Composite materials based on polyanylinе and natural minerals: short review. 1. Structure and morphology

Abstract

The article analyzes the research devoted to the study of the structure and morphology of composite materials based on polyaniline (PAn) and natural minerals (NM) such as montmorillonite, kaolinite, zeolite, glauconite, etc.,. It focuses on the experimental results received by the most important and widely used methods applied to study the structure and morphology of composite materials based on polyaniline and natural minerals (PAn/NM), namely X-ray diffraction, ultraviolet-visible and Fourier transformation infrared spectroscopy, scanning electron and transmission electron microscopy. X-ray analysis is the basis for determination of the phase state and structure, the presence of the effect of intercalation and separation (exfoliation) of layered silicates in nanocomposites of PAn. The type of PAn/NM composite determines the position of the peak of the basal reflex, which is within the range of 2θ = 5–8o. The displacement of this reflex in the direction of the smaller diffraction angles (in comparison to diffraction angles of the initial NM) confirms the presence of a regular multilayer structure inherent to the intercalated composite. The disappearance of this reflex occurs under an increase of the interlayer distance in the NM or due to disordering of silicate plates, which is inherent in fully separated (exfoliated) composites. The presence of two main peaks at 2θ = ~20.0o or 2θ = ~25.0o on the diffractograms of the PAn samples indicates the form of produced PAn, namely the emeraldine base (EMB) or the emeraldine salt (EMS), respectively. The presence of NM in the reaction mixture usually does not affect the crystallinity of PAn, deposited on their surfaces. To study the chemical structure, interphase interaction between PAn and NM, the characteristics of intercalation and separation states, the FTIR spectroscopy are used. A shift or change of intensity of the main adsorption bands (~1 640, ~1 470 cm –1 , etc.) characteristic of the PAn, an expansion, decrease of intensity or complete disappearance of the O–H band (~3 420 cm –1 ) in the spectra of PAn nanocomposites in comparison with same band in the FTIR spectrum of pure PAn are connected with the formation of hydrogen bonds between the surface O–H groups of NM and N–H groups in PAn macromolecules.These effects confirms the presence of interphase interactions and, respectively, the composite nature of the produced materials. Besides, an important element of the chemical structure of polyaniline is the consequtive mainly 1,4-addition of aniline molecules with the formation of macromolecular chains of PAn. Electron spectroscopy in the ultraviolet and visible spectral region allows us to quickly determine the form of PAn formed during the synthesis of composites with NM. The blue shift of the main peaks of the PAn can correspond to the interphase interaction between the PAn and the surface of NM. The characteristics of UV-vis spectra also are determined by the amount of encapsulated An in the interlayer expanses of NM. The morphology of the particles of polyaniline on the surface of the NM is usually heterogeneous. The polymer particles have basically quasispherical or semispherical forms, they are of varying sizes and are unevenly layed on particles of NM. An exception isthevirtually uniform layers of polyaniline on nanotubes of halloysite modified by hematite. Keywords: natural minerals, polyaniline, composites, structure, morphologies.