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Self-assembly in Melts of Block copolymer-based Systems Featuring Supramolecular Interactions

Författare:
  • Mehran Asad Ayoubi
Publiceringsår: 2012
Språk: Engelska
Sidor:
Dokumenttyp: Doktorsavhandling
Förlag: Department of Chemistry, Lund University

Sammanfattning

Popular Abstract in English

From everyday experience we know that water and oil do not mix. In the scientific language we say they phase separate from each other. This happens because a water molecule and an oil molecule are inherently incompatible, the former exhibiting a ‘polar’ character and the latter a ‘non-polar’ one.



Water and oil molecules are small, meaning that they are made up of only a few atoms. Now imagine that we tie together many of these small molecules and make a long chain-like ‘macromolecule’ (or as it is sometimes called a ‘polymer’) that consist of thousands of repeats units, each made up of a few atoms, by the help of a ‘chemical synthesis’ procedure (that can be both time-consuming and costly!). Evidently, the resultant macromolecule can be polar or non-polar depending on the character of its repeat units.



Now imagine that, utilizing a chemical synthesis procedure, we link together two macromolecules, one made up of polar repeat units and another composed of non-polar ones. The resultant macromolecule is called a ‘block copolymer’. We expect that, due to their inherent incompatibility, the two blocks want to become phase separated. On the other hand, they are tied together and cannot be separated from each other. Thus, they become phase separated on a microscopic length-scale (i.e. on about a few hundreds of nanometer) and very small domains (obviously non-visible to the naked eye!) appear in the system, which are filled by either of the repeat units. Such a phenomenon is called ‘microphase separation’. The shape of the microdomains can be spherical, cylindrical or lamellar, depending on the volume ratio of the two blocks. Logically, if the volume ratio is much less than one the shape of the microdomains is spherical and when it is close to one it becomes lamellar. Cylindrical microdomains appear between these two limiting cases.



We can utilize microphase separation properties of block copolymers for producing materials that are suitable for our everyday purposes. It is important for us to control the shape and the size characteristics of the resultant microdomains, because, for example, the mechanical properties of a block copolymer which is microphase separated into spherical microdomains is superior than the one which is microphase separated into lamellar microdomains. It is precisely for this reason that the outsoles of our shoes are made up of a block copolymer that microphase separates into spherical microdomains.



The subject of this thesis is microphase separation of polymeric materials. In the results presented in this thesis we have not used the polymeric materials for any specific applications. On the other hand, we have tried to show how it is possible to control the shape and the size of microdomains of a polymeric material without a need for a chemical synthesis. We have shown that the change in the volume ratio of the two blocks, required for changing the shape of the microdomains, can be achieved by ‘sticking’ small molecules to the repeat units of one of the blocks. Thus, in a facile and simple manner we can change both the shape and the size characteristic of the microdomains.
The subject of this thesis is experimental investigation of self-assembly in solvent-free (ionic) macromolecular systems that contain block copolymer chains as the basic constituent component in combination with low molecular weight amphiphiles. In particular, especial attention is paid to study thoroughly a new class of block copolymer-based ionic supramolecules, named as Linear-b-AmphComb, that feature novel hierarchical self-assembly characteristics. These Linear-b-AmphComb ionic supramolecules are produced by a facile and versatile supramolecular synthesis procedure that allows us to precisely control and fine-tune the molecular characteristics of the system. Through a wealth of experimental observations the relationships between the molecular characteristics of the system and its self-assembly properties, including the shape and the size characteristics of the resultant microdomains, are established. It is expected that, based on the results presented in this thesis, new routes are opened up in our (i) theoretical understanding of self-assembly in ionic macromolecular systems, and (ii) practical application capabilities to design new materials, where the desired structural properties are precisely controlled and fine-tuned by choosing the appropriate molecular characteristic of the system.

Disputation

2012-12-06
13:00
Lecture Hall C, Kemicentrum
  • Nitash Balsara

Nyckelord

  • Physical Chemistry
  • hierarchical self-assembly
  • melt
  • block copolymer
  • cationic surfactant
  • non-ionic surfactant
  • supramolecular interactions
  • microphase separation
  • Linear-b-AmphComb

Övriga

Published
  • Lennart Piculell
  • Ulf Olsson
  • ISBN: 978-91-7422-310-1

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