Nanowear studies in chemically heterogeneous responsive polymeric brushes by surface force microscopy

In this study, we present nanowear studies using surface force microscopy (SFM), on nanoscopic thin films of reversibly switchable binary polymer brushes [polystyrene (PS) + poly(2-vinylpyridine) (P2VP)] and respective monobrushes [polystyrene and poly(2-vinylpyridine)] synthesized via “grafting to” method. The aim was to tune the wear in nanothin polymer brush surfaces. Therefore, the effect of conformational switching of PS + P2VP brush on treatment with selective solvents for PS and P2VP chains on the wear process was investigated. Wear process on thick spin-coated films of PS and P2VP was also investigated for comparison. Nanowear experiments were performed using SFM tip by repeating scans over the surface to follow the wear process closely. The wear process on different surfaces was explained on the basis of molecular entanglement as well as adhesion and friction on the sample surface. For spin-coated PS film as well as PS and PS + P2VP brush surfaces (treated with toluene) with molecular entanglements at surface, wear mechanism involved formation of ripples. However, in case of spin-coated P2VP films as well as P2VP and PS + P2VP brush surfaces (treated with ethanol) with no molecular entanglements at surface, wear occurred via removal of polymer chains and their accumulation at the rim. For PS + P2VP surface treated with acidic water, wear mechanism was complex and inhomogeneous ripple formation was followed by formation of heaps of polymeric material in the center of scanned area. The extent of wear as measured either by root mean square roughness of the surface or spacing between the ripples, increased with the number of scans for all the surfaces. Our study shows that wear mode of polymer brush surfaces is different for different polymers and can be controlled/tuned by the use of binary polymer brushes.     

Stimuli-responsive polyelectrolyte block copolymer brushes synthesized from the Si wafer via atom-transfer radical polymerization

Surface-tethered oppositely charged weak polyelectrolyte block copolymer brushes composed of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) were grown from the Si wafer by atom-transfer radical polymerization. The P2VP-b-PAA brushes were prepared through hydrolysis of the second PtBA block to the corresponding acrylic acid. The P2VP-b-PAA brushes with different PAA block length were obtained. The P2VP-b-PAA brushes revealed a unique reversible wetting behavior with pH. The difference between the solubility parameters for P2VP and PAA, the changes of surface chemical composition and surface roughness, and the reversible wetting behavior illustrated that the surface rearrangement occurred during treatment of the P2VP-b-PAA brushes by aqueous solution with different pH value. The reversible properties of the P2VP-b-PAA brushes can be used to regulate the adsorption of the sulfonated PS nanoparticles.     

两亲性杂侧链聚合物刷的合成及其乳化功能

报道了一种随机高密度接枝亲水、疏水聚合物侧链的刷形两亲性聚合物.首先,结合可逆加成-断裂链转移(RAFT)聚合和后修饰方法,得到含叠氮侧基的聚甲基丙烯酸缩水甘油酯(PGMA-N3)作为主链;再分别合成端炔基聚苯乙烯(PS)和端炔基聚环氧乙烷(PEO),然后通过铜催化的叠氮-炔环加成反应,将疏水性PS和亲水性PEO同时高效的接到PGMA主链上,制得两亲性杂侧链的聚合物刷.由凝胶渗透色谱(SEC)分析得知,在主链叠氮基团与两侧链总炔基的摩尔投料比为1∶1的条件下,PS和PEO的接枝效率很高,都大于90%.通过调节主链长度和2种侧链的投料比,获得不同组成的聚合物刷.通过等质量的甲苯/水混合体系,考察两亲性聚合物刷的乳化能力,发现主链聚合度为100,PS∶PEO比例为70∶30的聚合物刷表现出最佳的乳化性能.     

Mixed polymer brushes by sequential polymer addition: anchoring layer effect

Smart surfaces can be described as surfaces that have the ability to respond in a controllable fashion to specific environmental stimuli. A heterogeneous (mixed) polymer brush (HPB) can provide a synthetic route to designing smart polymer surfaces. In this research we study HPB comprised of end-grafted polystyrene (PS) and poly(2-vinyl pyridine) (P2VP). The synthesis of the HPB involves the use of an "intermolecular glue" acting as a binding/anchoring interlayer between the polymer brush and the substrate, a silicon wafer. We compare anchoring layers of epoxysilane (GPS), which forms a self-assembled monolayer with epoxy functionality, to poly(glycidyl methacrylate) (PGMA), which forms a macromolecular monolayer with epoxy functionality. The PS and P2VP were deposited onto the wafers in a sequential fashion to chemically graft PS in a first step and subsequently graft P2VP. Rinsing the HPB in selective solvents and observing the change in water contact angle as a function of the HPB composition studied the switching nature of the HPB. Scanning probe microscopy was used to probe the topography and phase imagery of the HPB. The nature of the anchoring layer significantly affected the wettability and morphology of the mixed brushes.     

