Electrokinetic and solvatochromic studies of functionalized silica particles

Zeta potential plots, Kamlet-Taft's α (hydrogen bond-donating, HBD), β (hydrogen bond-accepting, HBA), and π* (dipolarity/polarizability) parameters as well as Gutmann's DN (donor numbers) are presented for 12 differently functionalized (i.e. alkyl, cyanoalkyl, aminoalkyl, and imidazolidine) silica particles. The pH-dependent zeta potential plots were measured in aqueous solution, whereas the solvatochromic studies were performed in 1,2-dichloroethane and cyclohexane as solvents using a special UV/visible spectroscopic technique. For the determination of the solvatochromic polarity parameters, a set of carefully characterized polarity indicators was employed: Cu(tmen)(acac)⁺B(C₆H₅)₄ ^- for β and DN; dicyano-bis(1,10-phenanthroline)iron(II) for α; 4,4′-bis(N,N-dimethylamino)benzophenone for π*; and an aminobenzofuranone derivative {3-(4-amino-3-methylphenyl)-7-phenyl-benzo[1,2b : 4,5b′]difuran-2,6-dione} (ABF) for α, β, and π*. The calculation of the polarity parameters was carried out via linear solvation energy (LSE) correlation equations using the Kamlet-Taft solvent parameters as a reference system. A linear correlation between the electrokinetically determined value of the isoelectric point and the β parameter of the functionalized silicas is demonstrated.     

Crack growth of natural rubber filled with functionalized silica particles

In the present work, functionalized liquid isoprene rubber (FLIR) was used to improve the filler dispersion and filler–rubber interaction in the silica filled natural rubber system. By the infrared spectra and scanning electron microscopy, it was proved that the FLIR was successfully grafted on the silica and the functionalized silica was dispersed in the NR matrix homogeneously. Based on the real‐time crack tip morphology monitoring method, the influence of FLIR on the crack growth behavior of NR filled with silica was analyzed. By the adding of FLIR, the crack resistance of the natural rubber embedded with functionalized silica is remarkably increased. When the weight ratio of FLIR to silica is 3:10, the NR composite has the best crack resistance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42972.     

Grafting of water‐soluble sulfonated monomers onto functionalized fumed silica nanoparticles via surface‐initiated redox polymerization in aqueous medium

Sulfonated polymer/fumed silica hybrid nanoparticles were prepared via surface‐initiated free radical polymerization of 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid (PAMPS‐g‐FSN), styrene sulfonic acid sodium salt (PSSA‐g‐FSN) and vinyl sulfonic acid sodium salt (PVSA‐g‐FSN) from the surface of aminopropyl‐functionalized fumed silica nanoparticles (AFSNs) dispersed in aqueous medium. Cerium(IV) ammonium nitrate/nitric acid and sodium dodecyl sulfate were used as redox initiator and stabilizer respectively. AFSNs were prepared by covalently attaching 3‐aminopropyltriethoxysilane onto the surface of fumed silica nanoparticles. Sulfonated monomers (AMPS, SSA or VSA) were then grafted onto the AFSNs ultrasonically dispersed in water via redox initiation at 40 °C. Structure, thermal properties, particle size and morphology of the AFSNs and PAMPS‐g‐FSN, PSSA‐g‐FSN and PVSA‐g‐FSN hybrid nanoparticles were characterized by Fourier transform infrared spectroscopy, TGA, SEM, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The results indicated that the sulfonated monomers were successfully grafted onto the fumed silica nanoparticles. Grafting amounts of the sulfonated polymers onto the fumed silica nanoparticle surface were estimated from TGA thermograms to be 59%, 13% and 29% for the PAMPS, PSSA and PVSA, respectively. From SEM, TEM and DLS analysis, polymer‐grafted fumed silica nanoparticles with an average diameter smaller than 70 nm and a (semi‐) spherical shape were observed. A significant bimodal particle size distribution was observed only for the PAMPS‐g‐FSN with average diameters of 39.6 nm (84.1% per number) and 106 nm (15.9% per number). The hydrophilic sulfonated polymer/grafted fumed silica obtained from the redox graft polymerization gave a stable colloidal dispersion in acidic aqueous medium. Copyright © 2012 Society of Chemical Industry     

