Academic literature on the topic 'Patterned polymer brushe'

We exploit a series of robust, but simple and convenient colloidal lithography (CL) approaches, using a microsphere array as a mask or as a guiding template, and combine this with surface-initiated atom-transfer radical polymerization (SI-ATRP) to fabricate patterned polymer-brush microstructures. The advantages of the CL technique over other lithographic approaches for the fabrication of patterned polymer brushes are (i) that it can be carried out with commercially available colloidal particles at a relatively low cost, (ii) that no complex equipment is required to create the patterned templates with micro- and nanoscale features, and (iii) that polymer brush features are controlled simply by changing the size or chemical functionality of the microspheres or the substrate.

This paper focuses on the effect of degree of polymerization (N), density ( σ ), and pattern size ( x ) on the interaction force between a periodically patterned Poly(N-isopropylacrylamide) (PNIPAM) brush and protein. The hydrophobic interaction, the Van der Waals attractive force, and the steric repulsive force were expressed in terms of N , σ , and x . The osmotic constant (k1) and the entropic constant (k2) were determined from the fit of the steric repulsive force to an experimentally obtained force distance curve. The osmotic constant was 0.105, and the entropic constant was 0.255. Using these constants, the steric repulsive force was plotted as a function of the separation distance(s) between the substrate and the protein. The forces were determined at a separation distance equal to 0.3 nm, where L0 is the equilibrium thickness of the PNIPAM brush. At this separation distance, the value of the steric repulsive force was much higher than the value of the sum of the hydrophobic interaction and the Van der Waals attractive force for large degree of polymerization ( N > 100 ) and density ( σ > 0.2 chains/nm2). However, the repulsive force was comparable to the sum of the hydrophobic interaction and the Van der Waals attractive force for a small degree of polymerization ( N < 100 ) and density ( σ = 0.2 ). Furthermore, the steric repulsive force was plotted as a function of pattern size x . The plot indicated that the steric repulsive force becomes nearly zero for all degrees of polymerization and density when the value of the initiator structure size was less than 200 nm. In addition to the steric repulsive force, the lateral extension of the chains in the periodically patterned PNIPAM brush was calculated by scaling low and compared with the experimental data taken from previously published literatures. The polymer brush structure was modelled as if the immediate bare substrate is so wide that even a stretched polymer segment cannot reach to the next polymer brush structure. In such models, the value of the lateral extension was equal to the thickness of the homogenous brush. It was independent of the pattern size. However, when the polymer brush structure was modelled as if there is another polymer brush structure at a distance half of the size of the period, the lateral extension was found to be dependent on the size of the initiator structure size due to chain bridging. This was witnessed by the patterning of polymer brushes using the interferometric patterning of PNIPAM brushes and an atomic force microscopy imaging of the polymer brush structures both in air and in water. The polymer brush structure resolution in water was much lower than the resolution in air, which indicates the lateral extension of the polymer chains in water. For such kind of periodic polymer brush structures, the gap between them was calculated, and it was found dependent on the degree of polymerization, density, and initiator structure size.

High densities of immobilized polymer brushes have been created on solid supports in a spatially addressable fashion. Octadecyltrichlorosilane was self-assembled on a silicon substrate to form an inert monolayer. The substrate was then patterned by low-energy electron beam lithography. Finally, the exposed region was back-filled with a second functionalized silane and the pattern was further amplified by surface-initiated ring-opening metathesis polymerization. The patterned substrate was imaged by scanning electron microscopy and atomic force microscopy.Key words: patterned thin film, e-beam lithography, ring-opening metathesis polymerization, polymer brushes.

A novel micro-patterned poly(AHMA) brush was prepared by a combination of photolithography and interface mediated RAFT polymerization for DNA hybridization. By this method, highly resolved micro-patterned polymer brush structures down to ∼2.0 μm lines were obtained.

