Polymer-grafted Surface Research Articles

Ultrastable highly-emissive amphiphilic perovskite nanocrystal composites via the synergy of polymer-grafted silica nanoreactor and surface ligand engineering for white light-emitting diode

Instability of perovskite nanocrystals driven by their ionic crystal characteristic poses a grand challenge for long-term practical applications in optoelectronic materials and devices. Herein, we report the crafting of amphiphilic perovskite nanocrystal composites (APNCCs) with a set of markedly improved stabilities via capitalizing on polymer-grafted silica nanosheets as nanoreactors in conjunction with surface ligand engineering. First, SiO2 nanosheets grafted with poly(acrylic acid)-block-polystyrene (denoted SiO2 @PAA-b-PS) are rationally designed and exploited as nanoreactors to form SiO2 @CsPbBr3 @PS. Subsequent passivation with small-molecule ligands (L) yields highly emissive SiO2 @CsPbBr3 @ (PS/L) APNCCs with an array of outstanding stabilities against UV, heat, water, long-term storage, and various polar organic solvents. Remarkably, our strategy integrating polymer-grafted SiO2 nanosheet nanoreactor with surface ligand engineering is general and viable. A diversity of stable APNCCs can be readily created. Finally, white light-emitting diode (WLED) with wide color gamut and excellent stability composed of green-emitting SiO2 @CsPbBr3 @ (PS/L) APNCCs is demonstrated. This work highlights the robustness of the synergy of judiciously-designed nanoreactor and surface ligand engineering to produce highly emissive, ultrastable perovskite nanocrystals shielded with soft and hard materials (i.e., possessing a Janus surface chemistry).

Optical measurement platform of temperature-dependent interaction between nanoliposomes and a polymer-grafted surface.

In this study, we report an opto-microfluidic platform integrated with dark-field light scattering imaging and fluorescence microspectroscopy to investigate the temperature-dependent behavior of nanoliposomes. This newly developed experimental platform enabled both in situ measurements of the temperature of the sample solution and observation of individual nanoliposomes. As a proof-of-concept, the temperature-dependent interaction between 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) nanoliposomes and a poly(ethylene glycol) (PEG) grafted surface was investigated using this opto-microfluidic platform. Temperature-dependent detachment behavior of DLPC nanoliposomes, which was because of the phase transition of DLPC, was observed. The opto-microfluidic platform for individual nanoparticle measurements may become a powerful tool for investigating temperature-dependent physicochemical properties of nanoparticles in aqueous solution.

FE-CLIP: A tool for the calculation of the solid–liquid interfacial free energy

In manufacturing industries, predicting the work of adhesion between complex solid and liquid surfaces has become essential. FE-CLIP offers a routine for evaluating the work of adhesion between solid and liquid surfaces by calling a subroutine from a molecular dynamics simulation code. When FE-CLIP is applied to the solid–liquid interface, liquid molecules are separated from the solid surface according to its shape using a set of spherical potentials. This is efficient when applied to the solid surfaces with complex structures such as polymer-grafted surfaces. An adaptive scheme for updating the parameters contained in the potential and automatic refinement of integration points are introduced to facilitate the application of FE-CLIP to various solid–liquid interfaces. We applied FE-CLIP to the separation of water from a polymer-grafted gold surface to demonstrate that the proposed method gives reliable results by suppressing the variation of the free energy gradient, which is important for accurate numerical integration. Program summaryProgram Title: FE-CLIPProgram Files doi:http://dx.doi.org/10.17632/7gmcvftfwj.1Licensing provisions: GPLv3Programming language: FortranNature of problem: The adhesion free energy of liquid–solid interfaces is one of the important properties for their industrial application. FE-CLIP enables quantitative evaluation of the strength of adhesion between solid and liquid surfaces using a molecular dynamics simulation. Unlike other existing methods, FE-CLIP is efficiently applicable to complex solid surfaces such as polymer-grafted surfaces.Solution method: The work of adhesion between solid and liquid surfaces is calculated using thermodynamic integration. The integration parameters of thermodynamic integration are the diameter and depth of artificial potentials of the Lennard-Jones-type, whose variation contributes to separating the liquid molecules from a solid surface. By putting a set of spherical potentials, the liquid on the solid surface is separated according to the surface shape. In addition, the parameters of the potentials are automatically updated so as to suppress the variation of the free energy gradient.

