Perpendicular oriented cylinders via directional coalescence of spheres embedded in block copolymer films induced by solvent annealing

Polystyrene-b-poly(methyl acrylate) (PS-b-PMA) block copolymer with PS volume fraction of 25.2 vol% was synthesized by atom transfer radical polymerization. Non-pretreated silicon wafers were used as the substrates to prepare perpendicular oriented PS cylinders in PMA matrix via solvent annealing which could induce the transformation of spheres to vertically oriented and hexagonally packed cylinders. The spherical microdomains were formed after the evaporation of solvents from the solutions of the block copolymer in selective solvents mixed from methanol, acetone and dichloromethane. The thickness of films could be as thick as 1000 nm, which were much thicker than usual cases and the cylinders came from the directional coalescence of the spheres, thus any pre-treatments of the substrates were not required for perpendicular orientation. The structures were characterized by small angle X-ray scattering (SAXS), transmission electron microscope (TEM), atom force microscopy (AFM) and grazing incidence small angle X-ray scattering (GISAXS).     

Morphology studies of multilayered HDPE/PS systems

Films with alternating layers of high density polyethylene (HDPE) and polystyrene (PS) were prepared by layer‐multiplying coextrusion, using two HDPEs differing in molecular weight. The crystal structure of extremely thin PE layers confined between PS layers was studied by small angle X‐ray scattering (SAXS), wide angle X‐ray diffraction (WAXS), and also by atomic force microscopy (AFM) and differential scanning calorimetry (DSC) technique including MDSC. The morphology of HDPE in the systems studied is greatly affected by the presence of HDPE/PS interfaces. In the HDPE layers, the texture component was observed with lamellae with their basal planes normal to the interface and (200) crystallographic planes parallel to the interface. Thus, the polymer chains in this texture component are parallel to the interface between both polymers. The small fraction of lamellae parallel to the interface in thicker HDPE layers disappears with the thinning of the layers beyond 100 nm. AFM images show in these samples straight, long lamellae positioned edge‐on at HDPE/PS interface. The thickness and perfection of lamellae decrease with the decrease of individual HDPE layer thickness. Those thinner and less perfect lamellae are more susceptible to reorganization during heating as it is observed by MDSC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 597–612, 2006     

Near-surface morphology effect on tack behavior of poly(styrene-b-butadiene-b-styrene) triblock copolymer/rosin films

The correlation between near-surface morphology and tack behavior of poly(styrene-b-butadiene-b-styrene) triblock copolymer (SBS)/rosin ester films was investigated using probe tack tests, transmission electron microscopy and small-angle X-ray scattering. The SBS/rosin films with rosin composition between 10 and 20 wt% rosin, prepared by slow evaporation of toluene during solvent casting, exhibited uniform near-surface morphology of lamellae oriented parallel to the surface. However, due to the limited solubility of rosin in the PS domains, the rosin started to phase-separate from the PS domains at 15 wt%, and formed fully separated micron-sized domains above 20 wt% rosin. The probe tack force of the SBS/rosin films increased steadily when the near-surface domain orientation changed from perpendicular cylinder to parallel lamellae on addition of rosin. Specifically, for a given lamellar morphology and surface orientation, macrophase separation of rosin plays a critical role in determining the tack properties of SBS/rosin films.     

Preparation of monodispersed and lipophilic attapulgite and polystyrene nanorods via surface‐initiated atom transfer radical polymerization

A new kind of initiator, 3‐(2‐bromo‐2‐methylacryloxy)propyltriethysiliane (MPTS‐Br), was prepared with a simply hydrobrominated commercial silane coupling agent (3‐methacryloxy‐proplytriethysilane, MPTS). It has been one‐step self‐assemble onto the surface of attapulgite (ATP) nanorods in the dispersion system, and by using this initiator‐modified nanorod (MPTS‐Br‐modified ATP nanoparticles, ATP‐MPTS‐Br) as macroinitiator for atom transfer radical polymerization (ATRP). Structurally well‐defined homopolymer polystyrene (PS) and block polymer poly(styrene‐b‐methyl methacrylate) (PS‐b‐PMMA) chains were then grown from the needle‐shaped nanorods surface to yield monodispersed nanorods composed of ATP core and thick‐coated polymer shell (ATP and PS). The graft polymerization parameters exhibited the characteristics of a controlled/”living” polymerization. The PS‐grafted ATP nanorods could be dispersed well in organic solvent with nanoscale. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ultraporous poly(l-lactide) scaffolds prepared with quaternary immiscible polymer blends modified by copolymer brushes at the interface

