Constraints, deuteration, and co-monomers: impacts on the internal structure of poly- (N-isopropylacrylamide) microgels

Brugnoni, Monia; Richtering, Walter (Thesis advisor); Wöll, Dominik (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Mimicking the self-organization and adaptivity of living systems by synthetic mate- rials is of on-going research in nanoscience and polymer chemistry. One of the key properties of living materials is the responsiveness to changes in their environment. Stimuli-responsive polymers form a group of functional materials with the ability to react and respond to external triggers making them promising candidates in ‘artificial biology’.Microgels are cross-linked polymeric networks in the colloidal domain. Typically, switchable microgels are referred to be ‘smart’ because they respond to changes in their environment. Their properties make them unique colloidal systems, which can be classified between macromolecules, hard colloids and amphiphiles. Poly(N-iso- propylacrylamide) (pNIPAM)-based microgels respond to temperature changes with a volume phase transition. Below a threshold temperature, the polymeric networks are swollen by water resulting in large microgels, which are soft and porous. Above this threshold temperature, the networks collapse by expelling water. The microgels strongly reduce their size and softness, resembling hard colloids. There is a high flexibility in the synthesis protocols of microgels. This enables to finely tune a wide variety of properties as the transition temperature, softness, size, functionalities, morphology, and shape.In this thesis, newly established synthesis procedures of various microgel types are presented, exploring the effects of constraints, monomer deuteration and various co-monomers on pNIPAM microgels. The morphologies of the microgels are mainly investigate by means of scattering techniques. Light scattering as well as small-angle neutron and X-ray scattering are used to investigate the temperature-sensitivity of various structures as regularly cross-linked, ultra-low cross-linked or hollow microgels. Doubly-thermoresponsive microgels are studied to investigate the influence of various constraints on a polymeric network. Further, studies on the effects of monomer deuteration on the microgel structures are presented. In addition, the importance of the knowledge of the relative positions of the various monomers in the polymeric networks is presented. A procedure is introduced to determine and tune the radial co-monomer distribution within microgels. Finally, the possibility to encapsulate guests in the cavity of hollow microgels, making them potential candidates as nanocarriers, e.g. for targeted drug delivery, is explored.

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