Effect of Overall Grafting Density on Microphase Separation of Mixed Homopolymer Brushes Synthesized from Y-Initiator-Functionalized Silica Particles

Phase Behavior of Polydisperse Y-Shaped Polymer Brushes under Good Solvent Conditions

Y-shaped polymer brushes represent a special class of binary mixed polymer brushes, in which a combination of different homopolymers leads to unique phase behavior. While most theoretical and simulation studies use monodisperse models, experimental systems are always polydisperse. This discrepancy hampers linking theoretical and experimental results. In this theoretical study, we employed dissipative particle dynamics to study the influence of polydispersity on the phase behavior of Y-shaped brushes grafted to flat surfaces under good solvent conditions. Polydispersity was kept within experimentally achievable values and was modeled via Schulz-Zimm distribution. In total, 10 systems were considered, thus covering the phase behavior of monodisperse, partially polydisperse and fully polydisperse systems. Using such generic representation of real polymers, we observed a rippled structure and aggregates in monodisperse systems. In addition, polydisperse brushes formed a stable perforated layer not observed previously in monodisperse studies, and influenced the stability of the remaining phases. Although the perforated layer was experimentally observed under good solvent conditions and in the melt state, further confirmation of its presence in systems under good solvent conditions required mapping real polymers onto mesoscale models that reflected, for example, different polymer rigidity, and excluded volume effects or direct influence of the surface, just to mention a few parameters. Finally, in this work, we show that mesoscale modeling successfully describes polydisperse models, which opens the way for rapid exploring of complex systems such as polydisperse Y-shaped brushes in selective or bad solvents or under non-equilibrium conditions.

Fundamentals and Applications of Polymer Brushes in Air

For several decades, high-density, end-tethered polymers, forming so-called polymer brushes, have inspired scientists to understand their properties and to translate them to applications. While earlier research focused on polymer brushes in liquids, it was recently recognized that these brushes can find application in air as well. In this review, we report on recent progress in unraveling fundamental concepts of brushes in air, such as their vapor-swelling and solvent partitioning. Moreover, we provide an overview of the plethora of applications in air (e.g., in sensing, separations or smart adhesives) where brushes can be key components. To conclude, we provide an outlook by identifying open questions and issues that, when solved, will pave the way for the large scale application of brushes in air.

Music Choreography Algorithm Based on Feature Matching and Fragment Segmentation

Choreography is an art form in and of itself. Because music and dance have always appeared at the same time throughout human history, music has had a significant influence on dance arrangement. It is important to arrange appropriate dance movements based on the music pieces chosen by users when creating choreography. This paper proposes a mixed density network-based music choreography algorithm in response to the current state of music choreography. The algorithm should be able to convert motion and music signals into a high-level semantic meaning that is compatible with human cognition, compare the degree of matching, and arrange the dance based on the music and motion segments that match. Furthermore, the consistency and authenticity of the movements in the dance created in this paper have been improved. Users' subjective feedback indicates that the choreography results in this paper are more closely aligned with the music. In the field of music choreography, it has some practical utility.

Mixed Polymer Brushes for "Smart" Surfaces

Mixed polymer brushes (MPBs) are composed of two or more disparate polymers covalently tethered to a substrate. The resulting phase segregated morphologies have been extensively studied as responsive "smart" materials, as they can be reversible tuned and switched by external stimuli. Both computational and experimental work has attempted to establish an understanding of the resulting nanostructures that vary as a function of many factors. This contribution highlights state-of-the-art MPBs studies, covering synthetic approaches, phase behavior, responsiveness to external stimuli as well as novel applications of MPBs. Current limitations are recognized and possible directions for future studies are identified.

Renewable Fabric Surface-Initiated ATRP Polymerizations: Towards Mixed Polymer Brushes

A totally new approach in the synthesis of mixed polymer brushes tethered on polyamide (PA) surfaces is presented herein. As a proof of concept, two types of homopolymers were synthesized in sequential surface-initiated atom transfer radical polymerization (SI-ATRP) reactions: poly(methyl methacrylate)/poly((2-dimethylamino)ethyl methacrylate) and polystyrene /poly((2-dimethylamino)ethyl methacrylate). The ATRP initiator was immobilized on the surface through PA chain-end groups in two subsequent steps, separated by homo-polymerizations. The amount of the PA chains' end groups available on the modified surface was tuned by the thermal rearrangement of the surface.

