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ABSTRACT: In this paper, the relationship between the surface structure of fluorinated polymers and their protein-resistant property was studied by preparing films of poly(n-alkyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate (FMA) (PFMA(y)-ec-PnAMA(x)-ec-PFMA(y)) with various ordered structures of perfluorinated alkyls. These fluorinated polymers were synthesized via a controlled/living atom-transfer radical polymerization (ATRP) method. Both the surface free energy and the CF(3)/CF(2) ratio obtained by X-ray photoelectron spectroscopy (XPS) were employed to scale the ordered structures of the perfluorinated alkyls. Protein adsorption studies using fibrinogen as a test molecule were undertaken on the various films by XPS. The results show that the adsorbed mass of fibrinogen decreased linearly with increasing CF(3)/CF(2) ratio on the fluorinated polymer surfaces. When the CF(3)/CF(2) ratio reaches 0.26, there was almost no fibrinogen adsorption. This work not only demonstrates the design of a fluorinated copolymer film on glass substrate with desirable protein-resistant performance, but also provides a fundamental understanding of how the orientation of perfluoroalkyl side chains affects protein-resistant behavior on fluorinated surfaces.
Journal of Colloid and Interface Science 10/2012; · 3.07 Impact Factor
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ABSTRACT: Previously, we developed several methods to use sum frequency generation (SFG) vibrational spectroscopy to probe buried polymer/metal interfaces in situ by depositing polymer films with different thicknesses on metal surfaces or sandwiching a polymer thin film between a metal surface and a fused silica window. In this study, we developed a new and easier method to directly probe the polymer/ metal interface by collecting ppp SFG spectra using a poly(ethyl methacrylate) (PEMA)/silver (Ag) interface as an example. We confirmed that for a thin polymer film on metal, the dominant SFG signals were contributed from the polymer surface in air and/ or the polymer metal interface, while the contribution from the polymer bulk could be ignored. Previously, we showed that the ssp spectra were contributed by both the polymer/air and polymer/metal interfaces. Here we demonstrated that the SFG ppp spectra were dominated by signals from the buried polymer/metal interface from which the structural information on the buried interface can be deduced. This method to probe the buried polymer/metal interface via SFG is relatively simple compared to our previous sample preparation techniques and/or data analysis methods.
Macromolecules 07/2012; · 5.17 Impact Factor
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ABSTRACT: Most research on copolymers with fluorinated monomers has focused on the relationship between fluorinated monomer content
and the corresponding surface structure. However, the influence of the non-fluorinated block on the surface structure of the
copolymer film is unknown. Various molecular weight poly(butyl methacrylates) (PBMA) end-capped with 2-perfluorooctylethyl
methacrylate (FMA) units (PBMA-ec-FMA) have been synthesized by atom transfer radical polymerization (ATRP). The effect of the PBMA block length on the surface
structure and properties of the polymers both in the solid state and in solution was investigated using various techniques.
X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy and X-ray diffraction (XRD)
analyses indicated that longer PBMA blocks enhanced both the enrichment of the fluorinated moieties and the order of the packing
orientation of the perfluoroalkyl side chains on the surface. This enhancement was attributed mainly to the molecular aggregate
structure of the end-capped polymers with long PBMA blocks in the solution and to the interfacial structure at the air/liquid
interface, which favors the -(CF2)7CF3 moieties self-assembling on the polymer surface during film formation. This observation suggests that the polyacrylate block
structure in fluorinated diblock copolymers, in addition to the fluorinated monomer content, plays an important role in structure
formation on the solid surface.
Science in China Series B Chemistry 04/2012; 52(12):2295-2306. · 1.20 Impact Factor
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ABSTRACT: The fluorinated copolymer poly (MMA–co–FMA), composed of methyl methacrylate (MMA) and 2-perfluorooctylethyl methacrylate
(FMA), was prepared by emulsion polymerization using a pre-emulsified monomer addition process. The results showed that the
contact angle of water on its solvent-borne film increased dramatically and reached 118º when the FMA content in the copolymer
was only 0.65mol%, approaching that of poly(2-perfluorooctylethyl methacrylate) homopolymer. Unlike the copolymer prepared
by solution polymerization, X-ray photoelectron spectroscopy (XPS), and sum frequency generation (SFG) vibrational spectroscopy
analysis results indicated that the fluorinated moieties in this polymer were very easily segregated at the surface of the
film. The interfacial structure and properties of this polymer in solution were investigated using SFG, surface tension, and
dynamic laser light scattering (DLS). It was found that emulsion polymerization produced a chain structure of the fluorinated
copolymer similar to that of FMA capped PMMA, thereby providing a possible way to produce fluorinated end-capped polymers
using a popular polymerization method.