Grafting of selected presynthesized macromonomers onto various dispersions of silica particles

A new process was developed which enables one to obtain surface‐modified silica with a high heavy metal ion complexing ability. The synthetic approach is based on grafting of vinyl‐terminated macromonomers onto silica via covalent bonding. A proper selection of the macromonomer structure, molecular weight, and molecular weight distribution allows materials to be obtained with a range of desirable properties. The process has been tested on various dispersions (ranging from 35 and 200 μm) of silica particles and two structurally related macromonomers. Native silica and the resulting mixed organic–inorganic products were fully characterized by IR spectroscopy, SEM, yield of grafting (elemental analysis and calcination), density (helium pycnometry), specific surface area (BET method), and pore size (gas adsorption and mercury porosimetry) measurements. It was found that the corresponding polymers are effectively grafted onto the surface; the density, surface area, and pore size of the silica particles decrease with polymer grafting. Preliminary results on metal‐ion uptake indicate that polymer‐grafted silica exhibits an excellent complexing ability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1287–1296, 2002     

Surface functionalized colloidal silica particles from an inverse microemulsion sol gel process

Colloidal silica particles are prepared via a sol gel technique carried out in an inverse microemulsion of water in a toluene solution of tetraethoxysilane (TEOS), stabilized by either an anionic surfactant AOT or isopropanol. Functionalized material was obtained using a functional coupling agent (RO)₃Si(CH₂)₃ X, X being a functional group such as methacryloyl, thiol, vinyl, amino group, or a chlorine atom. Functionalization can be carried out either directly via the direct copolycondensation of TEOS and the coupling agent, or in a two-step process involving a core-shell polycondensation of the coupling agent onto preformed silica particles. Kinetic studies of the copolycondensation are carried out using either²⁹Si NMR analysis or liquid chromatography. They show that the consumption of TEOS is more rapid than that of the coupling agent. The materials are characterized both chemically (elemental analysis, FTIR,¹³C and²⁹Si NMR CPMAS analysis), and by their particle size. The silica functionalized with a polymerizable methacryloyl group is encapsulated by a polymer layer in an inverse emulsion polymerization of acrylic acid. After inversion of the emulsion in water, the resulting material is covered with a layer of hydrophobic polymer in a conventional emulsion polymerization.     

Graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto silica surface by Michael addition

The introduction of peroxycarbonate groups onto a silica surface and the graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto a silica surface were investigated. The introduction of peroxycarbonate groups onto a silica surface was achieved by Michael addition of amino groups introduced onto the silica surface to t‐butylperoxy‐2‐methacryloyloxyethylcarbonate (HEPO). The amount of peroxycarbonate groups was determined to be 0.17 mmol/g. The graft polymerization of various vinyl monomers such as styrene (St), N‐vinyl‐2‐pyrrolidinone (NVPD), and 2‐hydroxyethyl methacrylate (HEMA) was initiated by peroxycarbonate groups introduced onto the silica surface to give the corresponding polymer‐grafted silicas. The percentage of poly(St)‐grafting reached about 120% after 5 h. This means that 1.20 g of poly(St) is grafted onto 1.0 g of silica. The surface of poly(St)‐grafted silica shows a hydrophobic nature, but the surfaces of poly(NVPD) and poly(HEMA)‐grafted silica show a hydrophilic nature. Furthermore, the poly(St)‐grafted silica was found to give a stable colloidal dispersion in a good solvent for the grafted polymer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1491–1497, 1999     

Grafting of hydrophilic monomers onto aminopropyl‐functionalized sodium montmorillonite via surface‐initiated redox polymerization

