Triblock Copolymer Thin Films Research Articles

UV laser-processed microstructure for building biohybrid actuators with anisotropic movement

Fabrication of a biohybrid actuator requires muscle cells anisotropically aligned in a line, curve, or combination of lines and curves (similar to the microstructure of living muscle tissue) to replicate lifelike movements, in addition to considering the arrangement of skeletal structure or muscular structure with anisotropic straight patterns. Here, we report a UV laser-processed microstructure for freely directing cellular alignment to engineer a biohybrid actuator composed of poly(styrene-block-butadiene-block-styrene triblock copolymer) (SBS) thin film with tailor-made microgrooves (MGs) and skeletal myotubes aligned along these MGs. Specifically, straight, circular, or curved MGs were transferred to SBS thin films from a UV laser-processed template, allowing for the successful alignment of myotubes along MGs. The biohybrid actuator, composed of anisotropically aligned myotubes on a curved microgrooved SBS thin film, was contracted by electrical stimulation. Contraction of biohybrid actuators with curved aligned myotubes permits twisted-like behavior, unlike straight microgrooved films. Therefore, the UV laser-ablation system is a unique maskless and rapid microfabrication technique that provides intriguing opportunities for omni-directional microgrooved structures to achieve the complex motion of living organisms.

Fine‐tuning in‐plane interdomain spacing of polystyrene‐b‐poly(ethene‐co‐butadiene)‐b‐polystyrene triblock copolymer adding monodisperse polystyrene

The influence of adding narrow molar mass distribution polystyrene (PS) homopolymer on the morphology and/or dewetting processing of polystyrene‐b‐poly(ethene‐co‐butadiene)‐b‐polystyrene triblock copolymer (SEBS) thin films was investigated. The addition of the homopolymer caused a transition from non‐straight ribbons (with regularly spaced necks) to a spherical microdomain structure for an amount of 75 vol% PS (SEBS/PS 1:3), which also shows an interdomain distance increase of three times with respect to the neat SEBS. This spacing and interdomain distance control coincides with the amount of homopolymer added in the blend. The blending with PS demonstrates an approach to fine‐tuning the block copolymer structure and tailoring in‐plane microdomain spacing. Smaller or higher amounts of PS changed the spontaneous patterned structure originally observed for the neat triblock copolymer, resulting in a non‐ordered microphase separation. © 2023 Society of Industrial Chemistry.

Molecular dynamics study of shear-induced lamellar alignment of ABA triblock copolymer thin films.

In this study, the shear-induced lamellar alignment of a thin-film ABA triblock copolymer melt was achieved via a non-equilibrium coarse-grained molecular dynamics simulation. The ABA triblock copolymer system displayed a slightly different phase behavior under different shear conditions compared to the AB diblock copolymer system. Unlike previous studies that only considered the wall velocity, the Flory-Huggins parameter was considered in our study as a factor that determines lamellar alignment. Pre-aligned lamellae and randomly mixed polymers were used as the initial states for the shear simulation to compare the shear-induced lamellar alignment on each. The two initial conditions displayed different alignment behaviors; specifically, in the pre-aligned lamellae, a tilted structure was observed when the system was not aligned in the shear direction. To explain the difference between the tilted and realigned structures, the potential energy over the simulation time, polymer dynamics from the Van Hove correlation function, and the directional order parameter were investigated. It was inferred that a tilted structure is induced by the energy barrier of realignment originating from the restricted movement of the local polymer chains. Once they cross the energy barrier, block copolymers tend to align in the shear direction to attain energy stabilization through the polymer flow.

Defect-Induced Order–Order Phase Transition in Triblock Copolymer Thin Films

Fil: Abate, Anabella Angela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto de Fisica del Sur. Universidad Nacional del Sur. Departamento de Fisica. Instituto de Fisica del Sur; Argentina

Order–Order Phase Transitions Induced by Supercritical Carbon Dioxide in Triblock Copolymer Thin Films

Fil: Abate, Anabella Angela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto de Fisica del Sur. Universidad Nacional del Sur. Departamento de Fisica. Instituto de Fisica del Sur; Argentina

Structural analyses of sphere- and cylinder-forming triblock copolymer thin films near the free surface by atomic force microscopy, X-ray photoelectron spectroscopy, and grazing-incidence small-angle X-ray scattering