Polymer Bulletin 04/2012; 64(1):81-97. · 1.53 Impact Factor
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ABSTRACT: Sum frequency generation (SFG) vibrational spectroscopy has been proved to be a powerful technique which substantially impacts
on many research areas in surface and interfacial sciences. This paper reviews the recent progress of applying this nonlinear
optical technique in the studies of polymer surfaces and interfaces. The theoretical background of SFG is introduced first.
Current applications of SFG in polymer science are then described in more detail to demonstrate the significance of this technique.
Finally, a short summary is presented on this relatively new but widely applicable spectroscopic technique.
Keywordssum frequency generation vibrational spectroscopy-SFG-nonlinear optical technique-surface and interface-polymer
Frontiers of Chemistry in China 04/2012; 5(4):435-444.
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ABSTRACT: In this paper, a series of poly(styrene-b-isoprene-b-styrene) triblock copolymers (SIS), with different chemical components, was synthesized by anionic polymerization. The relationships between surface structures of these block copolymers and their stick-slip phenomena were investigated. There is a transition from stick-slip to a closely smooth motion for the SIS films with increasing PS content; the patterns almost vanish and the three-phase line appears to move overall smoothly on the film surface. The results show that the observed stick-slip pattern is strongly dependent on surface viscoelasticity. The jumping angle Δθ, which is defined as θ(1) - θ(2) (when a higher limit to θ(1) is obtained, the triple line "jumps" from θ(1) to θ(2) with increases in drop volume), was employed to scale the stick-slip behavior on various SIS film surfaces. Scanning force microscopy/atomic force microscopy (AFM) and sum frequency generation methods were used to investigate the surface structures of the films and the contributions of various possible factors to the observed stick-slip behavior. It was found that there is a linear relationship between jumping angle Δθ and the slope of the approach curve obtained from AFM force measurement. This means that the stick-slip behavior may be attributed mainly to surface viscoelasticity for SIS block copolymers. The measurement of jumping angle Δθ may be a valuable method for studying surface structure relaxation of polymer films.
Langmuir 03/2012; 28(9):4283-92. · 4.19 Impact Factor
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ABSTRACT: Monolayer detection on metal surface requires ultra high sensitivity. Sum Frequency Generation Spectroscopy (SFG) and Surface Enhanced Raman Spectroscopy (SERS) are regarded as two powerful techniques with submolecular sensitivity to detect adsorbents on metal surface. However, in some cases it's still challenge to characterize molecules or groups with relatively high intramolecular symmetry, such as 4-Nitrothiophenol (4NTP), on flat metal surface even combining these two techniques. Basically, this is due to that 4NTP with para-substituted phenol groups is SFG insensitive while flat metal surface is unfavorable to yield strong SERS enhancement. In this concern, a simple and efficient method, silver mirror method, was employed to facilitate the detection of 4NTP SAM on flat gold surface. Silver nanopheres with diameters around 300 nm was fabricated through silver mirror reaction and in situ formed milky overlayer on top of 4NTP SAM adsorbed on gold surface. Significant enhancement on SERS signal can be achieved with such special assembly structure of the "metal-molecule-metal" system. Generally, the silver mirror method provided a complementary approach to facilitate the spectroscopic applications of molecule level detection on various metal surfaces in situ.
Journal of Nanoscience and Nanotechnology 01/2012; 12(1):361-4. · 1.56 Impact Factor
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ABSTRACT: New fluorinated copolymers of poly(methyl methacrylate)-b-poly(butyl methacrylate) or poly(n-octadecyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate (PMMA(x)-b-PBMA(y)-ec-PFMA(z) or PMMA(x)-b-PODMA(y)-ec-PFMA(z)) were synthesized by living atom transfer radical polymerization. Thin films made of PMMA(230)-b-PODMA(y)-ec-PFMA(1) were characterized by differential scanning calorimetry, angle-resolved X-ray photoelectron spectroscopy and X-ray diffraction. These films were found to exhibit robust surface segregation of the end groups. Furthermore, the fluorine enrichment factor at the film surface was found to increase linearly with increasing degree of polymerization of poly(n-octadecyl methacrylate) and its increasing fusion enthalpy in the second block, which enhances the segregation of the fluorinated moieties.
