Polystyrene Films Research Articles

Gradient in refractive indexreveals denser near free surface region in thin polymer films.

A gradient in refractive indexthat is linear in magnitude with depth into the film is used to fit ellipsometric data for thin polymer films of poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(2-vinyl pyridine) (P2VP). We find that the linear gradient model fits provide more physically realistic refractive indexvalues for thin films compared with the commonly used homogeneous Cauchy layer model, addressing recent reports of physically unrealistic density increases. Counter to common expectations of a simple free volume correlation between density and dynamics, we find that the direction of refractive index(density) gradient indicates a higher density near the free surface, which we rationalize based on the observed faster free surface dynamics needed to create vapor deposited stable glasses with optimized denser molecular packings. The magnitude of refractive indexgradient is observed to be three times larger for PMMA than for PS films, while P2VP films exhibit a more muted response possibly reflective of a decoupling in free surface and substrate dynamics in systems with strong interfacial interactions.

Reversible Adhesion Switching Using Spiropyran Photoisomerization in a High Glass Transition Temperature Polymer

Previous work has shown that photoisomerization of dopant molecules in a polystyrene film can either enhance or suppress its adhesion to a polar glass surface (Mostafavi, S. H. Macromolecules 2018, 51, 2388−2394; Mostafavi, S. H. Macromolecules 2019, 52, 6311–6317). In this paper, a different polymer host, Zeonex (ZX), is used in conjunction with the photochrome spiropyran. Nonpolar ZX has a higher glass transition temperature that makes it resistant to nanoscale mechanical deformations, while the spiropyran (SP) → merocyanine (MC) photoisomerization is a reversible reaction with a large polarity change. Ultraviolet light isomerizes SP to the polar MC form, increasing both the shear and pull-off adhesion forces to a clean glass surface by a factor of 5. Visible irradiation switches it back to the nonpolar SP form and returns the film back to its original weak adhesion, in contrast to the previously studied polystyrene films. The ability of visible light to switch off the polymer–glass adhesion is harnessed to make a light-controlled payload release device as well as to accelerate the polymer film delamination rate in water by a factor of 100. The kinetics of the water delamination, as well as the origin of residual adhesion after switching back to the SP form, are investigated. This work demonstrates how light-controlled noncovalent adhesion can be used as a solvent-free method to remove protective coatings or to disassemble structures.

Particularities of photonic and structural transformations in the polystyrene film during pulsed infrared laser irradiation

Two new kinds of the structural in-homogeneities in the polystyrene films were created by the irradiation of the film with nanosecond pulses of the infrared laser with 1064 nm wavelength. At the beginning of the irradiation dark micro-inclusions having unusual close to rectangular geometries appeared. After about 30 seconds of the irradiation one more kind structural distortions appeared having the geometries of the systems of the concentric micro-rings. Simultaneously with the creation of these concentric micro-rings the film started to emit bright blue luminescence all over its area and significant focusing of the laser beam during its propagation through the film was observed resulting in the generation of the bright white flashes at the screen installed behind the film. The creation of the dark rectangular spots as well as of the concentric micro-rings are ascribed to the non-linear interactions between the laser radiation and the structural distortions produced in the film due to photo-thermal processes excited in the film.

Inside Back Cover: Rational design for thermochromic luminescence in amorphous polystyrene films with bis‐o‐carborane‐substituted enhanced conjugated molecule having aggregation‐induced luminochromism

We designed and synthesized bis-o-carborane-modified luminophores for obtaining stimuli-responsive luminochromism in the solid state. The compounds show intense emission in condensed and crystalline states by suppressing aggregation-caused quenching. Especially, we fabricated dye-loaded polystyrene films and successfully observed thermochromic luminescence. Our materials are expected to be a versatile scaffold for developing film-type sensors. (Aggregate. 2021;2:e93)

Thermoplasmonic Patterning of Silver Nanocrystal/Polymer Composite Thin Films (Adv. Mater. Interfaces 19/2021)

Thermoplasmonic Patterning of Silver Nanocrystals on Polymer Films Absorption of light by plasmonic nanoparticles can result in local temperature increase due to the thermoplasmonic effect. In article number 2100738, Daniel Prezgot, Anatoli Ianoul, and co-workers use this phenomenon to achieve the controlled nano/micro scale lithographic patterning of a nanocomposite of silver nanocrystals on thin polystyrene films using a continuous-wave, visible laser.

