Journal Article

Temperature- and pH-Sensitive Nanohydrogels of Poly(N-Isopropylacrylamide) for Food Packaging Applications: Modelling the Swelling-Collapse Behaviour

Fuciños, Pablo, Katime, Issa, Míguez, Martín, Pastrana, Lorenzo M., Fuciños, Clara, Rúa, María L.

2014

Overview

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Acids / Acrylates - chemistry / Acrylic acid / Acrylic Resins - chemistry / Biology / Calorimetry / Calorimetry, Differential Scanning / Chemical synthesis / Chemistry / Collapse / Crosslinking / Delivery systems / Differential scanning calorimetry / Emulsion polymerization / Emulsions / Food / Food Packaging / Heat / Heat measurement / Hydrogels / Hydrogels - chemistry / Hydrogen-Ion Concentration / Isopropylacrylamide / Materials Science / Mathematical models / Microscopy, Electron, Transmission / Models, Theoretical / Molecular weight / Nanoemulsions / Nanogels / Nanoparticles / Optical properties / Packaging / Particle Size / pH effects / Phase transitions / Physicochemical properties / Poly(N-isopropylacrylamide) / Polyethylene Glycols - chemistry / Polyethyleneimine - chemistry / Polymer solubility / Polymerization / Polymers / Preservatives / Proteins / Solutions / Specific heat / Spectroscopy / Static Electricity / Swelling / Temperature / Temperature effects / Thermodynamics / Ultraviolet-visible spectroscopy