Journal of Colloid and Interface Science 01/2012; 365(1):260-7. · 3.07 Impact Factor
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ABSTRACT: The title racemic heterometallic dinuclear compound, [MnSn(C(2)H(2)O(2)S)(3)(H(2)O)(5)], (I), contains one main group Sn(IV) metal centre and one transition metal Mn(II) centre, and, by design, links the Mn(II) centre to the building unit of the (Δ/Λ) [SnL(3)](2-) complex anion (L is the 2-sulfidoacetate dianion). In this cluster, the Sn(IV) centre of the (Δ/Λ) [SnL(3)](2-) unit is coordinated by three O atoms and three S atoms from three L ligands to form an [SnO(3)S(3)] octahedral coordination environment. The Mn(II) centre is in an [MnO(6)] octahedral coordination environment, with five O atoms from five water molecules and the sixth from the μ(2)-L ligand of the (Δ/Λ) [SnL(3)](2-) unit. Between adjacent dinuclear molecules, there are many hydrogen-bond interactions of O-H···O, O-H···S, C-H···O and C-H···S types. Of these, eight pairs of O-H...O hydrogen bonds fuse all the dinuclear molecules into two-dimensional supramolecular sheets along the bc plane. Adjacent supramolecular sheets are further connected through O-H···S hydrogen bonds to give a three-dimensional supramolecular network.
Acta crystallographica. Section C, Crystal structure communications 12/2011; 67(Pt 12):m384-6. · 0.78 Impact Factor
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ABSTRACT: In the title salt, [Fe(C(12)H(8)N(2))(3)][Fe(2)Cl(6)O], the ionic components are linked into a two-dimensional supra-molecular layer by two pairs of C-H⋯Cl hydrogen bonds and π-π stacking inter-actions [centroid-centroid distances = 3.655 (4) and 3.498 (3) Å]. The salt is characterized as a mixed-valent Fe(II)-Fe(III) compound, in which an Fe(II) atom is coordinated by three phen ligands, forming a six-coordinated cationic entity and the anionic part is formed by two Fe(III) atoms in tetra-hedral coordination environments constructed by three chloride ions and one bridging oxide ligand. Intra-molecular C-H⋯N hydrogen bonds are observed.
Acta Crystallographica Section E Structure Reports Online 09/2011; 67(Pt 9):m1232-3. · 0.35 Impact Factor
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ABSTRACT: The effects of the alkyl group on the surface segregation of poly(n-alkyl methacrylate) end-capped with various numbers of units of 2-perfluorooctylethyl methacrylate (FMA) (PnAMA-ec-PFMA) were investigated by differential scanning calorimetry, angle-resolved XPS analysis, contact angle measurements, and X-ray diffraction (XRD). The results show that with similar numbers of FMA units at the polymer chain end the extent of fluorine segregation (Q) increased with increasing the number of carbon atoms in the side n-alkyl chains of poly(n-alkyl methacrylate). The surface fluorine content within 5 nm deep of the film of poly(n-octadecyl methacrylate) end-capped with one FMA unit (PODMA(160)-ec-PFMA(1.0)) was 208-fold higher than that of the bulk level. These observed differences in Q values were found due to the aggregate structure of the end-capped polymers in the solution, the flexibility, and the crystallinity of the n-alkyl side chains. When the nonfluorinated block was completely amorphous, the molecular aggregate structure of the end-capped polymers in the solution played an important role in the surface segregation of the fluorinated moieties on the resulting film. However, when the nonfluorinated block was crystalline, crystallinity would enhance greatly the segregation of the fluorinated moieties.
Journal of Colloid and Interface Science 07/2011; 359(1):269-78. · 3.07 Impact Factor
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ABSTRACT: On the basis of the development in the literature, a thin film model was used to interpret the thickness-dependent sum frequency generation (SFG) spectra collected from the air/silica/poly(n-butyl methacrylate) (PBMA)/water system. By taking into account the Fresnel coefficients of the PBMA layers at the silica/PBMA and PBMA/water interfaces, the SFG spectra of the silica/PBMA and PBMA/water interfaces were obtained. The side chain methyl vibrational modes at the two interfaces were found to have opposite phases. This suggests that the side chain methyl groups at the two interfaces adopt different absolute orientations. It is believed that methyl groups at both interfaces point toward the PBMA bulk considering the unfavorable interactions between the hydrophobic methyl groups and hydrophilic silica surface and water. Orientation analysis indicates the side chain methyl groups at both interfaces tilt more toward the interfaces rather than be perpendicular to them. Applying the thin film model to the air/PBMA/silica system, we found that the surface signals from PBMA in air dominate the SFG output on account of the relatively higher Fresnel coefficients at this surface over those of the buried PBMA/silica interface.
