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This dissertation focuses on the understanding of the optical manipulation of microgels dispersed in aqueous solution of azobenzene containing surfactant. The work consists of three parts where each part is a systematic investigation of the (1) photo-isomerization kinetics of the surfactant in complex with the microgel polymer matrix, (2) light driven diffusiosmosis (LDDO) in microgels and (3) photo-responsivity of microgel on complexation with spiropyran. The first part comprises three publications where the first one [P1] investigates the photo-isomerization kinetics and corresponding isomer composition at a photo-stationary state of the photo-sensitive surfactant conjugated with charged polymers or micro sized polymer networks to understand the structural response of such photo-sensitive complexes. We report that the photo-isomerization of the azobenzene-containing cationic surfactant is slower in a polymer complex compared to being purely dissolved in an aqueous solution. [...].
Microgels by Precipitation Polymerization: Synthesis, Characterization, and Functionalization, by A. Pich and W. Richtering * Hydrogels in Miniemulsions, by K. Landfester and A. Musyanovych * Nano- and Microgels Through Addition Reactions of Functional Oligomers and Polymers, by K. Albrecht, M. Moeller, and J. Groll * Synthesis of Microgels by Radiation Methods, by F. Krahl and K.-F. Arndt * Microgels as Nanoreactors: Applications in Catalysis, by N. Welsch, M.s Ballauff, and Y. Lu
Microgels are sub-micron to micron-size polymeric networks confined in limited space swollen by a good solvent, also called hydrogel microparticles or microspheres if swollen in water. Among all microgels investigated nowadays, poly(N-isopropylacrylamide), pNIPAm, microgels are one of the most extensively studied microgel particles due to their volume phase transition (VPT) at lower critical solution temperature (LCST). By incorporation of pH-responsive monomer, acrylic acid (AAc), copolymeric pNIPAm-AAc microgels further demonstrate multi-responsivity to temperature, pH, and ionic strength. A temperature-programmed polymerization protocol is proposed for the synthesis of large pNIPAm-AAc microgel particles with a hydrodynamic diameter of 2 5 m. Futhermore, to observe the phase behavior of pNIPAm-AAc microgel dispersions, pNIPAm-AAc dispersions at various pH values and concentrations were allowed to age and undergo phase transition in closed system. Finally, the Cu(I)-catalyzed azide-terminal alkyne 1,3-dipolar cycloaddition, also called Sharpless-Meldal "click" reaction, is used to functionalize pNIPAm-AAc microgel particles for microgel bioconjugation and medical applications.
Microgels by Precipitation Polymerization: Synthesis, Characterization, and Functionalization, by A. Pich and W. Richtering * Hydrogels in Miniemulsions, by K. Landfester and A. Musyanovych * Nano- and Microgels Through Addition Reactions of Functional Oligomers and Polymers, by K. Albrecht, M. Moeller, and J. Groll * Synthesis of Microgels by Radiation Methods, by F. Krahl and K.-F. Arndt * Microgels as Nanoreactors: Applications in Catalysis, by N. Welsch, M.s Ballauff, and Y. Lu
We present the phase behavior of soft sphere colloidal dispersions. The pH responsive and thermoresponsive microgels, poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc), were used as a new building block of colloidal crystals. The phase behavior of microgel dispersions was studied by different methods such as optical microscopy, particle trajectories, mean squared displacement (MSD) vs. lag time plots and radial distribution function. The results show that the phase of the sample relies on the particle concentration for dispersions of the same pH. As the pH approaches the pKa of microgels, the microgel dispersions show unusual crystalline phase at lower effective volume fraction than hard sphere melting transition. Also, at this pH regime, the microgel dispersions undergo slow and spatially heterogeneous crystal growth. The cooperative multi-body type attractive forces were proposed to explain the unusual stability at low effective volume fraction. Ion-dipole interactions were proposed to be the origin of the attractive forces. The melting point of bulk crystals at this pH regime is much higher than the volume phase transition temperature of the building block. These results are supportive of the attractive forces hypothesis.
This book is a printed edition of the Special Issue "Stimuli-Responsive Gels" that was published in Gels