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From Homogeneous to Segregated Structure of Poly(dimethylsiloxane)/Cellulose Derivative Mixed Langmuir Films Depending on Composition: An in Situ Neutron Reflectivity Study
journal contribution
posted on 2015-06-16, 00:00 authored by Alae El Haitami, Michel Goldmann, Fabrice Cousin, Gilberte Dosseh, Sophie CantinThe
mixing behavior of deuterated polydimethylsiloxane (PDMSd)
and cellulose acetate butyrate (CAB) spread as Langmuir films at the
air–water interface was studied by means of surface pressure–area
isotherms, Brewster angle microscopy (BAM) observations, and in situ
neutron reflectivity. The contrast variation method was used with
different D2O/H2O mixtures as subphase, allowing
contrast matching to either CAB, PDMSd, or PDMSd/CAB mixed film if
homogeneous. At PDMSd volume fractions Φ lower than 0.6, the
mixed film is a homogeneous monolayer throughout the film compression,
in agreement with the monophasic film observed by BAM and the attractive
interactions between PDMSd and CAB evidenced from the isotherm measurements.
In contrast, at PDMSd volume fractions Φ higher than 0.6, a
vertically segregated structure of the mixed film is highlighted.
Indeed, whatever the surface pressure, a bilayer structure is observed
with a PDMSd layer in contact with the air over a thin CAB layer in
contact with the subphase. These results show that the structure of
the film is mainly driven by the PDMSd volume fraction which allows
obtaining either a homogeneous membrane which composition can be tuned
or a vertically segregated system. In contrast, only the thickness
of the layers varies with the surface pressure while the structure
of the film is not affected.