06/2011;
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Procedia CS. 01/2011; 4:1193-1202.
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ABSTRACT: The effects of solvents, fluorinated monomer content and film-formation methods on the surface structures of random copolymers composed of methyl methacrylate (MMA) and 2-perfluorooctylethyl methacrylate (FMA) were investigated by contact angle goniometry, X-ray photoelectron spectroscopy, sum frequency generation (SFG) vibrational spectroscopy and surface tension measurement. It is found that, with cyclohexanone as the solvent, there is a critical FMA content of 9mol%, below which the copolymer films by spin coating have a more surface segregation extent of fluorinated moieties than those by solution casting; above which the copolymer films by solution casting have a more surface segregation extent of fluorinated moieties than those by spin coating. However, with toluene as solvent, the critical FMA content lowers down to 3mol%. We believe that the solvent nature and the content of fluorinated moieties in the random copolymer have the great effect because the combined effect of these two factors can determine the random copolymer chain conformations and their thermodynamic dominating factors in the solution and at the solution-air interface. A thermodynamic analysis combining the entropic and enthalpic effects is suggested to explain the observed phenomenon. This research is believed to obtain an enhanced understanding of the surface formation mechanism of the polymer films and thus demonstrate how to promote the segregation of fluorinated moieties at the polymer film surfaces.
Journal of Colloid and Interface Science 09/2010; 349(1):205-14. · 3.07 Impact Factor
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ABSTRACT: Surface-carboxylated nano-TiO2 was used to prepare poly (vinyl alcohol) (PVA) nanocomposites to improve the dispersity of nano-TiO2 particles in PVA and to enhance the interaction between nanofiller and matrix. The effects of the extents of carboxylation and carboxylated nano-TiO2 loading on mechanical properties of the nanocomposites were investigated. The results show that the tensile strength of the nanocomposites was greatly improved, both by increasing the carboxylated nano-TiO2 loading and by the extent of carboxylation of the nanoparticles, compared with unmodified nano-TiO2. The storage modulus within the rubbery state increased and the loss tangent decreased with increasing COOH content on the TiO2 surface and with increasing carboxylated nano-TiO2 loading. These observations were attributed to a high dispersion of modified nano-TiO2 in the PVA matrix and to crosslinking between OH groups in PVA chains and COOH moieties on inorganic nanoparticle surfaces. POLYM. COMPOS., 31:1184–1193, 2010. © 2009 Society of Plastics Engineers
Polymer Composites 08/2009; 31(7):1184 - 1193. · 1.23 Impact Factor
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ABSTRACT: The relationship between solution properties, film-forming methods, and the solid surface structures of random copolymers composed of butyl methacrylate and dodecafluorheptyl methylacrylate (DFHMA) was investigated by contact angle measurements, X-ray photoelectron spectroscopy, sum frequency generation vibrational spectroscopy, and surface tension measurements. The results, based on thermodynamic considerations, demonstrated that the random copolymer chain conformation at the solution/air interface greatly affected the surface structure of the resulting film, thereby determining the surface segregation of fluorinated moieties on films obtained by various film-forming techniques. When the fluorinated monomer content of the copolymer solution was low, entropic forces dominated the interfacial structure, with the perfluoroalkyl groups unable to migrate to the solution/air interface and thus becoming buried in a random-coil chain conformation. When employing this copolymer solution for film preparation by spin-coating, the copolymer chains in solution were likely extended due to centrifugal forces, thereby weakening the entropy effect of the polymer chains. Consequently, this resulted in the segregation of the fluorinated moieties on the film surface. For the films prepared by casting, the perfluoroalkyl groups were, similar to those in solution, incapable of segregating at the film surface and were thus buried in the random-coil chains. When the copolymers contained a high content of DFHMA, the migration of perfluoroalkyl groups at the solution/air interface was controlled by enthalpic forces, and the perfluoroalkyl groups segregated at the surface of the film regardless of the film-forming technique. The aim of the present work was to obtain an enhanced understanding of the formation mechanism of the chemical structure on the surface of the polymer film, while demonstrating that film-forming methods may be used in practice to promote the segregation of fluorinated moieties on film surfaces.
