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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 approximationgives $R_g$ 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.

An experimental physicist who coauthored evidence for the polymer brush regime in grafted chains. The collaboration used small-angle neutron scattering on polydimethylsiloxane attached by one end to silicon dioxide. Layer thickness changed with grafting density and solvent quality, showing how neighboring chains force one another to stretch away from a surface.^[ref]

Small-angle neutron scattering probes structure using a neutron beam deflected through small scattering angles. For elastic scattering at wavelength $\lambda$, if $\theta$ is the full angle between incident and scattered beams, the transferred wave vector has magnitudeThe corresponding structural length scale is roughly $2\pi /q$, so a small angle accesses larger structures than an atomic-scale diffraction angle at the same wavelength.^[ref]

A collimated neutron beam with selected wavelength passes through the sample; a distant position-sensitive detector records the angular distribution. Comparing different sample-to-detector distances accesses different $q$ ranges. The measured intensity depends on neutron scattering length density contrast, shape and spatial correlations, rather than giving a direct photograph. Subtracting background and specifying the measured $q$ range are essential to interpreting a fitted size or correlation length.^[ref]