Surface Of Polystyrene Films Research Articles

Development of a fire-proof coating containing silica for polystyrene

The possibility of applying a silica-containing coating to the surface of XPS extruded polystyrene foam, which is characterized by a high degree of flammability, was evaluated. The effect of the content and concentration (11, 22, 44 and 85 %) of orthophosphate acid on the optical properties of silicic acid sols obtained by the exchange reaction between aqueous solutions of liquid glass and acetic acid was studied. The fact of incorporation of orthophosphate acid into the gel structure was confirmed by the results of acid-base titration with a sodium hydroxide solution of the intermicellar liquid isolated as a result of gel syneresis. Using an optical microscope, the structure of the polystyrene film coating after treatment with orthophosphate and sulfuric acid solutions was investigated. In both cases, the effect of an increase in the pore area and a general increase in the looseness of the surface was noted, which can help reduce its hydrophobicity and improve adhesion to the coating. The increase in hydrophilicity of the surfaces of polystyrene films after treatment with acids was also confirmed by the flatter, non-spherical shape of the drops of the composition on them. The structure of the obtained coatings on polystyrene films was analyzed. The similarity of the directions of the cracks in the case of treatment of the films with solutions of both acids was noted, and an assumption was made about the presence of uniform deformation stresses during gel shrinkage. A microscopic study of coatings on the surface of extruded polystyrene foam was conducted, and a positive effect of orthophosphate acid on the density of their structure was established. It was determined that the optimal solution for obtaining a uniform coating is the modification of the sol with the help of a 22 % solution of orthophosphate acid. Schemes of the interaction of the silica coating and the polystyrene base in cases of electrostatic interaction and in the case of the formation of covalent bonds between the coating and the polystyrene surface are proposed.

Effect of molecular weight and architecture on nanoscale viscoelastic heterogeneity at the surface of polymer films

Dissipated energy mapping in amplitude-modulation atomic force microscopy was employed to characterize the nanoscale heterogeneous behavior of the viscoelastic response at the surface of polystyrene (PS) films of different molecular weight and architecture. By using an ultra-sharp probe with tip radius of ~1 nm, we were able to visualize the viscoelastic heterogeneities at the free surface of all PS samples. While the length scale of these heterogeneities at the surface of linear PS films was measured to be ~2.2 nm nearly independent of the molecular weight, it was significantly increased to ~3.1 nm at the surface of four-arm star-shaped PS films. We also demonstrated that similar nanoscale heterogeneous features were not observed when using a common probe with tip radius of ~10 nm, thereby confirming the intrinsic nature of the observed viscoelastic heterogeneities with sizes on the order of a few nanometers at the surface of PS films. This result provides important insights into the fundamental role of the molecular architecture in controlling the heterogeneous dynamics and many associated physical properties of amorphous polymer surfaces.

Microbial Sensor for Determination of Amoxicillin Activity

A sensor based on the electrodynamic microwave resonator has been developed to determine the antibacterial activity of antibiotics using amoxicillin as an example. Microbial cells immobilized on the polystyrene film surface were used as a sensitive element of the sensor. The optimal conditions for the immobilization of Escherichia coli Xl-1 microbial cells on the surface of a thin polystyrene film modified in high-frequency argon discharge plasma and deposited on a lithium niobate plate were determined. The effect of amoxicillin on immobilized microbial cells was studied using the developed sensor. It has been established that the increase in con- centration of amoxicillin from 5 to 50 μg/ml leads to a significant change in the reflection coefficient S11 at the resonance frequency from the lithium niobate plate in the range of -12.6 dB — -15.1 dB. It has been shown that the developed sensor allows determining the antibacterial activity of drugs in the studied concentration range with an analysis time of 15 min.

Formation of High-Density Brush of Liquid Crystalline Polymer Block Associated with Dewetting Process on Amorphous Polymer Film.

