Structure Of Brushes Research Articles

Salt concentration dependency of the hydrated swollen structure of cholinephosphate-type polyzwitterion brushes

Salt concentration dependency of the hydrated swollen structure of cholinephosphate-type polyzwitterion brushes

Structure and Organization of Amphiphilic Mikto-Grafted Molecular Brushes at Liquid/Liquid Planar Interfaces

Structure and Organization of Amphiphilic Mikto-Grafted Molecular Brushes at Liquid/Liquid Planar Interfaces

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.

Topology Effects of Poly(2-ethyl-2-oxazoline) Brushes with Various Architectures for Antifouling Behavior under Shear Flow.

Polymer brushes with different topological architectures exhibit unparalleled interfacial and physicochemical properties and are being widely utilized in antifouling applications. However, there is an absence of a thorough understanding of the antifouling process of dynamic flow mediated by the topological structure of polymer brushes. Here, it is highlighted how the interface parameters related to biofouling in flowing carrier fluid are tuned by topologically different architectures. The mechanism by which three brushes with various topological structures (cyclic, looped, and linear brushes) encounter biological media was revealed by relating protein adhesion with nanomechanics and protein conformational transitions on poly(2-ethyl-2-oxazoline) (PEtOx) brushes. In contrast to the classically linear analogue, the cyclic PEtOx brushes confered an enhanced steric barrier and excellent lubrication at the critical density region. The impenetrable and smoother layer prevented the approach and shortened the residence time for protein on the surface, providing optimal antifouling properties at low shear rates. The looped brushes also significantly inhibited protein adhesion under prolonged high shear rates due to their unshakable conformational characteristics. These findings detailed a new evaluation framework behind polymer brushes of topology-driven biofouling repulsion under flow conditions and pointed the way toward a promising approach for the effectiveness of biomaterial design.

Ion Specificity Influences on the Structure of Zwitterionic Brushes

Zwitterionic brushes have a wide range of applications, including use as lubricating surfaces and antifouling membranes. In this study, densely end-tethered poly(cysteine methacrylate) (PCysMA) brushes were synthesized using surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET-ATRP). The structure of the PCysMA brushes was investigated using ellipsometry, X-ray reflectivity (XRR), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy (AFM). The results of these characterization techniques were used to study the effect of SO42–, Cl–, NO3–, Br–, and SCN– anions, divalent Ca2+ and Ba2+ cations, and trivalent Y3+ cations on the structure of the PCysMA brushes. The results showed that the PCysMA brushes in solution exhibit an “antipolyelectrolyte” effect to a certain degree, which inversely follows the Hofmeister series of anions. The introduction of divalent cations Ca2+ and Ba2+ had a modest impact on the dimensions of the PCysMA brushes, indicating that chelating interactions between the cations and zwitterion units work against the “antipolyelectrolyte” effect. The complexation was even stronger in the presence of trivalent Y3+ cations, which caused the PCysMA brushes to shrink. These findings highlight the importance of ion specificity to the structure of zwitterionic brushes in aqueous solutions.

Electric double layer of spherical pH-responsive polyelectrolyte brushes in an electrolyte solution: A strong stretching theory accounting for excluded volume interaction and mass action law

In this paper, we study the electrostatics of pH-responsive polyelectrolyte-grafted spherical particles by using a strong stretching theory that takes into account the excluded volume interaction and the density of chargeable sites on the polyelectrolyte molecules. Based on free energy formalism, we obtain self-consistent field equations for determining the structure and electrostatics of spherical polyelectrolyte brushes. First, we find that the smaller the radius of the inner core, the longer the height of the polyelectrolyte brush. Then, we also prove that an increase in the excluded volume interaction yields a swelling of the polyelectrolyte brush height. In addition, we demonstrate how the effect of pH, bulk ionic concentration, and lateral separation between adjacent polyelectrolyte chains on the electrostatic properties of a spherical polyelectrolyte brush is affected by the radius of the inner core, the excluded volume interaction, and the chargeable site density.

