Nanopattern Formation from Tethered PS-b-PMMA Brushes upon Treatment with Selective Solvents

Polymer Brushes and Surface Nanostructures: Molecular Design, Precise Synthesis, and Self-Assembly

For over two decades, polymer brushes have found wide applications in industry and scientific research. Now, polymer brush research has been a significant research focus in the community of polymer science. In this review paper, we give an introduction to the synthesis, self-assembly, and applications of one-dimensional (1D) polymer brushes on polymer backbones, two-dimensional (2D) polymer brushes on flat surfaces, and three-dimensional (3D) polymer brushes on spherical particles. Examples of the synthesis of polymer brushes on different substrates are provided. Studies on the formation of the surface nanostructures on solid surfaces are also reviewed in this article. Multicomponent polymer brushes on solid surfaces are able to self-assemble into surface micelles (s-micelles). If the s-micelles are linked to the substrates through cleavable linkages, the s-micelles can be cleaved from the substrates, and the cleaved s-micelles are able to self-assemble into hierarchical structures. The formation of the surface nanostructures by coassembly of polymer brushes and "free" polymer chains (coassembly approach) or polymerization-induced surface self-assembly approach, is discussed. The applications of the polymer brushes in colloid and biomedical science are summarized. Finally, perspectives on the development of polymer brushes are offered in this article.

Surface Morphing of Azopolymers toward Advanced Anticounterfeiting Enabled by a Two-Step Method: Light Writing and Then Reading in Liquid

Surface morphing of organic materials is necessary for advances in semiconductor processing, optical gratings, anticounterfeiting etc., but it is still challenging, especially for its fundamental explanation and further applications like advanced anticounterfeiting. Here, we report one strategy to acquire surface deformation of the liquid-crystalline azopolymer film using a two-step method: selective photoisomerization of azopolymers and then solvent development. In the first step, surface tension of the polymer film can be patterned by the selective photoisomerization of azopolymers, and then in the second step, the flowing solvent drags the underlying polymer to transport, leading to the formation of surface deformation. Interestingly, the direction of mass transport is opposite to the traditional Marangoni flow, and the principle of solvents' choice is the matching of surface tensions between the azopolymer and the solvent. The two-step method shows characteristics of efficient surface morphing, which could be applied in advanced anticounterfeiting by the way of photomask-assistant information writing or microscale direct writing, and then reading in a specific liquid environment. This paves a new way for understanding the mechanism of mass transport toward numerous unprecedented applications using various photoresponsive materials.

Polymer brush-based nanostructures: from surface self-assembly to surface co-assembly

Surface structures play an important role in the practical applications of materials. The synthesis of polymer brushes on a solid surface has emerged as an effective tool for tuning surface properties. The fabrication of polymer brush-based surface nanostructures has greatly facilitated the development of materials with unique surface properties. In this review article, synthetic methods used in the synthesis of polymer brushes, and self-assembly approaches applied in the fabrication of surface nanostructures including self-assembly of polymer brushes, co-assembly of polymer brushes and "free" block copolymer chains, and polymerization induced surface self-assembly, are reviewed. It is demonstrated that polymer brush-based surface nanostructures, including spherical surface micelles, wormlike surface structures, layered structures and surface vesicles, can be fabricated. Meanwhile, the challenges in the synthesis and applications of the surface nanostructures are discussed. This review is expected to be helpful for understanding the principles, methods and applications of polymer brush-based surface nanostructures.

State- and water repellency-controllable molecular glass of pillar[5]arenes with fluoroalkyl groups by guest vapors

Molecular glasses are low-molecular-weight organic compounds that are stable in the amorphous state at room temperature. Herein, we report a state- and water repellency-controllable molecular glass by n-alkane guest vapors. We observed that a macrocyclic host compound pillar[5]arene with the C₂F₅ fluoroalkyl groups changes from the crystalline to the amorphous state (molecular glass) by heating above its melting point and then cooling to room temperature. The pillar[5]arene molecular glass shows reversible transitions between amorphous and crystalline states by uptake and release of the n-alkane guest vapors, respectively. Furthermore, the n-alkane guest vapor-induced reversible changes in the water contact angle were also observed: water contact angles increased and then reverted back to the original state by the uptake and release of the n-alkane guest vapors, respectively, along with the changes in the chemical structure and roughness on the surface of the molecular glass. The water repellency of the molecular glass could be controlled by tuning the uptake ratio of the n-alkane guest vapor.

