Regular Article

The European Physical Journal E

, Volume 32, Issue 2, pp 127-134

Osmotic shrinkage in star/linear polymer mixtures

  • A. WilkAffiliated withLaboratory for Neutron Scattering, ETH Zurich & Paul Scherrer InstitutFaculty of Physics, A. Mickiewicz University
  • , S. HuißmannAffiliated withDepartment of Physics, Heinrich-Heine-University of Düsseldorf
  • , E. StiakakisAffiliated withInstitute of Electronic Structure and Laser, FORTHInstitut für Festkörperforschung, Forschungszentrum Jülich
  • , J. KohlbrecherAffiliated withLaboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut
  • , D. VlassopoulosAffiliated withInstitute of Electronic Structure and Laser, FORTHDepartment of Materials Science & Technology, University of Crete Email author 
  • , C. N. LikosAffiliated withDepartment of Physics, Heinrich-Heine-University of DüsseldorfFaculty of Physics, University of Vienna
  • , G. MeierAffiliated withInstitut für Festkörperforschung, Forschungszentrum Jülich
  • , J. K. G. DhontAffiliated withInstitut für Festkörperforschung, Forschungszentrum Jülich
  • , G. PetekidisAffiliated withInstitute of Electronic Structure and Laser, FORTHDepartment of Materials Science & Technology, University of Crete
    • , R. VavrinAffiliated withLaboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

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.