Author(s): Brás, Adriano José Simões
Date: 2017
Persistent ID: http://hdl.handle.net/10362/42377
Origin: Repositório Institucional da UNL
Subject(s): PVP; PAAm; PAAc; Microgels; Colloidal Electrospinning; Fibers; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia dos Materiais
In the last decades, the focus in materials science has been the development of multifunctional materials with enhanced properties as “smart materials”. This new generation of materials possess adaptive capabilities to external stimuli, that is, they can change their properties due to an external stimulus. For instance, over the last years there has been an increasing interest in thermosensitive microgels, because of their potential applications on many distinct fields, mainly in biomedical engineering. This dissertation reports on the development of polymeric composite membranes toward smart systems. The production of the composite membranes was achieved by the confinement of positive thermosensitive microgels that might act as active sites inside a polymeric fiber, by means of colloidal electrospinning process, which is a variant of the classical electrospinning methodology. For the production of this composite membranes, first poly(acrylamide) and poly(acrylamide-acrylic acid) microgels were synthesized using inverse emulsion polymerization technique. The obtained UCST microgels were characterized in terms of their morphology, swelling properties and chemical structure. Then, the obtained microgels were dispersed in the polymeric fiber template solution (Polyvinylpyrrolidone /Ethanol) and further electrospun by means of colloidal electrospinning. Previous works already report the encapsulation of PNIPAAm microgels in electrospun fibers, and there is also reports of the synthesis of positive thermosensitive poly(acrylamide-acrylic acid) microgels. The novelty of this dissertation is the encapsulation of these positive microgels inside electrospun fibers. Tensile test experiments infer that the addiction of microgels improves the mechanical properties of composite membranes. The confinement of the microgels were further confirmed by SEM, resulting on a “bead-on-string” fiber morphology. The presence of water in the solvent system of the polymeric solution revealed to be a crucial factor in the confinement of the microgels inside the fibers, since it not only stabilized the microgels dispersed in the polymeric solution, but also reduced significantly the fiber diameters. Since the size of these “beads” on the fiber is tunable, this could mean that this system could have the ability to tune the roughness of the fibers, hydrophobicity and wettability. This results in a very versatile system with potential development for various applications.