This critical review summarizes recent developments in the fabrication of patterned polymer brushes. As top-down lithography reaches the length scale of a single macromolecule, the combination with the bottom-up synthesis of polymer brushes by surface-initiated polymerization becomes one main avenue to design new materials for nanotechnology. Recent developments in surface-initiated polymerizations are highlighted along with diverse strategies to create patterned polymer brushes on all length scales based on irradiation (photo- and interference lithography, electron-beam lithography), mechanical contact (scanning probe lithography, soft lithography, nanoimprinting lithography) and on surface forces (capillary force lithography, colloidal lithography, Langmuir–Blodgett lithography) (116 references)
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

This critical review summarizes recent developments in the fabrication of patterned polymer brushes. As top-down lithography reaches the length scale of a single macromolecule, the combination with the bottom-up synthesis of polymer brushes by surface-initiated polymerization becomes one main avenue to design new materials for nanotechnology. Recent developments in surface-initiated polymerizations are highlighted along with diverse strategies to create patterned polymer brushes on all length scales based on irradiation (photo- and interference lithography, electron-beam lithography), mechanical contact (scanning probe lithography, soft lithography, nanoimprinting lithography) and on surface forces (capillary force lithography, colloidal lithography, Langmuir–Blodgett lithography) (116 references).
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Self-assembly of well-defined polymer microstructures is of interest for applications such as polymer solar cells, light emitting diodes, microelectronics and biosensors. Chemically patterned substrates can direct the phase separation of thin films of polymer blends, producing controlled morphologies. This has been demonstrated using patterned self-assembled monolayers. Binary-patterned polymer brushes provide a robust, chemically and topographically patterned surface which can interact with the blend, potentially resulting in interesting new behaviour, and greater control over phase separation. Binary-patterned polystyrene/poly(methyl methacrylate) brushes were synthesised by a novel method. A self-assembled monolayer of triethoxysilane was patterned by exposure to ultraviolet light. This produced amine-terminated areas that could react with 2-bromoisobutyryl bromide to produce initiators for atom transfer radical polymerisation, allowing the synthesis of patterned polymer brushes. Dehalogenation of the first brush, followed by deprotection, modification and a second polymerisation produced binary-patterned brushes. Unpatterned and patterned polymer brushes were characterised using ellipsometry, x-ray photoelectron spectroscopy, contact angles, atomic force microscopy, lateral force microscopy, optical microscopy and secondary ion mass spectrometry. An alternative approach, based on direct microcontact printing of an atom transfer radical polymerisation initiator, 11-(2-bromo-2-methyl)propionyloxyundecyltrichlorosilane, was also investigated, although this approach was ultimately unsuccessful. The behaviour of thin films of polystyrene/poly(methyl methacrylate) blends on silicon, patterned self-assembled monolayers and binary-patterned polymer brushes was studied. The morphologies were investigated using atomic force microscopy, optical microscopy, nuclear reaction analysis and secondary ion mass spectrometry, in order to determine the effect of the binary-patterned polymer brushes on the domain structure of the blend. The blend morphology was complex and reflected interactions between the blend and the brushes (as well as other factors). When the natural length scale of the blend is commensurate with the underlying pattern, phase separation may be spatially directed by the substrate.

