Polymer Crystallization Influenced by Initial Orientation of Cylindrical Diblock Copolymers in Thin Films

The effect of the initial states (disordered perpendicular cylinder structure vs. parallel cylinder structure) on the crystallization of polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) thin films during cyclohexane annealing was investigated. The cylindrical domains perpendicular or parallel to the surface were obtained by controlling the film thickness. During solvent annealing, for the film with the perpendicular cylinders, the ordering degree of cylinders was increased. The enthalpic increase is large enough for the forming of square‐shaped crystals, and subsequently the square‐shaped single crystals surrounded by the ordered hexagonally packed perpendicular cylinders evolved to the dendrite ones. For the film with the parallel cylinders, the parallel cylinders were translated to the perpendicular ones. The increased enthalpy was not large enough for the formation of square‐shaped single crystals. Instead, the dendrite‐like crystals started at the edge of terraces.

     

Complex Macrophase‐Separated Nanostructure Induced by Microphase Separation in Binary Blends of Lamellar Diblock Copolymer Thin Films

The nanostructures of thin films spin‐coated from binary blends of compositionally symmetric polystyrene‐b‐polybutadiene (PS‐b‐PB) diblock copolymer having different molar masses are investigated by means of atomic force microscopy (AFM) and grazing‐incidence small‐angle X‐ray scattering (GISAXS) after spin‐coating and after subsequent solvent vapor annealing (SVA). In thin films of the pure diblock copolymers having high or low molar mass, the lamellae are perpendicular or parallel to the substrate, respectively. The as‐prepared binary blend thin films feature mainly perpendicular lamellae in a one‐phase state, indicating that the higher molar mass diblock copolymer dominates the lamellar orientation. The lamellar thickness decreases linearly with increasing volume fraction of the low molar mass diblock copolymer. After SVA, well‐defined macrophase‐separated nanostructures appear, which feature parallel lamellae near the film surface and perpendicular ones in the bulk.

     

Effects of Comonomers on Lamellar and Noncrystalline Microstructure of Ethylene Copolymers

Summary: A systematic investigation of the microstructure of ethylene copolymers has been carried out as a function of the comonomer type and content, employing small‐angle X‐ray scattering (SAXS) experiments to study the lamellar structure, and solid‐state NMR to study the local conformational freedom. The SAXS results clearly show that the major consequence of incorporating comonomers (butene and octene) is the absence of lamellar thickening during the crystallization. From solid‐state NMR study, applying the rotor‐encoded rotational echo double resonance technique (REREDOR), it is found that the extent of the orientational order in the noncrystalline region of semicrystalline polyethylene is substantial but this order is not significantly affected by the incorporation of comonomer units. Therefore, the major cause for the significant improvements of mechanical properties observed for ethylene copolymers is not a change in the thermodynamic state of the noncrystalline region, but most likely a significant change in the intermolecular topological structure due to the blocking of disentanglement processes required by the lamellar thickening step during crystallization.

     

Controlling Orientation and Functionalization in Thin Films of Block Copolymers

Functionalizing and controlling nanostructures resulting from block copolymer self‐assembly are key factors in defining their application. In this work, a simple but quite general route to achieve both goals simultaneously is discussed. In thin films of polystyrene‐block‐poly(vinyl pyridine) (PS‐b‐PVP) with small concentrations of a gold salt, the salt is found to complex with the PVP block which leads to an orientation of the microdomains normal to the surface after solvent annealing together with functionalization. By increasing the amount of gold salt, on the other hand, micelles are found to form in solutions leading to a range of different morphologies in the thin films.

     

Effect of Film Thickness on the Columnar Packing Structures of Discotic Supramolecules in Thin Films

The effects of film thickness on the columnar packing structure of discotic supramolecules in a thin supported film have been investigated by grazing‐incidence small‐angle X‐ray scattering technique using magnetically aligned cobalt octa(n‐decylthio)porphyrazine (CoS10) films on octadecyltrichlorosilane (OTS)‐functionalized substrates as model systems. Magnetically aligned CoS10 films with a range of film thicknesses (49–845 nm) form uniaxially oriented ‘edge‐on’ columnar superstructures with their columnar directors perpendicular to the applied magnetic field. However, the orientational ordering of the columnar packing in the plane perpendicular to the applied magnetic field is strongly dependent on the film thickness. While being damped by the elasticity of the side chains of CoS10, the strong interfacial interaction at the film‐substrate interface propagates up to 50–100 nm from the substrate, maintaining the orientation of columnar packing in the plane perpendicular to the applied magnetic field. When the distance from the film‐substrate interface becomes larger than about 100 nm, symmetric tilting of columnar layer orientation, which saturates at 11.5°, occurs due to longitudinal edge dislocations induced by accumulated elastic deformation.     