Phase Behavior of Mixed Polymer Brushes Grown from Ultrathin Coatings

Experimental validation of the predicted melt phase behavior of A/B mixed brush on planar substrate is presented using poly(methyl methacrylate) (A)/ polystyrene (B) (PMMA/PS) with equal number of A/B chains as an example. Well-defined mixed A/B brushes are synthesized using a single component inimer coating to achieve high grafting density (0.9 chains/nm²), uniformity of grafting sites, and predictable chain length. The inimer coating is a copolymer of nitroxide-mediated polymerization (NMP) inimer, atom transfer radical polymerization (ATRP) inimer, styrene, and glycidyl methacrylate (GMA). Cross-linking of the film provides the required stability to probe the melt morphology. Our studies show that even with equal grafting density of the A and B the morphology can be modulated by varying the length of B chains while keeping that of A fixed. We show the transition of self-assembled structures from disorder to cylinder to ripple phase at sub-30 nm length scale on a planar surface by thermal annealing of mixed brushes. These results are supported by a phase diagram established through Monte Carlo simulation using a coarse-grained particle-based model.

Characterizing Polymer-Grafted Nanoparticles: From Basic Defining Parameters to Behavior in Solvents and Self-Assembled Structures

Polymer-grafted nanoparticles, often called hairy nanoparticles (HNPs), are an intriguing class of nanostructured hybrid materials with great potential in a variety of applications, including advanced polymer nanocomposite fabrication, drug delivery, imaging, and lubrication. This Feature provides an introduction to characterization of various aspects of HNPs, from basic defining parameters to behavior of HNPs in solvents and self-assembled structures of multicomponent brush nanoparticles, by using a broad range of analytical tools.

Design, Synthesis, and Application of a Difunctional Y-Shaped Surface-Tethered Photoinitiator

Mixed homopolymer brushes have unique interfacial properties that can be exploited for both fundamental studies and applications in technology. Herein, the synthesis of a new catechol-based biomimetic Y-shaped binary photoinitiator (Y-photoinitiator) and its applications for surface modification with polymer brushes through both "grafting to" and "grafting from" strategies are reported. The "leg" of the Y consists of a catechol group as surface anchoring moiety. The arms are photoinitiator moieties that can be "addressed" independent of each other by radiation of different wavelengths. Using ultraviolet and visible light successively, each arm of the Y-photoinitiator was activated, thereby allowing the synthesis of Y-shaped block copolymer brushes with dissimilar polymer chains. The suitability of the Y-photoinitiator for surface modification was first investigated using N-vinylpyrrolidone and styrene as the model monomers for successive UV-photoiniferter-mediated polymerization and visible-light-induced polymerization, respectively. Switching of the wetting properties of the Y-shaped block copolymer brush poly( N-vinylpyrrolidone)- block-poly(styrene) (PVP- b-PS)-grafted surfaces by contact with different solvents was also investigated. To further exploit this novel Y-photoinitiator for the preparation of functional interfaces, Y-shaped block copolymer brushes poly(1-(2-methacryloyloxyhexyl)-3-methylimidazolium bromide)- block-poly( N-vinylpyrrolidone- co-glycidyl methacrylate) (PIL(Br)- b-P(NVP- co-GMA)) were also prepared and subsequently functionalized with the cell-adhesive arginine-glycine-aspartic acid (RGD) peptides by reaction with the glycidyl groups (PILPNG-RGD). The PILPNG-RGD grafted surfaces showed excellent cell-adhesive, bacteriostatic, and bactericidal properties. Thus, it can be concluded that further exploitation of this novel Y-photoinitiator for graft polymerization should allow the preparation of a wide range of functional interfaces with tailored properties.

Phase separation in mixed polymer brushes on nanoparticle surfaces enables the generation of anisotropic nanoarchitectures

The preparation of nanoparticles and their targeted connection with other functional units is one key challenge in developing nanoscale devices. Herein, we report an experimental strategy toward the development of anisotropic nanoparticle architectures. Our approach is based on phase separation of binary mixed polymer brushes on gold nanoparticle surfaces leading to Janus-type structures, as revealed by scanning transmission electron microscopy and electron energy-loss spectroscopy and, additionally, corroborated by computer simulation. We show that such structures can be used for the site-selective functionalization with additional nanosized entities.

Improved Lubricating Performance by Combining Oil-Soluble Hairy Silica Nanoparticles and an Ionic Liquid as an Additive for a Synthetic Base Oil

This article reports on improved lubricating performance by combining oil-soluble poly(lauryl methacrylate) brush-grafted silica nanoparticles (hairy NPs or HNP) and an oil-miscible phosphonium-phosphate ionic liquid (IL) as a friction-reducing additive for a polyalphaolefin (PAO) oil. The HNP was synthesized by surface-initiated reversible addition-fragmentation chain transfer polymerization. At a total concentration of 2% and sufficiently high individual concentrations for HNP and IL in PAO, high-contact stress, ball-on-flat reciprocating tribological tests showed that the friction decreased by up to 23% compared with 2% HNP alone in PAO and by up to 35% compared to the PAO mixed with 2% IL. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis revealed that the tribofilm formed from the PAO containing 1% HNP + 1% IL was enriched with both Si and P, indicating that both hairy NPs and IL were involved in the tribochemical reactions. In addition, the O 1s and Si 2p peaks in the core-level XPS spectra exhibited significant shifts for the mixture of 1% HNP + 1% IL compared to those for 2% HNP, suggesting the possible formation of new covalent bonds. These results indicated that HNP and IL reacted with each other and also with the metal substrate during the rubbing process, which likely strengthened the tribofilm and its bonding with the substrate and thus further improved the lubrication.