Pillar[5]arenes with C₂F₅ substituents showed reversible amorphous–crystal transitions by uptake and release of n-alkane vapors. The amorphous–crystal transitions triggered macroscopic property change such as water repellency.

Efficient electroosmotic mixing in a narrow-fluidic channel: the role of a patterned soft layer

We propose a novel and efficient mixing technique in a soft narrow-fluidic channel under the influence of electrical forcing. We show that a grafted polyelectrolyte layer (PEL) added as a patch to the channel wall modulates the electrical double layer (EDL) so that an applied electric field initiates a local electroosmotic flow (EOF) at the patched section. This EOF develops in the opposite direction to the primary pressure-driven flow. This localized EOF leads to the formation of Lamb vortices at the patched sections through the phenomenon of momentum exchange with the primary stream and promotes the mixing therein. Our study, consistent with the stream-function/vorticity approach, primarily focuses on the numerical analysis of the mixing phenomena. Through a quantitative description, we reveal the effect of different patterns on the underlying mixing phenomena in the convective mixing regime. We also discuss the impact of key parameters on the mixing efficiency, the onset of the recirculation zone, variation in the mixing length, and the shear-driven aggregation kinetics in soft matter systems. Finally, considering the practicability of the present problem, we unveil the values of several design parameters for which the mixing efficiency in the channel reaches the maximum.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm^-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.

Controlled Arrangement of Gold Nanoparticles on Planar Surfaces via Constrained Dewetting of Surface-Grafted RAFT Polymer

Linear and four-arm star polystyrene samples prepared by RAFT polymerization were grafted to gold surfaces directly via their thiocarbonylthio-end groups. Nanoscale polymer patterns were subsequently formed via constrained dewetting. The patterned polymer films then served as a template for the precise arrangement of gold nanoparticles in a monolayer with a well-defined and regular structure. Using star polymers as a linker between the planar gold surface and the particles, the structural stability of the arranged particles can be further enhanced. The surface-bound nanocomposite films made of polymer and nanoparticles can also reversibly switch their nanostructures by simple wetting or dewetting treatment.

Polymer Brushes Immersed in Two-Component Solvents with Pure Volume Exclusion: Effect of Solvent Molecular Shape

Polymer brushes have wide application in surface modification. We study dense, short polymer brushes immersed in a mixing solvent under athermal conditions using the classical density functional theory. The brush polymer is short so that the equilibrium behavior of the brush deviates far from the scaling laws for infinite brush chains. The excluded volume interaction is the only interaction in the system. We compare the excluded volume effect of solvent molecules of different shapes. Two types of mixing solvents are considered: solvent composed of linear oligomers and monomers, or that of spherical particles and monomers. The effects of grafting density, solvent molecular size, and solvent number density on the brush height, the density profiles, the relative excess adsorption, and the brush-solvent interface width are systematically analyzed. In the adsorption aspect, the spherical particles have stronger ability than the linear oligomers do to penetrate through the brush layer and gather at the substrate. In the screening aspect, the oligomers are more capable of screening the excluded volume interaction between the brush chains than the spherical particles. The brush-solvent interface width decreases monotonically with increasing oligomer length, but it has a minimum with the increasing spherical particle size. Our research differentiates the attractive-interaction-induced phenomenon and the volume-exclusion-induced phenomenon in dense brush systems and exhibits the difference in the antifouling properties of the brushes contacting solvent molecules of different shapes.

Surface Reconstruction by a Coassembly Approach

Materials with switchable surfaces, capable of changing surface properties under external stimuli, are playing a pivotal role in many applications, such as tissue engineering, biosensors, and drug/protein delivery. In this research silica particles with patterned and switchable surfaces are fabricated. Surface micelles on silica particles are formed by coassembly of polymer brushes and "free" block copolymer chains in a selective solvent. The cores of the surface micelles are crosslinked by anthracene photodimerization. After quaternization of the coronae, amphiphilic surface micelles are prepared. The surface micelles are able to rearrange in different media. After treatment with an organic solvent, the surfaces of silica particles are occupied by hydrophobic polymer components; in aqueous solution, the positively charged polymer chains are on the surfaces. The switching of the surface micelles results in changes in surface composition and wetting behaviors.

