Single light emitters in the confinement of polymers

This thesis presents developments in the field of nanoscale probing of polymers. New experimental methods based on single molecule fluorescence detection were developed and applied to polymer studies. Localization of, and communication with individual fluorescent molecules embedded in a glassy polymer or immersed in a polymer melt have been realized by using various, optical techniques e.g. Scanning Confocal Microscopy and Wide-Field Microscopy. Location of single molecules as well as their orientation, emission spectra or fluorescence lifetime have been followed in time. This allowed us to perform dynamical studies in the time domain. Since full distributions of single molecule behavior (e.g. rotational diffusion constants, fluorescence lifetimes) were obtained, systems with heterogeneous dynamics could be clearly identified and sub-ensembles, which could be characterized with different dynamic properties, were separated and investigated. Besides polymer probing studies, it was also shown how relatively simple structures can be prepared and used to engineer the emission properties of single molecules. In particular, the fluorescence emission of single molecules in thin polymer films and in electrospun polymer fibers was shown to depend on the size of the structures

Microcontact printed poly(amidoamine) dendrimer monolayers on silicon oxide surface

Patterning of silicon substrates with poly(amidoamine) generation 5 (PAMAM-G5) dendrimers using soft lithographic microcontact printing (μCP) is presented. μCP is shown to yield monolayers of dendrimers patterned with high level of definition over μm2 to mm2 areas. The patterns are stable over a period of weeks, which is attributed to the suppressed diffusion of partially charged G5 PAMAM on oxidized silicon. However, the dendrimers studied were shown to be relatively weakly bound to the substrate when subjected to lateral stresses. In aqueous conditions most of the dendrimers desorbed from the substrat

Polymer-coated quantum dots

Quantum Dots (QDs) are semiconductor nanocrystals with distinct photophysical properties finding applications in biology, biosensing, and optoelectronics. Polymeric coatings of QDs are used primarily to provide long-term colloidal stability to QDs dispersed in solutions and also as a source of additional functional groups used in further chemical derivatization of the nanoparticles. We review the coating methods, including multidentate and amphiphilic polymeric coatings, and grafting-to and grafting-from approaches. We highlight the most commonly used polymers and discuss how their chemical structure influences the coating properties

Self-assembled architectures with multiple aqueous compartments

A vital organizational feature of living cells is that of compartmentalization. This allows cells to run concurrently incompatible metabolic processes and to regulate these processes by selective trans-membrane transport. Although strategies that effectively mimic cell function in simple architectures have been researched extensively, soft matter systems with membranes that delineate distinct and multiple aqueous environments have only recently caught attention. We highlight a range of multi-compartmentalized soft matter systems including vesosomes, capsosomes, polymersomes, double emulsions, and their combinations, and demonstrate that the unique properties of the multi-compartmentalized architectures have the potential to add value to application areas such as drug-delivery and multi-enzyme biosynthesis

Protein Nanocage as a pH-Switchable Pickering Emulsifier

Encapsulation of active compounds in Pickering emulsions using bioderived protein-based stabilizers holds potential for the development of novel formulations in the fields of foods and cosmetics. We employ a dodecahedron hollow protein nanocage as a pH-switchable Pickering emulsifier. E2 protein nanocages are derived from pyruvate dehydrogenase multienzyme complex from <i>Geobacillus stearothermophilus</i> which adsorb at the oil/water interface at neutral and basic pH’s and stabilize the Pickering emulsions, while in the acidic range, at pH ∼4, the emulsion separates into emulsion and serum phases due to flocculation. The observed process is reversible for at least five cycles. Optimal formulation of a Pickering emulsion composed of rosemary oil, an essential oil, and water has been achieved by ultrasonication and results in droplets of approximately 300 nm in diameter with an oil/water ratio of 0.11 (v/v) and 0.30–0.35% (wt %). Ionic stabilization is observed for concentrations up to 250 mM NaCl and pH values from 7 to 11. The emulsions are stable for at least 10 days when stored at different temperatures up to 50 °C. The resulting Pickering emulsions of different compositions also form a gel-like structure and show shear thinning behavior under shear stress at a higher oil/water ratio

Amphiphilic polymer and processes of forming the same

Disclosed are an amphiphilic polymer, its synthesis and uses thereof. The polymer has a hydrocarbon backbone with —COOH side groups. It further has first aliphatic moieties with a main chain of about 3 to about 20 carbon atoms and 0 to about 3 heteroatoms, and second aliphatic moieties that have a main chain of about 3 to about 80 carbon atoms and about 2 to about 40 heteroatoms. The second aliphatic moieties have a copolymerisable group. In the synthesis a maleic anhydride polymer of formula (I) where n is an integer from about 10 to about 10000 and R1 is H or methyl, is reacted with a monofunctional compound with an alkyl chain of about 3 to about 20 carbon atoms and 0 to about 2 heteroatoms, and with an at least bifunctional compound with an alkyl chain of about 3 to about 80 carbon atoms and 0 to about 40 heteroatoms. The functional group of the monofunctional compound and one functional group of the at least bifunctional compound can form a linkage with an anhydride. Another functional group of the at least bifunctional compound, which is not allowed to react with the maleic anhydride polymer, is copolymerisable

Nanoscale Hydrophobic Recovery: A Chemical Force Microscopy Study of UV/Ozone-Treated Cross-Linked Poly(dimethylsiloxane)

Chemical force microscopy (CFM) in water was used to map the surface hydrophobicity of UV/ozone-treated poly(dimethylsiloxane) (PDMS; Sylgard 184) as a function of the storage/recovery time. In addition to CFM pull-off force mapping, we applied indentation mapping to probe the changes in the normalized modulus. These experiments were complemented by results on surface properties assessed on the micrometer scale by X-ray photoelectron spectroscopy and water contact-angle measurements. Exposure times of <_30 min resulted in laterally homogeneously oxidized surfaces, which are characterized by an increased modulus and a high segmental mobility of PDMS. As detected on a sub-50-nm level, the subsequent "hydrophobic recovery" was characterized by a gradual increase in the pull-off forces and a decrease in the normalized modulus, approaching the values of unexposed PDMS after 8-50 days. Lateral imaging on briefly exposed PDMS showed the appearance of liquid PDMS in the form of droplets with an increasing recovery time. Longer exposure times (60 min) led to the formation of a hydrophilic silica-like surface layer. Under these conditions, a gradual surface reconstruction within the silica-like layer occurred with time after exposure, where a hydrophilic SiOx-enriched phase formed <100-nm-sized domains, surrounded by a more hydrophobic matrix with lower normalized modulus. These results provide new insights into the lateral homogeneity of oxidized PDMS with a resolution in the sub-50-nm range

In Operando Characterization and Control over Intermittent Light Emission from Molecular Tunnel Junctions via Molecular Backbone Rigidity

10.1002/advs.201900390Advanced Science620190039