Tunable nanopatterns formed by polymer brushes A molecular dynamics simulation study of polymer brushes is presented. When exposed to a poor solvent, or when dried out in air, polymer brushes can undergo “constrained dewetting” and collapse into a nanopatterned layer. By changing the chemical environment of the polymer, the pattern can be switched on or off reversibly. Coarse-grained molecular dynamics was used to investigate the morphology and dynamics of these nanopatterns, and their influence on fluid flow and nanoparticle formation. Evaporation of a good solvent film from polymer brushes with a range of grafting densities was simulated in order to study the pattern morphology as a function of solvent content. The pattern type, dynamics, and size and number of features depended on the total amount of adsorbed material, including polymer and solvent. The result suggests the possibility for the use of polymer brushes as surfaces with reversibly tunable nanopatterns. Nonequilibrium molecular dynamics simulations were used to study the boundary condition of fluid flow over a polymer brush. In a good solvent the stagnation length for flow within the brush scaled with the chain spacing D as D-2/3, while the physical height scaled as D2. In a poor solvent the patterns formed by constrained dewetting created variations in the liquid velocity near the surface, suggesting a possible application as a switchable nanofluidic mixer. A simple model relates the boundary condition at the patterned surfaces to the height and polymer surface coverage. The patterns formed by constrained dewetting could be used as a template for surface nanoparticle formation to create surfaces with useful optical and electronic properties. Simulations showed that when a solution of molecular species was evaporated from a polymer brush, the constrained dewetting of the polymer could impart control over the nucleation of nanoparticles. The nanoparticle size and distribution depended on the concentration and solubility of the dissolved species.

