Disguise tactics: Peptide–polymer hybrid nanotubes are constructed in which self‐assembled cyclic peptides govern the structure, and a synthetic polymer coating determines the surface chemistry. Formation of the latter is initiated in situ from preorganized peptide building blocks. The picture shows an AFM image of nanotubes on a silicon wafer.

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. In the second case (Y-shaped mixed brushes), two chains of different types are attached to the same anchor group on the substrate. Whereas in the first case statistical fluctuations of the chemical composition occur on a local scale, such composition fluctuations are strongly suppressed in the latter case. The microphase-separated morphology is similar in both cases, but Y-shaped brushes exhibit a significantly weaker domain memory than do conventional PS-PMMA mixed brushes. The results of the experiment are compared with simulations, and a simple phenomenological argument and qualitative agreement are found. The observations demonstrate that small fluctuations in the grafting points are amplified by the microphase separation and nucleate the location of the domains in the mixed brush.

Polystyrene−poly(methyl methacrylate) (PS−PMMA) mixed brushes synthesized by surface-initiated polymerization show nanophase separation into defined pattern depending on the molecular parameters of the brushes. Two sets of mixed brushes are studied:  (i) with fixed grafting density and molecular weight of the PS chains, but differing in the molecular weight of PMMA polymer, and (ii) with varying grafting density of the PMMA chains while that of the PS chains and the molecular weight of PS and PMMA chains are kept constant. The local distribution of PS and PMMA chains within the monolayer and the size, shape, and position of the domains constituting the nanopattern are found to vary with the nature of the solvent to which the brushes are exposed. The brushes are treated cyclically first with either a good solvent for both blocks, leading to strong swelling and structure erasure, and then with a selective solvent, which induces the nanophase separation. It was found that in the case of the brush exposed to toluene solvent (good solvent for both polymers) the brush surface exhibiting a small variation in topography has a heterogeneous surface composition, with the nanoscopic areas having only PS or PMMA chains at the surface. When the brush is treated with acetone solvent, which is better for the PMMA chains, the surface consists only of PMMA chains, and the topography assumes a more pronounced relief. We introduce the concept of the local domain memory effect of the brushes, i.e., whether the brush locally forms always the same pattern or if the local assembly of the domains emerges in different places every time the transition to the structured state occurs.

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. Depending on the isomerization state, the surfactant molecules are either accommodated within the microgel (trans-state) resulting in its shrinkage or desorbed back into water (cis-isomer) letting the microgel swell. We have studied three surfactants differing in the number of amino groups, so that the number of charges of the surfactant head varies between 1 and 3. We have found experimentally and theoretically that the surfactant concentration needed for microgel compaction increases with decreasing number of charges of the head group. Utilization of polyamine azobenzene containing surfactants for the light triggered remote control of the microgel size opens up a possibility for applications of light responsive microgels as drug carriers in biology and medicine.

The idea of building motors or engines at nanometer dimensions that eventually could themselves manipulate structures of comparable size has grown along with the major breakthroughs in nanotechnology over the last 20 years. This mainly concerns manipulating nanometer-sized objects such as adsorbed macromolecules or nanometer-sized colloids directly using scanning force microscopy (SFM) techniques that first helped to give a closer look at the nanometer-scale world. Such simple mechanical methods still represent the most fruitful approaches for manipulation on the nanometer scale. [1][2][3][4][5][6][7][8] In a second line of research, attempts are made to construct nanometer-sized motors that are mostly based on natural complexes, mimicking and utilizing the peculiar properties of protein motors. [9][10][11][12][13] Both approaches are already optimized with respect to their specific field of application: for example, in the case of SFM, precise positioning of single colloids, molecules, and even atoms is possible, but manipulating ensembles of particles in parallel is a nearly intractable task. Protein motors such as kinesin microtubuli are highly efficient by their very nature, but only work in aqueous solutions and within a narrow temperature range where they can operate efficiently. Naturally, both approaches cannot cover all conceivable tasks that might emerge with the ongoing development of nanometer-scale science, such as parallel manipulation of nanometer-sized objects over large areas under a broad range of environmental conditions.Polymer systems in their diversity may offer a range of alternatives, especially in the form of suitably designed thin films. Recently, we have proposed to use the unique conformational properties of so-called polymer brushes to move nanometersized objects that are adsorbed on their top.[14] The brushes consist of polymer chains typically several hundreds of nanometers in length, with one end covalently attached to a solid substrate. [15][16][17] The distance between neighboring chains ranges from 0.5 to 5 nm. Such a high grafting density forces the flexible polymer chains to stretch away from the surface. [18,19] Particularly interesting are multicomponent brushes that consist of two or more different polymers, among which phase separation can occur (Fig. 1a). Such systems can be of two different types: i) brushes consisting of diblock or triblock copolymers covalently attached by one block type to a substrate and thus resulting in a variation in the composition along the chains, and ii) brushes made of a mixture of two homopolymers, each of which is attached to the surface, resulting in a lateral variation in composition. [20][21][22][23][24][25][26][27][28] Together with the restriction of the mobility due to grafting, the phase separation results in a topographical nanometer-scale pattern on the brush surface (Fig. 1b). The size, shape, and composition of these patterns depend on many parameters, such as molecular parameters of the attached chains, the surface free energy o...

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). To render PMMA-b-PMAA copolymers photosensitive, cationic azobenzene containing surfactants are attached to the negatively charged outer PMAA block. During irradiation with an ultraviolet (UV) interference pattern, the extent of photoisomerization of the azobenzene groups varies spatially and results in a topography change of the brush, i.e., formation of surface relief gratings (SRG). The SRG formation is accompanied by local rupturing of the polymer chains in areas from which the polymer material recedes. This opto-mechanically induced scission of the polymer chains takes place at the interfaces of the two blocks and depends strongly on the UV irradiation intensity. Our results indicate that this process may be explained by employing classical continuum fracture mechanics, which might be important for tailoring the phenomenon for applying it to poststructuring of polymer brushes.

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. It is shown that the trans isomer plays a major role in the DNA compaction process. The influence of the cis isomer on the DNA coil configuration is rather small. The construction of a phase diagram of the DNA concentration versus surfactant/DNA charge ratio allows distancing between three major phases: colloidally stable and unstable compacted globules, and extended coil conformation. There is a critical concentration of DNA above which the compacted globules can be hindered from aggregation and precipitation by adding an appropriate amount of the surfactant in the trans configuration. This is because of the compensation of hydrophobicity of the globules with an increasing amount of the surfactant. Below the critical DNA concentration, the compacted globules are colloidally stable and can be reversibly transferred with light to an extended coil state.

In searching for new and efficient mechanisms for moving or propelling nano-sized objects across a flat surface, we discuss the idea of using the periodically switchable topography of a certain class of polymer substrates. In this paper, we exploit the peculiar properties of diblock-copolymer and mixed brushes that can undergo transitions between very distinct topographical patterns and a flat state. We investigate if, during the transition process, the reshaping of the surface structure, accompanied by a microphase transition, could deliver a sufficient amount of mechanical work to move objects adsorbed on the surface. We show this by following the spatial distribution of an ensemble of silica particles adsorbed on several kinds of poly(methyl methacrylate–b-glycidyl methacrylate) diblock-copolymer brushes, when the surface topography undergoes many periods of the switching process.