Surface-initiated Atom Transfer Radical Polymerization Research Articles

Porous Morphology of High Grafting Density Mixed Polyelectrolyte Brushes Grown from a Y-Inimer Coating.

Mixed A/B polyelectrolyte (PE) brushes of opposite charges are grown from a Y-shaped initiator-bearing coating to facilitate intimate mixing of the A and B polyelectrolytes in a 1:1 grafting ratio. The design of the Y-shaped inimer includes both ATRP and NMP initiators attached to a common Y-junction. A copolymer of a Y-shaped inimer with glycidyl methacrylate is cross-linked to the substrate resulting in a stable ultrathin coating decorated with Y-shaped initiators. Weak PE A/B mixed brushes based on poly(methacrylic acid)/poly(2-vinylpyridine) (PMAA/P2VP) with a high grafting density of ∼1 chain/nm2 are grown by surface-initiated ATRP and NMP, respectively. Detailed morphological characterization of the PMAA/P2VP brushes in response to pH changes reveals a nanoporous morphology under conditions that maximize complex coacervate formation between oppositely charged brushes. The charge ratio between the A and B brushes is varied via the composition of the brushes to further study the morphology evolution. The effect of intimate contact between the A and B brushes on the morphology is probed by comparing with a mixed A/B PE system with random fluctuations in grafting composition. A quantitative and qualitative study of the pore evolution with pH as well as charge composition is presented using a combination of atomic force microscopy, water contact angle measurement, and image analysis using Gwyddion software. These studies demonstrate that the porous morphology is enhanced and most uniform when the brushes are grown from the Y-inimer, indicating that a 1:1 grafting ratio and intimate contact between A and B brushes are essential.

Hairy quaternary ammonium-functionalized metal organic framework integrated in polyacrylonitrile nanofiber membrane for efficient removal of arsenate

In this work, the metal–organic framework (MOF) particles (i.e., UiO-66-NH2) was covalently modified with poly(4-vinylpyridine) (P4VP) through surface-initiated atom transfer radical polymerization (SI-ATRP) method. The hair MOF product, referred to as UiO-66-g-P4VP, was then subjected to quaternization with 1-bromoethane, resulting in UiO-66-g-qP4VP (quaternized P4VP is denoted as qP4VP). Finally, these UiO-66-g-qP4VP particles were incorporated into a polymer matrix made of polyacrylonitrile (PAN) to develop a nanofibrous composite membrane using the electrospinning technique. After modification of quaternized P4VP, the surface of the MOFs carry strong positive charges. Therefore, the electrospun UiO-66-g-qP4VP/PAN nanofiber membrane can serve as an adsorbent in efficient removal of negatively charged arsenate through strong electrostatic interactions. The adsorptive efficacy of the nanofiber membrane exhibited considerable stability within the pH spectrum extending from 4 to 10, indicating that the membrane could potentially maintain its functionality across a broad range of pH conditions. Our developed approach opens up an avenue for manufacturing of polyelectrolyte-functionalized MOF nanofiber membranes, which hold great promise for application in water remediation.

Antibacterial Zirconia Surfaces from Organocatalyzed Atom-Transfer Radical Polymerization.

Antibacterial coatings are becoming increasingly attractive for application in the field of biomaterials. In this framework, we developed polymer coating zirconia with antibacterial activity using the "grafting from" methodology. First, 1-(4-vinylbenzyl)-3-butylimidazolium chloride monomer was synthesized. Then, the surface modification of zirconia substrates was performed with this monomer via surface-initiated photo atom transfer radical polymerization for antibacterial activity. X-ray photoelectron spectroscopy, ellipsometry, static contact angle measurements, and an atomic force microscope were used to characterize the films for each step of the surface modification. The results revealed that cationic polymers could be successfully deposited on the zirconia surfaces, and the thickness of the grafted layer steadily increased with polymerization time. Finally, the antibacterial adhesion test was used to evaluate the antibacterial activity of the modified zirconia substrates, and we successfully showed the antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa strains.