Most of the topics dealt with in this thesis belong to surface science. The starting point was the fundamental understanding of phenomena at the oxide-gas interface and the effect of its modification. Such knowhow was then used to solve (or, at least, to attempt to solve) issues of critical impact in everyday life: the increasing lifetime of building materials employed in low-impact smart houses; the fouling prevention in electroanalytical sensors for neurotransmitter detection; the unspecialized laboratories accessibility to microlithography, critical to device miniaturization. These challenges might seem not related, but they actually share deep scientific and technological foundations. The physicochemical modification of oxide surfaces, the creation of organic/inorganic hybrids and the exploiting / the enhancing of semiconductor peculiar properties allowed us, starting from the foundation, the realization of proof-of-concept protocols and devices, ready for the pre-commercial development. The Leitmotif of my research was the synthesis and the modification of titanium dioxide surfaces. TiO2 has been the main character in physico, physicochemical and material science researches of the last 50 years. Biocompatibility and low cost make it engaging for many applications. Its (near-UV active) semiconductor features, well known and abundantly investigated by the scientific community, are acquiring central interest also in many markets with the development of self cleaning coatings, windows and asphalts, anti-fogging mirrors and self-sterilizing surgery rooms and instrumentations. New generation batteries and solar cells are going to be developed as commercial prototypes. One of the biggest challenges in the titania fundamental research is the enhancement of activity in the solar spectrum. First, the most recent aspects in titania doping and promotion were touched. While, in the last twenty years, great effort has been made in the mono-atomic doping of titania and in the understanding of the influence of the dopant position in the titania lattice and its electronic behavior, the most recent literature describes the co-promotion of the material by two (or more) atoms doping. The metal/non-metal codoping seems especially promising; the synergetic effect of the two atoms in the TiO2 lattice was both theoretically and experimentally proved. In this contest, the N/Nb codoping was analyzed, investigating the effect of the atoms in the lattice from morphological (surface area, porosity and crystallographic structure) and electronic point of view (EXAFS, UV-Vis absorption and EPR analyses). N/Nb codoping was compared with N/Ta co-doped samples, synthesized by two different procedures. The photoactivity of the two sample families was tested by a model reaction (the degradation of ethanol, throughout acetaldehyde intermediate) both under UV and solar simulated irradiation. Then, a different approach in the modification of surfaces was tested. The assembly of organic/inorganic hybrids was tested; thanks to the formation of organic mono- or multi-layers at the surface,they can tune the chemistry, the polarity and the adhesion properties of the interface. Siloxanes were used as active agents, thanks to their compatibility with oxide materials and, especially, for the ability to self-assemble at the surface to form a monolayer. Siloxanes are able to react with the -OH groups at the surface, chemisorbing and polymerizing at the interface in such a way to form a monolayer with tunable functionalities. Many different silanes were tested and their dipole momenta were related to their wettability properties. Such siloxanes chemisorb strongly both from the gas phase and the liquid phase. Their reactivity, both on smooth and rough surfaces, was tested vs the temperature of functionalization in gas phase. Many characterization techniques were adopted to understand the behavior of such molecules from a molecular point of view: magnetic (solid state NMR), microscopic (SEM, TEM, AFM), optical and electrochemical (CV and EIS). The science of adhesion and wettability was also adopted for the development of superhydrophobic coatings. Titanium dioxide particles with engineered morphology were used as the best candidate to create superhydrophobic/superhydrophilic patch-wise surfaces, exploiting their photoactivity (photolithograpy). The core of the thesis was the synthesis, modification and application of transparent photoactive thin films. A procedure for the synthesis of smooth, transparent and photoactive TiO2 thin layers was developed, and used to produce highly applicative devices and protocols. Such synthetic strategy is highly tunable and reproducible; the obtained films are robust and active and, most of all, require simple instrumentation (sol-gel procedure), which is highly appealing for the market. The films were properly characterized both form the morphological/mechanical and photochemical point of view. Apart their transparency and their thickness, the films were highly crystalline (pure anatase phase). Such procedure was firstly designed as a proof-of-concept for self-cleaning windows, but, thanks to its versatility and the high activity of the films, it leads the path towards highly applicative procedures and devices. The smoothness and the photoactivity brought me to the field of photolithograpy, especially in the direction of microlithography. The high activity of the titania allowed the use of safe and low-energetic lamps. No collimation was required to obtain a resolution lower than 5 µm. First of all, I tested the lithography on siloxane monolayer films, as a proof-of-concept of resolution and efficiency. But siloxanes, as many other self-assembled monolayer molecules, can be the pillars for 3D fabrication. Such monolayers were used as polymerization initiators for polymer brushes. If the initiators of polymerization are patterned, patterned polymer brushes will be obtained. That was the first report of polymer-brushes lithography exploiting the photoactivity of TiO2. Remote photocatalytic lithography makes this procedure extremely versatile. Exploiting the remote photocatalysis, in principle, any material can be used as a support for patterned polymer brushes growth (provided that the initiator are able to graft the surface). The developed protocol for the synthesis of TiO2 thin films was also used to design and engineer complex electrodes for cyclovoltammetric analyses of biological samples. Electrochemistry seems to be the best candidate for the development of an analytical option with sensitivity comparable with present analytical procedures but reduced time-per-analysis and cost. Unfortunately, catecholamines chemisorb and polymerize on metal and oxide electrodes quickly, making the device useless. Covering the electrode by a homogeneous, nano-porous thin layer of titania makes the surface photoactive. That is the first example in literature of self-cleaning nano-engineered electrodes for cyclic voltammetry. After the detection, also in simulated human serum and liquor, a fast and simple irradiation of the device, under non-hazardous UV-A lamp, degrades all the fouling on the surface without altering its features. The sensor, after each UV treatment, recovers its pristine performances, with full recovery in terms of selectivity and sensitivity. Irradiation trials were also performed directly in the analytical mixture, as a proof of concept for on-site application. Modern era requires flexible and light materials for the building industry. Polymers are acquiring more and more interest thanks to their increasing performances and their smart properties. The drawbacks of such materials are connected to the low resistance to the UV light, the softness and the difficulties in cleaning procedure. The use of organic/inorganic hybrid, or better the coverage of plastic materials with an oxidic thin layer, can solve many of these problems, lengthening the lifetime of such materials. If the covering oxide is also photoactive, the material can be self-cleaned when exposed to solar light. That is a big chemical challenge, because of many synthetic problems. Two different approaches were tested to solve this relevant issue. On one side, the hydrophobicity of ionic liquid modified SPES (sulfonated polyether sulfone) was combined with designed morphological features to confer superhydrophobicity. On the other side, the polymeric surface was covered with a transparent titania layer active in the near UV-region, able to mineralize organic molecules chemisorbed at the surface. Eventually, a different approach to modify oxidic (and not only) surfaces is the creation of a homogeneous layer of Ag nanoparticles by an innovative microwave procedure. That simple and accessible strategy allowed us to produce plasmonic surfaces (thanks to the dimension and the homogeneity of the Ag particles) with countless applications. The layer was shown to be a very active substrate for surface enhancement Raman spectroscopy (SERS). Thanks to the versatility of the synthetic method, all shapes and dimensions can be covered. That makes it a perfect candidate for the production of new generation of SERS sensors. The sensitivity towards molecules of environmental and biomedical interest was proved.

