Espalhamento de Raios-X a Baixos Ângulos (SAXS)

3.1.4 Estudo das Propriedades Físico-Químicas

3.1.4.4 Espalhamento de Raios-X a Baixos Ângulos (SAXS)

O espalhamento de raios-X a baixos ângulos (SAXS) é um método analítico usado para investigar a estrutura de sistemas de partículas em relação aos tamanhos médios das partículas e suas conformações. A técnica de SAXS pode ser aplicada em diversas áreas para análises de materiais como polímeros em solução (Schnablegger e Singh, 2011).

Em um experimento de SAXS, os feixes de raios-X altamente colimado e monocromático com comprimento de onda entre 0,01 e 0,2 nm são espalhados elasticamente através de um sistema de partículas. As partículas que interagem com os raios-X enviam sinal para um detector, que mede a estrutura média de todas as partículas iluminadas do sistema, em um determinado ângulo  . A intensidade de espalhamento I (q) está relacionada com a diferença na densidade eletrônica entre diferentes partes de um sistema de partículas em estudo (Blazek e Gilbert, 2011; Schnablegger e Singh, 2011).

Os experimentos de espalhamento a baixos ângulos medem a intensidade de espalhamento em função do vetor de espalhamento (q), que é definido pela Equação 3.20 (Blazek e Gilbert, 2011):

...(3.20) Onde  é a metade do ângulo em que a radiação é espalhada e  é o comprimento de onda da radiação incidente.

O vetor de espalhamento na intensidade máxima do pico, q_max, está relacionado com o

comprimento de correlação ( ) ou distância entre cadeias de acordo com a Lei de Bragg ( 2 q _max ). Popa-Nita e colaboradores (2009) avaliaram quitosana com diferentes graus de acetilação (69%, 37%, 9% e 1,5%) em solução de acetato. Os autores observaram um deslocamento de q_max em direção aos valores mais altos de q com a diminuição do grau de

acetilação (Popa-Nita et al., 2009)

Boucard e colaboradores (2007) estudaram a gelificação da quitosana em solução aquosa ácida (13,7 g/L e GA = 46%) em contato com um gás amônia por SAXS. A estrutura

q  sen



do polieletrólito foi caracterizada pela posição da sua intensidade máxima. O pico do efeito polieletrolítico dos géis estudados desapareceu completamente em pH acima de 6,5, devido à neutralização dos grupos +

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