Self-Assembly Investigations of Sulfonated Poly(methyl methacrylate-block-styrene) Diblock Copolymer Thin Films

Poly(methyl methacrylate-block-styrene) block copolymers (BCs) of low dispersity were selectively sulfonated on the styrenic segment. Several combinations of degree of polymerization and volume fraction of each block were investigated to access different self-assembled morphologies. Thin films of the sulfonated block copolymers were prepared by spin-coating and exposed to solvent vapor (SVA) or thermal annealing (TA) to reach equilibrium morphologies. Atomic force microscopy (AFM) was employed for characterizing the films, which exhibited a variety of nanometric equilibrium and nonequilibrium morphologies. Highly sulfonated samples revealed the formation of a honeycomb-like morphology obtained in solution rather than by the self-assembly of the BC in the solid state. The described morphologies may be employed in applications such as templates for nanomanufacturing and as cover and binder of catalytic particles in fuel cells.

Tethering solvophilic blocks to the ends of polymer brushes: an effective method for adjusting surface patterns

The effect of different lengths of solvophilic A and C blocks on the assembled configuration of intermediate solvophobic B-blocks in both ABA and ABC polymer brush systems is investigated via dissipative particle dynamics simulations. For the AB diblock copolymer brush with solvophilic A-blocks being grafted to the surface, B-blocks self-assemble into spherical micelle structures that are immersed in a layer formed by the A-blocks. Tethering a very small solvophilic block A(C) at the free end of the polymer brush pulls the B-blocks toward the polymer brush/solvent interface and increases their local density which can significantly change the B-block self-assembled structure from spherical micelles to ripples. By increasing the length of the outermost solvophilic blocks, the lateral density distribution of B-blocks can be further changed, resulting in the domain size of the ripple structure first decreasing and then increasing. Compared to the ABA system, the incompatibility between the A and C blocks can effectively reduce the vertical domain separation caused by the fusion of the upper and lower A blocks. Then, based on an AB diblock copolymer brush system with self-assembled spherical micelles, we introduce extremely short free solvophilic blocks A(C) in dilute solution that can be tethered to the free ends of the polymer brush by using a reaction model [Liu et al., J. Chem. Phys., 2007, 127, 144903]. We find that the micelles' coalescence is mainly affected by the content of tethered reactive solvophilic blocks, and only weakly affected by the reaction rate of the reversible reactions. This strategy of tethering solvophilic blocks to the ends of polymer brushes can be an effective way for the fabrication of stimuli-responsive surfaces and for adjusting nanoscopic surface patterns.

Coordinated Responsive Arrays of Surface-Linked Polymer Islands-CORALs

The concept of co-ordinated responsive arrays of surface-linked islands (polymer CORALs) is introduced. This study targets a responsive system capable of revealing or covering the substrate surface in response to environmental changes in a reversible way. A convenient method of fabrication of polymer CORALs is proposed. It is based on microphase separation that occurs in thin films of supramolecular assemblies of block copolymers with reactive blocks. Such blocks form nanometer-size domains that may serve as anchors for surface-linked polymer islands. Two characteristics of the islands are critically important for the switching function: high grafting density within the islands and small lateral separation that allows interactions between polymer chains grafted to the neighboring islands. This combination permits complete coverage of the substrate surface upon exposure to a good solvent (relaxed state). In a weak solvent, the chains collapse within the islands, thus revealing the substrate (compact state). The morphology of the CORALs in both states and some details of the switching process were studied with atomic force microscopy, grazing incidence small-angle scattering, and coarse-grained molecular dynamic simulations.

Distinct Chemical and Physical Properties of Janus Nanosheets

Janus particles have recently garnered significant attention for their distinct properties compared to particles that are homogeneously functionalized. Moreover, high aspect ratio Janus particles that are rod-like or planar (i.e., nanosheets) are especially intriguing considering their interfacial properties as well as their ability to assemble into higher order and hybrid structures. To date, major challenges facing the exploration and utilization of 2D Janus particles are scalability of synthesis, characterization of tailored chemical functionalization, and ability to introduce a diverse set of functionalities. Herein, a facile method to access Janus 2D graphene oxide (GO) nanosheets by combining a Pickering-type emulsion and grafting-from polymerization via ATRP is reported. Janus GO nanosheets bearing PMMA on one face as well as the symmetrically functionalized analogue are prepared, and the chemical, thermal, structural, surface, and interfacial properties of these materials are characterized. Time-of-flight secondary ion mass spectrometry coupled with Langmuir-Blodgett films is shown to be an ideal route to conclusively establish asymmetric functionalization of 2D materials. This work not only provides a facile route for the preparation of Janus nanosheets but also demonstrates the direct visualization of polymer grown from the surface of GO.

