1 research outputs found
Dilational Properties of Novel Amphiphilic Dendrimers at Water–Air and Water–Heptane Interfaces
In this work, a series of novel amphiphilic dendrimers
taking polyamidoamine
dendrimer as the core with different hydrophobic tails QPAMC<sub>m</sub> were synthesized and the dilational properties were studied as monolayers
by dilational rheological measurements at the water–air and
water–<i>n</i>-heptane interfaces to explore the
nature of adsorption behaviors. The results showed that the maximum
values of the dilational modulus seemed to have no obvious variation
in a wide change of hydrophobic chain length at the surface. However,
there was considerable variability in the tendency of the influence
of bulk concentration on the dilational modulus at the two different
interfaces. It was interestingly found that the diffusion-exchange
process slowed down with the increase of alkyl chain length leading
to more elastic nature of adsorption film, which was contrary to the
tendencies of conventional single chain and gemini surfactants. It
is reasonable to consider that, in the case of the molecule having
short chain length such as QPAMC<sub>8</sub>, the alkyl chains are
too short to overlap across the headgroup, enable the intermolecular
hydrophobic interaction to be predominant with increasing of surface
concentration, which enhances the elasticity and shows the slowest
diffusion-exchange process. Whereas, when the chain length increases
to 12 or 16, the alkyl chains are long enough to act intramolecularly
to form intracohesion conformation, which results in enhancing the
diffusion-exchange process. In conclusion, the interfacial behaviors
are dictated by the size ratio between the tail and headgroup. A reasonable
model with respect to the molecular interaction was proposed on the
basis of experimental data. The results of interfacial tension relaxation
and dynamic light scattering (DLS) experiments, in accord with the
proposed mechanism, also present the unusual tendency comparing to
the traditional single or gemini surfactants