Polystyrene Surface Layer Research Articles

Stabilization of the Dynamic Layer of Composite Membranes by UV Radiation

To stabilize the dynamic layer of cellulose acetate (CA) and polystyrene (PS) membranes, the membrane was exposed to UV radiation using a laboratory setup in atmospheric air. As a base for dynamic membranes, a micro-filtration membrane made of nylon-66 and a membrane made of polytetrafluoroethylene (PTFE) grade MFFC-3G were used. Dynamic membranes PTFE-CA, PTFE-PSd nylon-CA, nylon-PS were obtained by forming a semi-permeable layer on the surface of a porous base from suspended microparticles of PS or CA present in a filtered aqueous solution of acetone with sizes of 81–504 nm and 42–130 nm, respectively, in a dynamic equilibrium with the solution. After obtaining the membranes, the surface was treated for 10 minutes with UV radiation in the wavelength range of 280–320 nm, with a UV radiation power of 36 W. Stabilization of dynamic membranes by UV radiation made it possible to increase the specific productivity of CA membranes 10 times and of PS by 1.5 times, while reducing the retention capacity of those membranes in terms of oil products by 9–17%. UV treatment of polymeric membranes can be used to increase the specific productivity and stabilization of dynamic membranes with a PS surface layer.

Dynamic Membrane with a Polystyrene Surface Layer for Ultrafiltration of Spent Coolant Lubricant

Ultrafiltration membranes with a dynamic layer of polystyrene particles 55–72 nm in size were obtained on a hydrophilic polytetrafluoroethylene substrate. The results of scanning electron microscopy showed the formation of a layer of spherical particles on the membrane surface. After applying a layer of polystyrene to the surface of a polytetrafluoroethylene substrate, a decrease in the specific productivity of the membranes is observed, and an increase in the hydrophobicity of the surface layer of the membrane is revealed. The dynamic membrane was used to separate spent cutting fluid (coolant). The separation efficiency of the emulsion was evaluated by the removal of petroleum products and fatty acids. The retention capacity of the membrane for oil products from the spent emulsion was 95% with a specific productivity of 167 dm3 /(m2· hr), which is not inferior to the performance of commercial ultrafiltration membranes. The HPLC method was used to study the content of fatty acids in the emulsion and its filtrates. The retention capacity of the dynamic membrane for fatty acids was more than 68%.

Synthesis and Characterization of a Multilayer Membrane with Surface Layers for Water Desalination

Multilayer dynamic membranes with a surface layer of polystyrene for the membrane desalination of water have been synthesized in this study. The dynamic layer is formed from polystyrene particles with a particle size of 55–92 nm that are suspended in a filtered aqueous solution of acetone with a pH of 5. The stability of the dynamic layer is provided by a heat treatment of the membrane at a temperature of 50°C for 10 min. The treatment leads to the compaction of the dynamic layer of the membrane. With an increase in the number of dynamic layers, the membrane flux decreases. After the deposition of each subsequent layer, the membrane flux decreases twofold. Thus, the flux of a four-layer nylon–polystyrene (nylon–PS) membrane with respect to distilled water is 142 dm3/(m2 h). The rejection ability of the membranes with respect to Cl–, NO3–, $${\text{SO}}_{{\text{4}}}^{{{\text{2}} - }},$$$${\text{NH}}_{{\text{4}}}^{ + },$$ K+, Na+, Ca2+, and Mg2+ ions from a model solution with a total salinity of 433 mg/dm3 is determined. The rejection ability with respect to singly charged and doubly charged ions is 58 and more than 80%, respectively, at a high flux of 118 dm3/(m2 h).

Effect of MW Radiation on Thin-Film Polymer Membranes

To improve physical-chemical properties of thin-film membranes from nylon and nylon membranes with a surface layer of polystyrene (PS), nylon-PS, the processing of the latter was carried out with microwave radiation (microwave) at a frequency of 2450 MHz and a power of 300 W in air. As a result of exposure to microwave radiation, changes were found in the mass of the membranes depending on the processing time for nylon membranes, up to 0.34% and, for nylon-PS membranes, up to 0.67%. The results of scanning electron microscopy showed the formation of melted and compacted areas on the membrane surface. An increase in the hydrophilicity and specific performance of membranes as a result of treatment with microwave radiation has been established. A decrease in the roughness of the surface layer of membranes and changes in the structure of the nylon-PS membrane were revealed according to the results of scanning electron microscopy. Changes in the supramolecular structure of the nylon-PS membrane were confirmed by the results of Fourier-transform infrared spectroscopy: a shift of the base of the absorption band to characteristic vibrations of the C–H bond of the phenyl group of polystyrene has been detected. The phenyl groups in the polymer macro-molecule interfere with crystallization of polystyrene and a displacement of the peak base indicates structural changes in the macromolecule, which leads to an increase in the degree of crystallinity of PS. Under the influence of microwave radiation in PS, the orientation of the phenyl group changes: it is located, alternating, on opposite sides of the main chain, which contributes to an increase in the number of crystallization centers, streamlining the structure. An increase in the intensity of the absorption bands of the IR spectra after the treatment of the nylon membrane with microwave radiation is associated with the destruction of the defective regions of the surface layer of the membrane.