Charged Metallopolymer-Grafted Silica Nanoparticles for Antimicrobial Applications

Inappropriate and frequent use of antibiotics has led to the development of antibiotic-resistant bacteria, which cause infectious diseases that are difficult to treat. With the rising threat of antibiotic resistance, the need to develop effective new antimicrobial agents is prominent. We report antimicrobial metallopolymer nanoparticles, which were prepared by surface-initiated reversible addition-fragmentation chain transfer polymerization of a cobaltocenium-containing methacrylate monomer from silica nanoparticles. These particles are capable of forming a complex with β-lactam antibiotics, such as penicillin, rejuvenating the bactericidal activity of the antibiotic. Disk diffusion assays showed significantly increased antibacterial activities against both Gram-positive and Gram-negative bacteria. The improved efficiencies were attributed to the inhibition of hydrolysis of the β-lactam antibiotics and enhancement of local antibiotics concentration on a nanoparticle surface. In addition, hemolysis evaluations demonstrated minimal toxicity to red blood cells.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Opportunities for dual RDRP agents in synthesizing novel polymeric materials

Dual RDRP agents provide access to new polymeric materials by combining ATRP, NMP, and RAFT polymerization without end group transformations.

Long-subchain Janus-dendritic copolymers from locally confined click reaction and generation-dependent micro-phase separation

Long-subchain Janus-dendritic copolymers composed of PSt and PtBA half-dendrons, up to the third generation, were prepared under alternating chemical and local confinement. All the Janus-dendritic copolymers exhibited generation-dependent microphase separation.

In Situ Characterization of Binary Mixed Polymer Brush-Grafted Silica Nanoparticles in Aqueous and Organic Solvents by Cryo-Electron Tomography

We present an in situ cryo-electron microscopy (cryoEM) study of mixed poly(acrylic acid) (PAA)/polystyrene (PS) brush-grafted 67 nm silica nanoparticles in organic and aqueous solvents. These organic-inorganic nanoparticles are predicted to be environmentally responsive and adopt distinct brush layer morphologies in different solvent environments. Although the self-assembled morphology of mixed PAA/PS brush-grafted particles has been studied previously in a dried state, no direct visualization of microphase separation was achieved in the solvent environment. CryoEM allows the sample to be imaged in situ, that is, in a frozen solvated state, at the resolution of a transmission electron microscope. Cryo-electron tomograms (cryoET) were generated for mixed PAA/PS brush-grafted nanoparticles in both N,N-dimethylformamide (DMF, a nonselective good solvent) and water (a selective solvent for PAA). Different nanostructures for the mixed brushes were observed in these two solvents. Overall, the brush layer is more compact in water, with a thickness of 18 nm, as compared with an extended layer of 27 nm in DMF. In DMF, mixed PAA/PS brushes are observed to form laterally separated microdomains with a ripple wavelength of 13.8 nm. Because of its lower grafting density than that of PAA, PS domains form more or less cylindrical or truncated cone-shaped domains in the PAA matrix. In water, PAA chains are found to form a more complete shell around the nanoparticle to maximize their interaction with water, whereas PS chains collapse into the core of surface-tethered micelles near the silica core. The cryoET results presented here confirm the predicted environmentally responsive nature of PAA/PS mixed brush-grafted nanoparticles. This experimental approach may be useful for the design of future mixed brush-grafted nanoparticles for nano- and biotechnology applications.

Environmentally responsive self-assembly of mixed poly(tert-butyl acrylate)-polystyrene brush-grafted silica nanoparticles in selective polymer matrices

Environmentally responsive self-assembly of nearly symmetric mixed poly(tert-butyl acrylate) (PtBA, 22.2 kDa)/polystyrene (PS, 23.4 kDa) brushes grafted onto 67 nm silica nanoparticles in selective homopolymer matrices [PtBA for the grafted PtBA chains and poly(cyclohexyl methacrylate) (PCHMA) for the grafted PS chains] was investigated using both conventional transmission electron microscopy (TEM) and electron tomography (i.e., 3D TEM). A variety of self-assembled phase morphologies were observed for the mixed brushes in selective polymer matrices with different molecular weights, and these can be explained by entropy-driven wet- and dry-brush theories. In a low molecular weight selective matrix, the wet-brush regime was formed with the miscible chains stretching out and the immiscible chains collapsing into isolated domains. In contrast, when the molecular weight of the selective matrix was higher than that of the compatible grafted polymer chains, the dry-brush regime was formed with the mixed brushes exhibiting the unperturbed morphology. In addition to the molecular weight, the size of nanoparticles (or the substrate curvature) was also observed to play an important role. For small particles (core size less than 50 nm), the wet brush-like morphology with a surface-tethered micellar structure was observed. Finally, the wet- and dry-brush regimes also significantly affected the dispersion of mixed brush particles in selective polymer matrices.

