Neutron reflectivity surface roughness

The use of neutron reflectivity at liquid interfaces, which is a method sensitive to both surface roughness and surfactant layer thickness, was reviewed with the examples of polydimethylsiloxane-surfactant layers.633 Sum-frequency generation (SFG) vibrational spectroscopy was applied to study surface restructuring behavior of PDMS in water in an attempt to understand antifouling properties of silicones.6 ... 

Shirai M, Nomura M, Asakura K, Iwasawa Y (1995) Development of a chamber for in situ polarized total-reflection fluorescence X-ray absorption fine structure spectroscopy. Rev Sci Inst 66 5493-5498 Sinha SK (1996) Surface roughness by X-ray and neutron scattering methods. Acta Phys Polonica A 89 219-234... 

Solvation of the head group has two effects on the adsorbed surfactant molecules one is the penetration depth of the ionic head group into the aqueous phase and the other surface roughness. For example, neutron reflection studies have found a difference in the penetration depth of the ionic head groups of SDS and hexadecyl-trimethylammonium bromide (HDTAB) at the air/water interface [50]. The measured separation between the position of the ionic head group and that of the mean position of the aqueous interface is (7.5 0.1) A for SDS and (8.0 0.1) A for HDTAB. These results are found to be independent of the structure of the adsorbed layer. 

Studies have been done to investigate the orientation and adsorption of surface active dyes at the oil/water interface using fluorescence [74, 75], resonance Raman scattering [76, 77]. Neutron reflectivity has been used [78] to determine the thickness of a surfactant (monodecyl tetraglycol ether) layer at the octane/water interface and the interfacial roughness, which was large (m. 90 A) due to the very low interfacial tension (7 = 0.08 mN rn ). 

Unique information about the unit cell in quasi-crystaUine monolayers can be obtained from X-ray °, neutron , heUum or low energy electron diffraction (LEED) data. In the grazing incidence X-ray diffraction (GIXD) experiment the beam is directed at the coated surface at a low angle and experiences total internal reflection from the metal support underneath the monolayer. The analysis of reflectivity and diffraction pattern of this reflected beam provides information about the molecular structure of the crystalline films, the thickness and refractive index of the layers and the roughness of the surface s . These experiments, however, require sophisticated and expensive equipment and are not therefore used routinely for monolayer characterization. 

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