Synthesis of enzyme-responsive theranostic amphiphilic conjugated bottlebrush copolymers for enhanced anticancer drug delivery

Synthesis of polyfluorene (PF) based theranostic amphiphilic copolymers with simultaneously high drug loading efficiency and tumor microenvironment-specific responsiveness for promoted intracellular drug release and enhanced cancer therapy has been rarely reported likely due to the lack of efficient synthetic approaches to integrate these desirable properties. In this work, we recorded the successful preparation of well-defined theranostic amphiliphilic bottlebrush copolymers composing of fluorescent backbone of PF and tunable enzyme-degradable side chains of polytyrosine (PTyr) and POEGMA by integrating Suzuki coupling, NCA ROP and ATRP techniques. Notably, the resulting copolymer, PF25-g-(PTyr26-b-(POEGMA28)2 (P4) with two branched POEGMA brushes tethered to one PTyr termini for each unit could form steady unimolecular micelles with higher fluorescence quantum yield of 18.3% in aqueous and greater entrapment efficiency (EE) of 91.0% for DOX ascribed to the efficient π–π stacking interactions between PTyr blocks and drug molecules and the unique structure of branched hydrophilic brushes with a moderate chain length. DOX@P4 micelles revealed visualization of intracellular trafficking and accelerated drug release due to the enzyme-triggered degradation of PTyr blocks with proteinase K and subsequent deshielding of POEGMA corona for micelle destruction. In vitro and In vivo animal study further verified the intensive therapeutic efficiency with attenuated systematic toxicity. Taken together, we provided a universal strategy toward multifunctional polymeric delivery vehicles based on conjugated PF and biocompatible and degradable polypeptide by integratied Suzuki coupling and NCA ROP, and identified the branched structure of hydrophilic brushes for better performance of bottlebrush copolymers-based micelles for drug delivery applications. Statement of significanceSynthesis of polyfluorene (PF)-based theranostic amphiphilic copolymers with simultaneously high drug loading efficiency and tumor microenvironment-specific responsiveness for promoted intracellular drug release and enhanced cancer therapy has been rarely reported likely due to the lack of efficient synthetic approaches to integrate these desirable properties. We reported herein successful preparation of enzyme-responsive theranostic amphiliphilic bottlebrush copolymers with simultaneously high drug loading efficiency and tumor microenvironment-specific responsiveness for enhanced chemotherapy in vivo. This study therefore not only developed a universal strategy for the construction of multifunction polymeric vehicles based on the conjugated polymer of PF and degradable polypeptide by integrated Suzuki coupling and NCA ROP, but also emphasized the better stability of micelles endowed by the branched hydrophilic brushes than linear ones.

Self-assembly in amphiphilic spherical brushes.

The structure of amphiphilic spherical brushes, consisting of the nano-SiO2 core, the hyperbranched polyamidoamine subshell, and a grafted layer of long hydrophobically modified polyacrylamide (HMPAM) chains, in aqueous solution was analyzed and described in the framework of the original mean-field approach. The scaling estimations of the hydrodynamic radius of such polymer brushes as a function of the number of grafted macromolecules allow concluding that the HMPAM shells are in a globular state and that the region of the stretched chains adjacent to the grafting surface is a minor part of the grafted macromolecules and does not have a significant impact on the self-assembly of the HMPAM shell caused by the complex hydrophobic-hydrophilic composition of their monomer units. In mean-field theory, the amphiphilic nature of HMPAM was taken into account by attaching the hydrophobic side group H to some fraction of monomer units of the hydrophilic P backbone. The strong attraction of H groups causes the aggregation of macromolecules, whereas the affinity of hydrophilic P groups to solvent forces the aggregates to increase their surface. Due to such effective surface activity, in poor solvent, the grafted amphiphilic macromolecules could form a spherical compacted structure around the nanoparticle or self-assemble into a "hedgehog" structure with several "spines" having hydrophobic core and hydrophilic shell. State diagrams, obtained theoretically, reveal that the "hedgehog" structure is preferable for a wide range of energetic parameters.