Nanowear studies in reversibly switchable polystyrene-poly(acrylic acid) mixed brushes

Wear studies were performed on polystyrene (PS)-poly(acrylic acid) (PAA) mixed polymer brushes and corresponding monobrushes in a dried state. The aim was to study the wear mechanism in polymer brush surfaces as well as to investigate the effect of switching of PS + PAA binary brush surfaces (on treatment with the selective solvents for the PS and PAA) on the wear process. Wear experiments were carried out using atomic force microscopy (AFM) under a controlled environment. The wear experiments were performed as a function of scan number using a sharp silicon nitride tip to induce the wear on the sample surfaces. The wear mechanism on different brush surfaces was influenced by molecular entanglement as well as adhesion and friction on the sample surface. The wear process on the PS monobrush surface treated with toluene took place via formation of the ripples. On the other hand, a typical wear mode observed on the PAA monobrushes was removal of the polymeric material from the surface. For the mixed brush surface treated with toluene (selective solvent for PS) where PS chains dominated the top of the sample surface, the typical wear mode observed was ripple formation similar to that observed for the PS monobrushes. However, when a mixed brush was treated with ethanol and pH 10 water so that PAA chains dominated the top layer, wear occurred via removal of material. The amount of wear on the surfaces increased with the number of scans. Furthermore, the load and scan velocity dependence of the wear process was also investigated. Wear on polymer brush surfaces increased on increasing the load and/or decreasing the scan speed. The present study shows that wear can be controlled/tuned using mixed responsive brushes.     

Functional colloidal particles stabilized by layered silicate with hydrophilic face and hydrophobic polymer brushes

In this study, we describe a new strategy for producing narrowly dispersed functional colloidal particles stabilized by a nanocomposite with hydrophilic clay faces and hydrophobic polystyrene (PS) brushes on the edges. This method involves preparation of polymer brushes on the edges of clay layers and Pickering suspension polymerization of styrene in the presence of the nanocomposites. PS brushes on the edges of clay layers were prepared by atom transfer radical polymerization. X‐ray diffraction and thermogravimetric analysis results indicated that PS chains were grafted to the edges of clay platelets. Transmission electron microscope results showed that different morphologies of clay‐PS particles could be obtained in different solvents. In water, clay‐PS particles aggregated together, in which PS chains collapsed forming nanosized hydrophobic domains and hydrophilic clay faces stayed in aqueous phase. In toluene, clay‐PS particles formed face‐to‐face structure. Narrowly dispersed PS colloidal particles stabilized by clay‐PS were prepared by suspension polymerization. Because of the negatively charged clay particles on the surface, the zeta potential of the PS colloidal particles was negative. Positively charged poly(2‐vinyl pyridine) (P2VP) chains were adsorbed to the surface of PS colloidal particles in aqueous solution at a low pH value, and gold nanoparticles were prepared in P2VP brushes. Such colloidal particles may find important applications in a variety of fields including waterborne adhesives, paints, catalysis of chemical reactions, and protein separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1535–1543, 2009     

Nonwettable thin films from hybrid polymer brushes can be hydrophilic

Hybrid brushes composed of two liquid polymers, poly(dimethylsiloxane) (PDMS) and a highly branched ethoxylated polyethylenimine (EPEI), were synthesized on Si wafers by the "grafting to" method and by applying a combinatorial approach (fabrication of gradient brushes). The combinatorial approach revealed a strong effect of "layer assisted tethering", which allowed us to synthesize hybrid brushes twice as thick as the reference homopolymer brushes. The hybrid brushes are stable thin films that can rapidly and reversibly switch between hydrophilic and hydrophobic states in water and air, respectively. The switching in water affects a rapid release of amino functional groups which can be used to regulate adhesion and reactivity of the material. The switching in air rapidly returns the brush to a hydrophobic state. The hybrid brush is hydrophilic because of two mechanisms: (1) exposure of EPEI chains to the brush-water interface under water, and (2) retention of some fraction of water via swollen EPEI chains (the EPEI chains swell by 2-3 times), which are conserved by a PDMS cap in air. The hybrid brush is wettable under water, and at the same time, the brush is nonwettable in air because water droplets are trapped in a metastable state when the water contact angle is above 90 degrees .     