Co-assembly of Patchy Polymeric Micelles and Protein Molecules

The development in the synthesis and self-assembly of patchy nanoparticles has resulted in the creation of complex hierarchical structures. Co-assembly of polymeric nanoparticles and protein molecules combines the advantages of polymeric materials and biomolecules, and will produce new functional materials. Co-assembly of positively charged patchy micelles and negatively charged bovine serum albumin (BSA) molecules is investigated. The patchy micelles, which were synthesized using block copolymer brushes as templates, leads to co-assembly with protein molecules into vesicular structures. The average size of the assembled structures can be controlled by the molar ratio of BSA to patchy micelles. The assembled structures are dissociated in the presence of trypsin. The protein-polymer hybrid vesicles could find potential applications in medicine.

Surfactant Behavior of Amphiphilic Polymer-Tethered Nanoparticles

In recent years, an emerging research area has been the surfactant behavior of polymer-tethered nanoparticles. In this feature article, we have provided a general introduction to the synthesis, self-assembly, and interfacial activity of polymer-tethered inorganic nanoparticles, polymer-tethered organic nanoparticles, and polymer-tethered natural nanoparticles. In addition, applications of the polymer-tethered nanoparticles in colloidal and materials science are briefly reviewed. All research demonstrates that amphiphilic polymer-tethered nanoparticles exhibit surfactant behavior and can be used as elemental building blocks for the fabrication of advanced structures by the self-assembly approach. The polymer-tethered nanoparticles provide new opportunities to engineer materials and biomaterials possessing specific functionality and physical properties.

New strategy to create ultra-thin surface layer of grafted amphiphilic macromolecules

It was found first that macromolecules made of amphiphilic monomer units could form spontaneously an ultra-thin layer on the surface which the macromolecules are grafted to. The width of such layer is about double size of monomer unit consisting of hydrophilic A (repulsive) and hydrophobic (attractive) B beads. The hydrophilic A beads are connected in a polymer chain while hydrophobic B beads are attached to A beads of the backbone as side groups. Three characteristic regimes are distinguished. At low grafting density, the macromolecules form ultra-thin micelles of the shape changing with decrease of distance d between grafting points as following: circular micelles-prolonged micelles-inverse micelles-homogeneous bilayer. Those micelles have approximately constant height and specific top-down A-BB-A structure. At higher grafting density, the micelles start to appear above the single bilayer of amphiphilic macromolecules. The thickness of grafted layer in these cases is different in different regions of grafting surface. Only at rather high density of grafting, the height of macromolecular layer becomes uniform over the whole grafting surface. The study was performed by computer modeling experiments and confirmed in framework of analytical theory.

Silica particles with immobilized protein molecules and polymer brushes

In this research thermo-responsive polymer brushes and protein molecules are immobilized on the surfaces of silica particles by covalent bonds. Pyridyl disulfide functionalized silica particles are prepared by surface chemical reactions, and thiol-terminated poly(oligo(ethylene glycol) monomethyl ether methacrylate) (POEGMA) and bovine serum albumin (BSA) molecules are grafted to the silica particles by thiol-disulfide exchange reactions. X-ray photoelectron spectroscopy, thermogravimetric analysis, dynamic light scattering, confocal laser scanning microscopy, far-UV circular dichroism and transmission electron microscopy are employed to characterize the polymer/protein mixed layers on silica particles. The POEGMA brushes not only protect the protein molecules but also improve the dispersibility of the hybrid particles in aqueous solution. The activity of the immobilized BSA protein can be controlled by the thermo-responsive POEGMA brushes. At a temperature below the lower critical solution temperature (LCST) of POEGMA, BSA activity is not affected by polymer brushes; however, BSA activity decreases significantly at a temperature above the LCST of POEGMA.

