Complex formation between a semiflexible nonionic polymer, hydroxypropylcellulose (HPC), and a cationic surfactant, hexadecyltrimethylamonium bromide (HTAB), is investigated by static and dynamic light scattering (DLS) and by viscometry. Upon addition of surfactant, at a fixed polymer concentration, the solution specific viscosity increases initially to a maximum value, and then decreases, in parallel with the hydrodynamic radius of the polymer-surfactant complex measured by DLS. The increase in specific viscosity and hydrodynamic radius is interpreted to reflect chain expansion due to the electrostatic interaction between bound micelles. The maximum occurs at the saturation of micelle binding, and the subsequent decrease, as more surfactant is added, is due to chain contraction because of electrostatic screening by free micelles and their Br- counter-ions. This behavior was observed at various polymer concentrations and we found that the maximum in the solution viscosity and in the hydrodynamic radius occurs always at [HTAB]/[HPC] = 0.18, from which we deduce that the average number of surfactant molecules bound to a single HPC chain is 28. The effect of electrostatic interactions between the bound micelles on the solution viscosity can be represented by the "interaction viscosity", eta(I), defined as the difference between the measured viscosity of the ternary polymer solution and that computed from the sum of solvent, polymer and surfactant. We find that the normalized interaction viscosity eta(I)/eta(I,max), where n(I,max) is the interaction viscosity at the maximum surfactant-polymer binding, is a common function of [HTAB]/[HPC], independent of polymer concentration and ionic strength. The origin of this observation appears to lie in the fact that the fraction of complex formed and the relative chain expansion are functions only of the ratio [HTAB]/[HPC].