Metal-Free Atom Transfer Radical Polymerization to Prepare Recylable Micro-Adjuvants for Dendritic Cell Vaccine.

In the development of dendritic cell (DC) vaccines, the maturation of DCs is a critical stage. Adjuvants play a pivotal role in the maturation of DCs, with a major concern being to ensure both efficacy and safety. This study introduces an innovative approach that combines high efficacy with safety through the synthesis of micro-adjuvants grafted with copolymers of 2-(methacrylamido) glucopyranose (MAG) and methacryloxyethyl trimethyl ammonium chloride (DMC). The utilization of metal-free surface-initiated atom transfer radical polymerization enables the production of safe and recyclable adjuvants. These micrometer-sized adjuvants surpass the optimal size range for cellular endocytosis, enabling the retrieval and reuse of them during the ex vivo maturation process, mitigating potential toxicity concerns associated with the endocytosis of non-metabolized nanoparticles. Additionally, the adjuvants exhibit a "micro-ligand-mediated maturation enhancement" effect for DC maturation. This effect is influenced by the shape of the particle, as evidenced by the distinct promotion effects of rod-like and spherical micro-adjuvants with comparable sizes. Furthermore, the porous structure of the adjuvants enables them to function as cargo-carrying "micro-shuttles", releasing antigens upon binding to DCs to facilitate efficient antigen delivery.

Fabrication of dextran-grafted magnetic polymer microspheres with low nonspecific protein adsorption as carriers for chemiluminescence immunoassays

Inhibiting the nonspecific protein adsorption on the surface of magnetic microspheres has become a pressing challenge for immunoassays. In this paper, a novel dextran-modified sandwich-type magnetic polymer microsphere was developed and demonstrated to be a promising carrier for chemiluminescence immunoassay (CLIA). Dextran-modified sandwich-type magnetic polymer microspheres (PFS-PGDN) were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) and ring-opening reaction of epoxy and aminodextran on the surface of magnetic P(GMA-MMA)-NH2@Fe3O4@SiO2 (PFS) microspheres. Then, carboxylated dextran-modified sandwich-type magnetic polymer microspheres (PFS-PGDC) were prepared by the surface carboxylation of the microspheres, which allowed the prepared microspheres to better couple with nucleic acids or antibodies. It is found that after grafting dextran, magnetic PFS-PGDC microspheres could significantly reduce the nonspecific protein adsorption by over 90%. The chemiluminescence immunoassay assay showed a reduction of the background value to a very low level, indicating that the magnetic spheres showed significant advantages in improving the sensitivity of the chemiluminescence assay. Moreover, the chemiluminescence sensitivity and signal values of the synthesized magnetic microspheres have reached high levels. Therefore, the magnetic microspheres synthesized here hold great promise for applications in the field of CLIA.

On the way to increase osseointegration potential: Sequential SI-ATRP as promising tool for PEEK-based implant nano-engineering

In the search of the ideal bone implant material, surface initiated atom transfer radical polymerization (SI-ATRP) techniques were successfully employed to modify the polyetheretherketone (PEEK) surface with complex architecture nanolayers featuring hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(2-hydroxyethyl methacrylate) (PHEMA) branches. As a result, polymer layers with height up to over 300 nm were synthesized to decrease the water contact angle from 92.8° to 23.0°. In-depth analysis of layer topography, structure and elemental composition realized with atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), time-of-flight secondary ions mass spectroscopy (TOF-SIMS) and X-ray photon spectroscopy (XPS) confirmed successful surface modification. Additionally, to demonstrate the applicability of proposed PEEK functionalization, the biomineralization assay in simulated body fluid (SBF) solution was conducted. The high density of hydroxyl and amine groups in branched polymer brushes structure enhanced the rate of hydroxyapatites (HAp) formation substantially. Compared to untreated PEEK, modification with polymer brushes resulted in the creation of cauliflower-like structures with high specific surface area and Ca/P ratio equal to 1.83–1.87 for PEEK grafted with brushes composed of PHEMA backbone segment and PDMAEMA or PHEMA as block polymer branches (PEEK-g-PHEMA-g-PDMAEMA or PEEK-g-PHEMA-g-PHEMA) after 2 weeks. Finally, the process of the hydroxyapatite formation and increase of the layer thickness in a range of 14 days to 6 weeks of immersion in SBF was thoroughly visualized by scanning electron microscopy (SEM).