STATEMENT OF SIGNIFICANCE

In this research, both protein molecules and polymer brushes were anchored to the silica particles by highly efficient thiol-disulfide exchange reaction, and their grafting density can easily be determined by UV-vis. Owing to the temperature-sensitive nature of the grafted polymer brushes, the protein molecules can be protected by the collapsed polymer brushes above the LCST, and their catalytic activity can be controlled. Moreover, the protein molecules on silica particles can be easily separated from the solution and can be reused.

Formation of polyoxazoline-silica nanoparticles via the surface-initiated cationic polymerization of 2-methyl-2-oxazoline

The fabrication of silica hybrid nanoparticles by a surface-initiated cationic ring-opening polymerization of poly(2-methyl-2-oxazoline)s has been described.

Polyelectrolyte brushes: theory, modelling, synthesis and applications

Polyelectrolyte (PE) brushes are a special class of polymer brushes (PBs) containing charges. Polymer chains attain "brush"-like configuration when they are grafted or get localized at an interface (solid-fluid or liquid-fluid) with sufficiently close proximity between two-adjacent grafted polymer chains - such a proximity triggers a particular nature of interaction between the adjacent polymer molecules forcing them to stretch orthogonally to the grafting interface, instead of random-coil arrangement. In this review, we discuss the theory, synthesis, and applications of PE brushes. The theoretical discussion starts with the standard scaling concepts for polymer and PE brushes; following that, we shed light on the state of the art in continuum modelling approaches for polymer and PE brushes directed towards analysis beyond the scaling calculations. A special emphasis is laid in pinpointing the cases for which the PE electrostatic effects can be de-coupled from the PE entropic and excluded volume effects; such de-coupling is necessary to appropriately probe the complicated electrostatic effects arising from pH-dependent charging of the PE brushes and the use of these effects for driving liquid and ion transport at the interfaces covered with PE brushes. We also discuss the atomistic simulation approaches for polymer and PE brushes. Next we provide a detailed review of the existing approaches for the synthesis of polymer and PE brushes on interfaces, nanoparticles, and nanochannels, including mixed brushes and patterned brushes. Finally, we discuss some of the possible applications and future developments of polymer and PE brushes grafted on a variety of interfaces.

Patchy micelles based on coassembly of block copolymer chains and block copolymer brushes on silica particles

Patchy particles are a type of colloidal particles with one or more well-defined patches on the surfaces. The patchy particles with multiple compositions and functionalities have found wide applications from the fundamental studies to practical uses. In this research patchy micelles with thiol groups in the patches were prepared based on coassembly of free block copolymer chains and block copolymer brushes on silica particles. Thiol-terminated and cyanoisopropyl-capped polystyrene-block-poly(N-isopropylacrylamide) block copolymers (PS-b-PNIPAM-SH and PS-b-PNIPAM-CIP) were synthesized by reversible addition-fragmentation chain transfer polymerization and chemical modifications. Pyridyl disulfide-functionalized silica particles (SiO2-SS-Py) were prepared by four-step surface chemical reactions. PS-b-PNIPAM brushes on silica particles were prepared by thiol-disulfide exchange reaction between PS-b-PNIPAM-SH and SiO2-SS-Py. Surface micelles on silica particles were prepared by coassembly of PS-b-PNIPAM-CIP and block copolymer brushes. Upon cleavage of the surface micelles from silica particles, patchy micelles with thiol groups in the patches were obtained. Dynamic light scattering, transmission electron microscopy, and zeta-potential measurements demonstrate the preparation of patchy micelles. Gold nanoparticles can be anchored onto the patchy micelles through S-Au bonds, and asymmetric hybrid structures are formed. The thiol groups can be oxidized to disulfides, which results in directional assembly of the patchy micelles. The self-assembly behavior of the patchy micelles was studied experimentally and by computer simulation.

