= Solution
\b[Taking the printed reference to part(iii) literally], measure an equilibrium <water> <contact angle> with a calibrated sessile-drop goniometer on a smooth homogeneous surface. With independently constrained interfacial tensions, test $\gamma_{SV}-\gamma_{SL}=\gamma_{LV}\cos\theta_C$. Advancing and receding measurements reveal pinning and hysteresis; <contact angle> alone cannot independently determine both unknown solid-interface energies.
If the intended reference was instead the polymer-size prediction in the preceding part, use <static light scattering> or <small-angle neutron scattering> at both temperatures on appropriately dilute solutions. At small scattering wave number $q$, the <Guinier approximation>
$$
I(q)\simeq I(0)\exp(-q^2R_g^2/3)
$$
gives $R_g$ from the slope of $\ln I$ against $q^2$. Control concentration, aggregation and scattering contrast, and compare the extracted radii. Dynamic light scattering normally measures a hydrodynamic size rather than directly the same <radius of gyration>. Answering both readings avoids silently correcting the printed cross-reference.
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