability of two empirical expressions for the concen tration depende nce, nam ely t he Martin equation and t he Baker relation, is examined .In addit ion, t he results are represented by m eans of poly nomials of suitable degr ee.The numerical procedures for t he e valuatio n of t he coeffi cien ts are discussed in detail.In t he concent ration r an ge investigated , t he in troduction of a reduced co ncen t rat ion scale S = ['1] c, places t he viscosity-con cen t ration curves for different molec ular weights in t he same solven t on a more nearly common scale.This scale, S, is simply rela ted t o another reduced scale c/co.H ere Co represen ts t he concentration a t which t he equivalent spher es of t he coiling m olec ul es, a s d efin ed at infinite dilu tion, would just begin to o verlap .At c/co « 1, t he con cent ration dependence can be described in terms of hydrody namic in teract ion.This intera ction involves single molecul es and can also involve t he int rinsic v iscosity and interactions of aggregates of low order .An a ttempt is made t o d educe from t he viscosi ty data and on t he basis of cer tain hydrody namic results, t he equilibrium constant s and relative p opulations of s uch aggregates.R easonable values are obt ained .On approaching Co, t he a verage volume a vailable t o a chain molec ule in a good solve nt is redu ced because of t he cage form ed by its nearest neighbors.The effective press ure is just t he internal osmo tic press ure.This leads to an expression for t he concent rat ion depe ndence of t he viscosi ty, in terms of t he vi rial coeffi cie nts of osmotic press ure, luolec ular weight, and size.These equat ions are s hown to be in satisfactory agreemen t wi t h t he experimen tal data.In part icul ar , in t he neighborhood of Co one obtains r easo nabl e values for t he molec ular exte nsio n f actors of t he chain .