NMR investigation of the thermogelling properties, anomalous diffusion, and structural changes in a Pluronic F127 triblo
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ORIGINAL CONTRIBUTION
NMR investigation of the thermogelling properties, anomalous diffusion, and structural changes in a Pluronic F127 triblock copolymer in the presence of gold nanoparticles Jyotsana Ojha 1 & Raju Nanda 2 & Kavita Dorai 1 Received: 4 January 2020 / Revised: 13 August 2020 / Accepted: 24 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We studied the thermogelation of a triblock copolymer Pluronic F127 (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)) in an aqueous solvent in the presence of gold nanoparticles, using pulsed field gradient diffusion, NMR temperature experiments, relaxation measurements, and 2D heteronuclear NMR experiments. Pulsed field gradient diffusion NMR is a powerful technique to study the transition between diffusive regimes in a polymer mesh which are modulated by phase transitions in the polymeric network. In the isotropic phase, the triblock copolymer diffusion is a classical Fickian process. As the onset of gelation occurs, diffusion in the system becomes anomalous and the mean square displacement in the direction of the applied magnetic field gradient shows a power law dependence. Our experiments show that the introduction of gold nanoparticles leads to a disruption of gelation and the shifting of the formation of the ordered phase of the triblock copolymer to a higher temperature. Keywords NMR spectroscopy . Pulsed field gradient NMR . Anomalous diffusion . Triblock copolymer . Gold nanoparticles
Introduction PEO-PPO-PEO triblock copolymers are commercially called Pluronics and at high concentrations and high temperatures undergo a phase transition from fluid to gel via a selfassociation process of micellization, thereby forming a mesh of connected micelles [1, 2]. The poor solubility of the PPO blocks in such triblock copolymers causes them to self-
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00396-020-04740-2) contains supplementary material, which is available to authorized users. * Kavita Dorai [email protected] Jyotsana Ojha [email protected] Raju Nanda [email protected] 1
Department of Physical Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City Sector 81, SAS Nagar, Manauli PO, Punjab 140306, India
2
Department of Chemistry, Bar Ilan University, 52900 Ramat Gan, Israel
aggregate into dehydrated cores with the hydrated PEO tails surrounding them [3]. Pluronics are readily incorporated into lipid bilayers and are hence useful as drug delivery vehicles and in encouraging drug uptake in vivo [4]. Pluronic F127 is a non-ionic triblock copolymer which is widely used as a drug carrier for different kinds of drugs and as a solvent matrix to improve solubility of hydrophobic drugs, due to its non-toxic and reverse thermal gelation properties [5–9]. The aggregation process of block copolymers has been extensively studied using NMR diffusion and spin relaxation experiments [10–12]. A major advantage of
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