Molecular mechanisms driving the microgels behaviour: A Raman spectroscopy and dynamic light scattering study

Publication date: 15 June 2019Source: Journal of Molecular Liquids, Volume 284Author(s): Valentina Nigro, Francesca Ripanti, Roberta Angelini, Angelo Sarra, Monica Bertoldo, Elena Buratti, Paolo Postorino, Barbara RuzickaAbstractResponsive microgels based on poly(N-isopropylacrylamide) (PNIPAM) exhibit peculiar behaviours due to the competition between the hydrophilic and hydrophobic interactions of the constituent networks. The interpenetration of poly-acrylic acid (PAAc), a pH-sensitive polymer, within the PNIPAM network, to form Interpenetrated Polymer Network (IPN) microgels, affects this delicate balance and the typical Volume-Phase Transition (VPT) leading to complex behaviours whose molecular nature is still completely unexplored.Here we investigate the molecular mechanism driving the VPT and its influence on particle aggregation for PNIPAM/PAAc IPN microgels by the combined use of Dynamic Light Scattering and Raman Spectroscopy. Our results highlight that PNIPAM hydrophobicity is enhanced by the interpenetration of PAAc promoting interparticle interactions, a crossover concentration is found above which aggregation phenomena become relevant. Moreover we find that, at variance with PNIPAM, for IPN microgels a double-step molecular mechanisms occurs upon crossing the VPT, the first involving the coil-to-globule transition typical of PNIPAM and the latter associated to PAAc steric hindrance.
Source: Journal of Molecular Liquids - Category: Molecular Biology Source Type: research