We investigated surface structures of three kinds of block copolymer (BCP) specimens forming hard spherical microdomains embedded in a soft matrix, by using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and grazing-incidence small-angle X-ray scattering (GISAXS). The three BCP specimens consist of different chemical species such as SEBS (polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene) and MAM (polymethylmethacrylate-block-poly(n-butylacrylate)-block-polymethylmethacrylate). Two of them form spherical microdomains at the thermodynamically equilibrium state (i.e., after fully long time thermal annealing), while the other exhibits spherical microdomains as a frozen state of the non-equilibrium structure (i.e., at the as-cast state using a selective solvent for the solution casting method), which was automatically frozen in by the vitrification of the hard component; the state is far from equilibrium). Nevertheless, such three different BCP specimens (chemically different in the molecular structure and thermodynamically different in the state) showed a common feature of the surface structure, as the outermost surface was completely covered with the single component having a lower value of the surface free energy, as revealed by XPS measurements. This finding significantly indicates that the AFM observation, which implies a coexistence of both BCP components on the free surface, misleads the conclusion. Although such surface coverage is reasonable and well-known, it was further found that the block chains are confined in a thin layer of the outermost region of the specimen. It is striking to find that the block chains are forced to be deformed (compressed) in order to meet the thermodynamic requirement of the surface coverage.

Dielectric behavior of sulfonated poly(styrene–isobutylene–styrene) triblock copolymer thin films

ABSTRACTSulfonated, block copolymers have traditionally been studied for applications in fuel cells and chemical protective clothing, among others. As such, most investigations have focused on the evaluation of transport properties and the selectivity and permeability of the polymer membranes. This work, however, focuses on the electrical characterization of sulfonated poly(styrene–isobutylene–styrene) (SIBS) triblock copolymer thin films. More specifically, the dielectric properties of SIBS are evaluated as a function of critical parameters such as frequency, sulfonation percent, and the polymer concentration. The results show that the dielectric constant increases with sulfonation percent and polymer concentration to values as high as 13,600. This work also provides insights into the correlation of SIBS electrical properties with its chemical structure and morphology. The structure–property relationship is derived through a combination of techniques including: elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and atomic force microscopy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45662.

Nanopattern transformation of ABC triblock copolymer thin films induced by strong solvent selectivity and annealing

Nanopattern transformation behaviors of polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (PI-b-PS-b-P2VP) asymmetric ABC triblock copolymer were investigated systematically with various control parameters, including different solvents for polymer solution and annealing conditions in this paper. Ordered nanopattern of PI-b-PS-b-P2VP with hexagonal cylinders could be obtained when PI-b-PS-b-P2VP toluene solution was spin-coated on silicon substrate followed by toluene vapor annealing process. When the film with hexagonal and cylindrical nanopattern was exposed to saturated toluene vapor, the order-order transition of cylindrical nanopattern to parallel nanopattern was observed due to the strong selectivity of toluene to PS and PI blocks. Furthermore, fingerprint nanopattern could also be obtained by solvent annealing in tetrahydrofuran vapor. The nanopattern transformation was due to different selectivity of solvents and incompatibilities of the three blocks of PI-b-PS-b-P2VP under various solvent annealing conditions.

Nanostructure development in polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) (SBM) thin films by atomic force microscopy: Effect of copolymer composition and solvent

Surface morphology development for SBM triblock copolymer thin films has been studied by atomic force microscopy. The effect of copolymer composition and solvent on the final morphology has been investigated. Obtained results indicated that depending on the block ratio (symmetric or asymmetric with minority middle block) and solvent, lamellar, hexagonal, cylindrical, or spheres in lamellae (ls)‐type morphologies can be achieved at film surfaces. The influence of the interaction parameters among blocks and solvents and cohesive energy values of block pairs on the final morphology has been proved. POLYM. ENG. SCI., 58:422–429, 2018. © 2017 Society of Plastics Engineers

Investigation of the electrochromic properties of tri-block polyaniline-polythiophene-polyaniline under visible light

This paper describes the synthesis and electrochromic properties of a novel soluble polyaniline-polythiophene-polyaniline tri-block copolymer. The measurements of optical absorbance as a function of voltage and time on tri-block copolymer thin films demonstrated an improvement in stability at ambient conditions and visible light irradiation during the application of voltages. Switching experiments showed an improvement of stability of tri-block copolymer up to 3 times in comparison to the polythiophene block only. A comparison of optical absorbance characteristics for the tri-block copolymer relative to the polyhiophene block indicated that the polyaniline blocks substantially increased film stability and therefore has influence on the optical and electrochemical properties of tri-block polyaniline-polythiophene-polyaniline.

Trilayered Single Crystals with Epitaxial Growth in Poly(ethylene oxide)-block-poly(ε-caprolactone)-block-poly(l-lactide) Thin Films

Manipulation of crystalline textures of biocompatible block copolymers is critical for the applications in the medical field. Here, we present the control of multiple-crystalline morphologies with flat-on chain orientation in biocompatible poly(ethylene oxide)-block-poly(e-caprolactone)-block-poly(l-lactide) (PEO–PCL–PLLA) triblock copolymer thin films using melt and solvent-induced crystallizations. Only single-crystalline morphologies of the first-crystallized blocks can be obtained in the melt-crystallized thin films due to the confinement effect. With solvent annealing by PCL-selective toluene, single-crystalline PLLA to double-crystalline PLLA/PCL and to triple-crystalline PLLA/PCL/PEO layered crystals in sequence are observed for the first time. With the control of solvent selectivity, different sequential crystallization involving first-crystallized PCL transferring to double-crystalline PCL/PLLA is obtained using PEO-selective n-hexanol for annealing. Surprisingly, the crystalline growth of the tr...