The understanding of polymer dewetting on solid surfaces is significant in both fundamental polymer physics and practical film technologies. When liquid crystalline (LC) polymers are dewetted, LC ordering is involved in the dewetting process. Here, we report on the characteristic dewetting processes of a diblock copolymer composed of a cyanobiphenyl side chain liquid crystalline polymer (SCLCP) block connected with polystyrene (PS) taking place on a PS base film. Thin films of the block copolymer were prepared by the water-floating method onto the PS film, and the dewetting process is observed in a softened state above the glass transition temperature of the PS. At the smectic A phase temperature of the SCLCP block, the dewetted surface layer generated a flat unique fingering pattern leading to a monolayered (two-dimensional) high-density LC polymer brush through the LC ordering. The important role of the anchoring PS block on the base PS film surface is suggested for the formation of highly stretched LC polymer brush. Above the isotropization temperature, in contrast, ordinary three-dimensional droplet morphologies with smooth round edges were observed. By photo-cross-linking the base PS film, the lateral diffusion rate was significantly reduced. This can be applied to an entropy-driven morphology patterning via dewetting. The polymer brush formation and its spatial controls are expected to provide new opportunities for the modification strategies of polymer surfaces.

The Role of DC Biased Plasma Treatment of Polystyrene on the Formation of the C≡N Functional Group Controlling Its Hydrophobicity

Nitrogen plasma treatment was carried out to modify the surface of polystyrene film deposited on a quartz crystal microbalance (QCM) sensor. The modification was intended to enhance the wettability of the film by inducing the formation of CN functional group on its surface. This work investigated the effect of DC bias controlling N* in the plasma on the effectiveness of the nitrogen plasma treatment. The polystyrene was deposited by a spin coating method on the surface of a quartz crystal normally used in an electronic resonator. The nitrogen plasma was generated in an aluminium vacuum chamber using a 2 MHz radio frequency (RF) generator. The vacuum pressure and the gas flow rate were kept constant during the experiments. The plasma character in the chamber was controlled by applying a DC bias between the RF electrodes and the sample stage. The DC voltage was varied from 100 to 500 volts at 100 volts’ step, while maintaining the RF voltage constant. During the process, the species in the plasma was characterized using an optical emission spectroscopy (OES). The wettability of the treated samples was tested using a contact angle measurement system. FTIR measurement was utilized to study the polar functional groups on the surface of the polystyrene before and after the treatment. The OES identified the existence of N radical (N*). The reduced intensity of emission line of the N* increased with the increase of the DC voltage. However, a small decrease was also evidence at DC voltage higher than 400 volts. The decrease of the line intensity was directly related to the decrease of the contact angle (CA < 40°). The relation of the N* and the resulted wettability is related to the polar functional group of the C≡N bond found in the treated polystyrene’s surface.

A Comparative Study of Surface Modification of PS Films Using DC Glow Discharge Plasma in N2 and Ar

In this paper, the polystyrene (PS) film surface was treated using DC glow discharge nitrogen (N2) and argon (Ar) plasma to improve the wettability and antibacterial properties. The untreated and plasma treated surfaces were characterized by contact angle, FTIR, XRD and SEM analysis. The antibacterial activity of untreated and plasma treated PS films was evaluated using optical density (OD) technique against Staphylococcus aureus bacteria. The results of the PS film surface treated in both N2 and Ar showed a noticeable increase in the wettability due to the increase in the roughness and the introduction of oxygen-containing polar groups as corroborated with SEM, weight loss calculations and FTIR spectra. The results of antibacterial activity showed that the treated samples inhibit the bacterial growth. The Ar treatment created more oxygen-containing polar groups and increase roughness on the PS film surface and extensively modified the polymer surface than the N2 treatment.

