Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3‐aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene‐alt‐maleic anhydride) (PSMA), and poly(ethylene‐alt‐maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT‐IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright © 2007 John Wiley & Sons, Ltd.     

Preparation of Thick Films by Electrophoretic Deposition Using Surface Modified Silica Particles Derived from Sol-Gel Method

Thick films were prepared by the electrophoretic sol-gel deposition of organically modified, sub-micron silica particles. The silica particles were modified with 3-aminopropyltriethoxysilane (APS) and vinyltriethoxysilane (VTES). Smooth and crack-free films ca. 15 m thick were obtained when APS modified silica particles were used for the cathodic electrophoretic deposition. Thick films with decreased open spaces among particles were obtained when silica particles modified with VTES were co-deposited with an organic polymer, polyethylene maleate.     

Preparation and applications of novel fluoroalkyl end‐capped oligomers/polyimide/silica nanocomposites

Fluoroalkyl end‐capped acrylic acid, N,N‐dimethylacrylamide, N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide and vinyltrimethoxysilane oligomers reacted with polyamic acid possessing trimethoxysilyl groups under alkaline conditions to yield the corresponding fluoroalkyl end‐capped oligomers/polyamic acid/silica nanocomposites. These isolated fluorinated composite powders were found to afford nanometer size‐controlled fine particles with a good dispersibility and stability in water and traditional organic solvents. We succeeded in preparing new fluoroalkyl end‐capped oligomers/polyimide/silica nanocomposites by the imidization of fluorinated polyamic acid silica nanocomposites through the stepwise heating at 110 and 270°C under air atmosphere conditions. These fluorinated polyimide/silica nanocomposites thus obtained were applied to the surface modification of glass and poly(methyl methacrylate) (PMMA) to exhibit good hydro‐ and oleo‐phobic characteristics imparted by fluoroalkyl groups in the composites on their surface. In addition, the surface morphology of the modified glass treated with these fluorinated nanocomposites were analyzed by using FE‐SEM and DFM. Copyright © 2011 John Wiley & Sons, Ltd.     

Photografting of polymers onto nanosized silica surface initiated by eosin moieties immobilized onto the surface

The photograft polymerization of various vinyl monomers onto nanosized silica surfaces was investigated. It was initiated by eosin moieties introduced onto the silica surface. The preparation of the silica with eosin moieties was achieved by the reaction of eosin with benzyl chloride groups on the silica surface.These were introduced by the reaction of surface silanol groups with 4‐(chloromethyl)phenyltrimethoxysilane in the presence of t‐butyl ammonium bromide as a phase‐transfer catalyst. The photopolymerization of various vinyl monomers, such as styrene, acrylamide, acrylic acid, and acrylonitrile was successfully initiated by eosin moieties on the silica surface in the presence of ascorbic acid as a reducing agent and by oxygen. The corresponding polymers were grafted from the silica surface. The grafting efficiency (percentage of grafted polymer to total polymer formed) in the photoinitiation system was much larger than that in the radical polymerization initiated by surface radicals; these radicals were formed by the thermal decomposition of azo groups introduced onto the silica surface. It was found that the polymer‐grafted silica gave stable dispersions in good solvents of grafted polymer and the wettability of the surfaces can be easily controlled by grafting of polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 600–606, 2005     

Surface Modification of Nano－SiO2 by Grafting PMMA／PBA

The surface of nano-SiO2 was modified by being encapsulated with hydroxy-propyl-methyl cellulose (HPMC), and then co-grafted with acrylates. The grafting conditions, such as pH of the medium, and initiator concentration have been studied. The modified nano-SiO2 particles were characterized by TEM, DSC and FT-IR spectra. TEM images show that the surface of the nano-particles has been successfully modified by a thick layer of film-like polymer in this way. The DSC results show that the decomposition temperature of modified nano-particles of SIO2 is 90 ℃ higher than that of grafted-on polymer. According to the FT-IR spectra, It is convinced that poly-methyl methacrylate ( PMMA ) and poly-acrylic butyl-ester ( PBA ) were co-grafted onto the surface of nano-SiO2.     