Selective adsorption and identification of penicillin G sodium in milk by molecularly imprinted polymer doped carbon dot.

A carbon dot (CD) was prepared by o-phenylenediamine and water, which showed bright yellow fluorescence under ultraviolet light irradiation (λ = 580nm), and verified good fluorescence quenching effect on penicillin G sodium (Png-Na). Using methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a crosslinker, and Png-Na as a template, a kind of composite microsphere combining CD and molecularly imprinted polymer (MIP) was synthesized by surface-initiated atomic transfer radical polymerization (SI-ATRP). For reasons ofcomparison, we also prepared MIP without CD and non-imprinted polymers (NIPs). Through static and dynamic adsorption experiments, the maximum adsorption capacity was 47.05mgg-1 and the equilibrium time was 30min. High-performance liquid chromatography (HPLC) was utilized to determine the content of Png-Na in the spiked milk samples. A sensitive, rapid, and simple method for determination of Png-Na in food samples was developed. The utilized approach enabled the quantification of Png-Na within theconcentration range 20-1000μg L-1 (with a limit of detection of 5μg L-1). The recoveries achieved were in the range 93.3-98.2%, with a relative standard deviation of 1.2-4.2%. The results demonstrated that CD@MIP possessed the capability of specific adsorption and fluorescence detection of Png-Na, enabling simultaneous detection and enrichment of Png-Na in real samples.

The effects of interfacial layers on dielectric properties of an acrylic co-polymer containing polymer-grafted reduced graphene oxide

In this study, the influence of interfacial layers, in addition to other effective parameters, on the dielectric efficiency of polymer nanocomposites in the rubbery state is presented. For this purpose, reduced graphene oxide (rGO) was grafted by poly (butyl acrylate) chains (rGO-PBA) via surface-initiated atom transfer radical polymerization (SI-ATRP) and incorporated into an acrylic co-polymer matrix with the glass-transition temperature (Tg) well below room temperature. The rGO exhibited poor dispersion and uneven distribution in acrylic co-polymer, whereas polymer grafted-rGO showed excellent dispersion. The grafted chains can penetrate and form entropic interactions with the matrix chains, which results in a strong interfacial region. The immobilized interfacial layer was characterized by DSC and dielectric measurements. The dielectric measurements in different temperatures provided the means to evaluate the contribution of the interfacial layers on dielectric properties. The findings confirmed that there exists an optimum chain mobility in which the chain polarization shows a major contribution to the dielectric properties of polymer nanocomposites. Reduction of temperature to a certain degree exhibited more rise in the dielectric properties of polymer/rGO-PBA nanocomposites than pure matrix which can be correlated to the interfacial region.

Surface Functionalization with Polymer Brushes via Surface-Initiated Atom Transfer Radical Polymerization: Synthesis, Applications, and Current Challenges.

