Dissertation / PhD Thesis

PUBDB-2019-02383

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Microfluidic Sample Environments for Time-resolved Macromolecular Structure Formation Studies

Vakili, M. (Corresponding author) ; Trebbin, M. (Thesis advisor)XFEL.EU*EMBL* ; Pearson, A. (Thesis advisor)Extern*EMBL*

2019
Hamburg

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Please use a persistent id in citations: doi:10.3204/PUBDB-2019-02383

Abstract: This thesis deals with the polymerization-induced self-assembly (PISA) of amphiphilic blockcopolymer nano-objects, which were synthesized using a controlled radical polymerization(CRP) method, in particular, the reversible addition-fragmentation chain-transfer (RAFT)aqueous polymerization in the presence of a poly(N,N-dimethylacrylamide) stabilizer agent(macro RAFT agent). Besides the use of N-isopropylacrylamide (NIPAm) as core-formingblock for thermo-responsive nanoparticle, the aqueous dispersion polymerization of 2-methoxyethyl acrylate (MEA) was pursued as a model to study hydrophilic-hydrophobic phasetransitions: as a monomer, MEA is water-soluble. However, upon chain growth, the poly(MEA)block becomes hydrophobic which eventually drives micellar self-assembly. The underlyingprocesses and the time scales of the self-assembly are still not completely understood.Finding the answers to such questions can be answered by the investigation of a system’s timeresolvedreaction kinetics and structural dynamics in situ. However, it can be challenging tocontrol the experimental conditions accurately, such as the precise initiation of a reaction byrapid mixing. This challenge can be overcome by using microfluidic reaction systems whichenable precise control over fluids within micron-sized channels. These very well defined flowand reaction conditions make microfluidics predestined for the time-resolved studies ofpolymers using X-ray sources. In microfluidic laminar flows, the temporal structural evolutionduring a polymerization process can be mapped onto different positions in the downstreammicrochannel. Besides the ability to access time scales down to the microseconds-scale, thisapproach has many advantages compared to more traditional set-ups in terms of a low sampleconsumption (experiments on the nanoliter scale), highly efficient and homogeneous mixing bydiffusion, as well as the possibility to adjust the temporal resolution by manipulation of the flowrates.Microfluidic channels can be fabricated using a number of different materials, each havingdifferent optical and mechanical properties as well as manufacturing challenges: glass, metaland most importantly polymers, such as polydimethylsiloxane (PDMS), thermoplastic cyclicolefin copolymers (TOPAS® COC) or highly inert polyimide films (Kapton®) are currentlyused. With the advent of more powerful and brighter X-ray sources, COCs and Kapton inparticular have received tremendous interest as sample environment due to their X-raycompatibility and low background signal. Another approach for low-background sampleenvironments are microfluidic liquid jet devices based on the gas dynamic virtual nozzle(GDVN) design. These devices contain a network of very narrow channels and nozzles andprovide a very defined free-flowing sample stream in vacuum, making them especiallydesirable for experiments at X-ray free electron laser (XFEL) facilities.In this work, the tailored design, fabrication and experimental implementation of novelmicrofluidic sample environments that address specific experimental conditions for controlledradical polymerization are described. In particular, these devices were applied to in situ timeresolveddiffusive mixing experiments to access very early stages of the PISA reaction. In situhere means monitoring the structural changes during chain growth/phase transition by probingthe sample with X-rays while the polymerization/self-assembly occurs.Supported by complimentary dynamic light scattering (DLS) experiments, fluorescentmicroscopy and 3D finite-element computational fluid dynamics (CFD) simulations, theinsights of these experiments aim to provide a better understanding of amphiphilic blockcopolymer self-assembly and, in general, may help to tailor polymers for their specificapplications, such as micellar drug delivery vehicles in medical applications.

Note: Dissertation, University of Hamburg, 2019

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Contributing Institute(s):

1. beauftragt von UNI (UNI/CUI)
2. Uni Hamburg / Physik (UNI/PHY)
3. Institute of Nanostructure and Solid State Physics (UNI/INF)

Research Program(s):

1. 6G3 - PETRA III (POF3-622) (POF3-622)
2. DFG project 194651731 - EXC 1074: Hamburger Zentrum für ultraschnelle Beobachtung (CUI): Struktur, Dynamik und Kontrolle von Materie auf atomarer Skala (194651731) (194651731)
3. PHGS, VH-GS-500 - PIER Helmholtz Graduate School (2015_IFV-VH-GS-500) (2015_IFV-VH-GS-500)

Experiment(s):

1. PETRA Beamline P03 (PETRA III)
2. Experiments at CFEL
3. Measurement at external facility

Appears in the scientific report 2019

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Database coverage:

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