title: Poly(N-isopropylacrylamide) microgels at the oil-water interface: interfacial properties as a function of temperature.
abstract: Highly monodisperse poly(N-isopropylacrylamide), PNiPAM, microgels were prepared by the conventional radical polymerization of NiPAM in the presence of dimethylamino ethyl methacrylate (DMAEMA) monomers at various concentrations. The effect of DMAEMA on the polymerization of PNiPAM microgels was examined at constant initiator (V50) and cross-linker (MBA) concentrations. The presence of DMAEMA in the synthesis batch allows for the preparation of PNiPAM microgels with controlled size and a narrow size distribution. The oil(dodecane)/water interfacial properties of the model PNiPAM microgels were then investigated. The pendant drop technique was used to measure the interfacial tensions as a function of temperature. Over the whole range of temperature (20-45 degrees C), the interfacial tension remains low (on the order of 17 mN/m) and goes through a minimum (12 mN/m) at a temperature of about 34 degrees C, which well matches the volume phase transition temperature (VPTT) of PNiPAM microgels. Below the VPTT, the decrease in the interfacial tension with temperature is likely to be due to the adsorption of dense layers because of the decrease of the excluded volume interactions. Above the VPTT, we suggest that the increase in the interfacial tension with temperature comes from the adsorption of loosely packed PNiPAM microgels. We also studied the effect of temperature on the stability of emulsions. Dodecane in water emulsions, which form at ambient temperature, are destabilized as the temperature exceeds the VPTT. In light of the interfacial tension results, we suggest that emulsion destabilization arises from the adsorption of aggregates above the VPTT and not from an important desorption of microgels. Aggregate adsorption would bring a sufficiently high number of dodecane molecules into contact with water to induce coalescence without changing the interfacial tension very much.
authors.affiliation: Laboratoire de Physico-Chimie des Polymères et Milieux Dispersés, UMR7615 UPMC-ESPCI-CNRS, Ecole Supérieure de Physique et de Chimie Industrielles ESPCI, 10 rue Vauquelin, 75231 Paris, Cedex 05, France. cécile.monteux@espci.fr
authors.forename: Cécile
authors.initials: C
authors.lastname: Monteux
authors.forename: Claire
authors.initials: C
authors.lastname: Marlière
authors.forename: Pauline
authors.initials: P
authors.lastname: Paris
authors.forename: Nadège
authors.initials: N
authors.lastname: Pantoustier
authors.forename: Nicolas
authors.initials: N
authors.lastname: Sanson
authors.forename: Patrick
authors.initials: P
authors.lastname: Perrin
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins; D000473:Alkanes / Q000737:chemistry*; D005782:Gels / Q000737:chemistry; D008689:Methacrylates / Q000737:chemistry; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D000473:Alkanes; D005782:Gels; D008689:Methacrylates; D011108:Polymers; D014867:Water; C007548:n-dodecane; C052970:poly-N-isopropylacrylamide; C049840:2-(dimethylamino)ethyl methacrylate