It is discovered that complexes of DNA and hydrophobically modified polyelectrolytes form a rigid network of threadlike or fibrous aggregates at the liquidgas interface whose morphology can dramatically affect the mechanical properties. While mixed solutions of DNA and poly(N,N-diallyl-N,N-dimethylammonium chloride) (PDADMAC) exhibit no notable surface activity, the complexes formed from DNA with poly(N,N-diallyl-N-butyl-N-methylammonium chloride) are surface active, in contrast to either of the separate components. Further, complexes of DNA and poly(N,N-diallyl-N-hexyl-N-methylammonium chloride) (PDAHMAC) with its longer hydrophobic side chains exhibit pronounced surface activity with values of the surface pressures up to 16 mN/m and dynamic surface elasticity up to 58mN/m. If the PDAHMAC nitrogen to DNA phosphate molar ratio, N/P, is between 0.6 and 3, abrupt compression of the adsorption layer leads unexpectedly to a noticeable decrease of the surface elasticity. Application of imaging techniques reveals that this effect is a consequence of the destruction of a rigid network of threadlike DNA/polyelectrolyte aggregates at the interface. The toroidal aggregates, which are typical for the bulk phase of DNA/PDADMAC solutions in this range of N/P ratios, are not observed in the surface layer. The observed link between the mechanical properties and interfacial morphology of surface active complexes formed from DNA with hydrophobically modified polyelectrolytes indicates that tuning the polyelectrolyte hydrophobicity in these systems may be a means to develop their use in applications ranging from nonviral gene delivery vehicles to conductive nanowires.
Application of dilational surface
rheology, surface tensiometry,
ellipsometry, Brewster angle, and transmission electron and atomic
force microscopies allowed the estimation of the structure of the
adsorption layer of a fullerenol with a large number of hydroxyl groups,
C60(OH)
X
(X = 30 ± 2). The surface properties of fullerenol solutions proved
to be similar to the properties of dispersions of solid nanoparticles
and differ from those of the solutions of conventional surfactants
and amphiphilic macromolecules. Although the surface activity of fullerenol
is not high, it forms adsorption layers of high surface elasticity
up to 170 mN/m. The layer consists of small interconnected surface
aggregates with the thickness corresponding to two–three layers
of fullerenol molecules. The aggregates are not adsorbed from the
bulk phase but formed at the interface. The adsorption kinetics is
controlled by an electrostatic adsorption barrier at the interface.
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