Formation and properties of a dynamic ultrafiltration membrane

AnnotationBy applying to the surface of the nylon membrane of polystyrene particles, dynamic nylon-polystyrene membranes with a final content of 3.4 % by weight were obtained. The content of polystyrene on the surface of the nylon membrane is indirectly confirmed by IR Fourier spectroscopy methods. An increase in the contact angle of the droplets of distilled water of the membrane as a result of depositing polystyrene particles on the surface of the initial membrane was revealed. According to the results of scanning electron microscopy, it was found that polystyrene particles with sizes from 0.05 to 0.2 microns are located on the surface and in pores of a nylon substrate. After applying a layer of polystyrene on the surface of the membrane, the specific productivity of the membranes decreases by an order of magnitude, due to the intensive accumulation of polystyrene particles in the pores and membrane surface. The maximum productivity of the initial and dynamic membranes is observed when the distilled water is passed through. Dynamic membrane ultrafiltration with a surface layer of polystyrene is designed to separate water-oil emulsions. The degree of separation of water-oil emulsion with a concentration of oil products of 10 g/dm3 is more than 98 %.

Simultaneous patterning of two different types of nanoparticles into alternating domains of a striped array of a polymer blend in a single spin-casting step

A fast and convenient method is developed for simultaneously patterning inorganic nanoparticles with different optical, electronic or magnetic functionality to specific surface regions, by spin-casting onto microcontact printed substrates blend solutions in which the two nanoparticle types are functionalized with surface polymer brush layers of different surface energies. The process is based on phase separation of different nanoparticles based on their immiscible brush layers during spin-casting, with the underlying surface energy heterogeneity of the patterned substrate directing the different NP types to domains of different surface energies. Here, we specifically demonstrate the simultaneous localization of cadmium sulfide quantum dots (CdS QDs), addressed with a surface layer of polystyrene (PS), and silver nanoparticles (Ag NPs), addressed with a surface layer of poly(methyl methacrylate) (PMMA), onto the non-polar and polar surface domains, respectively, of hydrophilic glass patterned with hydrophobic octadecyltrichlorosilane (OTS) stripe arrays with micron-scale periodicities. In order to prevent gelation of solvent-swollen polymer-brush coated NPs during spin casting, which effects strong kinetic constraints on phase separation and localization, PS, PMMA or PS/PMMA homopolymer blends of sufficiently high Mw were added to the NP blends to increase the free volume between approaching NPs. The process parameters were fine-tuned to obtain control over defects in the obtained patterns.

A new method for multilayered, site-directed immobilization of antibody on polystyrene surface

Polystyrene is a common substrate material for protein adsorption in biosensors and bioassays. Here, we present a new method for multilayered, site-directed immobilization of antibody on polystyrene surface through the linkage of a genetically engineered ligand and the assembly of staphylococcal protein A (SPA) with immunoglobulin G (IgG). In this method, antibodies were stacked on polystyrene surface layer by layer in a potential three-dimensional way and exposed the analyte-binding sites well. Enzyme-linked immunosorbent assay (ELISA) revealed that the new method showed a 32-fold higher detection sensitivity compared with the conventional one. Pull-down assay and Western blot analysis further confirmed that it is different from the ones of monolayer adsorption according to the comparison of adsorption capacity. The differentiated introduction of functional ligands, which is the key of this method, might offer a unique idea as a way to interfere with the dynamic behavior of a protein complex during the process of adsorption.

Optical methods in studies of structural transformations in thin organic films

The examples of phase transitions in Langmuir-Blodgett films of polyvinylidene fluoride (PVDF) and in the surface layer of polystyrene were chosen to demonstrate the great potential of using luminescent molecular probes for studying the heterogeneity of the surfaces of solids and thin films, as well as structural transformations and phase transitions in systems of different natures. The method provides unique information on the local properties of surfaces and thin films when used in combination with other techniques.