In-situ investigation of the adsorption of globular model proteins on stimuli-responsive binary polyelectrolyte brushes

Binary brushes constituted from two incompatible polymers can be used in the form of ultrathin polymeric layers as a versatile tool for surface engineering to tune physicochemical surface characteristics such as wettability, surface charge, chemical composition, and morphology and furthermore to create responsive surface properties. Mixed brushes of oppositely charged weak polyelectrolytes represent a special case of responding surfaces that are sensitive to changes in the pH value of the aqueous environment and therefore represent interesting tools for biosurface engineering. The polyelectrolyte brushes used for this study were composed of two oppositely charged polyelelctrolytes poly(2-vinylpyridine) (P2VP) and poly(acrylic acid) (PAA). The in-situ properties and surface characteristics such as as surface charge, surface tension, and extent of swelling of these brush layers are functions of the pH value of the surrounding aqueous solution. To test the behavior of the mixed polylelctrolyte brushes in contact with biosystems, protein adsorption experiments with globular model proteins were performed at different pH values and salt concentrations (confinement of counterions) of the buffer solutions. The influence of the pH value, buffer salt concentration, and isoelectric points (IEP) of the brush and protein on the adsorbed amount and the interfacial tension during protein adsorption as well as the protein adsorption mechanism postulated in reference to recently developed theories of protein adsorption on polyelectrolyte brushes is discussed. In the salted regime, protein adsorption was found to be similar to the often-described adsorption at hydrophobic surfaces. However, in the osmotic regime the balance of electrostatic repulsion and a strong entropic driving force, "counterion release", was found to be the main influence on protein adsorption.     

Wetting transition on hydrophobic surfaces covered by polyelectrolyte brushes

We study the wetting by water of complex "hydrophobic-hydrophilic" surfaces made of a hydrophobic substrate covered by a hydrophilic polymer brush. Polystyrene (PS) substrates covered with polystyrene- block-poly(acrylic acid) PS- b-PAA diblock copolymer layers were fabricated by Langmuir-Schaefer depositions and analyzed by atomic force microscopy (AFM) and ellipsometry. On bare PS substrate, we measured advancing angles theta A = 93 +/- 1 degrees and receding angles theta R = 81 +/- 1 degrees . On PS covered with poorly anchored PS- b-PAA layers, we observed large contact angle hysteresis, theta A approximately 90 degrees and theta R approximately 0 degrees , that we attributed to nanometric scale dewetting of the PS- b-PAA layers. On well-anchored PS- b-PAA layers that form homogeneous PAA brushes, a wetting transition from partial to total wetting occurs versus the amount deposited: both theta A and theta R decrease close to zero. A model is proposed, based on the Young-Dupre equation, that takes into account the interfacial pressure of the brush Pi, which was determined experimentally, and the free energy of hydration of the polyelectrolyte monomers Delta G PAA (hyd), which is the only fitting parameter. With Delta G PAA (hyd) approximately -1300 J/mol, the model renders the wetting transition for all samples and explains why the wetting transition depends mainly on the average thickness of the brush and weakly on the length of PAA chains.     

Stimuli-responsive binary mixed polymer brushes and free-standing films by LbL-SIP

We report a facile approach to preparing binary mixed polymer brushes and free-standing films by combining the layer-by-layer and surface-initiated polymerization (LbL-SIP) techniques. Specifically, the grafting of mixed polymer brushes of poly(n-isopropylacrylamide) and polystyrene (pNIPAM-pSt) onto LbL-macroinitiator-modified planar substrates is described. Atom transfer radical polymerization (ATRP) and free radical polymerization (FRP) techniques were employed for the syntheses of pNIPAM and pSt, respectively, yielding pNIPAM-pSt mixed polymer brushes. The composition of the two polymers was controlled by varying the number of macroinitiator layers deposited on the substrate (i.e., LbL layers = 4, 8, 12, 16, and 20); consequently, mixed brushes of different thicknesses and composition ratios were obtained. Moreover, the switching behavior of the LbL-mixed brush films as a function of solvent and temperature was demonstrated and evaluated by water contact angle and atomic force microscopy (AFM) experiments. It was found that both the solvent and temperature stimuli responses were a function of the mixed brush composition and thickness ratio where the dominant component played a larger role in the response behavior. Furthermore, the ability to obtain free-standing films was exploited. The LbL technique provided the macroinitiator density variation necessary for the preparation of stable free-standing mixed brush films. Specifically, the free-standing films exhibited the rigidity to withstand changes in the solvent and temperature environment and at the same time were flexible enough to respond accordingly to external stimuli.     