Smart MD-Sampling Method for Interfacial Free Energy between Polymer-Grafted Substrate and Liquid

ABSTRACTA novel and efficient scheme for evaluating the work of adhesion between a liquid and a polymer-grafted surface is proposed. A set of spherically symmetric potentials are gradually inserted at the interface to separate the liquid molecules from the surface according to its shape. This method is applied to the interface between the water and the gold substrate modified by poly(ethylene glycol). We find that the work of adhesion becomes maximum at the intermediate density of grafted poly(ethylene glycol). This is attributed to penetration of the water molecules into grafted poly(ethylene glycol) and hydrophilic interaction between them.

解離型分子を介した抗体固定化グラフト表面を用いた選択的な細胞捕獲・回収による細胞分離

解離型分子を介した抗体固定化グラフト表面を用いた選択的な細胞捕獲・回収による細胞分離

Grafting zwitterionic polymer onto cryogel surface enhances protein retention in steric exclusion chromatography on cryogel monolith

Cryogel monoliths with interconnected macropores (10–100μm) and hydrophilic surfaces can be employed as chromatography media for protein retention in steric exclusion chromatography (SXC). SXC is based on the principle that the exclusion of polyethylene glycol (PEG) on both a hydrophilic chromatography surface and a protein favors their association, leading to the protein retention on the chromatography surface. Elution of the retained protein can be achieved by reducing PEG concentration. In this work, the surface of polyacrylamide-based cryogel monolith was modified by grafting zwitterionic poly(carboxybetaine methacrylate) (pCBMA), leading the increase in the surface hydrophilicity. Observation by scanning electron microscopy revealed the presence of the grafted pCBMA chain clusters on the cryogel surface, but pCBMA grafting did not result in the changes of the physical properties of the monolith column, and the columns maintained good recyclability in SXC. The effect of the surface grafting on the SXC behavior of γ-globulin was investigated in a wide flow rate range (0.6–12cm/min). It was found that the dynamic retention capacity increased 1.4–1.8 times by the zwitterionic polymer grafting in the flow rate range of 1.5–12cm/min. The mechanism of enhanced protein retention on the zwitterionic polymer-grafted surface was proposed. The research proved that zwitterionic polymer modification was promising for the development of new materials for SXC applications.

High capacity cryogel-type adsorbents for protein purification

Cryogel bodies were modified to obtain epoxy groups by graft-copolymerization using both chemical and gamma irradiation initiation techniques. The free epoxy adsorbents were reacted further to introduce diethylaminoethanol (DEAE) functionalities. The resulting weak anion-exchange cryogel adsorbents showed dynamic binding capacities of ca. 27±3mg/mL, which was significantly higher than previously reported for this type of adsorbent material. Gamma irradiated grafting initiation showed a 4-fold higher capacity for proteins than chemical grafting initiation procedures. The phosphate capacity for these DEAE cryogels was 119mmol/L and also showed similar column efficiency as compared to commercial adsorbents. The large pores in the cryogel structure ensure convective transport of the molecules to active binding sites located on the polymer-grafted surface of cryogels. However, as cryogels have relatively large pores (10–100μm), the BET area available for surface activation is low, and consequently, the capacity of the cryogels is relatively low for biomolecules, especially when compared to commercial beaded adsorbents. Nevertheless, we have shown that gamma ray mediated surface grafting of cryogel matrices greatly enhance their functional and adsorptive properties.