Interdental space brushes. Design, structure and use of interdental brushes

The interdental spaces are the most difficult areas of the dentition to clean. In addition to being difficult to access, the interdental spaces are characterised by variability in size and anatomy. Conventional toothbrush bristles do not reach these tooth surfaces adequately and biofilm removal is incomplete.

Ion-Specific Effects of Divalent Ions on the Structure of Polyelectrolyte Brushes.

Polyelectrolyte brushes consist of charged polymer chains attached on one end to a surface at high densities. They are relevant for many practical applications ranging from biosensors to drug delivery to colloidal stability. Their structure and functionality can be dramatically influenced by multivalent counterions in the solution environment. In this work, the surface forces apparatus (SFA) and atomic force microscopy (AFM) were used to investigate the effects of three alkaline earth divalent cations, Mg2+, Ca2+, and Ba2+, on the structures of polystyrenesulfonate (PSS) brushes tethered to mica and silicon oxide surfaces. While all these ions caused significant shrinkage of the height of the PSS brushes, strong ion-specific effects were observed. Mg2+ and Ca2+ caused homogeneous shrinkage; Ba2+ led to pinned-micelle like inhomogeneous structures. Isothermal titration calorimetry (ITC) demonstrated that this ion specificity was mainly caused by the difference in binding energy between sulfonate groups and the divalent cations. Considering the abundance of divalent cations in industrial processes, natural environments, and biological systems, the understanding of strong ion-specific effects of divalent counterions is of great importance for theoretical studies and various applications involving polyelectrolytes.

Construction of controllable polyethylene glycol bioactive coating with hemocompatibility from the surface of modified glass substrate

A diblock copolymer, poly(ethylene glycol) methacrylate-block-glycidyl methacrylate (PEGMA-GMA), was prepared on glass substrate by surface-initiated atom transfer radical polymerization (SI-ATRP), and endothelial specific peptide Arg-Glu-Asp-Val (REDV) was immobilized at the end of the PEGMA-GMA polymer brush by ring opening reaction through the rich epoxy groups in the GMA. The structure and hydrophilicity of the polymer brushes were characterized by static water contact angle, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results showed that the REDV modified copolymer brushes were successfully constructed on the glass substrates. The REDV peptide immobilized onto surface was quantitatively characterized by ultraviolet-visible spectroscopy (UV-VIS). The blood compatibility of the coating was characterized by recalcification time and platelet adhesion assay. The results showed that the polymer coating had good blood compatibility. The multifunctional active polymer coating with PEGMA and peptide produced an excellent prospect in surface construction with endothelial cells selectivity.

Structure and properties of polydisperse polyelectrolyte brushes studied by self-consistent field theory.

Two complementary self-consistent field theoretical approaches are used to analyze the equilibrium structure of binary and ternary brushes of polyions with different degrees of polymerization. Stratification in binary brushes is predicted: the shorter chains are entirely embedded in the proximal sublayer depleted of end-points of longer chains while the peripheral sublayer contains exclusively terminal segments of longer chains. The boundary between sublayers is enriched with counterions that neutralize the residual charge of the proximal sublayer. These analytical predictions for binary brushes are confirmed and extended to ternary brushes using the numerical Scheutjens-Fleer approach.

Photoactive Surface‐Grafted Polymer Brushes with Phthalocyanine Bridging Groups as an Advanced Architecture for Light‐Harvesting

Surface-grafted polymer brushes of novel ladder-like architecture were proposed for inducing ordering of chromophores embedded therein. The brushes with acetylene side groups were obtained by surface-initiated photoiniferter-mediated polymerization. The acetylene moieties reacted then through a "click" process with an axially azide-bifunctionalized silicon phthalocyanine bridging the neighboring chains that inherently adopt extended conformations in dense brushes. FTIR, quartz crystal microbalance, and atomic force microscopy were used to study formation and structure of the photoactive brushes varying in grafting densities. Importantly, photophysical properties of the chromophores were virtually unaffected upon embedding them into the brushes, as evidenced by UV/Vis absorption and emission spectroscopy. Owing to the unique ordering of the chromophores, the proposed method may open new opportunities for the fabrication of light-harvesting systems suitable for photovoltaic or sensing applications.

