10.1021/acs.langmuir.6b00746.s001
Saba Lotfizadeh
Saba
Lotfizadeh
Hassan Aljama
Hassan
Aljama
Dan Reilly
Dan
Reilly
Themis Matsoukas
Themis
Matsoukas
Formation of Reversible Clusters with Controlled Degree
of Aggregation
American Chemical Society
2016
dispersion state
pH
aminosilane
silica nanoparticles
monolayer
aggregation
silane
surface coverage
gel
interaction
2016-04-28 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Formation_of_Reversible_Clusters_with_Controlled_Degree_of_Aggregation/3309436
We
develop a reversible colloidal system of silica nanoparticles
whose state of aggregation is controlled reproducibly from a state
of fully dispersed nanoparticles to that of a colloidal gel and back.
The surface of silica nanoparticles is coated with various amino silanes
to identify a silane capable of forming a monolayer on the surface
of the particles without causing irreversible aggregation. Of the
three silanes used in this study, <i>N</i>-[3-(trimethoxysilyl)propyl]ethylenediamine
was found to be capable of producing monolayers up to full surface
coverage without inducing irreversible aggregation of the nanoparticles.
At near full surface coverage the electrokinetic behavior of the functionalized
silica is completely determined by that of the aminosilane. At acidic
pH the ionization of the amino groups provides electrosteric stabilization
and the system is fully dispersed. At basic pH, the dispersion state
is dominated by the hydrophobic interaction between the uncharged
aminosilane chains in the aqueous environment and the system forms
a colloidal gel. At intermediate pH values the dispersion state is
dominated by the balance between electrostatic and hydrophobic interactions,
and the system exists in clusters whose size is determined solely
by the pH. The transformation between states of aggregation is reversible
and a reproducible function of pH. The rate of gelation can be controlled
to be as fast as minutes while deaggregation is much slower and takes
several hours to complete.