Light-Triggered Manipulations of Droplets All in One: Reversible Wetting, Transport, Splitting, and Merging.

Here, we establish different ways of light-triggered droplet manipulation such as reversible wetting, splitting, merging, and transport. The unique features of our approach are that the changes in the wetting properties of microscopic droplets of isotropic (oil) or anisotropic (liquid crystalline) liquids adsorbed on photoswitchable films can be triggered just by application of soft optical stimuli, which lead to dynamical, reversible changes in the local morphology of the structured surfaces. The adaptive films consist of an azobenzene-containing surfactant ionically attached to oppositely charged polymer chains.

Self-Assembly of Molecular Brushes with Polyimide Backbone and Amphiphilic Block Copolymer Side Chains in Selective Solvents.

Three-component molecular brushes with a polyimide backbone and amphiphilic block copolymer side chains with different contents of the "inner" hydrophilic (poly(methacrylic acid)) and "outer" hydrophobic (poly(methyl methacrylate)) blocks were synthesized and characterized by molecular hydrodynamics and optics methods in solutions of chloroform, dimethylformamide, tetrahydrofuran and ethanol. The peculiarity of the studied polymers is the amphiphilic structure of the grafted chains. The molar masses of the molecular brushes were determined by static and dynamic light scattering in chloroform in which polymers form molecularly disperse solutions.

Extremely Long-Range Light-Driven Repulsion of Porous Microparticles.

The repulsive surface forces, such as electrostatic or steric, acting between particles explain why they remain well separated in aqueous electrolyte solutions and are responsible for the stability of colloidal dispersions. However, the effective range of these interactions is always well below hundreds of nanometers and typically can be controlled by advanced manipulations such as tuning the electrolyte concentration or modifying the particle surface or, in some more specific cases, via subjecting the suspension to an external electric or magnetic field. Here we employ solutions with small additives of a photosensitive ionic surfactant to investigate if a repulsive interaction of microsized particles sedimented at the solid surface can be remotely controlled simply by illuminating it with an appropriate wavelength.

Light driven guided and self-organized motion of mesoporous colloidal particles.

We report on guided and self-organized motion of ensembles of mesoporous colloidal particles that can undergo dynamic aggregation or separation upon exposure to light. The forces on particles involve the phenomenon of light-driven diffusioosmosis (LDDO) and are hydrodynamic in nature. They can be made to act passively on the ensemble as a whole but also used to establish a mutual interaction between particles.

Anionic Polymer Brushes for Biomimetic Calcium Phosphate Mineralization-A Surface with Application Potential in Biomaterials.

This article describes the synthesis of anionic polymer brushes and their mineralization with calcium phosphate. The brushes are based on poly(3-sulfopropyl methacrylate potassium salt) providing a highly charged polymer brush surface. Homogeneous brushes with reproducible thicknesses are obtained via surface-initiated atom transfer radical polymerization.

Light-Induced Deformation of Azobenzene-Containing Colloidal Spheres: Calculation and Measurement of Opto-Mechanical Stresses.

We report on light-induced deformation of colloidal spheres consisting of azobenzene-containing polymers. The colloids of the size between 60 nm and 2 μm in diameter were drop casted on a glass surface and irradiated with linearly polarized light. It was found that colloidal particles can be deformed up to ca.

Mass production of polymer nano-wires filled with metal nano-particles.

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.

Photosensitive microgels containing azobenzene surfactants of different charges.

We report on light sensitive microgel particles that can change their volume reversibly in response to illumination with light of different wavelengths. To make the anionic microgels photosensitive we add surfactants with a positively charged polyamine head group and an azobenzene containing tail. Upon illumination, azobenzene undergoes a reversible photo-isomerization reaction from a trans- to a cis-state accompanied by a change in the hydrophobicity of the surfactant.

Light-Induced Reversible Change of Roughness and Thickness of Photosensitive Polymer Brushes.

We investigate light-induced changes in thickness and roughness of photosensitive polymer brushes containing azobenzene cationic surfactants by atomic force microscopy (AFM) in real time during light irradiation. Because the cis-state of azobenzene unit requires more free volume than its trans counterpart, the UV light-induced expansion of polymer thin films associated with the trans-to-cis isomerism of azobenzene groups is expected to occur. This phenomenon is well documented in physisorbed polymer films containing azobenzene groups.

