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Abstract Here we report on light-triggered generation of local flow utilizing a bio-compatible non-ionic photo-active surfactant. The mechanism is based on diffusioosmotic phenomenon, where the gradient of relative concentration with respect to different chemical species near a surface leads to an osmotic pressure gradient driving liquid flow along the surface. The application of a photo-responsive surfactant allows for easy and reversible changes in concentration gradient by positioning a light source at the desired place. Along with the so-inscribed concentration gradient one can change reversible the direction and strength of the flow even in a closed system. The phenomenology of light-driven diffusioosmotic flow (LDDO) can be used in a rather flexible way: colloids can be gathered or dispersed and bio-compatibility extends the range of colloid types also to living microorganisms such as soil bacterium Pseudomonas putida. We show that DO flow can be considered a versatile method to set hydrodynamic conditions along the sample for investigating the motility of living cells. Further advantages of employing LDDO are the flexibility of flow generation in a reversible way and with spatiotemporal control, without the need to either change the channel geometry by loading a different device, or the periphery of pumps and connectors.

Separation of equally sized particles distinguished solely by interfacial properties remains a highly challenging task. Herein, a particle fractioning method is proposed, which is suitable to differentiate between polymer‐grafted microparticles that are equal in size. The separation relies on the combination of a pressure driven microfluidic flow, together with simultaneous light illumination and temperature control. Heating the solution forces thermo‐responsive surface grafts to undergo a volume phase transition and therefore locally changing the interfacial properties of the microparticles. Light illumination induces the phoretic/osmotic activity of the microparticles and lifts them into a higher plane, where hovering particles experience a different shear stress proportional to the height. The light‐induced hovering height depends on the interfacial properties, and this complex interaction leads to different movements of the microparticles as a function of their surface grafting. The concepts are visualized in experimental studies, where the complex physical principle provides a simple method for fractioning a binary mixture with at least one thermo‐responsive polymer graft.

Abstract Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro- or macroscale elements is hampered by the lack of structural components that have both, nano- and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket.

Ionic complexation of azobenzene-containing surfactants with any type of oppositely charged soft objects allows for making them photo-responsive in terms of their size, shape and surface energy. Investigation of the photo-isomerization kinetic and isomer composition at a photo-stationary state of the photo-sensitive surfactant conjugated with charged objects is a necessary prerequisite for understanding the structural response of photo-sensitive complexes. Here, we report on photo-isomerization kinetics of a photo-sensitive surfactant in the presence of poly(acrylic acid, sodium salt). We show that the photo-isomerization of the azobenzene-containing cationic surfactant is slower in a polymer complex compared to being purely dissolved in aqueous solution. In a photo-stationary state, the ratio between the trans and cis isomers is shifted to a higher trans-isomer concentration for all irradiation wavelengths. This is explained by the formation of surfactant aggregates near the polyelectrolyte chains at concentrations much lower than the bulk critical micelle concentration and inhibition of the photo-isomerization kinetics due to steric hindrance within the densely packed aggregates.

Realization of all-optically controlled and efficient DNA compaction is the major motivation in the study of interactions between DNA and photosensitive surfactants. In this article, using recently published approach of phase diagram construction [Y. Zakrevskyy, P. Cywinski, M. Cywinska, J. Paasche, N. Lomadze, O. Reich, H.-G. Löhmannsroben, and S. Santer, J. Chem. Phys.140, 044907 (2014)], a strategy for substantial reduction of compaction agent concentration and simultaneous maintaining the light-induced decompaction efficiency is proposed. The role of ionic strength (NaCl concentration), as a very important environmental parameter, and surfactant structure (spacer length) on the changes of positions of phase transitions is investigated. Increase of ionic strength leads to increase of the surfactant concentration needed to compact DNA molecule. However, elongation of the spacer results to substantial reduction of this concentration. DNA compaction by surfactants with longer tails starts to take place in diluted solutions at charge ratios Z < 1 and is driven by azobenzene-aggregation compaction mechanism, which is responsible for efficient decompaction. Comparison of phase diagrams for different DNA-photosensitive surfactant systems allowed explanation and proposal of a strategy to overcome previously reported limitations of the light-induced decompaction for complexes with increasing surfactant hydrophobicity. [ABSTRACT FROM AUTHOR]

The preparation of polyaramide thin films on silicon wafers via stepwise layer buildup is described. Hydroxy- and amine-functionalized silicon wafers are reacted in step-and-repeat processes with aromatic dichlorides and diamines, which leads to a stepwise formation of a surface-attached polyamide layer. In the case of aromatic diamines and terephtaloyl dichloride the generation of an up to 115 nm thick polyaramide layer is described while the corresponding aliphatic compounds yield only very thin films. FTIR, ellipsometric measurements and atomic force microscopy (AFM) show a linear growth of the polyaramide layers for more than a thousand reaction cycles. The mechanism of the monomer-by-monomer layer formation process and the structure of the formed films are elucidated. [ABSTRACT FROM AUTHOR]

Heating of l-lactide with imidazole to 98−100 °C resulted in complete polymerization within 48 h. Even-numbered cycles resulting from end-to-end cyclization were the only reaction products after 4 h, but the polymerization process was accompanied by intensive racemization. Longer reaction times favored equilibration reactions with formation of odd-numbered cycles. Variation of the monomer−initiator ratio at 120 °C had little influence on the molecular weight. After 8 h at 150 °C, equal quantities of odd- and even-numbered cycles were found, indicating complete equilibration. Other protic heterocycles such as 1,2,4-triazole, benzimidazolyl acetonitrile, uracile, or hypoxanthine were not active as initiators/catalysts at 120 °C. However, the tertiary amine N-methylimidazole also catalyzes the formation of cyclic polylactides together with several byproducts. The reaction mechanisms are discussed. [ABSTRACT FROM AUTHOR]

Dithiolane-2,4-dione was polymerized either by heating in bulk to 140 °C or by reacting at 20 °C using pyridine and triethylamine as catalysts. Whereas the thermal polymerization almost exclusively yielded cyclic poly(thioglycolide), the samples prepared at 20 °C by means of tertiary amines contained cyclic and linear chains. The end groups of the linear chains varied with the nonsolvent used for the workup procedure, because chains having reactive end groups were immobilized by rapid crystallization and reacted at the electrophilic CO-chain end with the nonsolvent. d,l-5-Methyldithiolane-2,4-dione proved so stable that tertiary amines did not catalyze its polymerization even at 100 °C. Thermal polymerization at 160 °C yielded oligoester mainly consisting of cyles. A zwitterionic polymerization mechanism allowing for simultaneous chain-growth and step-growth polymerization is discussed. [ABSTRACT FROM AUTHOR]

5,5‘-Tetrahydroxy-3,3,3‘,3‘-tetramethyl spirobisindane (TTSBI) was deprotonated with potassium tert-butoxide and polycondensed with di(ethylene glycol) tosylate or tri(ethylene glycol) tosylate. Polycondensations in DMSO gave cleaner reaction products than in DMF. At concentrations of 0.1 or 0.2 mol/L no cross-linking was observed and multicyclic polyethers were isolated. The high yields (up to 99%), the 1H NMR and the MALDI−TOF mass spectra proved almost complete conversion. The DSC measurements indicated an amorphous character with two glass-transition temperatures. The SEC measurements showed rather narrow mass distributions with polydispersities below 2. The multicyclic polyethers dissolved lithium, sodium, potassium, and cesium benzoate in tetrahydrofuran at weight ratios around 1/50 (salt/multicycle). [ABSTRACT FROM AUTHOR]