Modeling and understanding smectic-phase formation in binary mixtures of rodlike polysilanes

Comparison of onsager theory and experiment

S. Varga, Enrique Velasco

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

We study a binary mixture of short and long parallel hard rods in the smectic A phase to understand the role of length ratio (weight ratio) in the formation of three different types of ordering which were observed in binary mixtures of helical polysilanes. Using Onsager's second virial theory of parallel hard rods, and modeling the short and long polymers as hard cylinders of different lengths (L1 ≠ L2) and same diameters (D), we show that the normal smectic A phase (S1) forms for length ratios (l = L2/L1) between 0.58 and 1, the microsegregated smectic structure (S2) takes place for 0.32 <l <0.56 and 0 <l <0.39 in short-rod-rich and long-rod-rich phases, respectively, and the two-in-one ordering (S3) is stable only in mixtures rich in long rods for 0.33 <l <0.58. These results are in very good agreement with the available experimental data of binary mixtures of polysilanes [Okoshi et al. Maeromolecules 2009, 42, 3443]. In addition, the theory predicts the existence of a partially microsegregated smectic structure (S4), in long-rod-rich mixtures, for 0.3 <l <0.39. Our theoretical results show that two or even three smectic order parameters should be measured, for all types of smectic phases, in order to obtain the correct positional distribution functions from the X-ray diffraction pattern.

Original languageEnglish
Pages (from-to)3956-3963
Number of pages8
JournalMacromolecules
Volume43
Issue number8
DOIs
Publication statusPublished - Apr 27 2010

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Polysilanes
Binary mixtures
Experiments
Diffraction patterns
Distribution functions
Polymers
X ray diffraction

ASJC Scopus subject areas

  • Organic Chemistry
  • Materials Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry

Cite this

Modeling and understanding smectic-phase formation in binary mixtures of rodlike polysilanes : Comparison of onsager theory and experiment. / Varga, S.; Velasco, Enrique.

In: Macromolecules, Vol. 43, No. 8, 27.04.2010, p. 3956-3963.

Research output: Contribution to journalArticle

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