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Testing the vesicular morphology to destruction: birth and death of diblock copolymer vesicles prepared via polymerization-induced self-assembly

DOI: 10.1021/ja511423m DOI Help

Authors: Nicholas Warren (University of Sheffield) , Oleksandr Mykhaylyk (The University of Sheffield) , Anthony J. Ryan (University of Sheffield) , Mark Williams (University of Sheffield) , Tristan Doussineau (Université de Lyon) , Philippe Dugourd (Université de Lyon) , Rodolphe Antoine (Université de Lyon) , Giuseppe Portale (European Synchrotron Radiation Facility) , Steven P. Armes (University of Sheffield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society , VOL 137 (5)

State: Published (Approved)
Published: January 2015
Diamond Proposal Number(s): 7586

Open Access Open Access

Abstract: Small angle X-ray scattering (SAXS), electrospray ionization charge detection mass spectrometry (CD-MS), dynamic light scattering (DLS), and transmission electron microscopy (TEM) are used to characterize poly(glycerol monomethacrylate)55-poly(2-hydroxypropyl methacrylate)x (G55-Hx) vesicles prepared by polymerization-induced self-assembly (PISA) using a reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization formulation. A G55 chain transfer agent is utilized to prepare a series of G55-Hx diblock copolymers, where the mean degree of polymerization (DP) of the membrane-forming block (x) is varied from 200 to 2000. TEM confirms that vesicles with progressively thicker membranes are produced for x = 200–1000, while SAXS indicates a gradual reduction in mean aggregation number for higher x values, which is consistent with CD-MS studies. Both DLS and SAXS studies indicate minimal change in the overall vesicle diameter between x = 400 and 800. Fitting SAXS patterns to a vesicle model enables calculation of the membrane thickness, degree of hydration of the membrane, and the mean vesicle aggregation number. The membrane thickness increases at higher x values, hence the vesicle lumen must become smaller if the external vesicle dimensions remain constant. Geometric considerations indicate that this growth mechanism lowers the total vesicle interfacial area and hence reduces the free energy of the system. However, it also inevitably leads to gradual ingress of the encapsulated water molecules into the vesicle membrane, as confirmed by SAXS analysis. Ultimately, the highly plasticized membranes become insufficiently hydrophobic to stabilize the vesicle morphology when x exceeds 1000, thus this PISA growth mechanism ultimately leads to vesicle “death”.

Journal Keywords: Copolymers; Membranes; Thickness; Vesicles; X-ray scattering

Subject Areas: Chemistry, Materials

Instruments: I22-Small angle scattering & Diffraction

Other Facilities: BM26 at ESRF

Added On: 06/02/2015 17:10


Discipline Tags:

Soft condensed matter physics Chemistry Materials Science Organic Chemistry Polymer Science

Technical Tags:

Scattering Small Angle X-ray Scattering (SAXS)