Polymer brushes have received great attention in recent years due to their distinctive properties and wide range of applications. The synthesis of polymer brushes typically employs surface-initiated atom transfer radical polymerization (SI-ATRP) techniques. To realize the control of the polymerization process in different environments, various SI-ATRP techniques triggered by different stimuli have been developed. This review focuses on the latest developments in different stimuli-triggered SI-ATRP methods, such as electrochemically mediated, photoinduced, enzyme-assisted, mechanically controlled, and organocatalyzed ATRP. Additionally, SI-ATRP technology triggered by a combination of multiple stimuli sources is also discussed. Furthermore, the applications of polymer brushes in lubrication, biological applications, antifouling, and catalysis are also systematically summarized and discussed. Despite the advancements in the synthesis of various types of 1D, 2D, and 3D polymer brushes via controlled radical polymerization, contemporary challenges remain in the quest for more efficient and straightforward synthetic protocols that allow for precise control over the composition, structure, and functionality of polymer brushes. We anticipate the readers could promote the understanding of surface functionalization based on ATRP-mediated polymer brushes and envision future directions for their application in surface coating technologies.

Grafting of Poly(ionic liquid) Brushes through Fe0-Mediated Surface-Initiated Atom Transfer Radical Polymerization for Marine Antifouling.

Surface-tethered poly(ionic liquid) brushes have attracted considerable attention in widespread fields, from bioengineering to marine antifouling. However, their applications have been constrained due to the poor polymerization efficiency and sophisticated operation process. In this work, we efficiently synthesized the poly(ionic liquid) brushes with unparalleled speed (up to 98 nm h-1) through Fe0-mediated surface-initiated atom transfer radical polymerization (Fe0 SI-ATRP) while consuming only microliter of monomer solution under ambient conditions. We also demonstrated that poly(ionic liquid) brushes with gradient thickness and wettability were easily accessible by regulating the distance between the opposite plates of Fe0 SI-ATRP. Moreover, the resultant poly(ionic liquid) brushes presented excellent antibacterial activities against Escherichia coli (99.2%) and Bacillus subtilis (88.1%) after 24 h and low attachment for proteins and marine algae (≤5%) for over 2 weeks. This research provided pathways to the facile and controllable fabrication of poly(ionic liquid) materials for marine antifouling applications.

One-Component Nanocomposites Made from Diblock Copolymer Grafted Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are bio-based, rod-like, high-aspect-ratio nanoparticles with high stiffness and strength and are widely used as a reinforcing nanofiller in polymer nanocomposites. However, due to hydrogen-bond formation between the large number of hydroxyl groups on their surface, CNCs are prone to aggregate, especially in nonpolar polymer matrices. One possibility to overcome this problem is to graft polymers from the CNCs' surfaces and to process the resulting "hairy nanoparticles" (HNPs) into one-component nanocomposites (OCNs) in which the polymer matrix and CNC filler are covalently connected. Here, we report OCNs based on HNPs that were synthesized by grafting gradient diblock copolymers onto CNCs via surface-initiated atom transfer radical polymerization. The inner block (toward the CNCs) is composed of poly(methyl acrylate) (PMA), and the outer block comprises a gradient copolymer rich in poly(methyl methacrylate) (PMMA). The OCNs based on such HNPs microphase separate into a rubbery poly(methyl acrylate) phase that dissipates mechanical energy and imparts toughness, a glassy PMMA phase that provides strength and stiffness, and well-dispersed CNCs that further reinforce the materials. This design afforded OCNs that display a considerably higher stiffness and strength than reference diblock copolymers without the CNCs. At the same time, the extensibility remains high and the toughness is increased up to 5-fold relative to the reference materials.

A Versatile Approach for the Synthesis of Antimicrobial Polymer Brushes on Natural Rubber/Graphene Oxide Composite Films via Surface-Initiated Atom-Transfer Radical Polymerization.

A simple strategy was adopted for the preparation of an antimicrobial natural rubber/graphene oxide (NR/GO) composite film modified through the use of zwitterionic polymer brushes. An NR/GO composite film with antibacterial properties was prepared using a water-based solution-casting method. The composited GO was dispersed uniformly in the NR matrix and compensated for mechanical loss in the process of modification. Based on the high bromination activity of α-H in the structure of cis-polyisoprene, the composite films were brominated on the surface through the use of N-bromosuccinimide (NBS) under the irradiation of a 40 W tungsten lamp. Polymerization was carried out on the brominated films using sulfobetaine methacrylate (SBMA) as a monomer via surface-initiated atom transfer radical polymerization (SI-ATRP). The NR/GO composite films modified using polymer brushes (PSBMAs) exhibited 99.99% antimicrobial activity for resistance to Escherichia coli and Staphylococcus aureus. A novel polymer modification strategy for NR composite materials was established effectively, and the enhanced antimicrobial properties expand the application prospects in the medical field.