Determination of Cross-Link Density in Ion-Irradiated Polystyrene Surfaces from Rippling

The irradiation of polymer surfaces with ion beams leads to pronounced chemical and physical modifications when the ions are scattered at the atoms in the polymer chain. In this way, different products of decomposition occur. Here we show that by changing the ion fluence and the mass of the ion the local mechanical properties as Young's modulus of a polystyrene surface layer can be tailored. By annealing prestretched irradiated PS near the glass transition, surface rippling occurs in the irradiated areas only, which can be described with an elastic model. The moduli obtained from rippling periodicities and elastic model assumptions are in the range between 8 and 800 MPa at the glass transition and characterize the irradiated PS as rubberlike. From these values the network density and the molar mass of entanglement are quantified. The obtained network density equals the density of hydrogen vacancies generated through the scattered ions, as confirmed by simulations of the atomic scattering and displacement processes. The obtained molar mass of entanglement reveals that the PS locally was densely cross-linked. Our results show that even for nondiscrete layered polymer systems relevant polymer parameters can be derived from the well-known surface rippling without the need for costly chemical analysis.

Study of vitrification of polystyrene surface layer by fluorescent molecular probes

Fluorescence spectroscopy with the application of fluorescent molecular probes is used to determine the temperature ranges in which vitrification of the surface layer of polystyrene with different molecular masses typically occurs. It is found that the surface vitrification temperature is significantly lower than the bulk values. The results of the study are in good agreement with the data obtained earlier using an independent technique.

Eliminating the Enhanced Mobility at the Free Surface of Polystyrene: Fluorescence Studies of the Glass Transition Temperature in Thin Bilayer Films of Immiscible Polymers

By selective placement of fluorescent dyes, we have measured the glass transition temperature (Tg) of individual layers within supported bilayer films of different polymers to determine the extent to which strong free-surface effects and substrate interactions are mediated by a narrow interface between immiscible polymers. We have discovered that the impact a free surface has on Tg within an ultrathin PS layer is extremely sensitive to the polymer species used in the underlayer. The large Tg reduction of ∼32 K relative to bulk Tg observed for a 14 nm thick surface layer of polystyrene (PS) supported on bulk PS is virtually eliminated when a 14 nm thick surface layer of PS is placed on an underlayer of poly(methyl methacrylate) or poly(2-vinylpyridine) (P2VP), even of bulk thickness. Thus, the cooperative segmental mobility associated with the Tg of the PS free-surface layer is greatly hindered by the narrow, several-nanometer-wide interfacial region formed with the dissimilar polymer underlayer. This indi...

Metal Nanoparticles on Polymer Surfaces: 5. Catalytic Activity of Colloidal Platinum Films Incorporated in Polystyrene Surface Layer

The fundamental possibility to enlarge Pt nanoparticles in monolayer ensembles formed on polystyrene surfaces by the adsorption from hydrosol in solution of isopropanol and K2PtCl4 is demonstrated for the first time. The enlargement of “seeding” nanoparticles is performed after their preliminary incorporation (partial embedding) into the polymer surface layer by the annealing of a system within the range between “surface” and “bulk” glass transition temperatures of polystyrene. It is shown that a colloidal film of metallic platinum with a thickness up to 200 nm is formed in the course of enlargement and it is mechanically fixed in the polymer surface layer. Such a system exhibits, over a long time, high catalytic activity in the model reaction of methyl viologen reduction with hydrogen.

Metal nanoparticles on polymer surfaces: 4. Preparation and structure of colloidal gold films

The process of the enlargement of gold hydrosol nanoparticles adsorbed on the surfaces of glassy polymers (polystyrene and poly(2-vinylpyridine)) in mixed aqueous solution of chloroauric acid and hydroxy- lamine is studied. It is established that the character of this process depends on the intensity of metal-polymer interaction and the density of nanoparticle packing in an initial monolayer. At a high coverage of a poly(2- vinylpyridine) surface by "seeding" gold particles, their rather uniform growth is observed, whereas, at low cov- erage, the enlargement of adsorbed particles, as well as the nucleation and growth of new particles take place. At the same time, new Au nanoparticles are not formed on the polystyrene surface in the enlargement process, even at low coverages by preliminarily deposited "seeding" hydrosol particles. Adsorbed gold particles can also be enlarged after their preliminary incorporation into the polystyrene surface layer. Such an incorporation (par- tial embedding) is ensured by the annealing of a system at a temperature between "surface" ( ) and "bulk" glass transition temperatures. In this case, the value can be considerably decreased (up to room temperature) by the addition of small amounts of a homologue with a much lower molecular mass in the polystyrene matrix. Lateral conductivity of colloidal Au films formed on a poly(2-vinylpyridine) surface by the enlargement of adsorbed seeding particles is measured. According to these measurements, contacts providing the formation of conductive channels are formed in the process of nanoparticle enlargement. T g T g