Surface modification of polymers. I. Vapour phase photografting with acrylic acid

Surfaces of low density polyethylene, high density polyethylene, and polystyrene have been modified by grafting with acrylic acid. Benzophenone and acrylic acid in the vapor phase were UV-irradiated in the presence of a polymer substrate. Grafting with acrylic acid took place in a thin layer on the surface, thus increasing the wettability of the polymer. After 5 min of irradiation, the contact angle against water had decreased to 20° for polystyrene and 50° for the polyethylene samples. ESCA measurements on samples irradiated for 5 min showed a 90% poly(acrylic acid) coverage of the surface for polystyrene, 63% for low density polyethylene, and 56% for high density polyethylene. Acetone or ethanol were used as carriers of monomer and initiator. Acetone was able to initiate grafting and was found to promote and direct grafting to the surface. The stability of the acrylic acid grafted surfaces was studied by contact angle measurements and ESCA. At room temperature, the grafted layer is confined to the surface, but when the material was heated in air the surface was reshaped into a hydrophobic one. The process was reversible. In aqueous surroundings at elevated temperatures the hydrophilic character of the surface was restored.     

Acrylic polymer/silica hybrids prepared by emulsifier‐free emulsion polymerization and the sol–gel process

Acrylic polymer/silica hybrids were prepared by emulsifier‐free emulsion polymerization and the sol–gel process. Acrylic polymer emulsions containing triethoxysilyl groups were synthesized by emulsifier‐free batch emulsion polymerization. The acrylic polymer/silica hybrid films prepared from the acrylic polymer emulsions and tetraethoxysilane (TEOS) were transparent and solvent‐resistant. Atomic force microscopy studies of the hybrid film surface suggested that the hybrid films did not contain large (e.g., micrometer‐size) silica particles, which could be formed because of the organic–inorganic phase separation. The Si? O? Si bond formed by the cocondensation of TEOS and the triethoxysilyl groups on the acrylic polymer increased the miscibility between the acrylic polymer component and the silica component in the hybrid films, in which the nanometer‐size silica domains (particles) were dispersed homogeneously in the acrylic polymer component. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 273–280, 2006     

pH responsive surfaces with nanoscale topography

We report the preparation of nanostructured adaptive polymer surfaces by diffusion of an amphihilic block copolymer toward the interface. The surface segregation of a diblock copolymer, polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA), occurred when blended with high molecular weight polystyrene employed as a matrix. On annealing, the polymer surfaces changed both the chemical composition and the hydrophilicity depending on the environment and pH, respectively. By exposure to either water vapor or air, the surface wettability varied between hydrophilic and hydrophobic. In addition, surface enrichment on diblock copolymer by water vapor annealing led to self‐assembly occurring at the interface. Hence, nanostructured domains can be observed by AFM in liquid media. Moreover, the PAA segments placed at the interface respond to pH and can switch from an extended hydrophilic state at basic pH values to a collapsed hydrophobic state in acidic media. Accordingly, the surface morphology changed from swelled micelles to nanometer size holes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2982–2990, 2010     

Adsorption of polyelectrolyte modified graphene to silica surfaces: monolayers and multilayers

