Preparation and Characterization of a pH‐ and Thermally Responsive Poly(N‐isopropylacrylamide‐co‐acrylic acid)/Porous SiO₂ Hybrid

Abstract

A multifunctional nanohybrid composed of a pH- and thermoresponsive hydrogel, poly(N-isopropylacrylamide-co-acrylic acid), poly(NIPAM-co-AAc) is synthesized in-situ within the mesopores of an oxidized porous Si template. The hybrid is characterized by electron microscopy and by thin film optical interference spectroscopy. The optical reflectivity spectrum of the hybrid displays Fabry-Pérot fringes characteristic of thin film optical interference, enabling direct, real-time observation of the pH- induced swelling and volume phase transitions associated with the confined poly(NIPAM-co-AAc) hydrogel. The optical response correlates to the percentage of AAc contained within the hydrogel, with a maximum change observed for samples containing 20% AAc. The swelling kinetics of the hydrogel are significantly altered due to the nanoscale confinement; displaying a more rapid response to pH or heating stimuli relative to bulk polymer films. The inclusion of AAc dramatically alters the thermoresponsiveness of the hybrid at pH 7, effectively eliminating the lower critical solution temperature (LCST). The observed changes in the optical reflectivity spectrum are interpreted in terms of changes in the dielectric composition and morphology of the hybrids.

pH, Temperature, and Magnetic Triple‐Responsive Polymer Porous Microspheres for Tunable Adsorption

“…Such increase was accompanied by the enhancement of the hydrophilicity of the shell layer and the expansion/swelling of the polymer chain, which rapidly increased the D h value of the microspheres. [36][37][38] UV-vis was performed to study the temperature-responsive property of the microspheres. A LCST of the polymer solution is generally used to characterize its temperatureresponsiveness.…”

Multifunctional Up‐Converting Nanocomposites with Smart Polymer Brushes Gated Mesopores for Cell Imaging and Thermo/pH Dual‐Responsive Drug Controlled Release

“…To date, different kinds of pore blocking caps, such as nanoparticles,13 organic molecules,14 and polymer chains or brushes15 have been introduced onto the surface or pore channels to keep compounds from leaching out and to permit their controlled release. Poly( N ‐isopropylacrylamide) (PNIPAm), the most prominent temperature‐sensitive polymer, exhibits a reversible phase transition in aqueous solution, thus is suitable for blocking pores to program the drug release 16. In addition, by incorporating co‐monomer units, such as MAA, the low critical solution temperature (LCST) of the PNIPAm homopolymer can be tuned to be above normal body temperature (37 °C).…”

“…However, previous work mainly focused on fabrication of magnetic silica nanoparticles together with smart polymers for diagnosis and treatment 16b, 16d, 20. Moreover, the conventional process to produce the uniform core‐shell materials consisting of oleic acid capped UCNPs and mesoporous silica usually requires the intermediate coatings of solid silica and calcination process, which lead to the complicated procedure and difficulties for post functionalization.…”

Light-triggered antifouling coatings for porous silicon optical transducers

“…Reflective interferometric Fourier transform spectroscopy (RIFTS) was used as a complementary tool to follow the optical changes occurring during the functionalization of the PSiO 2 surface, as previously described . Briefly, a tungsten light source was focused onto the sample surface with a spot size approximately 1–2 mm 2 , and the interferometric reflectance spectra were collected using an Ocean Optics USB4000 spectrometer (Ocean Optics Inc., Dunedin, FL, USA).…”