Surface interaction parameter measurement of solvated polymers via model end-tethered chains
Richard J. Sheridan, Sara V. Orski, Ronald L. Jones, Sushil K. Satija, Kathryn L. Beers
We present a method for the direct measurement of the relative energy of interaction between a solvated polymer and a solid interface. By tethering linear chains covalently to the surface, we ensured the idealized and constant configuration of polymer molecules for measurement, modeling, and parameter estimation. For the case of amine-terminated polystyrene bound to a glycidoxypropyl silane film submerged in cyclohexane-d12, we estimated the χ parameter for the temperature range 10.7 °C to 52.0 °C, and found a downward sloping trend that crosses the χ=0.5 threshold at 37 °C to 40 °C, in agreement with solution estimates for the same system. We simultaneously estimated the surface interaction parameter χ_s at each temperature, finding a decreasing affinity of the chains for the surface with increasing temperature, consistent with empirical observations. The theoretical model shows some limitations in a stronger solvent (toluene-d8) that prevent rigorous parameter estimation, but we demonstrate a qualitative change in χ and χ_s towards stronger solvency and weaker surface interaction with increasing temperature.