Hydrophilic polymer/sodium montmorillonite (Na‐MMT) hybrid nanomaterials were prepared via surface‐initiated redox polymerization of 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (PAMPS‐g‐MMT), acrylamide (PAAm‐g‐MMT) and styrenesulfonic acid sodium salt (PSSA‐g‐MMT) from surface of aminopropyl‐functionalized sodium montmorillonite (AMMT) dispersed in an aqueous medium. Cerium(IV) ammonium nitrate/nitric acid and aminopropyl groups on the surface of AMMT were used as oxidant and reducing groups, respectively. AMMT was prepared by covalently attaching 3‐aminopropyltriethoxysilane onto the surface of Na‐MMT. Hydrophilic monomers (AMPS, AAm and SSA) were then grafted onto AMMT dispersed in water via redox initiation at 40 °C. Structure, morphology and thermal properties of the AMMT, PAMPS‐g‐MMT, PAAm‐g‐MMT and PSSA‐g‐MMT hybrid materials were characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD) and thermogravimetric (TGA) analyses, respectively. FTIR results indicated that hydrophilic monomers were successfully grafted onto the surface of MMT. Grafting amounts of the hydrophilic polymers were estimated from TGA thermograms to be 28.8, 118.8 and 14.4% for PAMPS, PAAm and PSSA, respectively. XRD patterns showed an exfoliated morphology for PAMPS‐ and PAAm‐grafted MMT hybrid nanomaterials and an intercalated/exfoliated morphology for the PSSA‐grafted MMT one. The effect of the nature of hydrophilic monomer on the grafting efficiency is discussed in detail. © 2013 Society of Chemical Industry     

Antimicrobial silica and sand particles functionalized with an N‐halamine acrylamidesiloxane copolymer

The monomer 2‐acrylamido‐2‐methyl‐1‐(5‐methylhydantoinyl)propane (HA) was copolymerized with 3‐(trimethoxysilyl)propyl methacrylate (SL) and covalently attached onto silica gel and sand particles. As a result HASL copolymer‐grafted silica gel and sand particles (HASL SGPs and SPs) were obtained. These two types of HASL SGPs and SPs provided excellent biocidal efficacy against Gram positive S. aureus and Gram negative E. coli O157:H7 bacteria when the copolymer‐grafted particles were exposed to dilute sodium hypochlorite (household bleach) solution. In a flowing water application, seven logs of bacteria were inactivated within 10 s of contact time with the particles packed into a column. The treated particles also exhibited good washing and storage stabilities. The chlorine loss during extensive flow could be recovered by further exposure to dilute bleach solution. The antimicrobial particles have potential application for use in inexpensive disinfecting water filters for slow water flows. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43413.     

Effect of functionalized silica particles on cross-linked poly(vinyl alcohol) proton conducting membranes

A family of proton conducting membranes based on cross-linked poly(vinyl alcohol), PVA, has been synthesized and characterized. The influence of surface-functionalized silica particles on the membrane properties has been evaluated by means of ¹H-NMR, vibrational spectroscopy, thermal analysis and electrochemical characterization. The study revealed that the crystallinity of the polymer, the proton diffusivity and the water retention are strongly affected by the presence of the inorganic compound. Conductivity measurements and preliminary fuel cell tests agreed in determining the best PVA/silica ratio among the various compositions explored and demonstrated the potentiality of the selected membranes as electrolytes in fuel cell devices.     

Grafting of acrylate monomers onto chlorinated rubber

Grafting of chlorinated rubber with ethylacrylate and butyl methacrylate in xylene solution has been studied using benzoyl peroxide as the initiator. It is observed that the grafting reaction follows conventional kinetic behavior under the present experimental conditions. The energies of activation obtained for both monomers were 10.8 and 10.95 K.cals, respectively. The grafting efficiency and percent grafting were calculated. Additional proof for grafting onto chlorinated rubber was also obtained by characterization of the graft copolymer by gel permeation chromatography.     

