TY - JOUR
T1 - Specular neutron reflection at the mica/water interface - Irreversible adsorption of a cationic dichain surfactant
AU - Browning, Kathryn Louise
AU - Griffin, Lucy Rachael
AU - Gutfreund, Philipp
AU - Barker, Robert David
AU - Clifton, Luke Ashley
AU - Hughes, Arwel
AU - Clarke, Stuart Matthew
PY - 2014/1/1
Y1 - 2014/1/1
N2 - Neutron reflection from the important mineral mica at the solid/liquid interface is presented here using a new approach - a very thin mica crystal supported on a silicon substrate. This approach avoids the problems of crystal defects and surface undulations that have hindered previous work. The use of mica as a reflectivity substrate is important as it is a model surface, which is atomically smooth with a high structural charge. In this work the mica/water interface is fully characterized. In particular, a characteristic double critical edge is observed, arising from the higher scattering length densities of the mica and D2O subphase relative to the silicon support. The experimental data are modelled using a combined approach: conventional amplitude summation (matrix method) for the thin layers and reflected intensity summation with attenuation terms for the thick layers of mica and hydrocarbon adhesive. Reflection data from the adsorption of the dichain cationic surfactant didodecyldimethylammonium bromide (DDAB) to the surface of muscovite mica from aqueous solution are also presented. It is found that, at twice the critical micelle concentration, a bilayer of DDAB with a thickness of 24Å is observed, containing essentially no water. Its partial removal by washing and ion exchange is also presented.
AB - Neutron reflection from the important mineral mica at the solid/liquid interface is presented here using a new approach - a very thin mica crystal supported on a silicon substrate. This approach avoids the problems of crystal defects and surface undulations that have hindered previous work. The use of mica as a reflectivity substrate is important as it is a model surface, which is atomically smooth with a high structural charge. In this work the mica/water interface is fully characterized. In particular, a characteristic double critical edge is observed, arising from the higher scattering length densities of the mica and D2O subphase relative to the silicon support. The experimental data are modelled using a combined approach: conventional amplitude summation (matrix method) for the thin layers and reflected intensity summation with attenuation terms for the thick layers of mica and hydrocarbon adhesive. Reflection data from the adsorption of the dichain cationic surfactant didodecyldimethylammonium bromide (DDAB) to the surface of muscovite mica from aqueous solution are also presented. It is found that, at twice the critical micelle concentration, a bilayer of DDAB with a thickness of 24Å is observed, containing essentially no water. Its partial removal by washing and ion exchange is also presented.
KW - mica
KW - neutron reflection
KW - solid/liquid interfaces
KW - surfactant adsorption
UR - http://www.scopus.com/inward/record.url?scp=84907558473&partnerID=8YFLogxK
U2 - 10.1107/s1600576714016318
DO - 10.1107/s1600576714016318
M3 - Journal article
AN - SCOPUS:84907558473
SN - 0021-8898
VL - 47
SP - 1638
EP - 1646
JO - Journal of Applied Crystallography
JF - Journal of Applied Crystallography
IS - 5
ER -