The activity of polystyrene-block-poly(l-lactide) (PS-b-PLLA) and polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer brushes located at a PS/PLLA interface were employed as a route to control the final microstructure of 95% void volume, ultraporous PLLA scaffolds. The latter were initially prepared from melt-processed quaternary blends of ethylene propylene diene rubber/poly(?-caprolactone)/polystyrene/poly(l-lactide) (EPDM/PCL/PS/PLLA) 45/45/5/5%vol. modified with the diblock copolymers. The blends display a layer comprised of the PS and PLLA phases located at the interface of the co-continuous EPDM and PCL phases. When the PS-b-PLLA copolymer is added, sub-micrometric PLLA droplets are encapsulated within the PS continuous layer phase. In comparison, both the PS and PLLA phases compete for the encapsulation process when the PS-b-PMMA is used, indicating that the microstructure of the PLLA phase can be fine-tuned with an adequate choice of interfacial modifier. These effects were investigated by analyzing the microstructure of ternary high-density polyethylene (HDPE)/PS/PMMA 80/10/10%vol. blends displaying PS/PMMA shell/core composite droplets in a HDPE matrix. An inversion of the shell/core structure is observed when the PS-b-PLLA copolymer is used to compatibilize the PS/PMMA interface, whereas no such restructuring occurs with the PS-b-PMMA. These effects are explained by the activity and swelling powers of the copolymer brushes. For the EPDM/PCL/PS/PLLA quaternary systems modified with the PS-b-PMMA, the PLLA homopolymer phase significantly penetrates and swells the PMMA blocks due to their mutual high affinity, as compared to the classical like-prefers-like compatibilization approach. The swelling of the blocks will tend to bend the interface toward the PS phase in order to minimize the lateral compression of the PMMA blocks. A similar effect explains the reversal of the PS/PMMA shell/core structure in the HDPE/PS/PMMA ternary system. This level of control ultimately leads to quite significant differences in microstructures and surface textures for the PLLA scaffolds.     

Synthesis of binary mixed homopolymer brushes by combining atom transfer radical polymerization and nitroxide-mediated radical polymerization

This communication describes a novel strategy to synthesize binary mixed homopolymer brushes from mixed self-assembled monolayers (SAMs) on silica substrates by combining atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP). Mixed SAMs terminated by ATRP and NMRP initiators were prepared by coadsorption of two corresponding organotrichlorosilanes from toluene solutions. Mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes were synthesized by ATRP of MMA at 80 °C followed by NMRP of styrene at 115 °C. Corresponding ‘free’ initiators were added into the solutions to control the polymerizations. We have found that the brush thickness increases with molecular weight in a nearly linear fashion. For a series of binary brushes consisting of PMMA of molecular weight of 26,200 and PS of various molecular weights, we have observed a transition in water contact angles with increasing PS molecular weight after CH₂Cl₂ treatment. Moreover, binary mixed polymer brushes with comparable molecular weights for two grafted polymers undergo reorganization in response to environmental changes, exhibiting different wettabilities.     

Microstructure and mechanics of crazes in oriented polystyrene

Crazes are produced in oriented polystyrene (PS) thin films, bonded to copper grids, by applying a tensile strain to the grids in directions parallel to, or perpendicular to the axis of molecular orientation. The crazes produced by straining parallel to the molecular orientation direction (parallel crazes) have a higher fibril volume fraction (v_f=0.45) than crazes in unoriented PS (v_f=0.25). The crazes produced by straining perpendicular to the molecular orientation direction (perpendicular crazes) have a much lower fibril volume fraction (v_f=0.05) than either parallel crazes or crazes in unoriented PS. These differences in fibril volume fraction are reflected in the micromechanics of the crazes. Perpendicular crazes show a higher stress concentration at the craze tip and a larger stress relief behind the craze tip than do the parallel crazes. The fibrils in long perpendicular crazes break down readily to form cracks whereas no parallel craze breakdown at similar strains is observed. These differences in craze microstructure and micromechanics are believed responsible for the marked anisotropy in the fracture properties of oriented glassy polymers.     