Segregation of dioctyl phthalate to the surface of polystyrene films characterized by ToF‐SIMS and XPS

Polystyrene (PS)‐dioctyl phthalate (DOP) films were prepared by spin coating solutions of a mixture of PS and DOP on Si wafers and characterized by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and X‐ray photoelectron spectroscopy (XPS). ToF‐SIMS depth profile results showed that DOP mainly segregated to the top 10 nm of the surface of the PS‐DOP film as well as to the interface between the film and the substrate. The normalized intensities of the ions corresponding to DOP on the surface increased as the annealing temperature increased and reached a maximum at the annealing temperature of 60°C, and then decreased as the annealing temperature increased. XPS results indicate that the maximum amount of DOP segregated to the top surface of the PS‐DOP film can reach to 39 wt% at the annealing temperature of 60°C. In addition, DOP evaporated at 25°C under ultra‐high vacuum conditions; hence, ToF‐SIMS and XPS analyses need to be carried out at low temperatures (e.g., −40°C).

Plasma Surface Modified Polystyrene and Grafted with Chitosan Coating for Improving the Shelf Lifetime of Postharvest Grapes

The antimicrobial coating on plasma treated packaging polymer materials are potential and alternative techniques for extending the post harvest life of fresh fruits and vegetables. The present work is to evaluate the shelf life time of post harvest grapes stored in different plasma (air, argon and oxygen) treated and chitosan coated polystyrene (PS) petri plates at atmospheric condition (room temperature 28 °C). The plasma treatments were used to activate the inert PS film surface to enhance the adhesion of chitosan coating. Plasma treatments on the PS film changed the chemical and morphological properties were investigated by ATR-FTIR, EDS and FE-SEM analyses. The contact angle measurement conforms that the air, argon and oxygen plasma treatments greatly enhanced the hydrophilicity of PS and the greater decrease was found in oxygen plasma treatment. Further, the chitosan was immobilised onto PS surface utilizing dip coating and it was characterized by contact angle, ATR-FTIR and FE-SEM evaluations. XPS result indicates the chitosan was efficiently immobilized on the PS film. Subsequently the shelf life time and weight loss (%) was calculated for table grapes stored in the air, argon and oxygen plasma treated with chitosan coated PS. The result suggests that oxygen plasma treatment along with chitosan coating on PS demonstrates the active packaging to extend the self-life time of grapes than the other PS.

Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 2. Role of Gut Microorganisms.

The role of gut bacteria of mealworms (the larvae of Tenebrio molitor Linnaeus) in polystyrene (PS) degradation was investigated. Gentamicin was the most effective inhibitor of gut bacteria among six antibiotics tested. Gut bacterial activities were essentially suppressed by feeding gentamicin food (30 mg/g) for 10 days. Gentamicin-feeding mealworms lost the ability to depolymerize PS and mineralize PS into CO2, as determined by characterizing worm fecula and feeding with (13)C-labeled PS. A PS-degrading bacterial strain was isolated from the guts of the mealworms, Exiguobacterium sp. strain YT2, which could form biofilm on PS film over a 28 day incubation period and made obvious pits and cavities (0.2-0.3 mm in width) on PS film surfaces associated with decreases in hydrophobicity and the formation of C-O polar groups. A suspension culture of strain YT2 (10(8) cells/mL) was able to degrade 7.4 ± 0.4% of the PS pieces (2500 mg/L) over a 60 day incubation period. The molecular weight of the residual PS pieces was lower, and the release of water-soluble daughter products was detected. The results indicated the essential role of gut bacteria in PS biodegradation and mineralization, confirmed the presence of PS-degrading gut bacteria, and demonstrated the biodegradation of PS by mealworms.

Enhanced Polystyrene Surface Mobility under Carbon Dioxide at Low Temperature for Nanoparticle Embedding Control

The surface properties of polystyrene (PS) films under carbon dioxide (CO2) were studied via a particle embedding technique at quite a low temperature range (308–323 K) in which polystyrene is typically considered to be in a glassy state without CO2. The atomic force microscope (AFM) technique with a tapping mode was used to get the height profiles of gold nanoparticles on the PS film surfaces and PS colloidal crystals for statistical analysis. The embedding of gold nanoparticles demonstrates that the surface mobility of polystyrene was greatly enhanced by exposing it to CO2, with further experimental confirmation by the study of welding polystyrene colloidal crystals under CO2 conditions. Surface mobility as well as embedding depths (from 2 to 17 nm) of nanoparticles is adjustable depending on the CO2 condition applied.

