Ordering Effect of Lithium Ions in a Self-Assembled Hybrid System
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Ordering Effect of Lithium Ions in a Self-Assembled Hybrid System P.J. Retuert1, S. Fuentes2, G. González2, M. Yazdani-Pedram1. 1 Department of Chemistry, Faculty of Physical and Mathematical Science, University of Chile, Casilla 2777. Santiago, Chile. 2Faculty of Science, University of Chile, Casilla 653.Santiago, Chile.
ABSTRACT By blending 3-aminopropyl-siloxane oligomers (pAPS) with chitosan (CHI) selfassembled hybrid films have been obtained. The influence of the incorporation of LiClO4 on the morphology of these transparent and flexible hybrid films has been studied. It was found that when this salt is added in amounts slightly over the limit of the maximal homogeneous incorporation a process of anisotropical crystallization begins. For a hybrid with composition CHI/pAPS/LiClO4 = 0.6/1/0.8M, Video-Enhanced Differential Interference Contrast microscopy (VEC-DIC) of the first three layers of the films showed that each layer have oriented patterns with angles of exactly 60 degrees between the planes. These results in combination with FTIR analysis of the products indicate that lithium ions behave as strong structure directing agent. This system can be considered as a biomimetic model for biomineralization processes. An interaction scheme comprising the components of this hybrid system is proposed. INTRODUCTION Study of hybrid nanocomposites resulting from compatibility of organic and inorganic polymers has been an active research area in recent years1-8. Incorporation of organic polymers, specially those with amine or amide groups, into inorganic siliceous matrices allows the formation of molecular hybrids often stabilized by strong hydrogen bonding. The use of sol-gel processes has demonstrated to be very helpful to produce this type of materials under soft conditions (room temperature). In recent years, incorporation of biopolymers into inorganic networks has generated increasing interest for the preparation of biomimetic materials9-13. The morphological characteristics of this type of hybrid materials are therefore of special relevance. This kind of organic-inorganic nanocomposites often display complex multifunctional structure, potentially related to biomineralization processes14-19. Recently, we have studied the incorporation of LiClO4 into chitosan (CHI) based hybrid films20-21. In this work we report on the study of morphological characteristics of hybrid films by means of Video Enhanced Differential Interference Contrast microscopy (VEC-DIC). This technique allowed us to study the crystallization of the salt when it is added in excess over the homogeneous incorporation into the hybrid films and to compare the morphology changes induced for this process. Generally, the biomineralization has been studied by salt crystallization in the presence of templating agent. Very few works are related to the crystallization inside polymeric films or membranes. Our studies are aimed at the understanding of nucleating effect of metal ions on the morphological characteristics of self assembled structures. The system st
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