Directed synthesis of polymer mesostructures

Faul, C. F. J. (Charles Frederick James) (2000-12)

Thesis (PhD)--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: The objective of this research was to produce discrete, nano-shaped polymeric structures on the same length scale as, or one to one copies of, templates, deformable templates or structure-directing hosts. Polymerisation of hydrophobic organic monomers in high concentration surfactant solutions, leads to the formation of shaped particles (rod-like, plank-like and ribbon-like particles) in the micrometer size range. The origin of these regularly shaped particles was investigated. It is proposed that they were not polymeric in nature, but formed by the crystallisation of the surfactant in the presence of electrolytes and ethanol as solvent. The polymeric particles that were formed were found to be of spherical shape, and no directing of the shape was detected. Mesostructured hosts were then investigated for their possible use as structure-directing agents. A series of polyelectrolyte-surfactant complexes of polydiallylammonium chloride with sodium sulphate surfactants (ranging from C10 to C16) were synthesised and characterised in terms of their thermal, mechanical and structural properties. The complex of polydiallylammonium chloride and sodium dodecyl sulphate was selected as an appropriate self-assembled model system for investigations into the structure-directing properties of these new materials. The polymerisation of hydrophobic organic monomers, such as styrene and the di-functional monomer m-diisopropenylbenzene (m-DIB), within the above mesoscopically structured polyelectrolyte-surfactant complex as host, lead to the formation of unconventionally shaped polymeric particles. The influence of the presence of monomers and guest polymers on the phase morphology of the host was investigated by small angle X-ray analyses (SAXS) and dynamic mechanical analyses (DMA). SAXS analyses showed that these new, stable hosts can hold up to 17 % guest polymer before phase disruption is encountered. These findings were supported by changes in the mechanical properties, as determined by DMA. The transmission electron microscopy (TEM) images of particles obtained after polymerisation showed very clearly that the poly-(m-DIB) did not form a continuous copy of the 3D hexagonal structure of the host, but rather colloidal copies of a part of the host structure that swelled the most. The shapes of the polymer mesostructures were dictated by the morphology of the phase of the structure-directing host, to produce nanosized wires (dimensions 4 by 100 nm), cigar-shaped particles (dimensions 8 by 50 nm) and fibrillar bent shapes (larger than 200 nm), as revealed by TEM. According to literature these are the first shaped, polymer nano-particles produced in a soft, selfassembled, organic templating host.

AFRIKAANSE OPSOMMING: Die doel van hierdie navorsing was om diskrete, nano-gevormde polimeriese partikels van dieselfde lengteskaal as, of direkte een tot een kopië van, 'n templaat, 'n vervormbare of struktuur-rigtende gasheersisteem te produseer. Die polimerisasie van hidrofobiese organiese monomere in seep oplossings van hoë konsentrasie, het gelei tot die produksie van gevormde partikels. Die oorsprong van hierdie partikels is ondersoek. Dit word voorgestel dat die partikels nie polimeries van aard is nie, maar gevorm is deur die kristallisasie van die seep in die teenwoordigheid van elekotroliete en etanol as oplosmiddel. Die polimeriese partikels wat wel geproduseer is, was sferies in vorm, en geen rigtende invloed op die vorm van die partikels is waargeneem nie. Meso-gestruktureerde gasheersisteme is ook ondersoek vir moontlike gebruik as struktuur-rigtende agente. 'n Reeks poliëlektroliet-seep komplekse van polidiallielammoniumchloried en natriumsulfaat sepe (van C10 tot C16) is gesintetiseer en gekarakteriseer in terme van hul termiese, meganiese en strukturele eienskappe. Die kompleks van polidiallielammoniumchloried en natrium dodekielsulfaat is gekies as 'n toepaslike self-organiserende modelsisteem vir die ondersoeke na die struktuur-rigtende eienskappe van hierdie nuwe materiale. Polimerisasie van hidrofobiese organiese monomere, soos byvoorbeeld stireen en die di-funksionele monomeer m-di-isopropenielbenseen (m-DIB), in hierdie mesoskopies-gestruktureerde poliëlektroliet-seep kompleks, het gelei tot die vorming van nie-konvensionele gevormde polimeriese partikels. Die invloed van die teenwoordigheid van monomere en gaspolimere op die fasemorfologie van die gasheersisteem is ondersoek d.m.v. kleinhoek X-straal diffraksie (Eng. SAXS) en dinamiese meganiese analise (DMA). SAXS analises het aangetoon dat hierdie nuwe, stabiele gasheersisteem tot 17 % gaspolimeer kan inkorporeer voordat fasevernietiging plaasvind. Hierdie resultate is verder ondersteun deur veranderinge in die meganiese eienskappe soos waargeneem deur DMA. Transmissie elektronmikroskopie (TEM) afbeeldinge van partikels geïsoleer na polimerisasie het baie duidelik gewys dat, in die geval van poli-(m-DIB), die gaspolimeer nie 'n kontinue kopie van die drie dimensionele heksagonale struktuur van die gasheersisteem produseer nie. Daar word eerder 'kolloïdale kopieë' van dele van die gasheersisteem wat die meeste swel gevorm. Die vorms van die polimeer mesostrukture word dus bepaal deur die morfologie van die fase van die struktuur-rigtende gasheer, om nanogrootte draadjies (dimensies 4 x 100 nm), sigaarvormige partikels (8 x 50 nm) en fibrillêre gebuigde vorms (groter as 200 nm) te vorm, soos waargeneem met TEM. Volgens die literatuur is hierdie die eerste geval van gevormde polimeer nanopartikels geproduseer in 'n self-organiserende templaat gasheersisteem.

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