Enhancing Enzyme Stability by Construction of Polymer–Enzyme Conjugate Micelles for Decontamination of Organophosphate Agents

Enhancing the stability of enzymes under different working environments is essential if the potential of enzyme-based applications is to be realized for nanomedicine, sensing and molecular diagnostics, and chemical and biological decontamination. In this study, we focus on the enzyme, organophosphorus hydrolase (OPH), which has shown great promise for the nontoxic and noncorrosive decontamination of organophosphate agents (OPs) as well as for therapeutics as a catalytic bioscavanger against nerve gas poisoning. We describe a facile approach to stabilize OPH using covalent conjugation with the amphiphilic block copolymer, Pluronic F127, leading to the formation of F127-OPH conjugate micelles, with the OPH on the micelle corona. SDS-PAGE and MALDI-TOF confirmed the successful conjugation, and transmission electron microscopy (TEM) and dynamic light scattering (DLS) revealed ∼100 nm size micelles. The conjugates showed significantly enhanced stability and higher activity compared to the unconjugated OPH when tested (i) in aqueous solutions at room temperature, (ii) in aqueous solutions at higher temperatures, (iii) after multiple freeze/thaw treatments, (iv) after lyophilization, and (v) in the presence of organic solvents. The F127-OPH conjugates also decontaminated paraoxon (introduced as a chemical agent simulant) on a polystyrene film surface and on a CARC (Chemical Agent Resistant Coating) test panel more rapidly and to a larger extent compared to free OPH. We speculate that, in the F127-OPH conjugates (both in the micellar form as well as in the unaggregated conjugate), the polypropylene oxide block of the copolymer interacts with the surface of the OPH and this confinement of the OPH reduces the potential for enzyme denaturation and provides robustness to OPH at different working environments. The use of such polymer-enzyme conjugate micelles with improved enzyme stability opens up new opportunities for numerous civilian and Warfighter applications.

Nanoparticle Surface as Activation Site

The immense surface-to-volume (S/V) ratio in nanoparticles leads to large surface energy density. These high densities play the role of sites for activities that are not triggered in bulk materials. Here we present some examples of such distinctive activities taking place at nanoparticle surfaces. Our first example involves the morphological changes in silkworm (Bombyx mori L.) nuclear polyhedrosis virus (BmNPV) brought about by lipophilic amorphous silica nanoparticles (LASN). Microscopy studies show that nanoparticles severely alter the structure of the virus envelope by a 'deflation' of the viral polyhedron and formation of elongated structures. The second example shows the spatial variation in aggregation potential with temperature, for dodecanethiol-capped Au nanoparticles on an amorphous polystyrene film surface. We find that on increasing the temperature from 32 degrees C to 50 degrees C the aggregating potential becomes almost completely confined to the film surface, whereas going over to 100 degrees C the confining potential is overcome and out-of-plane growth takes place. A tentative and qualitative explanation has been attempted.

Effect of Polymer Confinement: Tuning Self-Assembled Growth of Monodisperse Au Nanoparticles on Polystyrene Films

X-ray reflectivity and tapping mode atomic force microscopy reveal that, Au, sputter-deposited on polystyrene films for film thickness ≤4Rg (Rg being unperturbed polymer gyration radius), diffuse and coalesce slowly, under ambient conditions and predominantly along the polymer surface, to form nanoparticles. The nanoparticles are highly monodisperse, and their in-plane dimensions increase with decrease in polystyrene film thickness. The observed directed coalescence is caused by sharply defined, higher surface energy zones or “traps”, corresponding to lower cohesion, between gyration spheres on polystyrene film surface. Lowering of in-plane cohesion and coalescence are found only when gyration spheres are layered along film depth due to thinning of the polystyrene film. The coalescing potential of these traps is given by the spatially localized increase in surface energy and can be increased by confinement. This fact is the principle behind this tunable self-assemblya new and generalized mode of self-asse...