An in situ GISAXS study of selective solvent vapor annealing in thin block copolymer films: Symmetry breaking of in-plane sphere order upon deswelling

Thin films of asymmetric poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymers are studied by means of in situ grazing-incidence small-angle X-ray scattering (GISAXS) during solvent vapor annealing in tetrahydrofuran, a solvent selective for the PS majority block of the copolymer. Upon swelling, PS-b-P4VP block copolymers form hexagonal arrays of spherical P4VP microdomains in a PS matrix in films 7–9 layers thick. Deswelling the films induces a transition from hexagonal to face-centered orthorhombic (fco) symmetry, which is stable only at ∼7 layers of spherical microdomains. Dry films show co-existing hexagonal and orthorhombic symmetries when the solvent is removed slowly, whereas instantaneous solvent removal suppresses the fco structure, resulting in films with only hexagonal structure. The in-plane order of microdomains is significantly deteriorated in dry films independent of the solvent removal rate.Spherical block copolymer microdomains are known to undergo a transition from hexagonal to orthorhombic packing in isothermally annealed thin films when the number of sphere layers is increased from 4 to 5. In this paper, in situ GISAXS experiments reveal that a similar transition occurs during solvent vapor annealing in a selective solvent. Interestingly, the transition from hexagonal to orthorhombic packing of spheres occurs as solvent is removed from a thin block copolymer film. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 331–338     

Estimating the segregation strength of microphase‐separated diblock copolymers from the interfacial width

The ever‐growing catalog of monomers being incorporated into block polymers affords exceptional control over phase behavior and nanoscale structure. The segregation strength, χN, is the fundamental link between the molecular‐level detail and the thermodynamics. However, predicting phase behavior mandates at least one experimental measurement of χN for each pair of blocks. This typically requires access to the disordered state. We describe a method for estimating χN from small‐angle X‐ray scattering measurements of the interfacial width between lamellar microdomains, t_x, in the microphase‐separated melt. The segregation strength is determined by comparing t_x to self‐consistent field theory calculations of the intrinsic interfacial width, t_i, as a function of the mean‐field χN. The method is validated using a series of independent experimental measurements of t_x and χN, measured via the order–disorder transition temperature, T_ODT. The average absolute relative difference between χN calculated from t_x and the value calculated from T_ODT is a modest 11%. Corrections for nonplanarity of the interfaces are investigated but do not improve the agreement between the experiments and theory. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. J. Polym. Sci., Part B: Polym. Phys. 2019 © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 932–940     

Phase separation and permeability in polyisobutylene‐based miktoarm star polymers

The phase behavior of (PS‐PIB)₂‐s‐PAA miktoarm star terpolymers with varying volume fractions of PAA was investigated directly by transmission electron microscopy, atomic force microscopy, and small‐angle X‐ray scattering, and indirectly by thermogravimetric analysis and degree of water sorption. The microdomains of (PS‐PIB)₂‐s‐PAA demonstrate a unique and unexpected progression from highly ordered cylinders, to lower ordered spheres, to gyroid structures with increasing PAA content from 6.6 to 47 wt %. Interestingly, the phase behavior in the miktoarm star polymer system is significantly different from that reported previously for the linear counterpart of similar composition (PAA‐PS‐PIB‐PS‐PAA), where a steady progression from cylindrical to lamellar morphology was observed with increasing PAA content. At low PAA concentrations, the morphology is driven primarily by the relative solubility of the components, while at high PAA content the molecular architecture dominates. Thermal annealing demonstrated the thermodynamic stability of the morphologies, indicating the potential for design of novel microstructures for specific applications through precise control of architecture, composition, and interaction parameters of the components. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 916–925     

Layer structure estimation of three‐dimensional crystal and two‐dimensional molecular film for fluorinated comb copolymers

Comb copolymers containing both hydrogenated and fluorinated side‐chains were prepared by copolymerization using acrylic or methacrylic monomers in several ratios. The crystal structures of these copolymers and layer structures of their organized molecular films were investigated by wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and out‐of plane X‐ray diffraction. Further, to selectively estimate the regularity of shorter fluorocarbon side‐chains, organized molecular films of copolymers were investigated by polarized near‐edge X‐ray adsorption fine structure (NEXAFS) spectroscopy. From the results of these measurements, it was inferred that these copolymers formed highly ordered layer structures, and a long spacing was predominantly determined by the arrangement of hydrogenated side‐chains, except in copolymers having extremely high fluorocarbon contents. In the case of the organized molecular films, the fluorinated side‐chains of methacrylate copolymers cannot form a highly ordered arrangement, whereas those of acrylate copolymers were oriented on monolayers. However, in both cases, the hydrogenated side‐chains predominantly formed layer structures in the organized films, and the fluorinated side‐chains did not contribute to the formation of the layer structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 534–546, 2008     