Conventional and rare-patched rod/coil matrix-dispersed patternings on single crystals affected by Rigidity, amorphism and crystallinity of brushes

Novel mixed-brushes subsuming rod-amorphous coil (polyaniline (PANI)-poly(styrene) (PS) or poly(methyl methacrylate) (PMMA)) and rod-crystallizable coil (PANI-poly(ε-caprolactone) (PCL) or poly(L-lactide) (PLLA)) were designed via growth of the single crystals of aforementioned materials block copolymers with poly(ethylene glycol) (PEG). In all rod-amorphous coil mixed-brushes, irrespective of the type of amorphous brushes (PS or PMMA), a matrix of amorphous coily brushes and disperses of conductive PANI nanorods were detected. Based on selected area electron diffraction (SAED) patterns obtained from the rod-crystallizable coil mixed-brushes, the presence of PANI nanorods induced a crystallinity to the crystallizable PCL and PLLA coily brushes, leading to the pseudorigid (crystalline brushes)-rigid (PANI nanorods) mixed-brushes. The rare-patched surface morphologies were acquired for both PANI-PCL and PANI-PLLA rod-coil brushes. Although the thicknesses and lateral sizes of PCL (2.3–4.6nm and 13.9–14.4nm) and PLLA (4.4–7.6 and 13.3–13.8nm) patches were different, their growth prisms were similar, i.e., (110) and (200). The PANI nanorod diameters ranged in 6–10 for rod-amorphous systems, and were 6 and 7nm in rod-crystalline ones. In addition to the osmotic pressure, the difficulty of arranging the crystallizable coily brushes in the crystalline structure of brushes could make further difficult the incorporation of their PEG blocks into the substrate. Hence, the rod and crystalline brushes were in the role of matrix and disperse, respectively. Generally, various morphologies in rod-crystalline and rod-amorphous mixed-brush single crystals were originated from a variance in the rigidity of rod and neighboring brushes as well as the difficulty of the entrance of different brushes into the systems.

Structure and lubrication of solvent-free dendron brushes

Using analytical and numerical self-consistent field (SCF) methods we analyze equilibrium structure of dry (solvent-free) brush of branched polymers in wide range of chain grafting densities. A detailed analysis is performed for starlike polymers end-tethered to planar surface by terminal monomer of one of their branches. At moderate grafting densities ensuring Gaussian elasticity of tethered stars the brush structure is described by strong stretching SS-SCF theory employing parabolic molecular potential. At high grafting densities an approximate analytical AA-SCF theory is used to describe stratification of dry brush. Analytical predictions are supplemented by results of numerical Scheutjens-Fleer SF-SCF model. Interpenetration between dry brushes is analyzed as a function of grafting density and degree of branching of tethered chains. Comparison of interpenetration and friction between dry brushes with varied chain architectures pointed at optimal lubrication by macrocycles tethered to the surface by branching point. It is demonstrated that shear stress in sliding brushes of starlike macromolecules sharply decreases at high grafting densities corresponding to almost full stretching of the longest elastic path in the polymers.

Scattering properties and internal structure of magnetic filament brushes

Practical applications of polymer brush-like systems rely on a clear understanding of their internal structure. In the case of magnetic nanoparticle filament brushes, the competition between bonding and nonbonding interactions-including long range magnetic dipole-dipole interactions-makes the microstructure of these polymer brush-like systems rather complex. On the other hand, the same interactions open up the possibility to manipulate the meso- and macroscopic responses of these systems by applying external magnetic fields or by changing the background temperature. In this study, we put forward an approach to extract information about the internal structure of a magnetic filament brush from scattering experiments. Our method is based on the mapping of the scattering profiles to the information about the internal equilibrium configurations of the brushes obtained from computer simulations. We show that the structure of the magnetic filament brush is strongly anisotropic in the direction perpendicular to the grafting surface, especially at low temperatures and external fields. This makes slice-by-slice scattering measurements a technique very useful for the study of such systems.