Activated physical properties at air-polymer interface

The surface molecular motion of monodisperse polystyrene (PS) films was examined using scanning viscoelasticity microscopy (SVM) in conjunction with lateral force microscopy (LFM). The dynamic storage modulus,E′, and loss tangent, tanσ, at a PS film surface with number-average molecular weights,Mn, smaller than 30 k were found to be smaller and larger than those for the bulk sample, even at room temperature, meaning that the PS surface is in a glass-rubber transition or fully rubbery sate at this temperature when theMn is small. In order to quantitatively elucidate the dynamics of the molecular motion at the PS surface, SVM and LFM measurements were performed at various temperatures. The glass transition temperature,Tg, at the surface was found to be markedly lower than the bulkTg, and this discrepancy between the surface and bulk became larger with decreasingMn. Such an intensive activation of the thermal molecular motion at the PS surfaces can be explained in terms of an excess free volume in the vicinity of the film surface induced by the preferential segregation of the chain end groups.

Molecular motions of different scales at thin polystyrene film surface by lateral force microscopy

Lateral force microscopy (LFM) was used to probe the molecular motions at thin polystyrene film surface. The effect of the applied load on the LFM measurements was investigated by presenting both the LFM results and the surface morphology after several scans over the same area. Depending on the loads, the scanning can be nonperturbative (without alternating the surface morphology) or perturbative (patterning the surface). Temperature-dependent LFM measurements were conducted in order to determine the apparent transitions at the surface. Perturbative scans under high loads (e.g., 150 nN) witnessed that the apparent transitions shifted to low temperatures with an increasing scan rate, while the transitions behaved oppositely under lower loads (1, 10, and 20 nN). The heating effect is suggested to account for the behavior under high loads. According to our results from nonperturbative LFM, the apparent glass transition temperature (T(g)s) is more than 10 K lower than the bulk value. Moreover, rate-dependent LFM measurements were performed under 1 nN in order to detect the surface molecular motions. Time-temperature superposition yields a master curve exhibiting three apparent relaxation peaks. The molecular motions at the surface are discussed on the context of the coupling model.

Particle nucleation for dewetting initiation of thin polymer films

AbstractA quantitative comparison between spontaneous dewetting and particle nucleation for thin (thickness = 17nm) polystyrene (PS) films on nonwettable silicon (Si) surfaces is presented both experimentally and theoretically. Performing experiments in a class 100 clean room, we found that ∼ 23% of the observed dry patches formed because of dust particles, while the majority of the holes formed via the well known spontaneous dewetting process. The result was verified qualitatively by diffusion theory, which, however, predicted a diminished role for the airborne particles, leading to the conclusion that pre‐existing particles on the Si surfaces and/or the polymer solutions contribute substantially to the dewetting process. The driving force of particle motion into the polymer film is examined by placing aluminum oxide (Al2O3) particles on PS films. Finally, the effect of particle geometry is studied by placing gold (Au) disks on the free surface of PS films. An optically continuous PS film is found to be present around the periphery of the disk particles, even after the completion of the dewetting process in the rest of the sample. An attempt to explain dewetting inhibition at the vicinity of the micro‐disks, on the basis of molecular interactions developed in the system Au/PS/Si, is finally presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 138–145, 2005

Effects of Electrode Positioning on the Atmospheric‐Pressure DBD Plasma Torch

AbstractSummary: Various positions of electrodes were examined for a double cylindrical barrier discharge plasma torch with a pulse‐modulated power source. It was found that a stable He plasma jet was generated when the inner electrode was earthed and withdrawn back into the outer electrode. The plasma jet could oxidize a polystyrene film surface and a greater effect was achieved when the film was treated in the plasma jet rather than in the afterglow region.Effect of applied voltage and He gas‐flow rate on plasma jet length.magnified imageEffect of applied voltage and He gas‐flow rate on plasma jet length.

