Magnetically Triggered Release of Active Molecules in Construction Materials Using Capsules Made by Microfluidic Technology
- Doctoral Thesis
Rights / licenseIn Copyright - Non-Commercial Use Permitted
Encapsulation systems for the on-demand release of cargo molecules find applications in several fields, ranging from agricultural and construction to pharmaceuticals, food and materials science. In the construction sector, encapsulation systems have been used in the form of phase change materials for smart insulation of buildings and have recently been envisioned as a possible approach to deliberately control the setting reaction of cementitious materials. Controlling the setting of cement in building materials is crucial to prevent losses and high costs associated with early or late hardening of concretes and mortars. Current solutions are not satisfactory because accelerators and retarder molecules cannot be activated on demand in a homogeneous manner throughout the cementitious material. In this thesis, encapsulation systems for the on-demand release of molecules in cementitious materials are designed and investigated. On-demand release is triggered remotely using an external alternating magnetic field to locally heat the microcapsules. Heating leads to capsule bursting and local release of cargo molecules. Microcapsules with such thermally-triggered response were produced from double emulsions templates made in glass capillary microfluidic devices. The middle oil phase of the water-oil-water double emulsion contains a mixture of monomers, photoinitiator and inert liquids, which can be polymerized under UV light to generate monodisperse capsules with microstructured shells. The shell microstructure is determined by the phase separation of the polymer from the inert diluent during conversion of the double emulsion into microcapsules. The composition of the Summary ii oil phase directly impacts the size of polymerized particles formed within the shell, providing a useful control parameter to tune the mechanical properties of the microcapsules. Interestingly, the use of an amphiphilic inert liquid such as undecanol enables the formation of shells with open pores upon removal of the liquid. By contrast, microstructured shells with a polymer skin in the outer and inner walls are generated if the inert liquid displays no surface activity. This leads to the entrapment of the liquid inside the shell. If a volatile inert liquid is used, local heating of the microcapsule in an alternating magnetic field causes bursting and release of the cargo molecules encapsulated in the core. To ensure local heating of the capsules without an undesirable increase of the temperature of the surrounding cementitious paste, millimeter-sized metal spheres are used as inductive heat sources. In this approach, the metal spheres are coated with the thermo-sensitive microcapsules to generate a raspberry-like encapsulation system that can be activated using an external magnetic field. Experimental results obtained using such model raspberry-like system demonstrate that this is a feasible strategy to enable the on-demand release of an accelerator compound in an aqueous medium. The use of metallic fibers already used in concrete formulations as heat sources can potentially allow for the implementation of this concept in real applications Show more
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ContributorsExaminer: Studart, André R.
Examiner: Vermant, Jan
Examiner: Creton, Costantino
Organisational unit03831 - Studart, André R. / Studart, André R.
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