PS Surface Research Articles

Amphiphilic Block Copolymer Films: Phase Transition, Stabilization, and Nanoscale Templates

A morphological transition of asymmetric poly(styrene-b-acrylic acid) (PS-b-PAA) films is observed by in situ scanning probe microscopy (SPM) in aqueous media. Upon initial exposure to buffer solution at pH 7.4, spherical PAA domains swell through a glassy PS surface layer to form negatively charged mushroom caps. With further exposure, the PAA caps coalesce to produce a smooth, highly wettable surface. However, if films are exposed to a buffer solution containing 3-aminopropyltriethoxysilane (APTES) for 1 h, the PAA domain swelling is greatly reduced and the mushroom caps stabilize at a diameter of 33 nm. This stabilization results from a cross-linking reaction between PAA and APTES, which also converts the PAA domains from a net negative to net positive charge. By varying molecular weights of PAA block in PS-b-PAA, the feature size and spacing can be tuned. To demonstrate an application for this template with positively charged domains, a cytoskeletal filament, F-Actin with a net negative charge, is org...

A FET Gas Sensor Device Based on Porous Silicon

The hydrogen-sensing property of new type field-effect gas sensor device was studied. The device had an FET structure based on porous silicon. Adsorption of molecules into the porous silicon strongly changes the electrical properties of the transistor structure. Interestingly, the current variation induced by Hydrogen gas vapour that is the sensitivity of the sensor can be electrically tuned by changing polarization voltage. It has been shown that the device exhibited excellent hydrogen-sensing characteristic at room temperature. The results show that current-voltage characteristics are modified by the gas reactivity on the PS surface. In conclusion, the FET gas sensor based on porous silicon shows a rapid response to low concentration of the hydrogen gas at room temperature.

An Effective Way To Hydrophilize Gigaporous Polystyrene Microspheres as Rapid Chromatographic Separation Media for Proteins

To overcome the disadvantages of protein denaturation and nonspecific adsorption on poly(styrene-divinylbenzene) (PS) medium as a chromatographic support, gigaporous PS microspheres prepared in our previous study were coated with hydrophobically modified agarose (phenoxyl agarose, Agap). Both the modification of agarose and the gigaporous structure of PS microspheres provided an advantage that facilitated the coating of Agap onto PS microspheres. The amount of Agap adsorbed onto the PS surface was examined as a function of the polymer concentration, and various samples of microspheres, differing in surface Agap density, were prepared. The adsorbed layer was then stabilized by chemical cross-linking and its stability was evaluated in the presence of sodium dodecyl sulfate. Results showed that PS microspheres were successfully coated with Agap, while the gigaporous structure could be well maintained. After coating, the nonspecific adsorption of proteins on PS microspheres was greatly reduced. Flow hydrodynamics experiments showed that the Agap-co-PS column had low backpressure, good permeability, and mechanical stability. Such a procedure could provide a hydrophilic low-pressure liquid chromatographic support for different types of chromatography, since the Agap layer may be easily derivatized by classical methods, and because of their good permeability, the coated microspheres have great potential applications in high-speed protein chromatography.

Research on immunosensor based on porous silicon

Porous silicon is functionalized using thermal oxidation and silanization. The HYSA antibodies are immobilized to the porous surface in this paper. The changes in the reflection spectrum and photoluminescence spectrum are investigated when BSA are attached to the PS surface. The result shows that the luminescence peak of PS disappears. After the antigen-antibody reaction, the higher light emission is observed and the reflection spectrum also red shifts. Therefore, this research lays a foundation for the development of sensitive label-free optical immunosensor.

Preparation of PS/Ag microspheres and its application in microwave absorbing coating

PS/Ag microspheres were prepared by electroless silver plating on PS microspheres. The PS microspheres with the average size of 1.6 μm were obtained by dispersed polymerization. Pretreatment was performed to adsorb palladium catalytic active centers on the PS surface, prior to plating. Effect of reaction temperature and loadage was studied. The proper temperature for electroless silver plating is determined to be 20 °C, and the loadage should be restricted in the range of 2.80–3.50 g to achieve ideal silver coating. It is found that the density decreases from 2.82 g/cm 3 to 2.32 g/cm 3 while the loadage increases from 2.86 g to 4.29 g. SEM, EDS, and XRD proved the successful formation of silver coating on PS microspheres. A waterborne microwave absorbing coating, based on PS/Ag microspheres and waterborne acrylic resin as binder, was developed. The result shows that nearly 70% of the incident wave is absorbed by this microwave absorbing coating in the frequency range of 10–18 GHz.

