Polyion-complexed multibilayer coatings of plastic optical fibres as a basis for optical fibre sensors

Abstract

Bilayer-forming polyion complexes, consisting of cationic lipids and polyanions such as poly(styrene sulfonate) and a triblock polyanion of poly(styrene sulfonate)-block-poly(methacrylic acid)-block-poly(styrene sulfonate)(SMS), have been assembled and immobilized on the core of a plastic optical fibre (POF). They display crystal to liquid crystal phase transitions and ordered multibilayer structures. The optical signals through these modified POFs show a drastic change near the phase-transition temperature of the corresponding multibilayers, indicating the refractive index change of the bilayer phase. The POF modified with a triblock polyion complex of SMS and a lipid provided a reversible optical signal change sensitive to pH and Cu²⁺ content. This indicates that conformational transitions of the poly(methacrylic acid) segment caused by varying pH and chelating with Cu²⁺ must affect the bilayer matrices, leading to the refractive index variation of bilayer phases. A kinetic mechanism for such optical signal responsiveness is discussed in terms of the crystal to liquid crystal phase transition of bilayer matrices.