Depletion Interactions: Effects of Added Homopolymer on Ordered Phases Formed by Spherical Block Copolymer Micelles

Journal Article · Tue Dec 09 04:00:00 EST 2008 · Macromolecules

DOI:https://doi.org/10.1021/ma8013838· OSTI ID:1006987

Abbas, Sayeed; Lodge, Timothy P ^[1]

---

1. UMM

Three distinct poly(styrene-b-isoprene) (SI) diblock copolymers with molecular weights of 16-16, 38-14, and 50-13 kDa for styrene and isoprene, respectively, formed spherical micelles when dissolved in diethyl phthalate (DEP). Since DEP is a styrene-selective solvent, micelles with polyisoprene in the core and polystyrene in the corona were formed. At block copolymer concentrations of 20%, 16%, and 14% in DEP, the spherical micelles of SI(16-16), SI(38-14), and SI(50-13) pack onto a face-centered cubic (FCC) lattice, a mixture of FCC and body-centered cubic (BCC) lattices, and a BCC lattice, respectively. Polystyrene homopolymers with molecular weights of 4, 48, and 180 kDa were added to these ordered solutions. The following general trends were observed: the FCC phase tended to disorder, and samples that originally behaved like soft solids exhibited liquidlike flow behavior. The effect increased strongly with both the molecular weight and concentration of homopolymer in the solution. Furthermore, the BCC lattice tended to be displaced by the FCC lattice, or to disorder, when homopolymer was added. These results can be explained by invoking depletion interactions, which have been studied extensively in colloid/polymer mixtures. However, the phenomenon differs in certain details from colloidal systems because the addition of homopolymer can also influence the aggregation number of the micelles, which in turn affects the lattice packing of the micelles.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE
• OSTI ID: 1006987
• Journal Information: Macromolecules, Journal Name: Macromolecules Journal Issue: (22) ; 2008 Vol. 41
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
BCC LATTICES
COPOLYMERS
FCC LATTICES
MICELLAR SYSTEMS
MOLECULAR WEIGHT
ORDER-DISORDER TRANSFORMATIONS
POLYISOPRENE
POLYSTYRENE
SPHERICAL CONFIGURATION