Abstract
Spherical silica nanoparticles with solid cores and mesoporous shells (SCMS) were decorated with thermoresponsive polymer brushes that were shown to serve as macromolecular valves to control loading and unloading of a model dye within the mesopores. Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) brushes were grafted from the surfaces of both solid core (SC) and SCMS particles of similar size using surface-initiated atom transfer radical polymerization. Both systems based on porous (SCMS-PNIPAM) and nonporous (SC-PNIPAM) particles were characterized using cryo-TEM, thermogravimetry and elemental analysis to determine the structure and composition of the decorated nanoparticles. The grafted PNIPAM brushes were found to be responsive to temperature changes enabling temperature-controlled gating of the pores. The processes of loading and unloading in the obtained systems were examined using a model fluorescent dye—rhodamine 6G. Polymer brushes in SCMS-PNIPAM systems were shown to serve as molecular valves enabling significant adsorption (loading) of the dye inside the pores with respect to the SC-PNIPAM (no pores) and SCMS (no valves) systems. The effective unloading of the fluorescent cargo molecules from the decorated nanoparticles was achieved in a water/methanol solution. The obtained SCMS-PNIPAM particles may be used as smart nanocontainers or nanoreactors offering also facile isolation from the suspension due to the presence of dense cores.
Highlights
Mesoporous silica has been intensively studied and applied since its invention in the 1990s [1,2].Especially mesoporous silica nanoparticles (MSNs), due to the large surface-to-volume ratio, offer some advantages in many applications
solid cores and mesoporous shells (SCMS) sample was synthesized at 35 ◦ C
SEM images) with solid cores and porous shells decorated with thermosensitive PNIPAM brushes (SCMS-PNIPAM) of various thicknesses were synthesized and studied
Summary
Mesoporous silica has been intensively studied and applied since its invention in the 1990s [1,2]. Mesoporous silica nanoparticles (MSNs), due to the large surface-to-volume ratio, offer some advantages in many applications. PNIPAM chains undergo a phase transition in water from a swollen to collapsed dehydrated state while heating above 32 ◦ C (LCST—lower critical solution temperature) that is related to breaking of hydrogen bonds. Later broadly studied and applied both in solutions and for surface grafted macromolecules [39, 40] This behavior of PNIPAM enables the fabrication of various porous and nonporous materials decorated with the polymer chains for e.g., temperature-triggered gating of pores or controlled adsorption/desorption leading to so-called “smart” surfaces [41,42,43,44]. Loading and unloading of a model dye in the mesoporous shells was investigated for various temperatures and solvents to show proper gating mechanism enabling efficient storing and the release of the encapsulated molecules on demand
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