The thesis is devoted to the development of general methods of preparation of tethered polymer layers with laterally changing properties and investigation of their properties with focus on controlled adsorption and liquid flow. The temperature dependent character of the grafting reaction is used for the design of mono- and bicomponent gradient polymer grafted layers. For this purpose, a special stage providing a lateral temperature gradient is designed. The stage consists of two elements, one heating and one cooling, between which the experimental sample is situated. The versatility of these approaches for both fundamental research and practical applications is demonstrated. In general, the gradient approach is proved to be useful for the combinatorial-like investigations of ultrathin polymer films. The systematic study allowed detailed investigation of the grafting kinetics, the morphologies of the grafted polymer layers, the switching mechanism of the mixed polymer brushes, adsorption of colloid particles. The second approach for the preparation of laterally resolved tethered layers consists of a novel strategy for reversible environment-responsive lithography. This strategy implies local fixation of the morphology of mixed polymer brushes via photocrosslinking by UV irradiation. Irradiated areas lose the ability to switch. Exposure to selective and non-selective solvent allows visualization or erasing of the written information, respectively. It is demonstrated that developed approaches are promising for design of smart sensors, microfluidics devices, combinatorial study of the adsorption (separation and identification) of protein molecules and colloids and for other applications.

The thesis is devoted to the development of general methods of preparation of tethered polymer layers with laterally changing properties and investigation of their properties with focus on controlled adsorption and liquid flow. The temperature dependent character of the grafting reaction is used for the design of mono- and bicomponent gradient polymer grafted layers. For this purpose, a special stage providing a lateral temperature gradient is designed. The stage consists of two elements, one heating and one cooling, between which the experimental sample is situated. The versatility of these approaches for both fundamental research and practical applications is demonstrated. In general, the gradient approach is proved to be useful for the combinatorial-like investigations of ultrathin polymer films. The systematic study allowed detailed investigation of the grafting kinetics, the morphologies of the grafted polymer layers, the switching mechanism of the mixed polymer brushes, adsorption of colloid particles. The second approach for the preparation of laterally resolved tethered layers consists of a novel strategy for reversible environment-responsive lithography. This strategy implies local fixation of the morphology of mixed polymer brushes via photocrosslinking by UV irradiation. Irradiated areas lose the ability to switch. Exposure to selective and non-selective solvent allows visualization or erasing of the written information, respectively. It is demonstrated that developed approaches are promising for design of smart sensors, microfluidics devices, combinatorial study of the adsorption (separation and identification) of protein molecules and colloids and for other applications.

Polymer brush patterns were prepared by a combination of electron beam induced damage in self-assembled monolayers (SAMs), creating a stable carbonaceous deposit, and consecutive self-initiated photografting and photopolymerization (SIPGP). This newly applied technique, reactive writing (RW), is investigated with 1H,1H,2H,2H-perfluorooctyltriethoxysilane SAM (PF-SAM) on silicon oxide, which, when modified by RW, can be selectively functionalized by SIPGP. With the monomer N,N-dimethylaminoethyl methacrylate (DMAEMA), we demonstrate the straightforward formation of polymer brush gradients and single polymer lines of sub-100 nm lateral dimensions, with high contrast to the PF-SAM background. The lithography parameters acceleration voltage, irradiation dose, beam current and dwell time were systematically varied to identify the optimal conditions for the maximum conversion of the SAM into a carbonaceous deposit. The results of this approach were compared to patterns prepared by carbon templating (CT) under analogous conditions, revealing a dwell time dependency, which differs from earlier reports. This new technique expands the range of CT by giving the opportunity to not only vary the chemistry of the created polymer patterns with monomer choice but also vary the chemistry of the surrounding substrate.