Design, Synthesis, and Use of Y-Shaped ATRP/NMP Surface Tethered Initiator

Heterogeneous polymer brushes on surfaces can be easily formed from a binary initiator on a silicon oxide substrate where two different types of polymers can be grown side-by-side. Herein, we designed a new Y-shaped binary initiator using straightforward chemistry for "grafting from" polymer brushes. This initiator synthesis takes advantage of the Passerini reaction, a multicomponent reaction combining two initiator sites and one surface linking site. This Y-shaped binary initiator can be synthesized in three steps with a higher yield than other similar initiators reported in the literature, and can be performed on a multigram scale. We were able to attach the initiator to a silicon oxide substrate and successfully grow polymer brushes from both initiators (separately and in combination), confirmed by NEXAFS, AFM, and contact angle.

Surface-initiated controlled radical polymerizations from silica nanoparticles, gold nanocrystals, and bionanoparticles

This review summarizes recent progress in surface-initiated controlled radical polymerizations from silica nanoparticles, gold nanocrystals, and bionanoparticles.

Surface modification of polydopamine coated particles via glycopolymer brush synthesis for protein binding and FLIM testing

Polymer coatings on silica cores as well as fluorescent protein binding and fluorescent lifetime analysis.

Hybrid micellar hydrogels of a thermosensitive ABA triblock copolymer and hairy nanoparticles: effect of spatial location of hairy nanoparticles on gel properties

This article reports a method for control of spatial location of nanoparticles (NPs) in hybrid micellar hydrogels of a thermosensitive ABA triblock copolymer and polymer brush-grafted NPs (hairy NPs), either inside or outside the core of micelles, and the study of the effect of different locations of NPs on gel properties. Two batches of thermosensitive polymer brush-grafted, 17 nm silica NPs with different lower critical solution temperatures (LCSTs) and a thermosensitive ABA triblock copolymer composed of a poly(ethylene oxide) central block and thermosensitive outer blocks (ABA-D) were synthesized. The different locations of NPs were achieved by controlling the LCST of hairy NPs (LCST(NP)) relative to that of the thermosensitive outer blocks of ABA-D (LCST(ABA)). When the LCST(NP) and LCST(ABA) were similar, the NPs resided in the core of micelles upon heating from below the LCST(NP) and LCST(ABA). When the LCST(NP) was significantly higher, the NPs were located outside the core of micelles as confirmed by fluorescent resonance energy transfer. The effects of different locations of hairy NPs and NP-to-polymer mass ratio on properties of hybrid micellar hydrogels formed from aqueous solutions of ABA-D with a concentration of 10 wt % and various amounts of hairy NPs were studied by rheological measurements. The sol-gel transition temperature (T(sol-gel)) and dynamic storage modulus G' of the gels with NPs inside the core of micelles did not change much with increasing the NP-to-polymer mass ratio. In contrast, the T(sol-gel) of gels with NPs in the interstitial space among micelles increased slightly and the G' decreased significantly with the increase of the NP-to-polymer ratio. The hairy NPs in the interstitial space appeared to affect the formation of polymer networks and increase the fraction of polymer loops, resulting in a lower density of bridging chains and thus a lower G'. In addition, for gels with NPs in the interstitial space, a noticeable increase in G' was observed in the heating ramps above 40 °C, which was likely caused by the collapsed hairy NPs adsorbing polymer chains in the dangling and loop forms, increasing the density of bridging chains.

Synthesis of mixed poly(ε-caprolactone)/polystyrene brushes from Y-initiator-functionalized silica particles by surface-initiated ring-opening polymerization and nitroxide-mediated radical polymerization

This article reports the synthesis of mixed brushes by ring-opening polymerization of ε-caprolactone and nitroxide-mediated radical polymerization of styrene from Y-initiator-functionalized silica particles.

One-pot polymer brush synthesis via simultaneous isocyanate coupling chemistry and “grafting from” RAFT polymerization

One-pot ‘grafting from’ of polystyrene on polydopamine particles was investigated using a newly developed carbonyl-azide reversible addition–fragmentation chain transfer (RAFT) agent.