Complex microstructures of ABC triblock copolymer thin films directed by polymer brushes based on self-consistent field theory.

The morphology and the phase diagram of ABC triblock copolymer thin film directed by polymer brushes are investigated by the self-consistent field theory in three dimensions. The polymer brushes coated on the substrate can be used as a good soft template to tailor the morphology of the block copolymer thin films compared with those on the hard substrates. The polymer brush is identical with the middle block B. By continuously changing the composition of the block copolymer, the phase diagrams are constructed for three cases with the fixed film thickness and the brush density: identical interaction parameters, frustrated and non-frustrated cases. Some ordered complex morphologies are observed: parallel lamellar phase with hexagonally packed pores at surfaces (LAM3 ll -HFs), perpendicular lamellar phase with cylinders at the interface (LAM⊥-CI), and perpendicular hexagonally packed cylinders phase with rings at the interface (C2⊥-RI). A desired direction (perpendicular or parallel to the coated surfaces) of lamellar phases or cylindrical phases can be obtained by varying the composition and the interactions between different blocks. The phase diagram of ABC triblock copolymer thin film wetted between the polymer brush-coated surfaces is very useful in designing the directed pattern of ABC triblock copolymer thin film.

Grazing incidence small-angle neutron scattering: challenges and possibilities

The enhancement of surface sensitivity by grazing incidence geometry facilitates the investigation of nanostructures in thin films and at surfaces. The technique provides information about the surface roughness, lateral correlations, sizes and shapes of objects (such as, nanoparticles and nanostructures) positioned on top of the surface or in a region near the surface. Grazing incidence small-angle neutron scattering (GISANS) overcomes the limitations of conventional small-angle neutron scattering for extremely small sample volumes in the thin-film geometry. Although real space analysis techniques, such as atomic force microscopy, provide easy access to surface structures, reciprocal space analysis techniques, such as GISANS, provide several advantages: (i) average statistical information over the large illuminated sample surface can be detected and (ii) buried lateral structures can be probed without damage, using the variable-probed depth as a function of the incident angle. To illustrate the potential applications and challenges of GISANS, several different examples of thin nanostructured polymer films are reviewed. Nanostructures in triblock copolymer thin films are studied in the bulk as well as at the polymer-air and the silicon–polymer interface. Confined nanostructures in a dewetted diblock copolymer film are also discussed in terms of contrast and experimental settings.

Spatial and Orientation Control of Cylindrical Nanostructures in ABA Triblock Copolymer Thin Films by Raster Solvent Vapor Annealing

We present a spatially resolved approach for the solvent vapor annealing (SVA) of block copolymer thin films that permits the facile and relatively rapid manipulation of nanoscale ordering and nanostructure orientation. In our method, a localized (point) SVA zone is created through the use of a vapor delivery nozzle. This point annealing zone can be rastered across the thin film using a motorized stage to control the local nanoscale structure and orientation in a cylinder-forming ABA triblock copolymer thin film. At moderate rastering speeds (∼100 μm/s) (i.e., relatively modest annealing time at a given point), the film displayed ordered cylindrical nanostructures with the cylinders oriented parallel to the substrate surface. As the rastering speed was decreased (∼10 μm/s), the morphology transformed into a surface nanostructure indicative of cylinders oriented perpendicular to the substrate surface. These perpendicular cylinder orientations also were created by rastering multiple times over the same region, and this effect was found when rastering in either retrace (overlapping) or crossed-path (orthogonal) geometries. Similar trends in nanostructure orientation and ordering were obtained from various nozzle diameters by accounting for differences in solvent flux and annealing time, illustrating the universality of this approach. Finally, we note that our "stylus-based" raster solvent vapor annealing technique allows a given point to be solvent annealed approximately 2 orders of magnitude faster than conventional "bell jar" solvent vapor annealing.