Elucidation of Protein Adsorption Behavior on Polymeric Surfaces: Toward High-Density, High-Payload Protein Templates

The elucidation of protein adsorption behavior on polymeric surfaces is very important, since their use as arrays and carriers of biomolecules is ever growing for a wide variety of bioapplications. We evaluate protein adsorption characteristics on chemically homogeneous and heterogeneous polymeric surfaces by employing polystyrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer, PS homopolymer, PMMA homopolymer, and PS/PMMA blend as protein templates. We also investigate distance-dependent protein adsorption behavior on the interfacial region between PS and PMMA. We observe selective protein adsorption exclusively onto PS areas for the chemically heterogeneous PS-b-PMMA and PS/PMMA blend templates. On blend films, protein adsorption is highly favored on the PS regions located near the PS:PMMA interface over that on the PS areas situated away from the interface. Protein density on PS domains is inversely proportional to the separation distance between two neighboring PS:PMMA interfaces. We also observe a higher protein density on the PS-b-PMMA than on the PS or PMMA homopolymer templates. This effect is due to the fact that chemically heterogeneous PS-b-PMMA presents periodically spaced PS:PMMA interfaces on the nanometer scale, whereas no such interfaces are present on homopolymer films. The density of protein molecules on the heterogeneous PS-b-PMMA surface is approximately 3-4-fold higher than on the homogeneous PS surface for the identical experimental conditions. These results demonstrate that self-assembling, chemically heterogeneous, nanoscale domains in PS-b-PMMA diblock copolymers can be used as excellent, high-payload, high-density protein templates. The unique advantages of the diblock copolymer may prove the spontaneously constructed protein nanotemplates to be highly suitable as functional substrates in many proteomics applications.

Interactions Between Positronium Atoms in Porous Silica

Interactions between pairs of positronium (Ps) atoms confined in porous silica films have been directly observed for the first time. Because of selection rules, the nature of such interactions should depend on the structure of the porous medium: if a Ps surface state exists, dipositronium (Ps2) molecules may be created, and if there is a continuum of cavity energy levels, spin exchanging collisions may occur. Using two structurally different silica films, we have been able to isolate and study these two processes. Our data indicate that Ps2 formation occurs primarily via a Langmuir-Hinshelwood-type mechanism on the internal pore surfaces, with an interaction length of the order of 7 x 10(-8) cm, and that the effective cross section for nonthermalized Ps-Ps spin exchange quenching in porous silica is around 9 x 10(-15) cm2.

Creating Surfactant Nanoparticles for Block Copolymer Composites through Surface Chemistry

A simple strategy to tailor the surface of nanoparticles for their specific adsorption to and localization at block copolymer interfaces was explored. Gold nanoparticles coated by a mixture of low molecular weight thiol end-functional polystyrene (PS-SH) (Mn = 1.5 and 3.4 kg/mol) and poly(2-vinylpyridine) homopolymers (P2VP-SH) (Mn = 1.5 and 3.0 kg/mol) were incorporated into a lamellar poly(styrene-b-2-vinylpyridine) diblock copolymer (PS-b-P2VP) (Mn = 196 kg/mol). A library of nanoparticles with varying PS and P2VP surface compositions (FPS) and high polymer ligand areal chain densities was synthesized. The location of the nanoparticles in the PS-b-P2VP block copolymer was determined by transmission electron microscopy. Sharp transitions in particle location from the PS domain to the PS/P2VP interface, and subsequently to the P2VP domain, were observed at FPS = 0.9 and 0.1, respectively. This extremely wide window of FPS values where the polymer-coated gold nanoparticles adsorb to the interface suggests a redistribution of PS and P2VP polymers on the Au surface, inducing the formation of amphiphilic nanoparticles at the PS/P2VP interface. In a second and synthetically more challenging approach, gold nanoparticles were covered with a thiol terminated random copolymer of styrene and 2-vinylpyridine synthesized by RAFT polymerization. Two different random copolymers were considered, where the molecular weight was fixed at 3.5 kg/mol and the relative incorporation of styrene and 2-vinylpyridine repeat units varied (FPS = 0.52 and 0.40). The areal chain density of these random copolymers on Au is unfortunately not high enough to preclude any contact between the P2VP block of the block copolymer and the Au surface. Interestingly, gold nanoparticles coated by the random copolymer with FPS = 0.4 were dispersed in the P2VP domain, while those with FPS = 0.52 were located at the interface. A simple calculation for the adsorption energy to the interface of the nanoparticles with different surface arrangements of PS and P2VP ligands supports evidence for the rearrangement of thiol terminated homopolymers. An upper limit estimate of the adsorption energy of nanoparticles uniformly coated with a random arrangement of PS and P2VP ligands where a 10% surface area was occupied by P2VP -mers or chains was approximately 1 kBT, which indicates that such nanoparticles are unlikely to be segregated along the interface, in contrast to the experimental results for nanoparticles with mixed ligand-coated surfaces.