Immobilization of a thermostable inorganic pyrophosphatase from the archaeon Pyrococcus furiosus onto amino‐functionalized silica beads

This study focuses on the preparation and application of a recombinant thermophilic inorganic pyrophosphatase from the archaeon Pyrococcus furiosus on amino‐functionalized silica beads. The amino‐functionalized silica beads were prepared by coating with 3‐aminopropyltriethoxysilane by silanization. The thermostable inorganic pyrophosphatase was rapidly and successfully immobilized onto the amino‐functionalized silica beads with glutaraldehyde as a coupling agent (within 12 min, >95.4% protein was immobilized onto the support). The results show that the protein could be immobilized efficiently, with up to 1 mg of protein/g of support with 92.9% activity. Compared with the free enzyme, the immobilized enzyme displayed a high activity toward inorganic pyrophosphate, less sensitivity toward the pH, and increased thermal stability. The immobilized enzyme retained 56.9% of its initial activity after hydrolysis of the inorganic pyrophosphate after 12 consecutive cycles (total = 330 min) at high temperature; this indicated a high protein stability suitable for practical applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40700.     

Graft polymerization of polyvinylpyrrolidone onto silica

A new technique is reported for the surface grafting of polyvinylpyrrolidone (PVP) to hydroxylated solid surfaces. Free radical graft polymerization of vinylpyrrolidone onto vinylsilane–modified impermeable silica particles was carried out in an aqueous slurry reactor. The graft yield and the monomer conversion were determined by thermogravimetric analysis and UV spectroscopy, respectively. The graft yield was shown to increase by increasing the initial monomer concentration. A comparison of the graft polymerization reaction with the adsorption of polyvinylpyrrolidone onto untreated, vinylsilane-modified, and PVP-grafted silica was performed.     

Organically functionalized sol-gel silica network growth

The detailed information about the growth of organically modified silica networks regarded as useful for barrier coatings and membrane coatings preparation are the subject of this paper. The networks obtained using different precursors containing non-hydrolysable organic groups: dimethyldiethoxysilane – dMdEOS, ethyltriethoxysilane – EtEOS, n-propyltriethoxysilane – nPtEOS have been investigated with rheology and Raman spectroscopy of solutions. The polycondensation degree during aging has been calculated. Individual networks have been monitored for selected points during 654 h of aging. Thanks to the completion of rheology and Raman spectroscopy investigations different influence of aging and physicochemical interaction occurring in particular sols and influencing their rheological behavior have been revealed. The observed differences also apply to the type of structures created by hydrolysis and condensation reaction and are connected with organic group functionalizing silica network.     

Graft copolymerization of hydrophilic monomers onto irradiated polypropylene fibers

A method of graft copolymerization of hydrophilic monomers, such as 1-vinyl-2-pyrrolidone, acrylonitrile, acrylic acid, and acrylamide, onto irradiated polypropylene fibers has been studied. γ ray as well as electron beam were employed for the irradiation processes. Graft-copolymerization kinetics and the properties of grafted fibers have been investigated. Moisture regain, dyes absorption, and melting point of the grafted fibers were found to increase with the increasing of the degree of grafting. Polypropylene for 1-vinyl-2-pyrrolidone grafted fibers showed excellent dye absorption for almost all kinds of dyes such as direct, basic, acid, reactive, disper, and naphthol dyes. However, for polypropylene acrylic acid grafted fibers, the colorfastness to washing was found to be unsatisfactory. The colorfastness to washing for polypropylene 1-vinyl-2-pyrrolidone grafted fibers was found to be fairly good for certain types of dyes such as vat and naphthol dyes.     

Studies on graft copolymerization of acrylate monomers onto casein

Poly(butyl acrylate) has been graft copolymerized onto casein using potassium peroxydisulfate–ascorbic acid as the initiating system. The proof of grafting has been obtained by ninhydrin test and IR studies. The effects of synthetic variables in the graft copolymerization have been discussed in the light of percent grafting, grafting efficiency, and the rates of polymerization.     

