Dimethyldodecylamine N-oxide (DDAO) shows high surface activity with two distinct energy states at the hydrophilic silica/aqueous solution interface studied by total internal reflection (TIR) Raman spectroscopy combined with ratiometric and kinetic analysis.
A simple
imaging add-on utilizing the combination of a relay lens
and an optical grating to a nulling ellipsometer for the purpose of
imaging and correcting angular distortion is designed, built, and
tested. Image contrast is achieved on a standardized silicon wafer,
graphene transferred on silicon wafer, a self-assembled monolayer
of 1-octadecanethiol on gold, and a 1:1 mixture of dilauroylphosphatidylcholine
/ distearoylphosphatidylcholine (DLPC/DSPC) on copper. The configuration
used in this paper corrects the angular distortion and depth of focus
with a spatial resolution of 4.38 μm in the laser’s incident
direction and 7.81 μm in the direction that is perpendicular
to the incident plane together with 3 Å of normal resolution
while still maintaining a large field of view of at least 720 μm
× 550 μm in focus without executing any line scanning,
post-image reconstruction, or specially customized objective method.
Better resolution is possibly attained with higher NA optics.
The
adsorption of dimethyldodecylamine oxide (DDAO) and Triton
X-100 (TX) as single components and mixed systems at the silica–water
interface has been studied using total internal reflection (TIR) Raman
spectroscopy combined with multivariate curve resolution (MCR). In
this study, the mixtures of DDAO and TX indicate minimal synergism
in the bulk solution; however, the cooperative adsorption behavior
on the silica surface is shown with various mixtures of DDAO (up to
1.3 mM) and TX (up to 1.1 mM). Adding the DDAO (up to 0.3 mM) to TX
solution, the surface excess of TX shows 30% enhancement, from 1.2
to 1.8 μmol m–2. Adding the DDAO also shifts
the TX adsorption isotherms, resulting in the Gibbs free energy change
of −2.87 ± 0.73 kJ mol–1. This free
energy change is interpreted as the decrease in surface energy when
the silica surface charged sites are screened by the DDAO adsorbed
layer. Alternatively, when a DDAO solution contains a small amount
of TX molecules, i.e., < 30 μM, its adsorption on the silica
surface quickly equilibrates. In addition, the formation of a more
ordered liquid-crystalline adsorbed layer, as in the case of single-component
DDAO adsorption, is not observed.
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