Exfoliated graphene particles stabilised by the cationic polyelectrolyte polyethyleneimine (PEI) were used in conjunction with an anionic polyelectrolyte, poly(acrylic acid), to construct multilayers using the layer-by-layer technique on a silica substrate. In the first adsorption step, the surface excess of the cationic graphene was dependent on the overall charge on the nanoparticle which in turn can be tuned through modifying solution pH as PEI has weakly ionisable charged amine groups. The adsorbed amount onto the silica surface increased as the solution pH increased. Subsequently, a layer of PAA was adsorbed on top of the cationic graphene through electrostatic interaction. The multilayer could be assembled through this alternate deposition, with the influence of solution conditions investigated. The pH of the adsorbing solutions was the chief determinant of the overall adsorbed amounts, with more mass added at the elevated pH of 9 in comparison with pH 4. Atomic force microscopy confirmed that the graphene particles were adsorbed to the silica interface and that the surface coverage of the disc-like nanoparticles was complete after the deposition of five graphene-polyelectrolyte bi-layers. Furthermore, the graphene nanoparticles themselves could be modified through the consecutive addition of the oppositely charged polymers. A multilayered assembly of negatively charged graphene sheets modified with a bi-layer of PEI and PAA was also deposited on a silica surface with adsorbed PEI.     

Adsorption of hydrophobically modified poly(acrylamide)-co-(acrylic acid) on an amino-functionalized surface and its response to the external solvent environment

The adsorption of hydrophobically modified poly(acrylamide)-co-(acrylic acid), designated as PAM-C14-AA (x%) (x = 5, 10, 20, representing the mole percent of acrylic acid units), at an amino-functionalized silicon surface was studied. The effect of polymer charge density was determined by varying the acrylic acid content of the copolymer. Characteristics of the adsorbed layer were evaluated by atomic force microscopy, water contact angle measurements, and X-ray photoelectron spectroscopy. The results showed that the adsorption behavior of PAM-C14-AA (x%) is influenced by the balance among the electrostatic, hydrogen-bonding, and hydrophobic interactions. Adjusting the solution pH and polymer charge density significantly affects the morphology and thickness of the adsorbed film. Furthermore, it was found that the adsorbed PAM-C14-AA undergoes conformational rearrangements when the surface is wetted by selected organic solvents. The resultant morphology and wettability of the films indicated that the different affinities of the solvents for different segments of PAM-C14-AA (x%) can be considered to be the possible cause of the conformational rearrangements of adsorbed polymer.     

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO₂ [P(St-BA-AA)/SiO₂] nanocomposites by in situ formation of SiO₂ nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Barrier properties of polymer/alumina nanocomposite membranes fabricated by atomic layer deposition

Novel polymer/ceramic nanocomposite membranes were fabricated, characterized and tested for their barrier performance. Atomic layer deposition (ALD) was used to deposit alumina films on primary, micron-sized (16 and 60 μm) high-density polyethylene (HDPE) particles at a rate of 0.5 nm/cycle at 77 °C. Well-dispersed polymer/ceramic nanocomposites were obtained by extruding alumina coated HDPE particles. The dispersion of alumina flakes can be controlled by varying the number of ALD coating cycles and substrate polymer particle size. The diffusion coefficient of fabricated nanocomposite membranes can be reduced to half with the inclusion of 7.29 vol.% alumina flakes. However, a corresponding increase in permeability was also observed due to the voids formed at or near the interface of the polymer and alumina flakes during the extrusion process, as evidenced by electron microscopy. The low surface wettability of the alumina outerlayers was believed to be one of the main reasons of void formation. Particle surface wettability was improved using 3-aminopropyltriethoxysilane (APS) to coat the particle ALD surface modified polymer particles prior to extrusion. The diffusion coefficient and permeability of the membrane using surfactant-modified particles decreased by 20%, relative to the non-modified case.     

Preparation of various Janus composite particles with two components differently combined

Janus composite particles with a combination of organic and inorganic substances were synthesized by soap-free emulsion polymerization in which an amphoteric initiator of 2,2′-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was employed to introduce a polystyrene (PSt) lobe onto silica cores surface-modified with 3-methacryloxypropyltrimethoxy silane (MPTMS). Thermogravimetric analysis and X-ray photoelectron spectroscopy were used to characterize the surface-modified silica particles and showed that a small amount of MPTMS introduced onto the surface of silica particles could successfully prepare SiO₂–PSt Janus particles. The oxide part of SiO₂–PSt Janus particles obtained with the polymerization was further surface-modified with 3-aminopropyltriethoxysilane (APS) to introduce positively charged amino groups on the silica surface. The silica surface modified with APS was covered with gold by electroless deposition in which a gold precursor of auric chloride was reduced with ascorbic acid in the presence of polyvinylpyrrolidone. The electroless deposition of gold successfully produced Janus particles with a combination of gold and PSt surfaces. Furthermore, dissolution of the polymer component of the Au–PSt Janus particles in tetrahydrofuran led to another Janus type of particles with an inorganic combination of Au and SiO₂.     