Fabrication of 3D Gradient of Polymer Brush Via Bipolar Electrochemical Method

Conducting substrates placed between driving electrodes are polarized by external electric field. When the external electric field is large enough, the substrate can behave as a bipolar electrode (BPE) possessing both anodic and chathodic surfaces with potential gradient. Bipolar electrochemical method is an ideal candidate for creating gradient materials by using its potential gradient. For example, we have reported the use of BPE for the gradient modification of conducting polymer surfaces [1]. In this study, we demonstrate the precise control of electrochemical introduction of small molecules onto BPE using bipolar electrochemistry, and following surface-initiated atom transfer radical polymerization (SI-ATRP) to give polymer-grafted surfaces with density gradient. Bipolar electrolysis and surface analysis; An aqueous solution of 1 mM of 4-(2-hydroxyethyl)phenyldiazonium tetrafluoroborate (for the attachment of phenethylalcohol moiety through cathodic reduction) and 1 mM of hydroquinone (as a sacrificial reagent at anodic oxdation) was used as electrolyte in a setup equipped with a pair of platinum electrodes (20 x 20 mm) as driving electrodes, and ITO electrode (20 x 5 mm) as BPE. After the bipolar electrolysis was conducted, the obtained phenethylalcohol-modified ITO plate were washed with solvents, and subjected into a solution of dichloromethane containing 0.5 M 2-bromoisobutyryl bromide and 0.05 M triethylamine for 3 h to achieve the surface with ATRP initiator. To estimate the contents of the ATRP-initiator on the substrate, the elemental ratio of C, O, N, and Br was calculated by X-ray photoelectron spectroscopy (XPS). The XPS analysis for each position of the initiator-modified substrate showed the gradual increase of bromine contents (derived from initiator moiety) with approaching to the cathodic surface. This result indicates that the electrochemical reactions successfully took place on the BPE, accompanying with the formation of density gradient of ATRP initiator. Moreover, by tuning the parameters such as voltage and reaction time, the steepness of the profile of bromine contents was successfully controlled. SI-ATRP; Surface-initiated polymerization of methyl methacrylate (MMA) was conducted under general conditions of ARGET-ATRP with the ITO substrate prepared above ([MMA]0/[free Initiator]0/[CuBr2]0/[bipyridine]0/[sodium ascorbate]0=1000/1/0.035/3.5/3.5), in the presence of the free initiator to estimate the degree of polymerization of PMMA. The density gradient of the grafted polymer was analyzed by infrared reflection absorption spectroscopy (IR-RAS). IR-RAS results measured at each position showed the gradual increase of absorption derived from PMMA from anodic surface to cathodic surface in a similar manner to the XPS results of the initiator-modified substrate. Thus the fabrication of polymer-grafted surface with density gradient was successfully demonstrated. Finally, the measurement of thickness of the polymer-grafted surface by stylus type surface roughness tester revealed that the thickness was dependent on the density of the initiator modified, showing 3D gradient of the polymer brush. Reference [1] N. Shida, Y. Ishiguro, M. Atobe, T. Fuchigami, S. Inagi, ACS Macro Lett., 2012, 1, 656-659.

Synthesis and characterization of poly[1-(N,N-bis-carboxymethyl)amino-3-allylglycerol-co-dimethylacrylamide] grafted to magnetic nano-particles for extraction and determination of letrozole in biological and pharmaceutical samples

In this paper, a new method is reported for the surface grafting of poly[1-(N,N-bis-carboxymethyl)amino-3-allylglycerol-co-dimethylacrylamide] onto magnetic nano-particles modified by 3-mercaptopropyltrimethoxysilane. The grafted nano-sorbent was characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and scanning electron microscopy. Agglomerated nano-particles with multi-pores were used for extraction and determination of trace letrozole in human biological fluids and pharmaceutical samples. The profile of the letrozole uptake by the magnetic nano-sorbent reflected good accessibility of the active sites in the grafted polymer. Scatchard analysis revealed that the sorption capacity of the functionalized nano-sorbent was 6.27 µmol g(-1) at an optimum pH of 4. The equilibrium adsorption data of letrozole by grafted magnetic nano-sorbent were analyzed by Langmuir, Freundlich, Temkin and Redlich-Peterson models. Conformation of the experimental data in the Langmuir isotherm model indicated the homogeneous binding site of functional polymer-grafted magnetic nano-sorbent surface. Nearly 89% of letrozole was released in simulated gastric fluid, pH 1.2, in 2h and 79% in simulated intestinal fluid, pH 7.4, in 30 h. These results show the utility of the letrozole loaded- polymer grafted magnetite nano-particles for enteric drug delivery.

Elastic Properties of a Protein–Polymer-Grafted Surface

Surfaces grafted with poly(methyl methacrylate) (PMMA) and streptavidin were synthesized through click chemistry to investigate the role of surface stiffness on protein adsorption as the hydrophilic and hydrophobic surface coverage of the substituents vary. Surface topographies coupled with the nanoindentation results indicated that, with the appropriate selections of polymer coverage and chain length, the extent of non-specific protein adhesion could be controlled by the hydrophobic interactions between PMMA, biotin, and streptavidin. It was shown that, when the molecular weight and stiffness of PMMA was close to that of streptavidin, patchy PMMA morphologies were obtained, which help inhibit the non-specific adsorption of streptavidin.

