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1.
Atomic force microscopy was used to study polystyrene‐modified silica surfaces produced by admicellar polymerization (polymerization of monomers solubilized in adsorbed surfactant aggregates). The goal was to examine changes in the location and nature of the formed polystyrene resulting from changes in the surfactant and monomer feed levels on precipitated silica. Normal tapping and phase‐contrast modes in air were used to image the topography of the polystyrene‐modified silica. Moderate‐to‐light force‐tapping mode was used to differentiate between the silica surface and adsorbed water or polymer. The formed polystyrene exists primarily in the pores, with patches extending onto the exposed surface of the silica particles. At moderate tapping forces, darker phase regions were observed in the valleys and pores of the silica in both the modified and the unmodified samples. Upon higher magnification, the darker regions disappear on unmodified silicas, whereas polymer bands become evident on the modified silicas. At lower loadings of surfactant and monomer, the number and extent of polymer patches decreased, with polymer being found only in pores. The polystyrene patches observed inside the valleys of the amorphous silica varied from 1 to 10 nm in thickness. The structure of the polystyrene film formed on precipitated silica was found to be insensitive to the surfactant feed concentration. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 290–299, 2003  相似文献   

2.
Exfoliated graphite nanoplatelets were modified by hexadecyltrimethylammonium bromide (C16TAB) and were used for the construction of [poly(acrylic acid)/graphite]n [(PAA/G)n] multilayer films using a layer‐by‐layer (LBL) self‐assembly method. The film thickness was monitored using X‐ray diffraction technique; the results showed that the thickness depended on pH of PAA. Under a lower pH value such as 1.5, the average bilayer thickness was 1.5 nm. Once the pH of PAA was increased to 6.5, the bilayer thickness was around 30 nm. The C16TAB modified (PAA/G)n multilayer films showed high thermal stability and electrical conductivity. A percolation phenomenon occurred at bilayer number of 11, and the mechanism was discussed. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers  相似文献   

3.
A poly(styrene‐co‐acrylic acid) copolymer was synthesized by surfactant‐free polymerization with the assistance of power ultrasound in water. Fourier transform infrared, NMR, and differential scanning calorimetry measurements revealed that the copolymer was random. Atomic force microscopy and laser light scattering were used to investigate the self‐assembly of the copolymer, and it was found that the copolymer chains formed micelles or other self‐assemble structures in solution. Atomic force microscopy also indicated that the self‐assembled structures developed into nanospheres with a poly(acrylic acid)‐rich or polystyrene‐rich surface in a film, depending on the solvent used for the preparation of the film. In particular, a wheel‐like structure could resulted in a film when the copolymer film was prepared in a moist environment; it resulted from heterogeneous aggregates of poly(acrylic acid) at the rim of water bubbles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:3718–3726, 2006  相似文献   

4.
Yutao Liu 《Drying Technology》2017,35(13):1619-1628
To overcome the problem of moisture re-adsorption of dried lignite with common evaporation drying methods, a set of linear alkyl quaternary ammonium surfactants (C10TAB, C12TAB, and C16TAB) were used to modify lignite surface, and the effects of alkyl chain length on the adsorption characteristics of surfactants and wettability of lignite surface were evaluated. Pseudo-first and pseudo-second-order kinetic models and Langmuir model were, respectively, used to simulate adsorption kinetics and adsorption isotherms. The results showed that three surfactants gradually formed double-layer adsorption on lignite surface and the loading of surfactant increased with the length of alkyl chain. X-ray photoelectron spectroscopy analysis showed that C3H9N+ moiety of the surfactants would preferentially interact with O?C?O groups of lignite. Results of wetting heating and moisture re-adsorption showed that three surfactants obviously decreased hydrophilicity and restrained moisture re-adsorption of lignite, but with the formation of double-layer adsorption, hydrophilic headgroups of surfactant faced outward, which caused increase in hydrophilicity of lignite. As a result of two opposite effects of surfactant chain length on lignite wettability, the effect of C12TAB on decreasing hydrophilicity was the best among the three chosen surfactants.  相似文献   