Monomeric and Dimeric Carboxylic Acid in Crystalline Cavities and Channels of Delta and Epsilon Forms of Syndiotactic Polystyrene.

Delta (δ) and epsilon (ε) co-crystalline forms of syndiotactic polystyrene with a carboxylic acid guest were obtained by sorption of liquid hexanoic acid in syndiotactic polystyrene films exhibiting delta and epsilon nanoporous-crystalline forms. The characterization study is facilitated by axially stretched syndiotactic polystyrene films, used both for polarized FTIR spectra and for WAXD fiber patterns. Particularly informative are two carbonyl-stretching FTIR peaks, attributed to monomeric and dimeric hexanoic acid. The dichroism of these carbonyl peaks indicates that both delta and epsilon phases are able to include hexanoic acid as isolated guest molecules, while only the epsilon phase is also able to include dimeric hexanoic acid molecules in its crystalline channels. The inclusion of both isolated and dimeric hexanoic acid species in the epsilon form crystalline channels produces extremely fast hexanoic acid uptakes by syndiotactic polystyrene epsilon form films.

Friction and Mechanical Properties of AFM-Scan-Induced Ripples in Polymer Films

When compliant samples such as polymer films are scanned with an atomic force microscope (AFM) in contact mode, a periodic ripple pattern can be induced on the sample. In the present paper, friction and mechanical properties of such ripple structures on films of polystyrene (PS) and poly-n-(butyl methacrylate) (PnBMA) are investigated. Force volume measurements allow a quantitative analysis of the elastic moduli with nanometer resolution, showing a contrast in mechanical response between bundles and troughs. Additionally, analysis of the lateral cantilever deflection when scanning on pre-machined ripples shows a clear correlation between friction and the sample topography. Those results support the theory of crack propagation and the formation of voids as a mechanism responsible for the formation of ripples. This paper also shows the limits of the presented measuring methods for soft, compliant, and small structures. Special care must be taken to ensure that the analysis is not affected by artefacts.

Atomic Layer Deposition on Polymer Thin Films: On the Role of Precursor Infiltration and Reactivity.

Inorganic barriers grown by atomic layer deposition (ALD) can overcome the stability issues originating from the permeation of foreign species (water and oxygen) into polymer thin films. Alternatively, infiltration of ALD species into the bulk of the polymer can be used to modify its characteristic properties. In this study, the feasibility of growing an inorganic barrier with ALD on polystyrene, poly(methyl methacrylate), and poly(ethylene terephthalate glycol) thin films is evaluated. The nucleation and growth of the ALD layer, including the infiltration into the polymer thin film, are monitored in situ using spectroscopic ellipsometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy for Al2O3-ALD with trimethylaluminum as the Al precursor and H2O as the reactant. The results show that the deposition temperature and the presence and location of functional groups in the polymer chain exert the strongest influence on the infiltration behavior and as such allow us to manipulate (i.e. to prevent or expedite) the infiltration into the polymer thin film.

Thermoplasmonic Patterning of Silver Nanocrystal/Polymer Composite Thin Films

AbstractThe lithographic patterning of polymer films is ubiquitous in manufacturing processes. In this work, the high photothermal conversion efficiency utilizes plasmonic nanoparticles to locally pattern polystyrene films. Silver nanocubes on polystyrene thin films are used as a heat source for photothermal lithographic patterning using a continuous‐wave, visible laser. Distinct states of the nanocomposite defined by their own far‐field optical properties and microscale topography are observed. At low intensities the nanocubes can be embedded into the polymer at a nanometer scale displacement precision and produce a notable shift in the distinct localized surface plasmon resonance, enabling two‐color optical patterning. Numerical modelling indicates the temperatures reached in the film surpass polystyrene's glass transition temperature (Tg, ≈90 °C). At higher laser intensities sufficient temperatures are reached to achieve pronounced polymer film displacement enabling direct‐write lithography. Temperature estimates highlight the role of collective contribution of nanoparticle heating in the process. The process can be controlled by selecting excitation wavelengths to tune the power absorbed by the nanocubes in accordance with their plasmonic absorption spectrum. The approach here outlines a general method of 2D optical patterning utilizing thermoplasmonics, which can be further expanded to other materials, applications, and potentially to subdiffraction length scales.