Preparation of Antibacterial Polymer-Grafted Silica Nanoparticle and Surface Properties of Composites Filled with the Silica (2)

Antibacterial polymer was grafted onto silica nanoparticle and the surface properties of various composites filled with the silica were investigated. The grafting of antibacterial polymer, poly(vinylbenzyltributylphosphonium chloride) (poly(St-CH2P+(Bu) 3Cl−)), onto silica surface was achieved by two methods: one is treatment of poly(vinylbenzylchloride) (poly(St-CH2Cl))-grafted silica with tributylphosphine and the other is direct grafting of poly(St-CH2P+ (Bu)3Cl−) by radical graft polymerization of the corresponding monomer. The grafting of poly(St-CH2Cl) and poly(St-CH2P+ (Bu)3Cl−) onto silica surface were initiated by the system consisting of trichloroacetyl groups on the silica surface and Mo(CO) 6. Trichloroacetyl groups were introduced onto the silica surface by the reaction of amino groups on the silica surface with trichloroacetyl isocyanate. The percentage of poly(St-CH2Cl) grafting during the graft polymerization initiated by the system increased with progress of the polymerization reached 116%. The grafting of poly(St-CH2P+ (Bu)3Cl−) onto silica surfaces was confirmed by FT-IR spectra, thermal decomposition gas chromatograms and mass spectra (GC-MS), and 13C-CP/MAS NMR. The surfaces of silicone rubber, polystyrene film, and paints filled with the poly(St-CH2P+ (Bu)3Cl−)-grafted silica shows strong antibacterial activity. These composites retained the antibacterial activity even after the boiling in water for 24 h.

Phase diagram of diblock copolymer confined in a cylindrical nanopore with polymer-grafted surface

Using self-consistent field calculation, the new equilibrium morphology of a diblock copolymer melt confined in a brush_covered cylindrical nanopore can be found. The morphology is formed as a function of brush density and A-monomer fraction f. When f=0.7, due to the wetting effect produced by polymer brush the outside concentric lamellar ring will come up again with increasing φAB. We carefully examined the intermediate phases and discovered a rich variety of new two_dimensional structures that have no analogue in the unconfined system, which include nonhexagonally coordinated cylinder phases and structures intermediate between lamellae and cylinders, like CRCR, when f=0.35. Then we map the stability regions and phase boundaries for all the structures we found.

Patterned Immobilization of Unprotected Carbohydrates on an Aminooxy Polymer-Grafted Solid Surface

Abstract We describe a graft-type modification of a solid surface to be able to immobilize unprotected carbohydrates with a desired pattern. Water soluble carbohydrate-trapping polymers were grown from a solid surface through surface-initiated polymerization. The polymerization of an N-tert-butonyloxycarbonyl (N-Boc)-protected aminooxy monomer 3 was carried out from the immobilized initiator on silicon or glass surfaces. The N-Boc protecting group was then removed in an acidic solution to generate an aminooxy group, which reacts with free carbohydrates through oxime bonds on immersion of the plate in a carbohydrate solution. Sugar attachment on the surface polymer was confirmed by using infrared reflection absorption spectroscopy (IR-RAS) and fluorescent images after sugar-specific binding of fluorescein-labeled lectin proteins. The polymer was also grafted in a desired pattern by partial UV-irradiation over a photomask, giving a new material to create carbohydrates arrays.

Preparation of Antibacterial Polymer-grafted Nano-sized Silica and Surface Properties of Silicone Rubber Filled with the Silica