Diblock and triblock copolymer thin films on a substrate with controlled selectivity

Using self-consistent field theory (SCFT), morphology development in symmetric linear ABC triblock copolymer films on neutral and selective substrates has been studied, and it is compared with the triblock copolymer morphologies in bulk. In particular, the effects of the substrate preferable to B (interior) block on nanopattern formation of the copolymer films are of our central interest. Here, we report various nanopatterns with tunable square morphologies. The domain patterns are much more diverse than those parallel to the substrate with substrate selectivity for end-block or those vertical to the substrate without substrate selectivity. Furthermore, in order to figure out an economical and efficient way to fabricate useful passive pattern transfer layers, which have potential applications in microelectronic processes and ultrahigh density storage media, we propose a two-step strategy and scrutinize the conditions for generating square symmetries using cylinder-forming or lamella-forming AB diblock copolymers deposited on substrates created from ABC triblock copolymer films. It is found that a thinner film with weak incompatibility can produce square patterns.

Controlling Particle Location with Mixed Surface Functionalities in Block Copolymer Thin Films

The controlled placement of gold nanoparticles (AuNPs) in poly(styrene-b-isoprene-b-styrene) [SIS] triblock copolymer thin films was achieved by tuning the surface chemistry of the AuNPs. Facile thiol ligand exchanges permitted quick and thorough exploration of the surface chemistry effects on AuNP segregation behavior. By using thiol-functionalized polystyrene (PS-SH) or 1-dodecanethiol (C12SH) ligands to tune nanoparticle surface chemistry, AuNPs were selectively incorporated into either the polystyrene (PS) or the polyisoprene (PI) domains. Nanocomposite polymer films were characterized by atomic force microscopy, transmission electron microscopy (TEM), and TEM tomography. AuNPs synthesized with a C12SH capping ligand preferentially segregated into PI-rich domains. However, after exchanging C12SH with PS-SH ligands to a C12SH:PS-SH molar ratio of approximately 5:1, AuNPs showed an affinity for PS-rich domains. The C12SH:PS-SH transition ratio was much higher than expected, based on molecule-averaged surface energy arguments that predicted a ratio of 0.4:1 to 0.8:1. The unexpected transition ratio was rationalized according to the area-averaged enthalpic contributions of the capping ligands. Furthermore, mixing and incorporating PI- and PS-preferential AuNPs created a well-mixed nanocomposite, which highlights the versatility of the AuNPs.

Phase Behavior of Sphere-Forming Triblock Copolymers in Films

The self-assembly of sphere-forming triblock copolymers confined between two thin homogeneous surfaces is investigated based on mean-field dynamic density functional theory. The morphologies deviating from the bulk sphere-forming phase are revealed, including cylinders oriented perpendicular to the surface, cylinders oriented parallel to the surface, perforated lamellae and lamellae by varying film thickness and surface field strength. The phase diagram of surface reconstruction is also constructed. By comparing the present phase diagram with the other relevant phase diagram for the cylinder-forming triblock copolymer film, the difference between the sphere-forming and the cylinder-forming triblock copolymer thin film is discussed.

Contrast matching of an Si substrate with polymer films by anomalous dispersion at the SiKabsorption edge

Anomalous dispersion at the SiKabsorption edge has been used to control the reflection from the interface between a film and an Si substrate, which otherwise complicates the nanostructure analysis of such a film, particularly for the soft-matter case, in grazing-incidence small-angle scattering. Such a reflectionless condition has been chosen for a triblock copolymer thin film, and two-dimensional grazing-incidence small-angle scattering patterns were obtained without the effect of the reflection. The present approach is useful for analysing nanostructures without introducing complicated corrections arising from the reflection.

Morphologies of Linear Triblock Copolymers from Monte Carlo Simulations

Recent developments in block copolymer lithography suggest that triblock copolymers could enable fabrication of ultrasmall features over large areas. While the majority of past work with block copolymers has focused on diblocks, triblocks and multiblocks in general could offer distinct advantages for sublithographic patterning. In order to guide selection of appropriate materials and strategies, it is important to first determine the phase behavior that distinct molecular architectures exhibit in the bulk. Theoretically informed Monte Carlo simulations of a coarse grain model are used to predict the bulk morphologies of several linear triblock copolymers in three dimensions. Some of these triblocks are representative of the styrene–isoprene–methyl methacrylate system. The morphologies predicted by simulations, which incorporate fluctuation effects, are compared to those predicted by self-consistent field theory (SCFT). While the two approaches predict similar morphologies, some differences are identified when some of the blocks are short. We then consider several morphologies of lamellae forming triblock copolymer thin films on a patterned substrate, and use free energy calculations to determine the equilibrium states.

Nanopatterns of ABA triblock copolymer thin films formed on water surface

Nanopatterns of hydrophobic triblock copolymer SEBS thin films formed on a water surface by using drop spreading casting and dilute solution casting methods have been studied. It is found that the surface morphologies of thin films, as well as the spreading behavior of polymer solutions on water, depend strongly on the selectivity of the solvent and the functional group which interacts with the water subphase. The resulting nanopatterns were examined in terms of the relative interaction parameter (Δ χ) and the copolymer volume fraction ( ϕ) in the solution, based on the physics of solvent annealing and evaporation.