Polarization Reversal Characteristics in Capacitors with a Metal/Insulator/Ferroelectric/Metal Structure.

A metal/insulator/ferroelectric/metal structure was fabricated using a covering of approximately 10 nm thick of an insulating polystyrene film on a ferroelectric poly(vinylidene fluoride-trifluoroethylene) film. To fabricate several samples, the thickness of the ferroelectric film was held constant while the thickness of the insulating film was varied from 8 to 24 nm. The polarization- voltage relationships were measured to extract the main parameters, in this case the remanent polarization, depolarization, coercive voltage and biased voltage values. As the insulating film becomes thicker, the remanent polarization and coercive voltage values tended to increase. On the other hand, depolarization and biased voltage values decreased. By analyzing the above mentioned parameters, a certain optimum insulator thickness could be predicted. This work shows that metal/insulator/ferroelectric/metal devices are more useful than metal/ferroelectric/metal capacitors.

Benzil Photoperoxidations in Polymer Films and Crosslinking by the Resultant Benzoyl Peroxides in Polystyrene and Other Polymers

Benzil (BZ) can be converted almost quantitatively to benzoyl peroxide (BP) in aerated polymer films upon irradiation at >400 nm (i.e., the long-wavelength edge of the n→π* absorption band of BZ, where BP does not absorb). Here, we summarize results for the photoperoxidation of BZ structures with molecular oxygen, principally in glassy polymer matrices. Some of the polymers are doped directly with BZ or its derivatives, and others, contain covalently attached BZ pendant groups from which BP groups are derived. While the decomposition of low-molecular-weight BP doped into polymer films (such as those of polystyrene (PS)) results in a net decrease in polymer molecular weight, thermal decomposition of pendant BP groups is an efficient method for chain crosslinking. Crosslinking of PS films doped with a molecule containing two covalently linked BZ or BP groups proceeds in a similar fashion. Free radicals from the covalently attached BP allow grafting of new monomers, as well. Additionally, the use of radiation filtered through masks has been used to create patterns of polymers on solid surfaces. Crosslinking of photodegradable poly(phenyl vinyl ketone) with BP structures obtained by photoperoxidation of BZ structures for the preparation of photodegradable polymer networks is described as well. In sum, the use of BZ and BP and their derivatives offers simple and convenient routes for modifying polymer chains and, especially, for crosslinking them. Specific applications of each use and process are provided. Although applications with PS are featured here, the methodologies described are amenable to a wide variety of other polymers.

Effect of Position and Structure of the Terminal Moieties in the Side Group on the Liquid Crystal Alignment Behavior of Polystyrene Derivatives.

We synthesized a series of polystyrene derivatives containing various side groups, such as the 4-(tert-butyl)-phenoxymethyl, 3-(tert-butyl)-phenoxymethyl, 2-(tert-butyl)-phenoxymethyl, 4-cumyl-phenoxymethyl, and 4-trityl-phenoxymethyl groups, through a polymer modification reaction to examine the liquid crystal (LC) alignment of these derivatives. In general, the vertical LC alignment on polymer films can be affected by the position and structure of the terminal moiety of the polymer side group. For example, the LC cells fabricated with 4-(tert-butyl)-phenoxymethyl-substituted polystyrene having a tert-butyl moiety as a para-type attachment to the phenoxy groups of the polystyrene derivatives exhibited vertical LC alignment, whereas the LC cells prepared from 3-(tert-butyl)- and 2-(tert-butyl)-phenoxymethyl-substituted polystyrene films exhibited planar LC alignment. In addition, the LC cells fabricated from 4-cumyl- and 4-trityl-phenoxymethyl-substituted polystyrene films with additional phenyl rings in the side groups exhibited planar LC alignment, in contrast to the LC alignment of the (tert-butyl)-phenoxymethyl-substituted polystyrene series. The vertical LC orientation was well correlated with the surface energy of these polymer films. For example, vertical LC orientation, which mainly originates due to the nonpolar tertiary carbon moiety having bulky groups, was observed when the surface energy of the polymer was lower than 36.6 mJ/m2.