5.
The composite double‐layered films, for the packaging application of postharvest fruits and vegetables, were prepared by laminating low‐density polyethylene (LDPE) and poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) modified with zeolite ZSM‐5. The film was characterized by scanning electron microscope and differential scanning calorimeter and tested for permeation of ethylene (C2H4), oxygen (O2), carbon dioxide (CO2), and water vapor. It was found that the C2H4 permeability of the films was improved because of an enhanced adsorption of C2H4 by the incorporated zeolite (0–10 wt%). The preconcentrated layer (zeolite/SEBS) leads to a higher C2H4 concentration gradient across the film. Moreover, the high dispersion of zeolite increased the C2H4 permeation. When compared with O2 and CO2, the composite films were more selective to C2H4. However, the C2H4 permeation decreased in the presence of O2 because of a competitive adsorption. In addition, the films possessed appreciate tensile properties for packaging application. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers  相似文献   

6.
The influence of CnTAB cationic surfactant chain length (n = 8, 10, and 12) on the reaction rate of zinc powder and 0.1 M HCl hydrochloric acid in aqueous solutions was determined at room temperature. Solutions of single surfactants consisting of dodecyl, decyl, and octyl-trimethyl-ammonium bromide surfactants CnTAB were prepared at room temperature. From the surface tension and conductivity measurements, the critical micelle concentration (CMC) values of the three surfactants were obtained in the presence and absence of the acid. No significant change was observed for CMC values in pure water and in 0.01 M HCl. Adsorption of CnTAB surfactants onto 1% wt./vol zinc (in powder form), using surface tension measurements, was then investigated. The adsorption tendency of CnTAB surfactants onto zinc powder followed the order: C8TAB > C10TAB > C12TAB. The role of surfactants in the reaction rate between zinc powder and 0.1 M M HCl was then investigated using conductivity measurements. A significant difference in the reaction rate was found depending on the surfactant chain length. Reaction times of 3830, 4963, 14,172, and 20,053 s were found for the zinc reaction with (0.1 M HCl), (0.1 M HCl + 40 mM C8TAB), (0.1 M HCl + 40 mM C10TAB), and (0.1 M HCl + 40 mM C12TAB), respectively, suggesting a significant dependency of the reaction rate on the CnTAB chain length. Finally, some corrosion parameters such as the corrosion rate, corrosion inhibition efficiency, and their dependency on CnTAB chain length were presented and discussed.  相似文献   

7.
Microporous carbons have been synthesized by the carbonization of cationic surfactant-resorcinol/formaldehyde (RF) composites, which were themselves formed by electrostatic organic-organic interaction. The porous structure produced by the decomposition of the surfactant plays an important role for the gasification of the RF polymer at higher temperatures. The pore size of the carbon prepared from tetrapropylammonium bromide (TPAB)-RF, cetyltrimethylammonium bromide (C16TAB)-RF and decyltrimethylammonium bromide (C10TAB)-RF mixtures can be estimated as 0.53 nm from the Horvath-Kawazoe method using N2 adsorption isotherms. Their pore size distributions were very narrow, showing that the microporous carbons derived from surfactant-RF mixture may have promise as adsorbents and membrane materials.  相似文献   

8.
In this paper, a comparative study with regard to the preparation and physical properties of as‐prepared polystyrene–silica mesocomposite (PSM) and polystyrene‐silica nanocomposite (PSN) materials is presented. Vinyl‐modified mesoporous silica particles with a wormhole structure were first prepared by doping a sol‐gel metal oxide with an optically active non‐surfactant (dibenzoyl‐L ‐tartaric acid) as a template, followed by template removal through Soxhlet extraction. The as‐prepared silica particles with/without mesopores were subsequently characterized using the Brunauer–Emmett–Teller method and transmission electron microscopy (TEM) and Fourier transform infrared, 13C NMR and 29Si NMR solid‐state spectroscopy. A specific feed amount of silica particles was subsequently reacted with styrene monomer by free radical polymerization to yield a series of PSM and corresponding PSN materials. Both as‐prepared composite systems were further characterized using TEM and scanning electron microscopy/energy‐dispersive X‐ray mapping studies. A systematic comparative study of the physical properties of both as‐prepared composite materials clearly illustrated that PSM had effectively enhanced thermal stability, optical clarity and dielectric properties compared to the corresponding PSN counterpart. Evaluation was carried out using thermogravimetric analysis, differential scanning calorimetry, UV‐visible transmission spectroscopy and dielectric constant measurements. Copyright © 2011 Society of Chemical Industry  相似文献   