Structure of Polyelectrolyte Brushes in the Presence of Multivalent Counterions

Polyelectrolyte brushes are of great importance to a wide range of fields, ranging from colloidal stabilization to responsive and tunable materials to lubrication. We synthesized high-density polystyrenesulfonate (PSS) brushes using surface initiated atom transfer radical polymerization and performed neutron reflectivity (NR) and surface force measurements using a surface forces apparatus (SFA) to investigate the effect of monovalent Na+, divalent Ca2+, Mg2+, and Ba2+, and trivalent Y3+ counterions on the structure of the PSS brushes. NR and SFA results demonstrate that in monovalent salt solution the behavior of the PSS brushes agrees with scaling theory well, exhibiting two distinct regimes: the osmotic and salted brush regimes. Introducing trivalent Y3+ cations causes an abrupt shrinkage of the PSS brush due to the uptake of Y3+ counterions. The uptake of Y3+ counterions and shrinkage of the brush are reversible upon increasing the concentration of monovalent salt. Divalent cations, Mg2+, Ca2+, and Ba2...

Side chain effects in the packing structure and stiffness of redox-responsive ferrocene-containing polymer brushes

This paper describes the preparation of ferrocene-containing polymer brushes with different side chain lengths by surface-initiated atom transfer radical polymerization (SI-ATRP). The polymer brushes are characterized by cyclic voltammetry to determine the surface coverage of the ferrocene (Fc) units, their thickness in air by atomic force microscopy (AFM) and ellipsometry, and their mechanical properties by AFM-based nanoindentation. The results are compared against an ideal packing model and we conclude that brushes with short linkers between the Fc units and the polymer back bone are stiff and stand up in air up to 40nm tall. In contrast, polymers with long linkers collapse and do not stand up in air. Our results indicate that the stiffness and packing structure of Fc-containing polymer brushes are affected by the length of the linkers between the Fc and polymer back bone.

The structure of brushes made of dendrimers: Recent advances

Abstract In recent publications, a couple of theoretical models, ranging from simple scaling approaches and box-like mean-field models to self-consistent field techniques, have been proposed to describe the structure of brushes that are composed of dendrimers. In this work, we carry out molecular dynamics simulations in various density regimes, and compare the resulting data with predictions of the latest theoretical models. This study enables us to access the ranges of validity and accuracy of the respective models, as well as their shortcomings. Significant differences in the predicted conformations of the dendrimers are observed and analyzed in the context of their elastic properties in the different models. This work offers guidelines for future research directions, which may lead to further progress regarding the understanding of branched polymer brushes.

The effect of multivalent counterions to the structure of highly dense polystyrene sulfonate brushes

Surface tethered polyelectrolyte brushes are scientifically interesting and technologically relevant to many applications, ranging from colloidal stabilization to responsive and tunable materials to lubrication. Many applications operate in environments containing multi-valent ions, media in which our scientific understanding is not yet well-developed. We synthesized high-density polystyrene sulfonate (PSS) brushes via surface initiated atom-transfer radical polymerization, and performed neutron reflectivity (NR) measurements to investigate and compare the effects of mono-valent Rb+ and tri-valent Y3+ counterions to the structure of the densely tethered PSS brushes. Our NR results show that in mono-valent RbNO3 solution, the dense PSS brush retained its full thickness up to a salt concentration of 1 M, whereas it immediately collapsed upon adding 1.67 mM of tri-valent Y3+. Increasing the concentration of Y3+ beyond this level did not lead to any significant further structure change of the PSS brush. Our findings demonstrate that the presence of multi-valent counterions can significantly alter the structure of polyelectrolyte brushes, in a manner different from mono-valent ions, which has implications for the functionality of the brushes.