Formation of Amphiphilic Zwitterionic Thin Poly(SBMA-co-TFEMA) Brushes on Solid Surfaces for Marine Antifouling Applications.

Water molecules can bind to zwitterionic polymers, such as carboxybetaine and sulfobetaine, forming strong hydration layers along the polymer chains. Such hydration layers act as a barrier to impede the attachment of marine fouling organisms; therefore, zwitterionic polymer coatings have been of considerable interest as marine antifouling coatings. However, recent studies have shown that severe adsorption of marine sediments occurs on zwitterionic-polymer-coated surfaces, resulting in the degradation of their marine antifouling performance. Therefore, a novel approach for forming amphiphilic zwitterionic polymers using zwitterionic and hydrophobic monomers is being investigated to simultaneously inhibit both sediment adsorption and marine fouling. In this study, amphiphilic zwitterionic thin polymer brushes composed of sulfobetaine methacrylate (SBMA) and trifluoroethyl methacrylate (TFEMA) were synthesized on Si/SiO2 surfaces via surface-initiated atom transfer radical polymerization. For this, a facile metal-ion-mediated method was developed for immobilizing polymerization initiators on solid substrates to subsequently form poly(SBMA-co-TFEMA) brushes on the initiator-coated substrate surface. Poly(SBMA-co-TFEMA) brushes with various SBMA/TFEMA ratios were prepared to determine the composition at which both marine diatom adhesion and sediment adsorption can be prevented effectively. The results indicate that poly(SBMA-co-TFEMA) brushes prepared with an SBMA/TFEMA ratio of 3:7 effectively inhibit both sediment adsorption and marine diatom adhesion, thereby exhibiting balanced marine antifouling properties. Thus, the findings of this study provide important insights into the design of amphiphilic marine antifouling materials.

Magnetite nanoparticles immobilized on hydrophilic polyelectrolyte-grafted carbon nanotube as efficient organic–inorganic hybrid heterogeneous catalyst for Knoevenagel condensation in aqueous medium

In this work, a novel organic–inorganic hybrid heterogeneous catalyst was fabricated for Knoevenagel condensation. First, the surface of carbon nanotube (CNT) was covalently functionalized with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) polyelectrolyte (i.e., organic polybase) through the surface-initiated atom transfer radical polymerization (SI-ATRP) method. Subsequently, magnetic iron oxide nanoparticles (Fe3O4 NPs) (i.e., inorganic Lewis acid) are densely and homogeneously grown on the CNT surface using the CNT-g-PDMAEMA template. The as-prepared acid–base bifunctional catalyst (i.e., CNT-g-PDMAEMA/Fe3O4NPs) was investigated in the model reaction, i.e., Knoevenagel condensation between naphthol, malononitrile and benzaldehyde. The CNT-g-PDMAEMA/Fe3O4NPs catalyst shows high catalytic activity in the Knoevenagel condensation between naphthol, malononitrile and benzaldehyde due to its unique structure and specific chemical constitution. In addition, this acid–base bifunctional catalyst can be readily recovered with an applied magnetic field and reused with negligible loss in the catalytic activity even after six cycles.

Electrochemically Mediated Surface-Initiated Atom Transfer Radical Polymerization by ppm of CuII/Tris(2-pyridylmethyl)amine.