9.
The polystyrene–silica hybrid materials have been successfully prepared from styrene and tetraethoxysilane in the presence of silane‐coupling agents by an in situ sol‐gel process. Triethoxysilyl group can be incorporated into polystyrene as side chains by the free‐radical copolymerization of polystyrene with silane‐coupling agents, and simultaneously polystyrene–silica hybrid materials with covalent bonds between two phases were formed via the sol‐gel reaction. The 3‐(trimethoxysilyl)‐propyl‐methacrylate (MPS) systems were found to be more homogeneous than the corresponding allytrimethoxysilane hybrid system of equal molar content. In the MPS‐introduced system, the thermal properties of the materials were greatly affected by the presence of MPS. FTIR results indicate successful formation of the silica networks and covalent bonding formation of coupling agents with styrene. The homogeneity of polystyrene–silica systems was examined by scanning electron microscope and atomic force microscope. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2074–2083, 2002  相似文献   

10.
The present study is about the foaming and defoaming properties of the CO2-switchable surfactant N,N-dimethyltetradecylamine (C14DMA) and its advantages compared with the non-switchable counterpart tetradecyltrimethylammonium bromide (C14TAB). In the absence of CO2, C14DMA is a water insoluble organic molecule without any surface activity thus being unable to stabilize foams. In the presence of CO2, the head group becomes protonated which transforms the water insoluble molecule into a cationic surfactant. Comparing the surface properties and foamability of C14DMA and C14TAB one finds a very similar behavior. However, the foam stabilities differ depending on the gas. Foaming the two-surfactant solutions with CO2 leads to very unstable foams in both cases. However, foaming the two surfactant solutions with N2 reveals the switchability of C14DMA: while the volume of foams stabilized with C14TAB hardly changes over 1600 s, the volume of foams stabilized with C14DMA decreases significantly in the same period of time. This difference is due to the fact that the surface activity, that is, the amphiphilic nature, of C14DMA is continuously switching off since CO2 is displaced by N2 thus deprotonating and deactivating the surfactant.  相似文献   

11.
Pre-formed polycrystalline Palladium aggregates (ca. 200 nm in diameter) were coated by thin mesoporous silica layers to form metal-mesoporous silica composite materials. To synthesize the composites, Pd aggregates were dispersed in an aqueous solution of C16H33N(CH3)3Br to which tetraethylorthosilicate (TEOS) was then added to give composite precipitates. The surfactant template in the precipitate was subsequently removed by extraction with an acetic acid/ethanol solvent. TEM images of the composite (containing as much as 65 wt% Pd) revealed that the Pd aggregates were fully surrounded by mesoporous silica layers (ca. 50 nm in thickness) having ordered pores that penetrate to large extent from the exterior to the surface of Pd aggregates. When the materials were used as catalysts for cinnamaldehyde hydrogenation in toluene, the reactant molecules were concentrated in the meso channels by a factor of ca. 3. Accordingly, the composites showed comparable or higher activity than that observed for neat Pd aggregates. This study highlights the preparation of unique metal-mesoporous silica composite materials by simple synthetic procedures and which are usable as active Pd catalysts.  相似文献   

12.
Film formation from surfactant‐free polystyrene (PS) latex was performed in the presence of 5% Na‐montmorillonite (NaMMT). The composite films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures above the glass‐transition (Tg) temperature of polystyrene. Scattered light (Is) and fluorescence intensity (IP) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T0, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities. POLYM. COMPOS., 27:299–308, 2006. © 2006 Society of Plastics Engineers  相似文献   