Self-organization of polymer particles on hydrophobic solid substrates in aqueous media. II. Self-organization of cationic polymer particles on polymer films and wettability control with particle monolayers

Self-organization of cationic polymer particles through hydrophobic interaction on polymer films in aqueous system and characteristic properties of the resulting particle monolayers were investigated. Cationic polymer particles bearing quaternary ammonium groups on their surfaces effectively self-organized on polymer films. With an increase of the particle surface charge density, the surface coverage and average aggregate size (N _a) decreased. The surface coverage control was accomplished by tuning the ionic strength of the media. The wettability of polymer films for water was imparted by the formation of particle monolayers on them. Annealing of the particle monolayers resulted in the increase of the adhesive strength, while the wettability for water was lost. Further improvements of both wettability and adhesive strength of particle monolayers were achieved by the immobilization of silica colloids on the particle monolayers. This method would be effective for the hydrophilization of polymer films.     

PAA/PEO comb polymer effects on rheological properties and inter-particle forces in aqueous silica suspensions

The effects of a poly(acrylic acid) (PAA)-poly(ethylene) (PEO) comb polymer dispersant on the rheological properties and inter-particle forces in aqueous silica suspensions have been studied under varying pH conditions. The comb polymer was found to adsorb more strongly under acidic than basic conditions, indicating that the PAA backbone of the copolymer preferentially adsorbs onto silica surfaces with the PEO "teeth" extending out from the surface into the solution. In the presence of low concentrations of copolymer, the silica suspensions were stable due to electrostatic repulsions between the silica surfaces. At higher copolymer concentrations and under neutral and basic conditions, where the copolymer interacted only weakly with silica, the suspensions showed a transition from a dispersed to weakly flocculated state and attractive forces were measured between silica surfaces. Under acidic conditions, the silica dispersion also destabilized at intermediate copolymer adsorbed density and then was re-stabilized at higher adsorbed coverage. The silica suspensions were stable at high copolymer coverage due to steric repulsions between the particles. The destabilization at intermediate coverage is thought to be due to polymer bridging between particles or possibly depletion forces.     

Size control of polystyrene nodules formed on silica particles in soap-free emulsion polymerization with amphoteric initiator

An amphoteric initiator of 2,2′-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was applied to fabrication of raspberry-shaped composite particles in soap-free emulsion polymerization of styrene in the presence of silica particles surface-modified with 3-methacryoxypropyltrimethoxysilane. In the polymerizations, pH of the solution was ranged from 7.9 to 9.9 to alter dissociation degree of ionizable groups in the initiator. Raspberry-shaped particles were obtained in a pH range of 8.0 to 9.3 followed by a tendency in which average size of polystyrene (PSt) nodules adsorbed onto the silica particles decreased with pH. This tendency was similar to that of polymer particles formed in conventional soap-free emulsion polymerization in the absence of the silica particles. An increase in silica particle concentration led to a decrease in the final size in PSt nodules. The decrease was caused by the stabilization of polymer particles fixed to the silica surface against polymer particle aggregation in water phase.     

Adhesion mechanisms of grafted polyolefins

By comparing surface properties assessed by wettability measurements with polymer-metal adhesion strength determined by peeling for different grafted polyolefins (acrylic acid grafted polyethylene, acrylic acid and maleic anhydride grafted poly(ethylene-vinyl acetate), maleic anhydride grafted polypropylene), a general adhesion mechanism can be proposed. The surface polarity is not the main determining parameter for adhesion. Polyolefin-aluminium adhesion is obtained through chemical bonding of acid groups grafted in the polymer bulk and basic groups present on the aluminium.     