Atom transfer radical polymerization (ATRP) is one of the most widely used methods for modifying surfaces with functional polymer films and has received considerable attention in recent years. Here, we report an electrochemically mediated surface-initiated ATRP to graft polymer brushes onto solid substrates catalyzed by ppm amounts of CuII/TPMA in water/MeOH solution. We systematically investigated the type and concentrations of copper/ligand and applied potentials correlated to the polymerization kinetics and polymer brush thickness. Gradient polymer brushes and various types of polymer brushes are prepared. Block copolymerization of 2-hydroxyethyl methacrylate (HEMA) and 3-sulfopropyl methacrylate potassium salt (PSPMA) (poly(HEMA-b-SPMA)) with ultralow ppm eATRP indicates the remarkable preservation of chain end functionality and a pronounced "living" characteristic feature of ppm-level eATRP in aqueous solution for surface polymerization.

Oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient friction and wear reduction

AbstractNanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure, suitable mechanical property, and tunable surface functionalities. However, the poor compatibility between nanomaterials and base oil limits their further applications. In this work, we demonstrated oil-soluble poly (lauryl methacrylate) (PLMA) brushes-grafted metal-organic frameworks nanoparticles (nanoMOFs) as lubricating oil additives that can achieve efficient friction reduction and anti-wear performance. Macroinitiators were synthesized by free-radical polymerization, which was coordinatively grafted onto the surface of the UiO-67 nanoparticles. Then, PLMA brushes were grown on the macroinitiator-modified UiO-67 by surface-initiated atom transfer radical polymerization, which greatly improved the lipophilic property of the UiO-67 nanoparticles and significantly enhanced the colloidal stability and long-term dispersity in both non-polar solvent and base oil. By adding UiO-67@PLMA nanoparticles into the 500 SN base oil, coefficient of friction and wear volume reductions of 45.3% and 75.5% were achieved due to their excellent mechanical properties and oil dispersibility. Moreover, the load-carrying capacity of 500 SN was greatly increased from 100 to 500 N by the UiO-67@PLMA additives, and their excellent tribological performance was demonstrated even at a high friction frequency of 65 Hz and high temperature of 120 °C. Our work highlights oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient lubricating additives.

Long-term stability of antifouling poly(carboxybetaine acrylamide) brush coatings

A comprehensive understanding how storage conditions affect functional surface properties of antifouling organic coatings remains a persistent challenge across industry and research worldwide. This study investigates the long-term storage stability of state-of-art antifouling functionalizable zwitterionic poly(carboxybetaine acrylamide) (pCBAA) brushes using spectroscopic ellipsometry (SE), infrared reflection-absorption spectroscopy (IRRAS), surface plasmon resonance (SPR), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The pCBAA brushes, prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) on SPR substrates, were subjected to various storage conditions for 43 days: kept in dry state at room temperature or −20 °C, and immersed in water or phosphate-buffered saline (PBS) and kept at 6 °C or −20 °C. The IRRAS, SE and AFM data confirm only negligible release of pCBAA under these storage conditions. However, SE indicated a slightly lower brush swelling ratio depending on storage. The SPR was used to evaluate the resistance of unmodified pCBAA, pCBAA activated by EDC/NHS chemistry and deactivated with 2-(2-aminoethoxy)acetic acid (AEAA), and pCBAA functionalized with anti-E. coli antibodies against fouling from undiluted human blood plasma. The results confirm that pCBAA brushes maintain or may even improve their exceptional antifouling performance after prolonged storage, while displaying a slight deterioration in their binding capacity for anti-E. coli antibodies.

