title: Temperature- and pH-sensitive nanohydrogels of poly(N-Isopropylacrylamide) for food packaging applications: modelling the swelling-collapse behaviour.
abstract: 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).
authors: Grupo de Bioquímica, Departamento de Química Analítica y Alimentaria, Universidad de Vigo, Ourense, Spain.
authors: Clara
authors: C
authors: Fuciños
authors: Grupo de Reciclado y Valorización de Materiales Residuales (REVAL), Instituto de Investigaciones Marinas (CSIC), Vigo, Spain.
authors: Pablo
authors: P
authors: Fuciños
authors: Grupo de Bioquímica, Departamento de Química Analítica y Alimentaria, Universidad de Vigo, Ourense, Spain.
authors: Martín
authors: M
authors: Míguez
authors: Grupo de Nuevos Materiales y Espectroscopía Supramolecular, Departamento de Química Física, Universidad del País Vasco, Leioa, Spain.
authors: Issa
authors: I
authors: Katime
authors: Grupo de Bioquímica, Departamento de Química Analítica y Alimentaria, Universidad de Vigo, Ourense, Spain.
authors: Lorenzo M
authors: LM
authors: Pastrana
authors: Grupo de Bioquímica, Departamento de Química Analítica y Alimentaria, Universidad de Vigo, Ourense, Spain.
authors: María L
authors: ML
authors: Rúa
mesh_terms: D000179:Acrylates / Q000737:chemistry; D000180:Acrylic Resins / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D018857:Food Packaging; D020100:Hydrogels / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D008962:Models, Theoretical; D000080385:Nanogels; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry*; D011094:Polyethyleneimine / Q000737:chemistry*; D012996:Solutions; D055672:Static Electricity; D013696:Temperature
chemical_list: D000179:Acrylates; D000180:Acrylic Resins; D020100:Hydrogels; D000080385:Nanogels; D012996:Solutions; C413692:polyethylene glycol polyethyleneimine nanogel; C052970:poly-N-isopropylacrylamide; D011092:Polyethylene Glycols; D011094:Polyethyleneimine; C036658:acrylic acid