Topography and Wettability of Nanopatterned PMMA and PS Surfaces Embossed with Various Anodized Aluminum Oxide Nanotemplates

The interactions between biological cells and nanometer-scale structured surfaces are very important issues in nanobiotechnology. Most current methods of fabricating such surfaces are costly and are not suitable for the production of a nanometer-scale structured surface that will be used merely as a disposable tool in cell biological studies. We developed and optimized an embossing method of polymers with nanoporous AAOs which is easy, cheap and fast in fabricating nanometer-scale structures on the surface of polymers. We think this method can be applied not only in cellular nanobiotechnogy but also in other areas of nanotechnogy.

Comparative study of surface free energy and surface resistivity of polypropylene and polystyrene thin films after DC plasma treatment

30 o C, pressure 200 Pa). The effects of time (up to 110 s) and power (1 W or 5 W) of the treatment on the values of free energy (γs) of PS and PP samples and γS components — dispersive (γS D ) and polar (γS P ) ones — were determined. With prolonged time of interaction the values of γS and γS P increased, especially in the region of first 35—50 s, while γS D values kept the similar level during the whole time of exposure. The dependence of PP and PS surface resistance on the same parameters as above (time and power of interaction) has been also found. For both polymers this resistance decrease with prolonged time and growing power of exposure.

CC Chemokine Receptor 6 Expression by B Lymphocytes Is Essential for the Development of Isolated Lymphoid Follicles

Isolated lymphoid follicles (ILFs) are organized lymphoid structures that facilitate the efficient interaction of antigen, antigen-presenting cells, and lymphocytes to generate controlled adaptive immune responses within the intestine. Because CC chemokine receptor 6 (CCR6) deficiency affects the generation of mucosal immune responses, we evaluated a potential role for CCR6 in the development of ILFs. We observed that CCR6 and its ligand CCL20 are highly expressed within ILFs and that B lymphocytes are the largest CCR6-expressing population within ILFs. ILF development was profoundly arrested in the absence of CCR6. Concordant with a block in ILF development at a stage corresponding to the influx of B lymphocytes, we observed that CCR6-deficient mice had a diminished population of intestinal B lymphocytes. Bone marrow reconstitution studies demonstrated that ILF development is dependent on CCR6-sufficient B lymphocytes, and adoptive transfers demonstrated that CCR6(-/-) B lymphocytes were inefficient at localizing to intestinal lymphoid structures. Paralleling these findings, we observed that CCR6-deficient mice had a reduced proportion of Peyer's patch B lymphocytes and an associated re-duction in the number and size of Peyer's patch follicular domes. These observations define an essential role for CCR6 expression by B lymphocytes in localizing to intestinal lymphoid structures and in ILF development.