Isolation, Identification, and Characterization of Polystyrene-Degrading Bacteria From the Gut of Galleria Mellonella (Lepidoptera: Pyralidae) Larvae.

Polystyrene (PS) is a widely used petroleum-based plastic, that pollutes the environment because it is difficult to degrade. In this study, a PS degrading bacterium identified as Massilia sp. FS1903 was successfully isolated from the gut of Galleria mellonella (Lepidoptera: Pyralidae) larvae that were fed with PS foam. Scanning electron microscopy and X-ray energy dispersive spectrometry showed that the structure and morphology of the PS film was destroyed by FS 1903, and that more oxygen appeared on the degraded PS film. A water contact angle assay verified the chemical change of the PS film from initially hydrophobic to hydrophilic after degradation. X-ray photoelectron spectroscopy further demonstrated that more oxygen-containing functional groups were generated during PS degradation. After 30 days of bacterial stain incubation with 0.15 g PS, 80 ml MSM, 30°C and PS of Mn 64400 and Mw 144400 Da, the weight of the PS film significantly decreased, with 12.97 ± 1.05% weight loss. This amount of degradation exceeds or is comparable to that previously reported for other species of bacteria reported to degrade PS. These results show that Massilia sp. FS1903 can potentially be used to degrade PS waste.

Correlation of physical aging and glass transition temperatures in ultrathin polystyrene films supported on [formula omitted

This study examined the effects of the aging temperature (Tage) on structural relaxation in ultrathin-supported polystyrene (PS) films with thickness ~0.2Rg. X-ray reflectivity and differential scanning calorimetry were used to evaluate the glass transition temperature (Tg) of ultrathin PS and bulk PS, respectively. The ultrathin films in their confined state showed anomalous thickness relaxation behaviors that could be classified into three types: (1) Tage≤60°C, a slow increase in thickness with time and a decrease in relaxation magnitude with temperature; (2) 70°C≤Tage≤110°C, a slow decrease in thickness with time and an increase in relaxation magnitude with temperature; (3) Tage>110°C, an increase in thickness with time due to dewetting of PS films deposited on SiO2. Such an interesting relaxation behavior can arise from the enhanced dynamics at the surface and reduced mobility at the interface inherent in ultrathin-supported films. Two distinct Tgs peculiar to ultrathin films were confirmed. The lower Tg has not been reported for supported PS films. The relaxation summarized above revealed a strong correlation with the Tg values. The de Gennes modified sliding motion model was applied to explain the correlation with relaxation dynamics.

Temperature dependence of vibrational motions of thin polystyrene films by infrared reflection-absorption spectroscopy: A single measurement tool for monitoring of glass transition and temperature history

A method for monitoring of vibrational response and temperature region of glass transition by a single analysis is introduced with the use of an otherwise well-known spectroscopic method. The temperature-dependent changes of polystyrene (PS) thin films were investigated by polarization-modulated infrared reflection-absorption spectroscopy. The study revealed that changes in individual spectral regions with the temperature increase are specific and provide the relation to the processing and thermal history of the thin film. Temperature responses of infrared spectral region areas; an abrupt change of Car-H stretching, a step-like change of Car-H out-of-plane bending, a linear decrease of C–H stretching and C–H bending area, granted information on the temperature domain represented by local molecular motion change (β-transition) of PS. The different behavior of spectral regions is rationalized by consideration of vibrational free volume contribution to the total free volume of the system that is certainly influenced by functional groups nature, such as their size, geometry and involvement of non-bonding interaction.

Additive Manufacturing of Sandwich–Structured Conductors for Applications in Flexible and Stretchable Electronics

Additive manufacturing methods have shown great potentials to substitute the costly and time‐consuming conventional subtractive methods in the processing of electronically conductive materials for applications in flexible and stretchable electronics. Herein, additive manufacturing of highly conductive, sandwich‐structured conductors with high‐temperature processibility and versatility in applicable substrates is reported. The sandwich‐structured conductors with silver nanoparticles (Ag NPs) as electronic conductors and polyimide (PI) as encapsulation are layer‐by‐layer deposited by aerosol printing into PI/Ag/PI composites. A high annealing temperature of 250 °C contributes to the high electronic conductivity of the Ag layer at 1.14 × 107 S m−1, which is in the same order of magnitude to the conductivity of bulk Ag at 6.3 × 107 S m−1. The high annealing temperature also significantly improves the interfacial bonding between the Ag and PI layers. For applications in flexible and stretchable electronics, the sandwich‐structured conductors are transferrable to various substrates through a thiol−epoxy bonding process, including polystyrene (PS), polyethylene terephthalate (PET), Kapton, and polydimethylsiloxane (PDMS) thin films. The sandwich‐structured conductors transferred to flexible and stretchable substrates exhibit highly retained electronic conductivity under deformations such as bending and stretching.

