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Evidence of pre-micellar aggregates in water solution of amphiphilic PDMS-PEO block copolymer

Abstract

The self-assembly process in water solution of amphiphilic polydimethylsiloxane-b-polyethyleneoxide (PDMS-PEO) diblock copolymer was investigated by means of Small Angle X-rays Scattering (SAXS) experiments in the concentration region below (and near) the critical micellar concentration (c.m.c.=0.007 g/cm3). In the highly diluted region, at the copolymer concentration of c=0.002 g/cm3 the early stage of the self-assembly process was characterized by the formation of small (primary) micellar units (with radius of R=2.7 nm) with a core-shell morphology, that coexist with larger supramolecular aggregates of entangled micelles (with average radius of R=9.5 nm). The increase in the copolymer concentration (to c=0.005 and c=0.01 g/cm3) caused a size increase of both the small micelles and supra-micellar aggregates. Interestingly, at the concentration of c=0.005 g/cm3, both the size and micellar aggregation number Nagg were found to increase with increasing temperature, in the range 10≤T≤55 °C. This phenomenon was characterised by dehydration process of the ethylene oxide (EO) segments, as evidenced by a calculation of the excess water in the micelles hydrophilic shell. The more compact (less hydrated) structure of the hydrophilic PEO chains, that strongly influences the spontaneous curvature of the amphiphile hydrophilic region, turned out to be the driving factor that favours the increase of micelles aggregation number with increasing temperature. The obtained results evidence that the self-assembly process of PDMS-PEO copolymer amphiphiles is a gradual process which is present already at the very low concentration region (far below the macroscopically determined c.m.c.) and is characterised by a multi-stage organization process where the primary building blocks self-assemble into (more complex) secondary structures that encompass multiple length-scales

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Supplementary files

Publication details

The article was accepted on 09 May 2019 and first published on 09 May 2019


Article type: Paper
DOI: 10.1039/C9CP02195G
Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Evidence of pre-micellar aggregates in water solution of amphiphilic PDMS-PEO block copolymer

    D. Lombardo, G. Munao, P. Calandra, L. Pasqua and M. T. Caccamo, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP02195G

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