The European Physical Journal E

, Volume 32, Issue 2, pp 127–134

Osmotic shrinkage in star/linear polymer mixtures

Authors

  • A. Wilk
    • Laboratory for Neutron ScatteringETH Zurich & Paul Scherrer Institut
    • Faculty of PhysicsA. Mickiewicz University
  • S. Huißmann
    • Department of PhysicsHeinrich-Heine-University of Düsseldorf
  • E. Stiakakis
    • Institute of Electronic Structure and LaserFORTH
    • Institut für FestkörperforschungForschungszentrum Jülich
  • J. Kohlbrecher
    • Laboratory for Neutron ScatteringETH Zurich & Paul Scherrer Institut
    • Institute of Electronic Structure and LaserFORTH
    • Department of Materials Science & TechnologyUniversity of Crete
  • C. N. Likos
    • Department of PhysicsHeinrich-Heine-University of Düsseldorf
    • Faculty of PhysicsUniversity of Vienna
  • G. Meier
    • Institut für FestkörperforschungForschungszentrum Jülich
  • J. K. G. Dhont
    • Institut für FestkörperforschungForschungszentrum Jülich
  • G. Petekidis
    • Institute of Electronic Structure and LaserFORTH
    • Department of Materials Science & TechnologyUniversity of Crete
  • R. Vavrin
    • Laboratory for Neutron ScatteringETH Zurich & Paul Scherrer Institut
Regular Article

DOI: 10.1140/epje/i2010-10607-2

Cite this article as:
Wilk, A., Huißmann, S., Stiakakis, E. et al. Eur. Phys. J. E (2010) 32: 127. doi:10.1140/epje/i2010-10607-2

Abstract.

Multiarm star polymers were used as model grafted colloidal particles with long hairs, to study their size variation due to osmotic forces arising from added linear homopolymers of smaller size. This is the origin of the depletion phenomenon that has been exploited in the past as a means to melt soft colloidal glasses by adding linear chains and analyzed using dynamic light scattering experiments and an effective interactions analysis yielding the depletion potential. Shrinkage is a generic phenomenon for hairy particles, which affects macroscopic properties and state transitions at high concentrations. In this work we present a small-angle neutron scattering study of star/linear polymer mixtures with different size ratios (varying the linear polymer molar mass) and confirm the depletion picture, i.e., osmotic star shrinkage. Moreover, we find that as the linear/star polymer size ratio increases for the same effective linear volume fraction ( c/c*with c*the overlapping concentration), the star shrinkage is reduced whereas the onset of shrinkage appears to take place at higher linear polymer volume fractions. A theoretical description of the force balance on a star polymer in solution, accounting for the classic Flory contributions, i.e. elastic and excluded volume, as well as the osmotic force due to the linear chains, accurately predicts the experimental findings of reduced star size as a function of linear polymer concentration. This is done in a parameter-free fashion, in which the size of the cavity created by the star, and from which the chains are excluded, is related to the radius of the former from first principles.

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© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010