13.
C60‐bonded polystyrene was produced with a novel initiator system, C60Cln/CuCl/2,2′‐bipyridine (where the average value of n is 20). The molar ratio of styrene/C60Cln/CuCl/bpy was 100:1/20:1:2, and the polymerization temperature was 130°C. Gel permeation chromatography detected with an ultraviolet detector demonstrated that C60 was chemically bonded to polystyrene. The linear increase in the number‐average molecular weight (by gel permeation chromatography) with the conversion indicated that this novel initiator system had some characteristics of living polymerization. A possible polymerization mechanism was examined. The photoconducting properties of C60‐bonded polystyrene were better than those of polystyrene initiated with CCl4. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3001–3004, 2002  相似文献   

14.
This study addresses the effect of particle structure and composition on the mobility and orientation of sodium dioctyl sulfosuccinate (SDOSS) surfactant molecules in polybutyl acrylate/polystyrene core/shell-type latex films near the film-air (F-A) and film-substrate (F-S) interfaces. In an effort to determine how the surface tension of the substrate influences the migration and orientation of the SDOSS surfactant molecules, polytetrafluoroethylene (PTFE) and liquid Hg substrates were used. It appears that, as the concentration of styrene monomer in the latex increases, SDOSS migrates toward the F-A and F-S interfaces. As the surface tension of the substrate changes from 18 mN/m in PTFE to 400 mN/m for liquid Hg, the surfactant also migrates toward the two interfaces. For the latex particles composed of 50%/50% styrene/n-butyl acrylate (Sty/n-BA) latex copolymer, the hydrophilic SO3Na+ groups of SDOSS surfactant are present primarily near the F-A interface, and they appear to be mostly parallel to the surface for the films cast on the PTFE surface. For the latex films cast on the liquid Hg surface, the SDOSS hydrophilic surfactant groups are found to be preferentially parallel near the F-A interface and perpendicular near the F-S interface. These studies indicate that the surfactant concentration and its orientation throughout the latex film change as a function of the initial monomer composition and the surface tension of the substrate. Furthermore, the SDOSS concentration appears to vary with depth into the latex interfaces. © 1996 John Wiley & Sons, Inc.  相似文献   

15.
End silane functionalized polystyrene and polymethylmethacrylate were prepared through radical chain‐transfer reaction and characterized with gel‐permeation chromatography. The chain‐transfer constants of mercaptopropyltrimethoxysilane for the polymerization of styrene and methylmethacrylate were determined to be 8.48 and 0.67, respectively, from the slopes of 1/DPn versus [S]/[M] lines. The ultrathin films of the end silane–terminated polymers were prepared by self‐assembly onto hydroxylated silicon wafers. The water contact angle on the resulting ultrathin films and the film thickness were measured. The morphology and chemical features of the films were observed and investigated by means of atomic force microscopy and X‐ray photoelectron spectroscopy. Results indicated that the chain‐transfer agent played a key role in making it possible for the silane‐terminated polystyrene and polymethylmethacrylate to be self‐assembled on Si(111), whereas the thickness and surface quality of the ultrathin films were dependent on the molecular weights of the polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1695–1701, 2004  相似文献   

16.
Pentaerythritol (PT) was converted into four‐arm initiator pentaerythritol tetrakis(2‐chloropropionyl) (PT‐Cl) via reaction with 2‐chloropropionyl chloride. Uniform (monodisperse) star‐polystyrene nanoparticles were prepared by emulsion atom transfer radical polymerization of styrene, using PT‐Cl/CuCl/bpy (bpy is 2,2′‐dipyridyl) as the initiating system. The structures of PT‐Cl and polymer were characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. The morphology, size and size distribution of the star‐polystyrene nanoparticles were characterized by transmission electron microscopy, atomic force microscopy and photon correlation spectroscopy. It was found that the average diameters of star‐polystyrene nanoparticles were smaller than 100 nm (30–90 nm) and monodisperse; moreover, the particle size could be controlled by the monomer/initiator ratio and the surfactant concentration. The average hydrodynamic diameter (Dh) of the nanoparticles increased gradually on increasing the ratio of styrene to PT‐Cl and decreased on enhancing the surfactant concentration or increasing the catalyst concentration. Copyright © 2011 Society of Chemical Industry  相似文献   