Enhanced interlayer interaction in cellulose single nanofibre and poly(l-lactic acid) layered films by plasma-initiated surface grafting of poly(acrylic acid) onto poly(l-lactic acid) films

The surface of a poly(l-lactic acid) (PLLA) film was modified with poly(acrylic acid) (PAA) by plasma-initiated polymerization to increase the interaction between PLLA and cellulose single nanofibres (CSNF). The surface wettability of the PAA grafted PLLA film (PLLA-PAA film) was investigated by contact angle measurements. Modification of the PLLA film with PAA decreased the contact angle from 61° to 50°. The surface morphologies of the PLLA film, PLLA-PAA film and CSNF-coated PLLA-PAA film were studied by atomic force microscopy. The interaction between the CSNF and PLLA layers was strengthened by incorporation of a PAA layer onto the PLLA films and it is higher than 2N as proved by a peeling test. This is probably because the carboxyl groups of PAA form hydrogen bonds with the hydroxyl groups of CSNF.     

Preparation and controlled self-assembly of Janus magnetic nanoparticles

Janus magnetic nanoparticles (~20 nm) were prepared by grafting either polystyrene sodium sulfonate (PSSNa) or polydimethylamino ethylmethacrylate (PDMAEMA) to the exposed surfaces of negatively charged poly(acrylic acid) (PAA)-coated magnetite nanoparticles adsorbed onto positively charged silica beads. Individually dispersed Janus nanoparticles were obtained by repulsion from the beads on reversal of the silica surface charge when the solution pH was increased. Controlled aggregation of the Janus nanoparticles was observed at low pH values, with the formation of stable clusters of approximately 2-4 times the initial size of the particles. Cluster formation was reversed, and individually dispersed nanoparticles recovered, by restoring the pH to high values. At intermediate pH values, PSSNa Janus nanoparticles showed moderate clustering, while PDMAEMA Janus nanoparticles aggregated uncontrollably due to dipolar interactions. The size of the stable clusters could be controlled by increasing the molecular weight of the grafted polymer, or by decreasing the magnetic nanoparticle surface availability for grafting, both of which yielded larger cluster sizes. The addition of small amounts of PAA-coated magnetic nanoparticles to the Janus nanoparticle suspension resulted in a further increase in the final cluster size. Monte Carlo simulation results compared favorably with experimental observations and showed the formation of small, elongated clusters similar in structure to those observed in cryo-TEM images.     

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) as a probe of macromolecule adsorption kinetics at functionalized interfaces

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been employed to study the interfacial adsorption kinetics of coumarin-tagged macromolecules onto a range of functionalized planar surfaces. Such studies are valuable in designing polymers for complex systems where the degree of interaction between the polymer and surface needs to be tailored. Three tagged synthetic polymers with different functionalities are examined: poly(acrylic acid) (PAA), poly(3-sulfopropyl methacrylate, potassium salt) (PSPMA), and a mannose-modified glycopolymer. Adsorption transients at the silica/water interface are found to be characteristic for each polymer, and kinetics are deduced from the initial rates. The chemistry of the adsorption interfaces has been varied by, first, manipulation of silica surface chemistry via the bulk pH, followed by surfaces modified by poly(L-glutamic acid) (PGA) and cellulose, giving five chemically different surfaces. Complementary atomic force microscopy (AFM) imaging has been used for additional surface characterization of adsorbed layers and functionalized interfaces to allow adsorption rates to be interpreted more fully. Adsorption rates for PSPMA and the glycopolymer are seen to be highly surface sensitive, with significantly higher rates on cellulose-modified surfaces, whereas PAA shows a much smaller rate dependence on the nature of the adsorption surface.