title: Hydrostatic pressure effect on PNIPAM cononsolvency in water-methanol solutions.
abstract: When methanol is added to water at room temperature and 1atm, poly (N-isopropylacrylamide), PNIPAM, undergoes a coil-to-globule collapse transition. This intriguing phenomenon is called cononsolvency. Spectroscopic measurements have shown that application of high hydrostatic pressure destroys PNIPAM cononsolvency in water-methanol solutions. We have developed a theoretical approach that identifies the decrease in solvent-excluded volume effect as the driving force of PNIPAM collapse on increasing the temperature. The same approach indicates that cononsolvency, at room temperature and P=1atm, is caused by the inability of PNIPAM to make all the attractive energetic interactions that it could be engaged in, due to competition between water and methanol molecules. The present analysis suggests that high hydrostatic pressure destroys cononsolvency because the coil state becomes more compact, and the quantity measuring PNIPAM-solvent attractions increases in magnitude due to the solution density increase, and the ability of small water molecules to substitute methanol molecules on PNIPAM surface.
authors.affiliation: Dipartimento di Scienze Chimiche, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte Sant'Angelo, Via Cintia, 80126 Napoli, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pica
authors.affiliation: Dipartimento di Scienze e Tecnologie, Università del Sannio, Via Port'Arsa 11, 82100 Benevento, Italy. Electronic address: graziano@unisannio.it.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Graziano
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D006874:Hydrostatic Pressure; D000432:Methanol / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D000180:Acrylic Resins; D014867:Water; C052970:poly-N-isopropylacrylamide; D000432:Methanol
keywords: Cononsolvency; Hydrostatic pressure; PNIPAM; Polymer collapse