Synthesis and pH-dependent micellization of diblock copolymer mixtures

This work focused on the preparation and the aqueous solution properties of hybrid polymeric micelles consisting of a hydrophobic poly(epsilon-caprolactone) (PCL) core and a mixed shell of hydrophilic poly(ethylene oxide) (PEO) and pH-sensitive poly(2-vinylpyridine) (P2VP). The hybrid micelles were successfully prepared by the rapid addition of acidic water to a binary solution of PCL(34)-b-PEO(114) and PCL(32)-b-P2VP(52) diblock copolymers in N,N-dimethylformamide. These micelles were pH-responsive as result of the pH-dependent ionization of the P2VP block. The impact of pH on the self-assembly of the binary mixture of diblocks-thus on the composition, shape, size and surface properties of the micelles-was studied by a variety of experimental techniques, i.e., dynamic and static light scattering, transmission electron microscopy, Zeta potential, fluorescence spectroscopy and complement hemolytic 50 test.     

Local chemical composition of nanophase-separated polymer brushes

Using scattering scanning nearfield infrared microscopy (s-SNIM), we have imaged the nanoscale phase separation of mixed polystyrene-poly(methyl methacrylate) (PS-PMMA) brushes and investigated changes in the top layer as a function of solvent exposure. We deduce that the top-layer of the mixed brushes is composed primarily of PMMA after exposure to acetone, while after exposure to toluene this changes to PS. Access to simultaneously measured topographic and chemical information allows direct correlation of the chemical morphology of the sample with topographic information. Our results demonstrate the potential of s-SNIM for chemical mapping based on distinct infrared absorption properties of polymers with a high spatial resolution of 80 nm × 80 nm.     

Memory of surface patterns in mixed polymer brushes: simulation and experiment

The correlation between the morphology of mixed polymer brushes and fluctuations of the grafting points is investigated by single-chain-in-mean-field simulations and experiments. The local topography of two types of mixed polystyrene-polymethylmethacrylate (PS-PMMA) brushes that differ in their modes of attachment has been studied during repeated microphase separation into laterally structured and homogeneous morphologies upon changing solvents. In the first type of brush (conventional), each of the surface-attached initiator groups starts the growth of either a PS or a PMMA chain in a random fashion. In the second case (Y-shaped mixed brushes), two chains of different types are attached to the same anchor group on the substrate. Whereas in the first case statistical fluctuations of the chemical composition occur on a local scale, such composition fluctuations are strongly suppressed in the latter case. The microphase-separated morphology is similar in both cases, but Y-shaped brushes exhibit a significantly weaker domain memory than do conventional PS-PMMA mixed brushes. The results of the experiment are compared with simulations, and a simple phenomenological argument and qualitative agreement are found. The observations demonstrate that small fluctuations in the grafting points are amplified by the microphase separation and nucleate the location of the domains in the mixed brush.     

Reorganization of hydrogen-bonded block copolymer complexes

Poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymers and poly(acrylic acid) (PAA) have been mixed in organic solvents. Complexation via hydrogen bonding occurs between the P4VP and PAA blocks. Those insoluble complexes aggregate to form the core of micelles surrounded by a corona of PS chains. Reorganization of these structures occurs upon addition of acidic or basic water, which results in the breaking of the hydrogen bonds between the P4VP and PAA blocks. After transfer of the initial complexes in acidic water, micelles consisting of a PS core and a protonated P4VP corona are observed. In basic water, well-defined nanoparticles formed by the PS-b-P4VP copolymers are obtained. It is demonstrated that these nanoparticles are stabilized by the negatively charged PAA chains. Finally, thermally induced disintegration of the micelles is investigated in organic solvents.     

