3 research outputs found
Self-Assembled Molecular Platforms for Bacteria/Material Biointerface Studies: Importance to Control Functional Group Accessibility
Highly
controlled mixed molecular layers are crucial to study the role of
material surface chemistry in biointerfaces, such as bacteria and
subsequent biofilms interacting with biomaterials. Silanes with non-nucleophilic
functional groups are promising to form self-assembled monolayers
(SAMs) due to their low sensitivity to side-reactions. Nevertheless,
the real control of surface chemistry, layer structure, and organization
has not been determined. Here, we report a comprehensive synthesis
and analysis of undecyltrichlorosilane- and 11-bromoundecyltrichlorosilane-based
mixed SAMs on silicon substrates. The impact of the experimental conditions
on the control of surface chemistry, layer structure, and organization
was investigated by combining survey and high-resolution X-ray photoelectron
spectroscopy analysis, wettability measurements, and ellipsometry.
The most appropriate conditions were first determined for elaborating
highly reproducible, but easily made, pure 11-bromoundecyltrichlorosilane
SAMs. We have demonstrated that the control is maintained on more
complex surfaces, i.e., surfaces revealing various chemical densities,
which were obtained with different ratios of undecyltrichlorosilane
and 11-bromoundecyltrichlorosilane. The control is also maintained
after bromine to amine group conversion via S<sub>N</sub>2 bromine-to-azide
reactions. The appropriateness of such highly controlled amino- and
methyl-group revealing platforms (NH<sub>2</sub>–<i>X</i>%/CH<sub>3</sub>) for biointerface studies was shown by the higher
reproducibility of bacterial adhesion on NH<sub>2</sub>–100%/CH<sub>3</sub> SAMs compared to bacterial adhesion on molecular layers of
overall similar surface chemistry but less control at the molecular
scale
Characterization of Carbon Surface Chemistry by Combined Temperature Programmed Desorption with in Situ X-ray Photoelectron Spectrometry and Temperature Programmed Desorption with Mass Spectrometry Analysis
The analysis of the surface chemistry of carbon materials
is of prime importance in numerous applications, but it is still a
challenge to identify and quantify the surface functional groups which
are present on a given carbon. Temperature programmed desorption with
mass spectrometry analysis (TPD-MS) and X-ray photoelectron spectroscopy
with an in situ heating device (TPD-XPS) were combined in order to
improve the characterization of carbon surface chemistry. TPD-MS analysis
allowed the quantitative analysis of the released gases as a function
of temperature, while the use of a TPD device inside the XPS setup
enabled the determination of the functional groups that remain on
the surface at the same temperatures. TPD-MS results were then used
to add constraints on the deconvolution of the O1s envelope of the XPS spectra. Furthermore, a better knowledge
of the evolution of oxygen functional groups with temperature during
a thermal treatment could be obtained. Hence, we show here that the
combination of these two methods allows to increase the reliability
of the analysis of the surface chemistry of carbon materials
Nanosized Films Based on Multicharged Small Molecules and Oppositely Charged Polyelectrolytes Obtained by Simultaneous Spray Coating of Interacting Species
Simultaneous spraying of polyelectrolytes
and small multicharged
molecules of opposite charges onto a vertical substrate leads to continuous
buildups of organic films. Here, we investigate the rules governing
the buildup of two such systems: poly(allylamine hydrochloride)/sodium
citrate (PAH/citrate) and PAH/sulfated α-cyclodextrin (PAH/CD-S).
Special attention is paid to the film growth rate as a function of
the spraying rate ratio of the two constituents. This parameter was
varied by increasing the spraying rate of one of the constituents
while maintaining constant that of the other. For PAH/CD-S systems,
whatever the constituent (PAH or CD-S) whose spraying rate was kept
fixed, the film growth rate first increases and passes through a maximum
before decreasing when the spraying rate of the other constituent
is increased. For PAH/citrate, the film growth rate reaches a plateau
value when the spraying rate of citrate is increased while that of
PAH is maintained constant, whereas when the spraying rate of citrate
is maintained constant and that of PAH is increased, a behavior similar
to that of PAH/CD-S is observed. The composition of PAH/CD-S sprayed
films determined by X-ray photoelectron spectroscopy is independent
of the spraying rate ratio of the two constituents and corresponds
to one allylamine for one sulfate group. For PAH/citrate, by increasing
the PAH/citrate spraying rate ratio, the carboxylic/nitrogen ratio
in the film increases and tends to 1. There is thus always a deficit
of carboxylic groups (COO<sup>–</sup> + COOH) with respect
to amines (NH<sub>2</sub> + NH<sub>3</sub><sup>+</sup>). Yet, the
ratio (COO<sup>–</sup>/NH<sub>3</sub><sup>+</sup>) is always
close to 1, ensuring exact charge compensation. The film morphology
determined by atomic force microscopy is granular for PAH/CD-S and
is smooth and liquid-like for PAH/citrate. A model based on strong
(respectively weak) interactions between PAH and CD-S (respectively
citrate) is proposed to explain these features