Effect of organically modified layered silicates on the morphology of symmetrical blends of polystyrene and poly(methyl methacrylate)

The changes in morphology caused by the addition of organically modified layered silicate on equal volume fraction blends of polystyrene and poly(methyl methacrylate) are investigated. In thin films supported on silicon, without layered silicates, the PMMA forms a layer on the silicon, while the PS tend to minimize contact with both the hydrophilic silicon substrate and the PMMA phase, and tend to form discrete domains on top of the PMMA layer. With the introduction of layered silicates, the characteristic length scale of the structure decreases. On the other hand, in bulk samples, without the layered silicates, the equal volume fraction blend has the PS domains in a PMMA matrix. At 0.6 wt% of added silicate, in both thin film and bulk, the blend morphology converts from discrete to co-continuous. Electron micrographs reveal well dispersed silicate sheets locating at the interface between small PS domains in the PMMA phase. The change in morphology is conjectured to be the result of the interfacial location of the layered silicates rather than the change in viscosity ratio between the two phases.     

Rim instability in polymethylmethacrylate films on self-assembled monolayers with the hydrophilicity

The solvent-induced dewetting of polymethylmethacrylate (PMMA) films prepared on self-assembled monolayers (SAMs) supported by Si substrates was investigated with the hydrophilicity of the SAMs. Dewetting of the PMMA film was characterized as a function of the surface energy of the SAMs. At lower surface energies, the rim instability was found to be of type B. Type B instability created undulations in the rims of holes. As the holes merged, fingers and then droplets formed. At higher surface energies, the rim instability of the PMMA films was of type A. Type A instability did not form fingers. The formation of PMMA droplets was dominated by the total spreading coefficient (S) of the PMMA film on the SAMs, which can be expressed as the sum of the dispersion (S^d) and the polar components (S^p) of the spreading coefficient. S^d of the PMMA films decreased, whereas S^p increased as ultraviolet (UV) irradiation for periods of time between 0 s and 100 s, respectively. This result suggests that S^d destabilized but S^p stabilized the PMMA films.     

Polymer Masks Fabrication by Micropatterning Surfaces of Composite Polymer Coatings

Abstract

Micropatterning of surfaces has been demonstrated using composite polymer coatings of PS and PMMA of equal molecular weights in different volume proportions with varying surface topographies on silicon surfaces. The creation of PMMA masks with various surface morphological features has also been demonstrated by removal of PS from the composite coatings using cyclohexane. Atomic force microscopy (AFM) investigations revealed that the surface pattern and the dimensions of these masks significantly changed with the change in the volume proportions of each homopolymer. The composite coatings of 20/80 vol% PS/PMMA, 50/50 vol% PS/PMMA, and 80/20 vol% PS/PMMA resulted in PMMA masks with holes (depth ～300 nm), wrinkles (height ～350 nm) and pillars (height ～600 nm), respectively. Surface compositional analysis carried out using FTIR and XPS investigations confirmed the presence of polymer coatings of PS, PMMA and PS/PMMA. XPS investigations also confirmed the successful removal of PS from the PMMA mask by showing the presence of the silicon substrate on those masks where PS was previously present. The water contact angle of the composite polymer masks ranged from 70 to 90° which increased with the increase of PS vol% in the composite. The wetting behavior of certain PMMA masks showed hydrophobicity with water contact angle values above 90°.     

Foaming behavior of isotactic polypropylene in supercritical CO2 influenced by phase morphology via chain grafting

Polystyrene (PS) and poly(methyl methacrylate) (PMMA) grafted isotactic polypropylene copolymers (iPP-g-PS and iPP-g-PMMA) with well-defined chain structure were synthesized by atom transfer radical polymerization using a branched iPP (iPP-B) as polymerization precursor. The branched and grafted iPP were foamed by using supercritical CO₂ as the blowing agent with a batch method. Compared to linear iPP foam, the iPP-B foams had well-defined close cell structure and increased cell density resulted from increased melt strength. Further incorporating PS and PMMA graft chains into iPP-B decreased the crystal size and increased the crystal density of grafted copolymers. In iPP-g-PS foaming, the enhanced heterogeneous nucleation by crystalline/amorphous interface further decreased the cell size, increased the cell density, and uniformized the cell size distribution. In contrast to this, the iPP-g-PMMA foams exhibited the poor cell morphology, i.e., large amount of unfoamed regions and just a few cells distributed among those unfoamed regions, although the crystal size and crystal density of iPP-g-PMMA were similar to those of iPP-g-PS. It was found that the iPP-g-PMMA exhibited PMMA-rich dispersed phase, which had higher CO₂ solubility and lower nucleation energy barrier than copolymer matrix did. The preferential cell nucleation within the PMMA-rich phase or at its interface with the matrix accounted for the poor cell morphology. The different effect of phase morphology on the foaming behavior of PS and PMMA grafted copolymers is discussed with the classical nucleation theory.     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Surface phase separations of PMMA/SAN blends investigated by atomic force microscopy