Atmospheric plasma treatment of porous polymer constructs for tissue engineering applications

Porous 3D polymer scaffolds prepared by TIPS from PLGA (53:47) and PS are intrinsically hydrophobic which prohibits the wetting of such porous media by water. This limits the application of these materials for the fabrication of scaffolds as supports for cell adhesion/spreading. Here we demonstrate that the interior surfaces of polymer scaffolds can be effectively modified using atmospheric air plasma (AP). Polymer films (2D) were also modified as control. The surface properties of wet 2D and 3D scaffolds were characterised using zeta-potential and wettability measurements. These techniques were used as the primary screening methods to assess surface chemistry and the wettability of wet polymer constructs prior and after the surface treatment. The surfaces of the original polymers are rather hydrophobic as highlighted but contain acidic functional groups. Increased exposure to AP improved the water wetting of the treated surfaces because of the formation of a variety of oxygen and nitrogen containing functions. The morphology and pore structure was assessed using SEM and a liquid displacement test. The PLGA and PS foam samples have central regions which are open porous interconnected networks with maximum pore diameters of 49 microm for PLGA and 73 microm for PS foams.     

Transmission electron microscopy study of solvent-induced phase morphologies of environmentally responsive mixed homopolymer brushes on silica particles

We report in this work a transmission electron microscopy study of phase morphologies of environmentally responsive mixed poly( t-butyl acrylate) (P tBA)/polystyrene (PS) brushes and mixed poly(acrylic acid) (PAA)/PS brushes on 180 nm silica particles after treatments with nonselective good solvents and selective solvents, respectively. Mixed P tBA/PS brushes were grown from Y-initiator-functionalized silica particles by sequential atom transfer radical polymerization and nitroxide-mediated radical polymerization. Mixed PAA/PS brushes were prepared from mixed P tBA/PS brushes by removal of the t-butyl groups. For mixed P tBA/PS brushes with P tBA M n of 24.2 kDa and PS M n of 23.0 kDa and the corresponding mixed PAA/PS brushes, random worm-like, nearly bicontinuous nanostructures were formed from lateral microphase separation when the particles were cast from nonselective good solvents (chloroform for mixed P tBA/PS brushes and N, N-dimethylformamide for mixed PAA/PS brushes). The feature sizes were on the order of polymer chain root-mean-square end-to-end distances ( approximately 10 nm). In contrast, mixed P tBA/PS brushes with lower molecular weights (P tBA M n = 10.4 kDa and PS M n = 11.9 kDa) did not strongly phase separate after being cast from chloroform. After the solvents in the particle dispersions were gradually changed to selective solvents ( n-octane for mixed P tBA/PS brushes and H 2O for mixed PAA/PS brushes), isolated microdomains with an average size of 14-19 nm were formed as one grafted polymer collapsed and associated to form isolated microdomains, which were shielded by another grafted polymer yielding surface-tethered micellar structures. These results confirmed the theoretical predictions of the formation of "rippled" nanostructures and surface micellar structures of mixed homopolymer brushes induced by nonselective and selective solvents, respectively.     

Bioadhesive control of plasma proteins and blood cells from umbilical cord blood onto the interface grafted with zwitterionic polymer brushes

In this work, bioadhesive behavior of plasma proteins and blood cells from umbilical cord blood (UCB) onto zwitterionic poly(sulfobetaine methacrylate) (polySBMA) polymer brushes was studied. The surface coverage of polySBMA brushes on a hydrophobic polystyrene (PS) well plate with surface grafting weights ranging from 0.02 mg/cm(2) to 0.69 mg/cm(2) can be effectively controlled using the ozone pretreatment and thermal-induced radical graft-polymerization. The chemical composition, grafting structure, surface hydrophilicity, and hydration capability of prepared polySBMA brushes were determined to illustrate the correlations between grafting properties and blood compatibility of zwitterionic-grafted surfaces in contact with human UCB. The protein adsorption of fibrinogen in single-protein solutions and at complex medium of 100% UCB plasma onto different polySBMA brushes with different grafting coverage was measured by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies. The grafting density of the zwitterionic brushes greatly affects the PS surface, thus controlling the adsorption of fibrinogen, the adhesion of platelets, and the preservation of hematopoietic stem and progenitor cells (HSPCs) in UCB. The results showed that PS surfaces grafted with polySBMA brushes possess controllable hydration properties through the binding of water molecules, regulating the bioadhesive and bioinert characteristics of plasma proteins and blood platelets in UCB. Interestingly, it was found that the polySBMA brushes with an optimized grafting weight of approximately 0.1 mg/cm(2) at physiologic temperatures show significant hydrated chain flexibility and balanced hydrophilicity to provide the best preservation capacity for HSPCs stored in 100% UCB solution for 2 weeks. This work suggests that, through controlling grafting structures, the hemocompatible nature of grafted zwitterionic polymer brushes makes them well suited to the molecular design of regulated bioadhesive interfaces for use in the preservation of HSPCs from human UCB.     