Surface photografting of hydrophilic vinyl monomers onto diethyldithiocarbamated polydimethylsiloxane

Photografting of vinyl monomers has been studied to make hydrophilic polydimethylsiloxane (PDMS) surfaces. A chlorine-containing polydimethylsiloxane (C-PDMS) prepared by polymerization of chloromethylheptamethylcyclotetrasiloxane was photocured on a glass plate. The crosslinked C-PDMA was subjected to a reaction with sodium diethyldithiocarbamate. The diethyldithiocarbamated PDMS was then photoirradiated in the presence of hydrophilic vinyl monomers such as 2-hydroxyethylmethacrylate and acrylamide to afford surface-grafted PDMS. Several vinyl monomers were found to graft onto the PDMS surface, as revealed by their attenuated total reflectance infrared and ESCA spectra. Hydrophilicity of the grafted PDMS surfaces was confirmed by the decrease in their water contact angle.     

Graft polymerization of some vinyl monomers onto alkali-treated cellulose

Treatment of cellulose by different concentrations of alkali, namely, 5–30% NaOH, changed its fine structure and transferred cellulose I into cellulose II. The decreased crystallinity due to alkali treatment and the transformation of cellulose I into cellulose II lowered the reactivity of cellulose toward the grafting polymerization reactions. Compactness of the structure as a result of the treatment of cellulose with 5% sodium hydroxide concentration decreased the rate of the grafting reaction and the grafting yield. On the other hand, such treatment of cellulose with different concentrations of alkali increased the rate of ceric consumption, i.e., increased the rate of oxidation of cellulose. Thus, the termination reaction of the grafting polymerization process may occur as a result of such oxidation and because of the increase of the active sites onto cellulose, leading to a decrease of the grafting yields and rate of grafting polymerization reaction by using the free-radical grafting process. The use of the ionic-xanthate method of grafting polyvinyl- and polyallyl-on alkali-treated cellulose shows an increase of grafting efficiency and grafting yields. Maximum grafting efficiency and yields were achieved when cellulose was treated with sodium hydroxide concentration below 15%, and maximum crystallinity indices were obtained. Using 15–25% sodium hydroxide lowered the indices of crystallinity, and lower grafting yields and grafting efficiency were achieved. Thus, transformation of cellulose I into cellulose II decreased the reactivity of these treated celluloses toward graft polymerization reactions by the use of the ionic-xanthate method. In our opinion, termination reactions may also occur and affect the results.     

Graft polymerization of vinyl acetate onto silica

The free‐radical graft polymerization of vinyl acetate onto nonporous silica particles was studied experimentally. The grafting procedure consisted of surface activation with vinyltrimethoxysilane, followed by free‐radical graft polymerization of vinyl acetate in ethyl acetate with 2,2′‐azobis(2,4‐dimethylpentanenitrile) initiator. Initial monomer concentration was varied from 10 to 40% by volume and the reaction was spanned from 50 to 70°C. The resulting grafted polymer, which was stable over a wide range of pH levels, consisted of polymer chains that are terminally and covalently bonded to the silica substrate. The experimental polymerization rate order, with respect to monomer concentration, ranged from 1.61 to 2.00, consistent with the kinetic order for the high polymerization regime. The corresponding rate order for polymer grafting varied from 1.24 to 1.43. The polymer graft yield increased with both initial monomer concentration and reaction temperature, and the polymer‐grafted surface became more hydrophobic with increasing polymer graft yield. The present study suggests that a denser grafted polymer phase of shorter chains was created upon increasing temperature. On the other hand, both polymer chain length and polymer graft density increased with initial monomer concentration. Atomic force microscopy–determined topology of the polymer‐grafted surface revealed a distribution of surface clusters and surface elevations consistent with the expected broad molecular‐weight distribution for free‐radical polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 300–310, 2003     

Graft polymerization of vinyl acetate onto silica

A method is reported for the surface grafting of polyvinyl acetate (PVAc) onto modified, nonporous silica. The silica surface was modified by silylation with vinyl(triethoxy) silane followed by graft polymerization of vinyl acetate. The graft yield was measured by thermogravimetric analysis and the monomer conversion was monitored by UV spectral analysis. The rate of the graft polymerization and the graft yield were proportional to the initial monomer concentration. Vinyl acetate conversion followed first-order kinetics and displayed a trend of increasing initial rate with increasing monomer concentration.