Polymer brush patterns were prepared by a combination of electron beam induced damage in self-assembled monolayers (SAMs), creating a stable carbonaceous deposit, and consecutive self-initiated photografting and photopolymerization (SIPGP). This newly applied technique, reactive writing (RW), is investigated with 1H,1H,2H,2H-perfluorooctyltriethoxysilane SAM (PF-SAM) on silicon oxide, which, when modified by RW, can be selectively functionalized by SIPGP. With the monomer N,N-dimethylaminoethyl methacrylate (DMAEMA), we demonstrate the straightforward formation of polymer brush gradients and single polymer lines of sub-100 nm lateral dimensions, with high contrast to the PF-SAM background. The lithography parameters acceleration voltage, irradiation dose, beam current and dwell time were systematically varied to identify the optimal conditions for the maximum conversion of the SAM into a carbonaceous deposit. The results of this approach were compared to patterns prepared by carbon templating (CT) under analogous conditions, revealing a dwell time dependency, which differs from earlier reports. This new technique expands the range of CT by giving the opportunity to not only vary the chemistry of the created polymer patterns with monomer choice but also vary the chemistry of the surrounding substrate.

Abstract Labyrinth seals are used in the clearance between rotor and stator such as steam turbines and centrifugal compressors in order to suppress loss of leakage. The leakage flow is induced in labyrinth seal by pressure difference between the inlet and outlet of the seal. This leakage flow produces destabilization fluid force on the rotor in association with the swirl flow. Destabilization fluid force can lead the rotor system unstable by its phase delay from subsynchronous whirling vibration of the rotor. Recently, this kind of problems have been reported sometimes with increasing power output and improving performance by decreasing leakage flow. In order to understand detailed characteristics of this destabilization fluid force, so many CFD calculations have been performed and unsteady pressure measurements have been conducted using rotational test rig. However, CFD calculation results often do not agree with test result especially for complex seal configurations. Although unsteady pressure was also measured by pressure sensors, measurement results were not enough for validation of CFD results and detailed understand of the fluid force mechanisms because of insufficient spatial resolution. In this study, unsteady pressure filed in labyrinth seal cavity of rotational test rig was visualized using fast-responding polymer-ceramic pressure sensitive paint (PC-PSP). The unsteady pressure distribution on the surface of seal cavity was measured by high-speed camera. For the experiment, a 500mm diameter rotor was used so that size of the labyrinth seal and flow pattern in the cavity can be close to the large-scale steam turbine. And the rotor was excited in a circular whirl orbit by an electromagnetic actuator. The stator side cavity wall was made by transparent material in order to obtain optical access. In the case of existing PSP measurements, only rotor side pressure distribution could be measured in this set up. However, measuring rotor side surface by PSP is extremely challenging because of its high peripheral speed. The back side illumination measurement technique has been developed and applied in this study. PSP is coated on the inner surface of transparent stator wall. Excitation light sources were delivered from outside of the transparent wall and highspeed camera was also installed outside. This procedure allows PSP measurement only by processing motionless image of the stator wall. Furthermore, composition of the PC-PSP has been optimized for this measurement because back illumination procedure decreases response speed of the PSP. As a result, high-accuracy, high-definition pressure distribution data was obtained. Pressure data measured by PSP were compared with pressure sensor data and CFD calculation results. Unsteady pressure levels measured by PSP agreed well with pressure data measured by pressure sensors. Unsteady pressure distributions measured by PSP agreed well with pressure distribution calculated by CFD. From these results, detailed characteristics of destabilization fluid force were understood. And these data can be used for brush-up of CFD calculation model and procedure.