Area Selective Polymer Brush Deposition

Polymer brush films with chemical functionality to attach to site specific substrate areas are introduced for area selective deposition (ASD) application. It is demonstrated that polymer brushes with chemically defined end sites can be selectively bound to copper‐specific regions of patterned copper/silica (Cu/SiO₂) substrates. The process described overcomes various limitations of currently used technology including cost, complexity, and throughput, with potential implications for future electronic devices and nanomanufacturing. A comparative study of amine‐terminated polystyrene and amine‐terminated poly‐2‐vinyl pyridine polymer brushes (i.e., PS‐NH₂ and P2VP‐NH₂) with similar molecular weights display contrasting behavior on patterned Cu/SiO₂ line features. Further, a thiol terminated poly‐2‐vinyl pyridine polymer brush (i.e., P2VP‐SH) is investigated as a direct spin‐on process to fabricate a metal oxide layer atop Cu areas only. The results presented here detail a novel methodology and open a new exciting process for ASD practices that can facilitate the precise deposition of dense metal, semiconductor, or dielectric films. We also discuss the applicability of polymer brushes to ASD uses going forward.     

PS-b-PAA嵌段共聚物修饰的智能表面的制备及其响应行为的研究

利用原子转移自由基聚合(ATRP), 再经水解后得到了嵌段共聚物聚苯乙烯-b-聚丙烯酸(PS-b-PAA), 接枝到硅烷偶联剂γ-(2,3环氧丙氧)丙基三甲氧基硅烷[γ-(2,3-glycidoxypropyl)trimethoxysilane, GPS]修饰的Si表面得到了对溶剂具有响应性的智能表面, 并通过凝胶渗透色谱(GPC)、傅立叶变换红外光谱(FTIR)、核磁共振(¹H NMR)和原子力显微镜(AFM)等测试手段对产物进行了表征. 然后, 通过接触角测试研究了所得智能表面对不同溶剂的响应行为. 结果显示, PS-b-PAA接枝表面的润湿性与接枝共聚物的组成及表面处理的溶剂性质有关. 在相同的溶剂处理条件下, 共聚物中PS/PAA比值越小, 表面亲水性越大; 乙醇和碱性溶液处理后的表面呈亲水状态, 甲苯和酸性水溶液处理后的表面又切换到疏水状态, 同时其表面的酸碱响应行为具有非常稳定的可逆性.     

Gold nanoparticle/polymer nanocomposites: dispersion of nanoparticles as a function of capping agent molecular weight and grafting density

The dispersion of polymer-covered gold nanoparticles in high molecular weight (MW) polymer matrixes is reported. Complete particle dispersion was achieved for PS125-Au in the polystyrene (PS) matrixes studied (up to and including Mn = 80 000 g/mol). PS19-Au, on the other hand, exhibits complete dispersion in a low MW PS matrix (Mn = 2000 g/mol) but only partial dispersion in higher MW matrixes (up to 80 000 g/mol). Similarly, PEO45-Au is fully dispersed in a low MW poly(ethylene oxide) (PEO) matrix (Mn = 1000 g/mol) but only partially in a higher MW PEO matrix (Mn = 15 000 g/mol). Wetting of the polymer-Au brushes by the polymer matrix is associated with dispersibility. Theory predicts that, for dense polymer brushes, wetting is achieved when the MW of the polymer brush equals (and is greater than) that of the polymer matrix. The observed partial dispersion of the PS19-Au and PEO45-Au nanoparticles in matrixes whose MW is greater than the brush MW is attributable to the existence of a high volume fraction of voids within the brush. These voids arise from the unique geometry of the nanoparticle surface arising from the juxtaposed facets of the gold nanoparticle. PS125-Au brushes are wetted by PS matrixes whose degree of polymerization is larger than 125, probably because of their lower grafting density on the gold core or the high fraction of void volumes caused by the facets on the gold cores. Dispersion thus occurs when the matrix MW is greater than that of the brush.