The study of polystyrene surface layer glass transition by luminescent molecular probes

Producing of 2D ensembles of nanoparticles on polymer substrates is one of the key tasks in many fields of fundamental research and practical applications. A successful development of such nanocomposites is impossible without an intimate knowledge of polymer surface layer properties at a nanolevel. The glass transition process in a thin surface layer of polystyrene was studied in the present work by the method of luminescent molecular probes. A significant difference of polymer “surface” ( T g s) and “bulk” ( T b g) glass transition temperatures was proven. A strong dependence on the polymer molecular weight was found for the T g s value and probe dye molecules' mobility.

Grafting of Polystyrene from Narrow Disperse Polymer Particles by Surface-Initiated Atom Transfer Radical Polymerization

Grafting of polystyrene from narrow disperse polymer particles by surface-initiated atom transfer radical polymerization was investigated. Poly(DVB80) particles prepared by precipitation polymerization were used as starting particles. Their residual surface vinyl groups were hydrochlorinated to form chloroethylbenzene initiating sites for subsequent ATRP of styrene using CuBr/2bipy as catalyst system. Polystyrene was found grafted not only from the particle surfaces but also from within a thin shell layer, leading to particles size increases from 2.96 to 3.07 μm. The surface layer of polystyrene improved colloidal stability and facilitated formation of colloidal arrays. Block copolymers of poly(styrene-b-4-methylstyrene) were grown from the particles, and the living nature of surface-initiated ATRP is discussed.

Metal Nanoparticles on Polymer Surfaces: 1. A New Method of Determining Glass Transition Temperature of the Surface Layer

New experimental approach allowing to study the structure and properties of polymer surface layers at a nanolevel is proposed. According to this method, metal nanoparticles are first adsorbed on a polymer surface from colloidal solution, then resultant system is stepwise annealed, and the particle embedding in a polymer is examined with atomic force microscope. Potentialities of the method are demonstrated using the gold nanoparticles–polystyrene system (including polystyrene modified with the UV radiation) as an example. It was established that the glass transition temperature of polystyrene surface layer is noticeably lower compared with the bulk value and decreases even more after the UV modification of a polymer surface. Possible use of the results obtained for the solution of other, independent problem, namely for the creation of “two-dimensional” nanocomposites by embedding nanoparticle monolayer ensemble in the surface layer of a glassy polymer at a temperature lower than the glass transition temperature of its bulk is analyzed.

RBS study on Na-implanted polystyrene at various doses

A study on the composition of Na-implanted polystyrene has been made by Rutherford backscattering spectroscopy (RBS). Substrates used were polystyrene (PS) dishes. Na ion implantation was performed at an energy of 50 keV with does ranging from 5×1015 to 1×1017 ions/cm2. RBS was carried out with 1.5-MeV He+-ion beams and a fluence of 60 μC. The depth distribution of Na atoms showed a Gaussian distribution for the low dose. The profile is in a good agreement with a theoretical distribution calculated by a TRIM code. At the intermediate dose, the Na depth profile changed to a trapezoidal distribution. At the high dose, Na enrichment was found at the surface. Oxygen incorporation into PS is also observed. Na distribution behaviors in PS surface layer were discussed as a link to the O distribution.

Experimental Proof of the Relation between Thickness of the Probed Surface Layer and Absorbance in FT-IR/ATR Spectroscopy

Experimental investigation has been made of the relation of absorbance of a band in FT-IR/ATR spectroscopy to the thickness of the probed surface layer from the measurements of two-layered samples. The two-layered samples are composed of a polystyrene surface layer varying in thickness from 0.01 to 3.64 μm and a polyurethane base layer of 100 *im thickness. The component spectrum of the surface or base layer was separated by spectral subtraction. FT-IR/ATR spectroscopic measurements were mostly measured by nonpolarized incident light. The relation of observed absorbances of several selected bands of both the surface and base layers to the thickness of the surface layer was compared with the theoretical calculations from Harrick's equation. In the comparison, the effect of “nonpolarization” of the incident light was corrected for the observed absorbances. The agreement was excellent between the observation of and the theoretical calculation for both the surface and base layers. A method was proposed to determine the thickness of the spectrally separable surface layer on a film. The usefulness of this method was demonstrated by application to the redetermination of the thickness of the surface layer of the present two-layered samples. An expression was proposed to give the contribution of a surface layer of a certain thickness to the total absorbance of a band in ATR spectroscopy.