The thin films of poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (SAN) and their blends were prepared by means of spin-coating their corresponding solutions onto silicon wafers, followed by being annealed at different temperatures. The surface phase separations of PMMA/SAN blends were characterized by virtue of atomic force microscopy (AFM). By comparing the tapping mode AFM (TM-AFM) phase images of the pure components and their blends, surface phase separation mechanisms of the blends could be identified as the nucleation and growth mechanism or the spinodal decomposition mechanism. Therefore, the phase diagram of the PMMA/SAN system could be obtained by means of TM-AFM. Contact mode AFM was also used to study the surface morphologies of all the samples and the phase separations of the blends occurred by the spinodal decomposition mechanism could be ascertained. Moreover, X-ray photoelectron spectroscopy was used to characterize the chemical compositions on the surfaces of the samples and the miscibility principle of the PMMA/SAN system was discussed.     

Effects of molecular weight and plasticization on dissolution rates of thin polymer films

The dissolution rates (DR) in methyl ethyl ketone (MEK) of thin films of poly(methyl methacrylate), (PMMA), were measured using interferometry. Films were spun on silicon-oxide coated wafers. After baking at 155°C for one hour the dry films were about 1 μm thick. PMMA samples with M_n of 6000 to 320 000 were prepared by (a) polymerization and fractionation, and (b) electron beam bombardment of coated wafers. Both preparations resulted in non-linear behaviour when log DR was plotted against log M_n. The irradiated samples uniformly had DR values that were about 2.5 × those of the unexposed samples of the same M_n. Plasticization of PMMA by poly(ethylene oxide), PEO, of M_n = 4000 also changed DR in direct proportion to the amount of PEO added. With a weight fraction of 0.2 PEO, the DR was double that for PMMA alone.     

Plastic deformation of oriented lamellae: 3. Drawing behaviour of β-phase isotactic polypropylene

Specimens consisting of oriented β-phase lamellae of isotactic polypropylene, obtained by crystallization in a temperature gradient, were drawn at various temperatures. The deformation behaviour was investigated by means of stress-strain measurement, X-ray scattering and scanning electron microscopy. Drawings were carried out in two directions, parallel to the lamellar axis (parallel drawing) and perpendicular to it (perpendicular drawing). The maximum apparent stress and Young's modulus on parallel drawing were always larger than those on perpendicular drawing. Wide-angle X-ray scattering patterns from the specimens drawn at various temperatures showed different deformation behaviours between parallel and perpendicular drawings, which may be explained by the difference of deformation mechanism at the initial stage. As a conclusion, the deformation mechanism is classified into two steps. In the initial stage of deformation, the β-phase material is deformed mainly by interlamellar slippage (the first step). Then, the β-phase crystals are destroyed by Petermann-type unfolding or local melting (the second step). The final c-axis-oriented texture is recrystallized through destruction of the β-phase material.     

Morphology of polystyrene/polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) composite particles

Polystyrene/polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) (PS/PS-b-PMMA/PMMA) composite particles were prepared by releasing toluene from PS/PS-b-PMMA/PMMA/toluene droplets dispersed in a sodium dodecyl sulfate aqueous solution. The morphology of the composite particles was affected by release rate of toluene, the molecular weight of PS-b-PMMA, droplet size, and polymer composition. ‘Onion-like’ multilayered composite particles were prepared from toluene droplets of PS-b-PMMA and of PS/PS-b-PMMA/PMMA, in which the weights of PS and PMMA were the same. The layer thicknesses of the latter multilayered composite particles increased with an increase in the amount of the homopolymers. PS-b-PMMA/PS composite particles had a sea-islands structure, in which PMMA domains were dispersed in a PS matrix. On the other hand, PS-b-PMMA/PMMA composite particles had a cylinder-like structure consisting of a PMMA matrix and PS domains.     

