Materials Science and Technology of Polymers at the University of Twente

Particles in Polymer-Functionalized Microchannels. Electrochemical experiments and molecular dynamics simulations

Thesis cover Bram Zoetebier: Functional macromolecules and smart polymer networks for ion separation, reduction and delivery

The aim of this thesis has been to provide the ground work for the electrochemical sensing of analytes in polymer-functionalized microchannels via gold-coated microfabricated microchannel electrodes and for the in-situ study of the adsorption of particles in polymer brushes through molecular dynamics simulations. Both these objectives encompass polymer systems that are out of equilibrium and reveal how particles interact with these polymers. The aim was accomplished via the successful fabrication of in-channel gold-coated electrodes within a microfluidic device. To these gold-coated electrodes a redox-active polymer, poly(ferrocenylsilane) (PFS), was attached, via which sodium ascorbate could be sensed. To further understand the effect of particles in polymer systems, molecular dynamics (MD) simulations were performed on the insertion of particles of various size, shape and orientation, into a polymer brush. The force-distance curves were successfully modelled by two different models, one using scaling arguments and one aided through MD. Furthermore, the effect of shaking the wall, to which the polymer brushes are attached, on the penetration depth of particles into the brush was simulated, to approximate biological microsystems. From these could be concluded that if the brush is oscillated at its resonance frequency at a complementary resonance amplitude, the increase in penetration depth is at its maximum

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Chapter 1 consists of a short introduction into the topic of this work, as well as an overview of the thesis.

Chapter 2 encompasses a short review of the most relevant research done on the fabrication of in-channel electrodes, the in-chip electrochemical detection of various analytes and the MD simulations performed on polymer brushes. Furthermore, a concise overview of the electrochemical methods is given, and an introduction into the topic of MD is presented.

Chapter 3 covers the use of polymer coatings in glass microfluidic devices in depth, where polymers were employed both as active and passive layers.

Chapter 4 describes various electrochemical experiments performed on a microfluidic device with integrated gold electrodes. Both the fabrication and characterization of the device are discussed. In this device, a PFS layer was grafted to the gold electrodes, via which sodium ascorbate could be detected by electrochemical means.

Chapter 5 concerns the first of the two MD-focused chapters. This chapter describes how particles of various size, orientation and shape, were inserted into a polymer brush, resulting in different inclusion energies. The forces on the particles were modelled via two models, and a size- and shape-dependent pre-factor could be determined.

In chapter 6, the second MD simulation is reported, where a polymer brush is shaken at the grafting wall. The effect of this motion on the penetration depth of spherical particles is determined. By varying the size of the particles and the amplitude and period of oscillation, an optimum period and amplitude for particle absorption could be found. This optimum corresponded with a resonance period and complementary amplitude of oscillation.

Finally, chapter 7 gives an outlook towards future research on brush-covered microchannels. Moreover, recommendations for other applications of PFS within microchannels is provided.