Opto-mechanical scission of polymer chains in photosensitive diblock-copolymer brushes.

In this paper we report on an opto-mechanical scission of polymer chains within photosensitive diblock-copolymer brushes grafted to flat solid substrates. We employ surface-initiated polymerization of methylmethacrylate (MMA) and t-butyl methacrylate (tBMA) to grow diblock-copolymer brushes of poly(methylmethacrylate-b-t-butyl methacrylate) following the atom transfer polymerization (ATRP) scheme. After the synthesis, deprotection of the PtBMA block yields poly(methacrylic acid) (PMAA).

Soft matter beats hard matter: rupturing of thin metallic films induced by mass transport in photosensitive polymer films.

The interface between thin films of metal and polymer materials play a significant role in modern flexible microelectronics viz., metal contacts on polymer substrates, printed electronics and prosthetic devices. The major emphasis in metal-polymer interface is on studying how the externally applied stress in the polymer substrate leads to the deformation and cracks in metal film and vice versa.

DNA compaction by azobenzene-containing surfactant.

We report on the interaction of cationic azobenzene-containing surfactant with DNA investigated by absorption and fluorescence spectroscopy, dynamic light scattering, and atomic force microscopy. The properties of the surfactant can be controlled with light by reversible switching of the azobenzene unit, incorporated into the surfactant tail, between a hydrophobic trans (visible irradiation) and a hydrophilic cis (UV irradiation) configuration. The influence of the trans-cis isomerization of the azobenzene on the compaction process of DNA molecules and the role of both isomers in the formation and colloidal stability of DNA-surfactant complexes is discussed.

Photomechanical degrafting of azo-functionalized poly(methacrylic acid) (PMAA) brushes.

We report on the preparation and characterization of photosensitive polymer brushes. The brushes are synthesized through polymer analogous attachment of azo-benzene groups to surface-attached poly(methacrylic acid) (PMAA) chains. The topography of the photosensitive brushes shows a strong reaction upon irradiation with UV light.

A new approach to nucleation of cavitation bubbles at chemically modified surfaces.

Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm(-2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy.

Self-assembling carbohydrate-functionalized oligothiophenes.

Carbohydrate-functionalized oligothiophenes have been synthesized applying mild Sonogashira cross-coupling conditions. In an aqueous environment the amphiphilic hybrids self-assemble into chiral superstructures as a result of multiple hydrogen bond interactions and the helicity of the aggregates is controllable by the configuration of the carbohydrate unit. By means of atomic force microscopy highly ordered layer arrangements on substrates were characterized.

Self-organizing oligothiophene-nucleoside conjugates: versatile synthesis via "click"-chemistry.

A versatile synthesis of novel oligothiophene-nucleoside conjugates based on Cu(I)-catalyzed alkyne-azide cycloaddition ("click-reaction") has been developed. Complementary thymidine- and adenosine-functionalized quaterthiophenes form recognition-driven superstructures via hydrogen bonding and other competing intermolecular forces. Self-aggregated fibers up to 30 microm in length were characterized with atomic force microscopy.

Memory of surface patterns in mixed polymer brushes: simulation and experiment.

The correlation between the morphology of mixed polymer brushes and fluctuations of the grafting points is investigated by single-chain-in-mean-field simulations and experiments. The local topography of two types of mixed polystyrene-polymethylmethacrylate (PS-PMMA) brushes that differ in their modes of attachment has been studied during repeated microphase separation into laterally structured and homogeneous morphologies upon changing solvents. In the first type of brush (conventional), each of the surface-attached initiator groups starts the growth of either a PS or a PMMA chain in a random fashion.

Domain memory of mixed polymer brushes.

The nano-phase-separation in mixed polymer brushes consisting of polystyrene and poly(methyl methacrylate) (PS-PMMA) chains attached to a silicon surface is studied. The topographies of the mixed brushes are examined after they have been exposed to solvents which induce or erase nano-phase-separation. It is discussed whether the brush locally forms the same pattern every time the transition from the smooth and featureless to the nanopatterned state occurs ("domain memory") or if the local assembly of the domains emerges in a different arrangement after each cycle of topography switching.