Direct Metallization of Gold Nanoparticles on a Polystyrene Bead Surface using Cationic Gold Ligands

AbstractGold nanoparticles are formed to cover the surface of sulfonated‐polystyrene (PS) beads by the in‐situ ion‐exchange and chemical reduction of a stable cationic gold ligand, which makes it different from the physical adsorption or multiple electroless metallization methods. PS beads are synthesized by dispersion polymerization with a diameter of 2.7 µm, and their surface is modified by introducing sulfonic acid groups (SO) to give an ion exchange capacity of up to 2.25 mequiv. · g−1, which provides 1.289 × 1010 SO per bead. Subsequently, the anionic surface of the PS beads is incorporated with a cationic gold ligand, dichlorophenanthrolinegold(III) chloride ([AuCl2(phen)]Cl), through an electrostatic interaction in the liquid phase to give gold nanoparticles (ca. 1–4 nm in diameter) formed on the PS surface. Assuming that approximately three SO groups interact with one [AuCl2(phen)]+ ion in the ion‐exchange process, the gold coverage on a PS bead is estimated as 12.0 wt.‐%, which compares well with the 16.8 wt.‐% of gold loading measured by inductively coupled plasma–mass spectrometry. Because of the adjustable IEC values of the polymer surface and the in‐situ metallization of Au in the presence of S atoms, both of which are of a soft nature, the developed methodology could provide a simple and controllable route to synthesize a robust metal coating on the polymer bead surface.magnified image

Selective assembly of nanoparticles on block copolymer by surface modification

We have developed a method to selectively deposit nanoparticles on the orderednanoscale elements of PS–PI–PS (polystyrene–polyisoprene–polystyrene) blockcopolymer film. The process utilizes reactive ion plasma to selectively modifythe PS surface with amine groups to electrostatically attract negatively chargedAu nanoparticles. In spite of the strong interparticle Coulombic repulsion, thedeposition on PS domains is significantly high. It is observed that the deposition atthe edges of the domain is particularly high, forming a percolating nanoparticlenecklace. The latter may lead to interesting avenues to fabricate electronic devices.

Facile method to fabricate stable superhydrophobic polystyrene surface by adding ethanol

A stable superhydrophobic PS surface was obtained by a simple method in atmosphere. The water contact angle and sliding angle of the superhydrophobic PS surface are 156 ± 1.9°and 2 ± 1.9°, respectively. Kept at temperatures between 5 °C and 40 °C in ambient atmosphere for 3 months, and any decrease in water contact angle was not observed. SEM shows that the surface structure is comprised of many uniform micro-spheres with the diameter range of 1–4 μm. A brief explanation to the formation of the special microstructure was put forward.

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Origin of Higher Friction for Elastomers Sliding on Glassy Polymers

We have designed a novel approach to couple infrared−visible sum frequency generation (SFG) spectroscopy with adhesion and friction measurements to determine the molecular structure of the surface molecules at the contact and sliding interfaces. The frictional force of crosslinked poly(dimethyl siloxane) (PDMS) lens sliding on poly(styrene) (PS) is a factor of 4 higher than that of PDMS sliding on poly(vinyl n-octadecyl carbamate-co-vinyl acetate) (PVNODC). This higher frictional force of PDMS/PS interface cannot be explained by its adhesion energy or hysteresis. The SFG results indicate that the hydrocarbon PVNODC surface consists of well-ordered crystalline side chains that do not restructure upon mechanical contact and during sliding of the PDMS lens. On the contrary, the SFG results show that the PS phenyl groups are more tilted upon mechanical contact and during sliding compared to that at the PS surface before contact. The change in phenyl orientation can be due to local chain interpenetration that occurs at temperatures much below the Tg of PS at the PDMS/PS interface and is the reason behind higher friction forces for PDMS elastomer sliding on glassy PS compared to that on crystalline PVNODC.

Macrophage Serum‐Based Adhesion to Plasma‐Processed Surface Chemistry is Distinct from That Exhibited by Fibroblasts

Plasma-polymerized films deposited from AlAm, HxAm, NVP, NVFA, AA and FC were compared to TCPS and PS surfaces in supporting cellular attachment, viability, and proliferation in serum-based culture in vitro for extended periods of time (>7 d). Surface patterns were created using multi-step depositions with physical masks. Cell adhesion in the presence of serum was compared for (monocyte-) macrophage and fibroblast cell lines. Cellular response was tracked over time, reporting adhesive behavior, proliferative rates, and morphological changes as a function of surface chemistry. Micropatterned surfaces containing different surface chemistries and functional groups (e.g. -NH(2), -COOH, -CF(3)) produced differential cell adhesive patterns for NIH 3T3 fibroblasts compared to J774A.1, RAW 264.7 or IC-21 (monocyte-) macrophage cell types. Significantly, macrophage adhesion is substantial on surfaces where fibroblasts do not adhere under identical culture conditions.