17.
Hyung Woo Lee  Kyu Yong Choi 《Polymer》2005,46(14):5032-5039
The physical transitions and nascent morphology of syndiotactic polystyrene (sPS) synthesized over heterogeneized embedded Cp*Ti(OMe)3/MAO catalyst in n-heptane slurry polymerization have been investigated. The homogeneous metallocene catalyst is heterogenized by embedding active titanium sites into an sPS prepolymer phase. At low styrene concentrations, the reaction mixture is well-dispersed slurry of sPS particles and at high styrene concentrations, swollen sPS particles form aggregates that become a wet powder phase. For a wide range of styrene concentrations, no global gelation occurs with the embedded catalyst. Complex nascent morphology of sPS polymers is also presented. Scanning electron microscopic images show that spherical as well as irregular-shaped microparticles, films, and fibers are formed and that particle generation and growth mechanisms are different from that of heterogeneously catalyzed α-olefin polymerization processes.  相似文献   

18.
Structured latex particles with a slightly crosslinked poly(styrene‐n‐butyl acrylate) (PSB) core and a poly(styrene–methacrylate–vinyl triethoxide silane) (PSMV) shell were prepared by seed emulsion polymerization, and the latex particle structures were investigated with Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, transmission electron microscopy, and dynamic light scattering. The films that were formed from the structured core (PSB)–shell (PSMV) particles under ambient conditions had good water repellency and good tensile strength in comparison with films from structured core (PSB)–shell [poly(styrene–methyl methyacrylate)] latex particles; this was attributed to the self‐crosslinking of CH2?CH? Si(OCH2CH3)3 in the outer shell structure. The relationship between the particle structure and the film properties was also investigated in this work. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1824–1830, 2006  相似文献   

19.
Qunwei Tang  Qinghua Li  Jianming Lin 《Polymer》2008,49(24):5329-5335
Exfoliated graphite (G) nanoplatelet was modified with hexadecyltrimethylammonium bromide (C16TAB) and was constructed as multilayer films by electrostatic self-assembly. A [poly(sodium styrenesulfonate)/graphite]n (PSS/G)n multilayer film was self-assembled by alternate adsorption of polyanionic PSS and cationic graphite nanoplatelets G. An uniform deposition process was detected by UV-vis absorption spectra. The (PSS/G)n multilayer film exhibits an excellent electrical conductivity in the range of 50-200 S cm−1, when bilayer number (n) exceeds a threshold value four, the conductivity of the multilayer film increases dramatically. Cyclic voltammogram measurement reveals that the (PSS/G)n film with more bilayer has small charge-transfer resistance and high electrocatalytic activity.  相似文献   

20.
Electrochemical properties of eight methanofullerene films, prepared on electrodes by casting, were examined by means of cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) technique in acetonitrile solution. Compared with C60 film, the film stability with respect to dissolution is associated with the length of the alkyl chains introduced into C60 cage and is strongly dependent on the nature of the cation of the supporting electrolyte. TBA+, Li+, K+, and Na+ were selected to observe the effect of countercations on the electrochemical behavior of methanofullerene films. In TBAPF6 solution, when short chains, such as formic ether or butyl butyrate groups, were introduced into C60 cage, the film stability was less than that of C60. When the length of the alkyl chain was extended to butyl 12 alkanoate group, the film would not dissolve until the third reduction process because the long alkyl chain could inflect and encase the cations into the film. In KPF6 or NaClO4 solution, however, the solubility of the salt formed by K+ or Na+ with methanofullerene anion was higher than that formed by TBA+ with methanofullerene anion. Li+ (alkali metal) affected the behavior of the films in different ways. The possible electron‐transfer mechanisms of methanofullerene films in various supporting electrolyte solutions were presented. Furthermore, the film images observed by atomic force microscopy indicated that TBA+ and Li+ affected the behavior of the methanofullerene films in different ways. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3634–3640, 2006  相似文献   

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