Langmuir 02/2009; 25(4):2248-57. · 4.19 Impact Factor
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ABSTRACT: A simple method of changing pre-treatment temperature in the course of film formation was used to tune the surface structures of PVA membranes. Surface structure and property of the resulting membranes were characterized by X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, and contact angle measurements. The results show that PVA have different molecular conformations at the membrane surface while those membranes were prepared at different pre-treatment temperature. At higher pre-treatment temperatures, polar acetoxyl residues and hydroxyl groups of the PVA chains oriented in a more orderly fashion, as induced by the faster evaporation of water. When the membranes were in air, CH(3) groups adjacent to the acetoxyl groups covered the surface in order to minimize the surface free energy, while backbones of the PVA were rarely observed. These surfaces exhibited a hydrophilic nature upon contact with water due to rapid surface reconstruction. Conversely, at lower pre-treatment temperatures, the backbone CH(2) groups dominated the surface, forming a less hydrophilic surface. When the PVA membranes were employed to separate ethanol/water mixtures, it was found that the PVA membranes with more hydrophilic surface exhibited higher water selectivity. Our investigation indicates that molecular conformations on the membrane surface have considerable influence on pervaporation performance.
Journal of Colloid and Interface Science 02/2009; 333(1):346-53. · 3.07 Impact Factor
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ABSTRACT: A series of diblock copolymers composed of methyl methacrylate and 2-perfluorooctylethyl methacrylate (PMMA144-b-PFMA
n
) with various PFMA block lengths were prepared by atom transfer radical polymerization (ATRP). The surface structures and
properties of these polymers in the solid state and in solution were investigated using contact angle measurement, X-ray photoelectron
spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, surface tension and dynamic laser light scattering
(DLS). It was found that with increasing PFMA block length, water and oil repellency decreased, the ratio of F/C increased
with increasing film depth, and the degree of ordered packing of the perfluoroalkyl side chains at the surface decreased.
When the number of PFMA block units reached 10, PMMA segments were detected at the copolymer surface, which was attributed
to the PFMA block length affecting molecular aggregation structure of the copolymer in the solution and the interfacial structure
at the air/liquid interface, which in turn affects surface structure formation during solution solidification. The results
suggest that copolymer solution properties play an important role in structure formation on the solid surface.
Science in China Series B Chemistry 01/2009; 52(2):203-211. · 1.20 Impact Factor
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ABSTRACT: The surface structure and stability (the resistance to surface reconstruction) of end-capped poly(methyl methacrylate) films were greatly affected by the solvents used for film preparation. Films of end-capped PMMA with about four 2-perfluorooctylethyl methacrylate units cast with benzotrifluoride solution exhibited excellent stability and resistance to polar environments compared with those cast with cyclohexanone and toluene solutions. The observed difference in stability between these fluorinated surfaces is attributed to their surface microstructures formed during the film formation processes, which are closely related to the associative behavior of the end-capped PMMA in the solution. A relatively perfect close-packed and well-ordered structure of the perfluoroalkyl side chains at the surface of the PMMA(857)-ec-FMA(3.3) film was formed when the film was cast with benzotrifluoride solution, in which only unimers existed. This study indicates that such a solvent effect may be used to promote the formation of a well-ordered packing structure of the fluorinated moieties at the film surface. The ordering of the packing structure is to a certain extent more important than the content of the fluorinated moieties at the surface for improving the surface stability.
Journal of Colloid and Interface Science 06/2008; 321(2):373-83. · 3.07 Impact Factor
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ABSTRACT: It is a challenge to fabricate fluorine-containing polymer surface with low-energy properties and superior long-lasting barrier
properties as well as lower fluorine content. In this paper, poly(butyl methacrylate) end-capped with 2-perfluorooctylethyl
methacrylate units (PBMA-ec-FMA) , having the so-called push-me/pull-you structures, have been synthesized by ATRP and their
surface properties were investigated. This structure was in favorable of the longer -(CF2)7CF3moieties self-assembling on the polymer surface during film formation, which resulted in better chain alignment and packing
of the longer -(CF2)7CF3moieties. Therefore, the contact angles of water and paraffin oil on the surface of the end-capped PBMA were 118° and 84°,
respectively, approaching that of poly(2-perfluorooctylethyl methacrylate) homopolymer, even though the content of FMA was
0.34mol% (the average polymerization degree of PFMA units is 1). However, more than 9mol% was necessary for the relative
random copolymer (PBMA-r-PFMA) to reach these values of the contact angle. Regardless of the wetting properties, the end-capped
PBMA by fluorinated methacrylate has better resistance to surface reconstruction than PBMA-r-PFMA random copolymer even though
FMA content in PBMA-ec-FMA is much lower than that in random copolymer. Therefore, it may be a facile method to create stable
hydrophobic surfaces with lower price.
Polymer Bulletin 05/2007; 59(1):105-115. · 1.53 Impact Factor