Temperature-dependent interaction parameters of poly(methyl methacrylate)/poly(2-vinyl pyridine) and poly(methyl methacrylate)/poly(4-vinyl pyridine) pairs

Temperature-dependent interaction parameters (α) of poly(methyl methacrylate)/poly(2-vinyl pyridine) (PMMA/P2VP) pair and PMMA/poly(4-vinyl pyridine) (PMMA/P4VP) pair were obtained from the SAXS profiles at various temperatures, and curve fitting to the random phase approximation theory. For this purpose, symmetric P2VP-block-PMMA and P4VP-block-PMMA copolymers were synthesized anionically. The molecular weights of both block copolymers were controlled to exhibit the disordered state over the entire experimental temperatures. We found that the value of α for PMMA/P4VP was larger than PMMA/P2VP, similar to polystyrene (PS)/poly(vinyl pyridine) pairs. However, the difference between in α between PMMA/P2VP and PMMA/P4VP was much smaller than that between PS/P2VP and PS/P4VP. This might be attributed to the hydrophilic PMMA block compared with hydrophobic PS block. Finally, the order-to-disorder transition temperature for symmetric P2VP-block-PMMA copolymers was determined by small angle X-ray scattering and birefringence methods.     

Self-Assembled Monolayers of Vinyltriethoxysilane and Vinyltrichlorosilane Deposited on Silicon Dioxide Surfaces

Abstract

This study was aimed at deposition of self-assembled monolayers (SAMs) using vinyltriethoxysilane (VTES) and vinyltrichlorosilane (VTCS) molecules chemisorbed on silicon dioxide surfaces. The kinetics of SAM formation on planar glass substrates and silicon wafers was characterized by contact angle measurements. The surface free energy and its dispersion and polar components enabled to estimate the time of immersion required to deposit compact SAMs. Adsorption of organosilane molecules as a function of immersion time was characterized by X-ray photoelectron spectroscopy. The SAM thickness was evaluated by spectroscopic ellipsometry. Surface topography of deposited layers was investigated by atomic force microscopy (AFM). The VTCS/glass combination exhibited the fastest kinetics but the deposit was not uniform and included local agglomerates. The hydrophobic vinyl groups at deposit surface resulted in a surface free energy of 32 mJ/m².     

Dissolution rates for thin films of miscible polymer blends

The dissolution rates of thin polymer films were measured and compared. Mixtures of various ratios of poly(methyl methacrylate), PMMA, and poly(p-hydroxystyrene), PPHS, were dissolved in methyl isobutyl ketone, MIBK. The polymer solutions were then spun into thin films on silicon wafers and dried. The coated wafers were immersed in an MIBK bath and the rate of dissolution was observed using laser interferometry. The results show that pure PPHS films have dissolution rates 1000 times greater than films of pure PMMA at comparable molecular weights. However, for films containing both PPHS and PMMA, a minimum dissolution rate occurs for a mixture with about 20% (by weight) PPHS. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2015–2020, 1997     

Comparison of morphologies and mechanical properties of crosslinked epoxies modified by polystyrene and poly(methyl methacrylate)) or by the corresponding block copolymer polystyrene-b-poly(methyl methacrylate)

Polystyrene (PS, M_n=28,400, PI=1.07), poly(methyl methacrylate) (PMMA, M_n=88,600, PI=1.03), and PS (50,000)-b-PMMA (54,000) (PI=1.04), were used as modifiers of an epoxy formulation based on diglycidyl ether of bisphenol A (DGEBA) and m-xylylene diamine (MXDA). Both PS and PMMA were initially miscible in the stoichiometric mixture of DGEBA and MXDA at 80 °C, but were phase separated in the course of polymerization. Solutions containing 5 wt% of each one of both linear polymers exhibited a double phase separation. A PS-rich phase was segregated at a conversion close to 0.02 and a PMMA rich phase was phase separated at a conversion close to 0.2. Final morphologies, observed by scanning electron microscopy (SEM), consisted on a separate dispersion of PS and PMMA domains. A completely different morphology was observed when employing 10 wt% of PS-b-PMMA as modifier. PS blocks with M_n=50,000 were not soluble in the initial formulation. However, they were dispersed as micelles stabilized by the miscible PMMA blocks, leading to a transparent solution up to the conversion where PMMA blocks began to phase separate. A coalescence of the micellar structure into a continuous thermoplastic phase percolating the epoxy matrix was observed. The elastic modulus and yield stress of the cured blend modified by both PS and PMMA were 2.64 GPa and 97.2 MPa, respectively. For the blend modified by an equivalent amount of block copolymer these values were reduced to 2.14 GPa and 90.0 MPa. Therefore, using a block copolymer instead of the mixture of individual homopolymers and selecting an appropriate epoxy-amine formulation to provoke phase separation of the miscible block well before gelation, enables to transform a micellar structure into a bicontinuous thermoplastic/thermoset structure that exhibits the desired decrease in yield stress necessary for toughening purposes.