Antibacterial polymer was grafted onto nano-sized silica surface and the surface properties of silicone rubber filled with the silica were investigated. The grafting of antibacterial polymer was carried out by two-step reactions as follows. Poly(p-styrene sodium sulfate) (poly(St-SO3−Na+)) was successfully grafted onto nano-sized silica surface by the radical polymerization of St-SO3−Na+ initiated by the system consisting of trichloroacetyl groups on the silica surface and Mo(CO)6: trichloroacetyl groups were introduced onto the silica surface by the reaction of amino groups with trichloroacetyl isocyanate. The percentage of poly(St-SO3−Na+) grafting increased with progress of the polymerization and reached about 30%. The poly(St-SO3−Na+)-grafted silica was treated with tributyltetradecylphosphonium chloride (Bu3RP+Cl−) to convert the SO3−Na+ groups to alkyl phosphonium salt, SO3−P+Bu3R, groups. The grafting of poly(St-SO3−P+Bu3R) onto the silica surface was confirmed by IR spectra. The poly(St-SO3−P+Bu3R)-grafted silica gave a stable dispersion in DMSO and poly(dimethylsiloxane). It was found that silicone rubber filled with the poly(St-SO3−P+Bu3R)-grafted silica shows extremely strong antibacterial activity. The silicone rubber surface has an ability to inhibit the reproduction of a Staphylococcus aureus and an Escherichia coli.

PH-dependent elution profiles of selected proteins in HPLC having a stationary phase modified with pH-sensitive sulfonamide polymers

An approach to controlling protein interactions with silica (glass) beads grafted with pH-sensitive copolymers of a sulfonamide and N, N-dimethylacrylamide is proposed. The bead surface was modified with poly(N, N-dimethyl acrylamide-co-methacryloyl sulfadimethoxine), which exhibits hydrophobic/hydrophilic switching around pH 7.0. Phase transition in the aqueous solution, the wettability change of the modified surface and surface tension of the polymer-grafted glass surface was characterized by changes in turbidity and the dynamic contact angle as a function of pH. The discontinuous phase transition in the copolymer solution shifted to a higher pH region as the composition of sulfadimethoxine monomer (SDM) was increased. However, the transition pH in continuous wettability changes on the modified surface was not affected by polymer composition due to differences in the dynamic motion. The ionized SDM of the copolymers enhanced wettability. Therefore, the advancing contact angle of the surface decreased by 45° above pH 7.0, whereas wettability at low pH values was low due to the hydrophobic surface. Elution behavior of the selected four model proteins with different pI (bovine serum albumin (pI 5.0), insulin (pI 5.3), fibrinogen (pI 6.1) and myoglobin (pI 7.1)) was investigated by using pH-sensitive copolymer-modified glass beads at four pH values (5.0, 6.0, 7.0 and 8.0). Retention time of the proteins in pH-sensitive aqueous chromatography was easily regulated by eluent pH that controls the proportion of electrostatic and hydrophobic interactions between the stationary phase and the protein. At pH 5.0, hydrophobic interaction on the deionized polymer-grafted surface is an important force in separating the proteins. However, identification of the proteins at pH 7.0 was effectively facilitated due to the electrostatic interaction between the negatively charged polymer support and positive charges on protein.

Effects of polymer grafting on a glass surface for protein chip applications

Glass surfaces were modified using several hydrophilic polymers for the fabrication of protein chips and biosensors. Surface activation was carried out by silanization, and polymer films were introduced to the glass substrates by using two methods. First, preformed amino group containing polymers, capable of reacting with appropriate surface sites, were coupled to the glass substrates. Second, polymer layers were formed by free radical chain polymerization using immobilized initiators. Covalent binding and non-specific antibody adsorption were examined by quantifying IgG-peroxidase conjugates immobilized to the polymer-grafted glass substrates. Polymer-grafted glass substrates showed that non-specific adsorption was reduced by 10–60% as compared with 3-aminopropyltriethoxysilane (APTS)-treated substrate. In particular, chitosan-grafted substrates exhibited very low non-specific protein adsorption. Despite this protein-rejecting phenomenon of the surface-bound polymer, the quantity of antibodies immobilized by covalent binding to the polymer-grafted glass substrates was comparable to that immobilized on the non-polymer-grafted surface. We also performed a protein patterning experiment on the polymer-grafted surface by using maskless photolithography. We found that the chitosan-grafted glass substrate, with good protein repellency, displayed a very clear streptavidin-patterned surface.

Protein patterning by maskless photolithography on hydrophilic polymer-grafted surface

With the help of a microfabrication process and surface modification technology, a method of fabricating protein patterned chips was developed which can be utilized as a powerful tool for performing bioassays in a high-throughput manner. A digital micromirror array (MMA) system was used as a virtual photomask, so that a maskless photolithography process was able to be used to build patterned biomolecules on a chip by selective illumination onto the chip surface. We utilized the nitroveratryloxycarbonyl (NVOC) group as a photolabile protecting group for protein patterning. The NVOC-protected surface was selectively irradiated by a UV illuminator using an MMA. After removing the NVOC group, biotin was coupled to the NVOC-cleaved site, onto which a buffered streptavidin solution was eluted. At this point, we could obtain a streptavidin-patterned surface and observe the effect of the polymer-grafted surface in reducing nonspecific binding.

