Síntese e aplicação do nanocompósito de PDMS-Au como um substrato SERS e propriedades mecânicas e vibracionais de cadeias lineares de carbono em função da temperatura e pressão

Abstract

The current technological landscape drives nanoscience and nanotechnology as one of the most promising areas of the 21st century. Studies involving materials with increasingly smaller dimensional scales are subject to the barrier imposed by the light diffraction limit and, therefore, are real challenges through conventional techniques, such as Raman Spectroscopy. In this thesis, we propose a new method to manufacture small, highly standardized blocks of PDMS loaded in gold nanoparticles, PDMS-Au. The convenience of preparation, stability and use makes it a promising candidate for the application of SERS in rapid laboratory analysis. The Para-mercaptobenzoic acid (p-MBA) is used as a probing molecule to investigate the SERS. The substrate PDMS-Au exhibited high reproducibility of the Raman p-MBA signal (10-6 mol L-1) in a low concentration of Au nanoparticles in the PDMS. In a second part of the thesis, we investigate the optical and structural properties of linear carbon chains LCCs, which are one of the simplest yet versatile materials, presenting a truly unidimensional character (1D) with exclusive electronic, vibrational and mechanical properties. In this part, we investigate LCCs in two different approaches; first the LCCs inserted in multilayer nanotube MWCNTs isolated under the pressure variation P, and second the LCCs encapsulated by MWCNTs and double layer nanotube DWCNTs are analyzed under the temperature variation T. The Raman frequency of the C band around 1850 cm-1, which is a spectroscopic signature for the chains, decreases linearly with increasing pressure and increases when the temperature is gradually decreased from room temperature. The LCCs under P, we propose a simple model of constant-force anarmonic that not only describes such softening, but also shows that Young's modulus (E), Grüneisen's parameter (γ) and voltage (ε) follow universal laws in P- 1 and P2, respectively. In particular, γ also presents a unified behavior for all LCCs. In the study of LCCS under T, neglecting phonon-phonon interactions, we show that the temperature dependence of the C band frequency of the optical Raman mode works as a probe for the thermal properties of the LCCs. Such a probe allowed us to demonstrate that LCCs are described within the Debye formalism, leading to an unforeseen experimental evaluation of thermodynamic quantities, such as internal energy, specific heat, thermal expansion coefficient, thermal deformation and Grüneisen's parameter.