SYNTHESIS AND APPLICATIONS OF NOVEL FLUOROALKYL END-CAPPED OLIGOMERS CONTAINING 3,5-DIMETHYL-4-HYDROXYBENZYL AND 3-(2H-BENZOTRIAZOL-2-yl)-4-HYDROXYPHENYL SEGMENTS

New fluoroalkyl end-capped co-oligomers containing 3,5-dimethyl-4-hydroxybenzyl segments [RF‒(DMHB)x‒(DMAA)y–RF] were prepared by the reactions of fluoroalkanoyl peroxides with N-(3,5-dimethyl-4-hydroxybenzyl)methacrylamide [DMHB] and N,N-dimethylacrylamide (DMAA). Similarly, fluoroalkyl end-capped homo- and co-oligomers containing 3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl segments [RF–(BTRI)x–(Co–M)y–RF] were prepared by the reactions of fluoroalkanoyl peroxides with 2-[3–(2H‒benzotriazol–2–yl)–4–hydroxyphenyl]ethyl methacrylate [BTRI] and co-monomers [Co–M] such as acrylic acid (ACA), DMAA, and acryloylmorpholine (ACMO). The fluoroalkyl end-capped DMHB and BTRI co-oligomers thus obtained were soluble not only in water but also in common organic solvents. In addition, these fluorinated co-oligomers were able to reduce the surface tension of 0.1 N NaOH solutions quite effectively to around 20 mN/mlevels, although the corresponding non-fluorinated co-oligomers were not effective in reducing the surface tension of 0.1 N NaOH solutions. A modified polystyrene film surface treated with these fluoroalkyl end-capped DMHB and BTRI co-oligomers was found to exhibit a good oleophobicity imparted by fluorine with an excellent hydrophilicity. XPS analyses showed that end-capped fluoroalkyl groups in RF-(BTRI)n-RF homo-oligomer were arranged regularly above the modified polystyrene surface. Of particular interest, it was demonstrated that the self-assembled molecular aggregates formed by RF-(DMHB)x-(DMAA)y-RF co-oligomers could interact strongly with 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a guest molecule to form a host–guest intermolecular complex, though such a host–guest interaction was not observed in the corresponding non-fluorinated DMHB co-oligomer.

New Clues to the Factors Governing the Perpendicular Alignment of Liquid Crystals on Rubbed Polystyrene Film Surfaces

We have investigated the surfaces of rubbed polystyrene (PS) films in detail using atomic force microscopy and have discovered a previously unknown surface feature: submicroscale meandering groove-like structures composed of gravel-like grooves in tens of nanometers are present, oriented perpendicular to the rubbing direction. This unusual surface morphology is a significant departure from the surface topographies observed so far for rubbed PS and other polymer films, for which grooves are usually only found parallel to the rubbing direction. We also conclude from retardation analysis and linearly polarized infrared (IR) spectroscopy that the phenyl side groups of the PS chains are reoriented perpendicular to the rubbing direction, with para-directions that are nearly normal to the film plane, whereas the vinyl backbones of the PS chains are reoriented along the rubbing direction. This is the first time IR spectroscopic techniques have been used to determine the three-dimensional reorientation geometry o...

Direct imaging of nanoparticle embedding to probe viscoelasticity of polymer surfaces.

Atomic force microscopy was used to study the embedding of gold nanoparticles into the surface of polystyrene films. The rate of embedding was determined at temperatures near the bulk glass transition temperature T(g) by measuring the apparent nanosphere height as a function of annealing time. In particular, relative height measurements of the adhered particles were made at temperatures below the bulk T(g) value. In the absence of enhanced surface dynamics or yield processes no embedding is expected to occur for T<T(g). Measurements on 10 and 20 nm particles both indicated that the particles did embed 3-4 nm into the polymer for T<T(g). Both the extent and time frame for engulfment appear to be independent of the particle diameter. The results suggest a more mobile surface region on the order of 3-4 nm thick, with a lower glass transition temperature than the bulk.