Electrospinning of Fluorinated Polymers: Formation of Superhydrophobic Surfaces

AbstractSummary: Superhydrophobic surfaces are generated by a simple one‐step method of electrospinning of fluorinated homopolymers and copolymers of PFS. The hydrophobicity and superhydrophobicity can be changed by simply changing the surface morphology, which is possible by changing the electrospinning conditions. The appropriate combination of surface morphology and fluorinated materials led to the formation of super‐water‐resistant coatings showing the ‘water‐roll’ effect at an angle of 0°, i.e. placement of water droplets on such surfaces was not possible as they immediately rolled away. The effect is compared with the corresponding nonfluorinated PS and found to be clearly distinct in terms of water‐roll effect. Incorporation of about 30 mol‐% PFS onto the PS backbone could also convert hydrophobic PS surfaces to superhydrophobic surfaces. The effect is generalized by also using a new fluorinated poly(p‐xylylene) derivative. The molecular weight of the polymers has no noticeable effect on hydrophobicity/superhydrophobicity behavior.SEM micrographs PFS–styrene copolymer, 10% solution in THF:DMF (1:1 v/v); 5% solution in THF:DMF (1:1 v/v) and homo‐PPFS < 2% solution in THF:DMF (1:1 v/v).magnified imageSEM micrographs PFS–styrene copolymer, 10% solution in THF:DMF (1:1 v/v); 5% solution in THF:DMF (1:1 v/v) and homo‐PPFS < 2% solution in THF:DMF (1:1 v/v).

White Light Emission from the Composite System of ZnO/PorousSi

We report that the composites of ZnO/porous Si (PS) can exhibitintensively white photoluminescence (PL) under proper excitationwavelength. The PS sample is formed by electrochemical anodization ofn-type (111) silicon. ZnO films are then deposited on the PS surface bypulsed laser deposition (PLD). ZnO is transparent in the visibleregion, so the red PL from PS can be transmitted through the ZnO films.White PL from the ZnO layer on PS can be obtained, which consists ofblue-green emission from ZnO and red emission from PS. The x-raydiffraction (XRD) pattern shows that the ZnO films deposited on PSsurface are non-crystalline. Due to the roughness of the PS surface,some cracks appear in the ZnO films, which could be seen from thescanning electron microscopy (SEM) images.

Screening and Characterization of Affinity Peptide Tags Specific to Polystyrene Supports for the Orientated Immobilization of Proteins

Dodecapeptides that exhibit a high affinity specific to a polystyrene surface (PS-tags) were screened using an Escherichia coli random peptide display library system, and the compounds were used as a peptide tag for the site-specific immobilization of proteins. The various PS-tags obtained after 10 rounds of biopanning selection were mainly composed of basic and aliphatic amino acid residues, most of which were arranged in close proximity to one another. Mutant-type glutathione S-transferases (GSTs) fused with the selected PS-tags, PS19 (RAFIASRRIKRP) and PS23 (AGLRLKKAAIHR) at their C-terminus, GST-PS19 and GST-PS23, when adsorbed on the PS latex beads had a higher affinity than the wild-type GST, and the specific remaining activity of the immobilized mutant-type GSTs was approximately 10 times higher than that of the wild-type GST. The signal intensity detected for GST-PS19 and GST-PS23 adsorbed on hydrophilic and hydrophobic PS surfaces using an anti-peptide antibody specific for the N-terminus peptide of GST was much higher than that for the wild-type GST. These findings indicate that the mutant-type GSTs fused with the selected peptide tags, PS19 and PS23, could be site-specifically immobilized on the surface of polystyrene with their N-terminal regions directed toward the solution. Thus, the selected peptide tags would be useful for protein immobilization in the construction of enzyme-linked immunosorbent assay (ELISA) systems and protein-based biochips.