Synthesis of thermosensitive hybrid structure gold nanotriangles coated with poly(N-isopropylacrylamide) for reversible confinement of molecules

In this work, we investigate a synthesis method for novel systems that involve the use of gold nanotriangles arrays (AuNTs) coated with poly(N-isopropylacrylamide) (pNIPAM) brushes, designed as smart platforms for the reversible confinement of bio-particles. Initially, we employed cost-effective nanosphere lithography to fabricate gold nanotriangles arrays. Next, polymer initiator groups were attached to the AuNTs surface through a spontaneous reduction approach, enabling exclusive functionalization of pNIPAM on the gold surface. Finally, we utilized surface-initiated atom transfer radical polymerization to graft pNIPAM brushes onto the gold surface. We systematically investigated the polymer initiator groups’ grafting time and the polymerization time to control the thickness of the grafted pNIPAM brushes. Subsequently, we characterized the thermoresponsive properties of these hybrid structures using Atomic Force Microscopy (AFM) measurements, evaluating their ability to undergo on/off adsorption and desorption of polystyrene (PS) beads on their surface. Indeed, the combination of the thermosensitive pNIPAM polymer with AuNTs arrays results in the development of a precisely regulated two-dimensional active device which exhibits tunable properties with external temperature changes, making it a versatile platform suitable for a wide range of applications.

High-Sensitivity Mechanochromic Sensor Using Core-Shell Colloidal Crystals

The Colloidal Crystals-based mechanochromic sensor changes color as the arrangement of colloidal particles changes in response to mechanical deformation, which can be detected through optical measurement. This type of sensor can be used in various applications, such as automobile collision detection, structural deformation detection, and medical equipment, among others. In this study, we prepared a stretchable film by dispersing surface-functionalized colloidal particles in an elastic polymer matrix. Surface of silica colloidal particle was modified with an initiator for Atom Transfer Radical Polymerization (ATRP), followed by surface-initiated ATRP of poly(t-butyl methacrylate) (PtBMA). The core-shell colloidal particles were composited with various acrylic monomers, to fabricate crystalline colloidal array which transforms to elastic film by photopolymerization exhibiting structural color. The prepared film showed a clear color change for deformation within 10%, and the peak reflectance showed more than 30%.

Threshold of Surface Initiator Concentration for Polymer Brush Growth by Surface-Initiated Atom Transfer Radical Polymerization.

The surface modification of various materials by grafting functional molecules has attracted much attention from fundamental research to practical applications because of its ability to impart various physical and chemical properties to the surfaces. One promising approach is the use of polymer brushes synthesized by atom transfer radical polymerization (ATRP) from surface-tethered initiators (SIs). In this study, for the purpose of controlling the grafting amounts/densities of polymer brushes, we developed a facile method to precisely regulate SI concentrations of SI layers (SILs) by serial dilution based on a sol-gel method. By simply mixing organosilanes terminated with and without an initiator group ((p-chloromethyl) phenyltrimethoxysilane (CMPTMS) and phenyltrimethoxysilane (PTMS), respectively) with tetraethoxysilane (TEOS), SI concentrations of SILs could be arbitrarily tuned precisely by varying dilution factors of (CMPTMS + PTMS)/CMPTMS (DFs, 1-107). The resulting SILs prepared at different DFs were highly smooth and transparent. X-ray photoelectron spectroscopy (XPS) also confirmed that the SIs were homogeneously distributed at the topmost surface of the SILs and their concentrations were proven to be accurately and precisely controlled from high to extremely low, comparable to theoretical values. Subsequent SI-ATRP in air ("paint-on" SI-ATRP) of two different types of monomers (hydrophobic/nonionic (2,3,4,5,6-pentafluorostyrene) and hydrophilic/ionic (sodium 4-styrenesulfonate)) demonstrated that polymer brushes with different grafting amounts/densities were successfully grafted only from SILs with DFs of 1-104 (theoretical SI concentrations: 3.9 × 10-4 ∼ 3.5 units/nm2), while at DFs of 105 and above (theoretical SI concentrations: <3.9 × 10-5 units/nm2), no sign of polymer brush growth was confirmed by thickness, XPS, and water contact angle data. Therefore, we are the first to gather evidence that the approximate threshold of SI concentration required for "paint-on" SI-ATRP might be on the order of 10-4 ∼ 10-5 units/nm2.