Photo-triggered surface relief formation of polystyrene films based on the Marangoni flow driven by a surface photoresponsive skin layer

Surface relief gratings (SRGs) are widely investigated in azobenzene-containing polymer films. We have recently demonstrated that a photoresponsive azobenzene layer existing only at the surface of a non-photoresponsive liquid crystalline polymer film can induce mass migration by patterned UV light irradiation, resulting in the SRG structure. This process is explained by the Marangoni flow triggered by the photoinduced surface tension change of the surface layer. In this work, we newly propose that the same strategy is applicable to an amorphous polymer material of polystyrene. The results obtained here indicate that photoinduced SRG formation is expanded for general amorphous polymers.

Polypyrrole-coated electrospun polystyrene films as humidity sensors

We report the preparation of flexible polystyrene/polypyrrole (PS/PPy) mats and their successful use as a resistive humidity sensor. These composite membranes were prepared by first obtaining PS films through the electrospinning technique, and then incorporating PPy chains by an in situ chemical polymerization of the pyrrole monomer. The PS fibers were homogeneously distributed, with diameters that obeyed a normal distribution with an average value of (1.04 ± 0.12) μm. The deposition of conducting PPy chains on the surface of the PS fibers was confirmed after characterizing the PS/PPy mats by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), contact angle measurements, and electrochemical impedance spectroscopy (EIS). When used as humidity sensors, the PS/PPy mats exhibited a sensor response of 128.6%, with fast response ((54.9 ± 3.5)s) and recovery times ((76.8 ± 11.1)s), and stable response under different humidity conditions over several days. These performance characteristics compare favorably to those of previous resistive humidity sensors discussed in the literature.

Rational design for thermochromic luminescence in amorphous polystyrene films with bis‐o‐carborane‐substituted enhanced conjugated molecule having aggregation‐induced luminochromism

AbstractWe designed the triad molecule, bis‐o‐carborane‐substituted bis(thienylethynyl)benzene, as a filler for realizing thermochromic luminescent behaviors based on conventional polymer films, such as polystyrene. From the optical measurements, it was found that the triad can show solid‐state emission and dual‐luminescent properties with variable intensity ratios depending on media. From the mechanistic studies including the experiments with the methyl‐substituted model compound, it was revealed that dual emission should be originated from the locally excited and twisted intramolecular charge transfer states, and the latter emission band is significantly enhanced in the solid states. We prepared amorphous films containing variable concentrations of the triad with the spin‐coating method and investigated optical properties. It was found that intensity ratios were drastically changed by altering the concentration of the triad. By increasing the proportion of the triad, aggregation occurred, and emission color was apparently varied through the changes in intensity ratios of the dual emission property. Based on the aggregation‐induced luminochromic property of the triad, thermochromic luminescence was finally realized by heating the amorphous films. The rational design for obtaining thermochromic luminescent amorphous films is illustrated in this paper.

Directly Probing the Fracture Behavior of Ultrathin Polymeric Films.

Understanding fracture mechanics of ultrathin polymeric films is crucial for modern technologies, including semiconductor and coating industries. However, up to now, the fracture behavior of sub-100 nm polymeric thin films is rarely explored due to challenges in handling samples and limited testing methods available. In this work, we report a new testing methodology that can not only visualize the evolution of the local stress distribution through wrinkling patterns and crack propagation during the deformation of ultrathin films but also directly measure their fracture energies. Using ultrathin polystyrene films as a model system, we both experimentally and computationally investigate the effect of the film thickness and molecular weight on their fracture behavior, both of which show a ductile-to-brittle transition. Furthermore, we demonstrate the broad applicability of this testing method in semicrystalline semiconducting polymers. We anticipate our methodology described here could provide new ways of studying the fracture behavior of ultrathin films under confinement.