Temperature-responsive chromatographic separation of amino acid phenylthiohydantions using aqueous media as the mobile phase.

Recently, green chemistry has become one of the most important subjects of science for environmental pollution prevention. Here, we report development of a novel chromatographic technology for phenylthiohydantoin (PTH)-amino acid analyses in which only aqueous solution is used as the mobile phase. We have devised HPLC adsorbents (stationary phase) by modifying the surfaces of microparticulate silica gel using functional polymers. The thermoresponsive copolymer, poly(N-isopropylacrylamide-co-n-butyl methacrylate) (IBc) was used to modify the silica stationary phase surfaces. This polymer-grafted surface exhibits temperature-regulated hydrophilic/hydrophobic property changes in water. PTH-amino acid interactions with this surface are readily modulated by changing the column temperature using an isocratic aqueous mobile phase. Increasing hydrophobic interactions between more hydrophobic PTH-amino acids with hydrophobized polymer-grafted surfaces at elevated mobile phase temperatures is used for the effective separation of PTH-amino acids in aqueous solution. This study is aimed at the development of novel separation processes, which are also environmentally benign, for use with biochemical substances in order to meet the growing needs of the life sciences and biotechnology. The method is useful for various separations in life science so that proteins can maintain their biological activity and enzymes, their enzymatic activity.

Ultrastructure of the interface between cultured osteoblasts and surface-modified polymer substrates.

Osteoblasts derived from rat bone marrow cells were cultured on surface-modified poly(ethylene terephthalate) films in the presence of ascorbic acid, beta-glycerophosphate, and dexamethasone. The surfaces employed for cell culture included the untreated hydrophobic surface and three modified surfaces possessing immobilized phosphate polymer chains, collagen molecules, and a thin hydroxyapatite-deposited layer. They all were produced by photo-induced graft polymerization with subsequent surface modifications of the graft chains. The ultrastructural morphology of the substrate/cell interfaces formed in in vitro osteoblast culture on these substrates was studied by transmission electron microscopy. The osteoblasts cultured for 1 week on the modified surfaces showed rough endoplasmic reticula rich in intracellular space and early matrix production in the extracellular space, irrespective of the surface chemistry. After 2 weeks of culture, osteoblasts exhibited active elaboration of extracellular matrix proteins, mostly composed of collagen, on all the surfaces. A remarkable result observed at this stage was direct deposition of an electron-dense, afibrillar layer of 180 nm thickness onto the surface having phosphate polymer chains. This layer became much more electron dense after 3 weeks of culture. Energy dispersive X-ray microanalysis revealed the presence of calcium phosphate in this layer. It was further found that the predeposited hydroxyapatite layer on the phosphate polymer-grafted surface promoted mineral deposition in the extracellular matrix that surrounded cuboid, osteocyte-like cells.

Pivot Algorithm Computer Simulation of the Effect of Grafted Polymers on the Adsorption of Polymers by a Surface

Monte Carlo simulations are used to calculate monomer distribution profiles and adsorption isotherms of moderately dense end-grafted and adsorbed polymer chains. Modified variants of the pivot algorithm on a cubic lattice are combined with a fixed end points pivot algorithm to allow simulation in regimes where normal pivoting is ineffective due to excluded volume effects. Scaling behavior that agrees with analytical theory for low density and a brush is obtained for the end-grafted case, which illustrates the accuracy of this method applied to polymers that are overlapping. For polymers in the solution phase a Monte Carlo move of the center of mass of the polymer is added to the normal pivot moves. The surface excess is obtained by integrating O(z)-Ob and can be treated by the Langmuir model to obtain the apparent maximum surface excess (Γ exc max ) as a function of the bulk monomer concentration (O b ). It is found that the presence of end-grafted nonadsorbing polymers can affect competitive adsorption of different length chains. In particular, high molecular weight polymers may be preferentially excluded from a polymer-grafted surface, unlike a bare surface.