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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.

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...

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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. A memory measure parameter is introduced, which characterizes quantitatively the domain memory effect in the nanopattern. It is shown that at constant grafting density but with increasing molecular weight of the brush chains the memory measure parameter decreases. In contrast to this, brushes with constant molecular weight, but differing in grafting density, all have a similar domain memory. We discuss a possible origin of the domain memory effect in the mixed brush systems studied and point out its impact on the motion of nanoparticles adsorbed on top of such systems.

The benefits of teams and teamwork are popular and propounded in management discourse. The use of this lexicon is based on beliefs in the resultant mutual gains for both organizations and individuals. Yet, are all teams, irrespective of the characteristics of membership composition, the same in terms of such beneficial outcomes? This study investigates the importance of team member characteristics, particularly cognitive and demographic, on team effectiveness and which characteristics matter more in team activities, especially where labour turnover is high, such as in software development. The Shared Mental Model is outlined and used as the representative construct for cognitive similarities; while age, tenure and gender are the demographic aspects used. From the relevant literature we develop a hypothesis and subject it to a range of tests based on empirical fieldwork using software development teams in South Korea. Our analysis shows that team effectiveness is more influenced by cognitive than demographic similarities. The implications and limitations of this work are detailed, with its wider relevance to international management, business and practice and other countries, noted.

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