Cleavage of diblock copolymer brushes in a selective solvent and fusion of vesicles self-assembled by pinned micelles

Lipid membrane fusion is a fundamental process in nature. In the fusion process two distinct bilayers merge the hydrophobic layers, and an interconnected structure is produced. In this research, the fusion of polymer membrane self-assembled by cleaved pinned micelles is investigated. Disulfide-tethered poly(tert-butyl acrylate-block-styrene) diblock copolymer brushes on the surfaces of silica particles were prepared by the "grafting to" or "grafting from" method. In acetone, the diblock copolymer brushes self-assemble into pinned micelles. Upon cleavage from the surfaces of the silica particles with n-tributylphosphine, the pinned micelles self-assemble into vesicles. In the meanwhile, thiol groups at the ends of the block copolymer brushes were produced in the cleavage reaction. Because of the oxidation of the thiol groups and the formation of the disulfide bonds, the vesicle structures are fused into bigger hollow structures and fiber-like structures. The further fusion of the fiber-like structures results in precipitation of the polymer from the solution.

Self-assembled morphologies of ABA triblock copolymer brushes in selective solvents

A simulated annealing method is used to investigate the self-assembled morphologies of symmetric ABA triblock copolymer brushes, formed by one end of the A-blocks tethered onto a planar surface, immersed in a solvent selective for the middle B-blocks. The morphological dependences of the brushes on polymer grafting density and block lengths are investigated systematically. Phase diagrams for systems with different grafting densities are constructed. The simulation results show that the grafted amphiphilic triblock copolymers can self-assemble to form a variety of complicated morphologies which can be classified in terms of the number of A-rich layers in the morphology. In particular, the formation of the structures with one A-rich layer or called "folded" brush structures is consistent with the speculation from the experimental studies of ABA triblock copolymer brushes. More detailed structures depend on the grafting density and the lengths of the blocks. Furthermore, at a high grafting density, the effects of the lengths of blocks and the interaction energies between different species in the system on the conformation of chains are investigated to illustrate the formation mechanisms of self-assembled morphologies of the amphiphilic triblock copolymer brushes.

Chemical patterns from surface grafted resists for directed assembly of block copolymers

We demonstrate a direct e-beam patternable one-component block copolymer (BCP) resist to fabricate a chemical pattern for the directed assembly of a symmetric block copolymer. The resist consists of a low molecular weight poly(styrene-block-methyl methacrylate) with a hydroxyl group at the PMMA chain end (PS-b-PMMA-OH), which anchors the chains to the surface. This short-tethered PMMA block provided sufficient sensitivity to allow scission by e-beam. The length of the untethered PS block was fine-tuned to impart the required contrast between the patterned and the unpatterned region for 1:1 assembly of an overlying BCP blend. Two BCP resists with a PS fraction of 0.25 (16SM) and 0.34 (18SM), with a total molecular weight less than 20K, were synthesized, and the assembly of a ternary BCP blend was studied. 16SM- and 18SM-anchored substrates showed nonpreferential and PS preferential surfaces, respectively. Both 18SM and 16SM could be patterned by e-beam to fabricate a 1:1 chemical pattern with a line pitch of 70 nm for the assembly of a BCP ternary blend. 18SM gave fewer defects than 16SM due to an increased contrast in interfacial energies between adjacent stripes in the chemical surface pattern. Two additional PS-b-PMMA-OH polymers with a molecular weight of 39K (F(PS) = 0.76) and 69K (F(PS) = 0.83) were synthesized to study the effect of PS cross-linking upon exposure to e-beam. As the PS fraction increases, the line pattern becomes blurred and ultimately ineffective in guiding the BCP assembly. The blurring is attributed to cross-linking of adjacent PS chains.

Synthesis and morphological study of thick benzyl methacrylate-styrene diblock copolymer brushes

We demonstrate, for the first time, the synthesis of model poly(benzyl methacrylate) [P(BnMA)] brushes of very high thickness (>300 nm) on silicon wafer. P(BnMA) brush is also synthesized from the surface of silica nanoparticles, from a covalently anchored initiator monolayer, using ambient temperature ATRP. The kinetic studies and block copolymerization from the surface anchored P(BnMA)-Br macroinitiator showed that the polymerization was controlled in nature. AFM, ellipsometry, and water contact angle were used for the characterization of the polymer brush. The grafting density of the P(BnMA) brush, formed by immersion in a dilute monomer solution, was relatively less (∼11% less) in comparison to that obtained by immersion in neat monomer under similar conditions. The P(BnMA)-Br macroinitiator brushes were used to synthesize P(BnMA-b-S) diblock copolymer brushes by the ATRP of styrene at 95 °C. The P(BnMA-b-S) brushes showed stimulus response to a selective solvent and various nanopatterns were observed according to the composition of the block copolymer.