Synthesis and self‐assembly of highly incompatible polybutadiene–poly(hexafluoropropylene oxide) diblock copolymers

A versatile coupling reaction for the preparation of polybutadiene–poly‐(hexafluoropropylene oxide) (BF) diblock copolymers is described. Six diblock copolymers with different block lengths were characterized by nuclear magnetic resonance spectroscopy and size exclusion chromatography; all six had total molecular weights below 15,000. Microphase separation of the block copolymers in the bulk state was established by small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry. SAXS data suggest that the diblocks are characterized by an unusually large Flory‐Huggins interaction parameter, χ, on the order of 10. However, extraction of χ from the order–disorder transition gave large (order 1) but significantly different values, thereby suggesting that these copolymers are too small and too strongly interacting to be described by block copolymer mean‐field theory. Dynamic light scattering was used to analyze dilute solutions of the title block copolymers in four selective organic solvents; the sizes of the micelles formed were solvent dependent. The micellar aggregates were large and nonspherical, and this is also attributed to the high degree of incompatibility between the two immiscible blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3685–3694, 2005     

Morphology Tailoring of Thin Film Block Copolymers on Patterned Substrates

It is well known that chemically patterned substrates can direct the assembly of adsorbed layers or thin films of block copolymers. For a cylinder‐forming diblock copolymer on periodically spot‐patterned substrates, the morphology of the block copolymer follows the pattern at the substrate; however, with different periodic spacing and spot size of the pattern, novel morphologies can be created. Specifically, we have demonstrated that new morphologies that are absent in the bulk system can be tailored by judiciously varying the mismatch between the width of the pattern and the periodic spacing of the bulk block copolymer, the top surface affinity, and spot size. New morphologies can thus be achieved, such as honeycomb and ring structures, which do not appear in the bulk system. These results demonstrate a promising strategy for fabrication of new nanostructures from chemically patterned substrates.     

Confinement Effect on the Body‐Centered‐Cubic Phase of Diblock Copolymers in Film

In this paper, we study the morphology of diblock copolymers with the body‐centered‐cubic (bcc) phase confined between two flat surfaces. Employing the Landau–Brazovskii mean field theory and the single mode approximation, we obtain three amplitude parameters as functions of temperature, surface field strength, and film thickness. Because of the effect of confinement size and the surface inducement, the morphology of confined diblock copolymers is different from the bulk structure. By controlling confinement size and surface field strength, lamella, undulated lamella, cylinder, and distorted cylinder can be observed in the bcc bulk phase of diblock copolymers. Also, we construct a “phase diagram” of confinement‐induced structures at different surface field strengths. We compare the present theoretical results with the other relevant theoretical results. The predictions about these interesting confinement‐induced structures should be observable in the experiments under suitable conditions.

     

Grazing-incidence transmission small angle X-ray scattering from thin films of block copolymers

Thin films of lamellar and cylindrical block copolymers are popular systems for low-cost nanolithography. To be useful as nanoscale templates, the lamellae or cylinders must be oriented perpendicular to the substrate. Domain orientations are usually characterized by microscopy measurements of the film surface, but these techniques cannot detect tilted, bent, or tortuous domains in the film interior. We report a simple method to quantify out-of-plane disorder in thin films of block copolymers based on a variant of grazing-incidence small angle X-ray scattering (GI-SAXS). A typical GI-SAXS experiment illuminates the center of a substrate-supported film at a grazing angle of incidence (near the film/substrate critical angle), and the strong reflected signal is interpreted with the distorted-wave Born approximation. In a new approach, the beam footprint is moved to the far edge of the sample, allowing the acquisition of a transmission pattern. The grazing-incidence transmission data are interpreted with the simple Born approximation, and out-of-plane defects are quantified through analysis of crystal truncation rods and partial Debye-Scherrer rings. Significantly, this study demonstrates that grazing-incidence transmission small angle X-ray scattering can detect and quantify the buried defect structure in thin films of block copolymers. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Anomalous small‐angle X‐ray scattering characterization of composites based on sulfonated poly(ether ether ketone), zirconium phosphates,and zirconium oxide

The morphology and distribution of zirconium oxide and zirconium phosphates in a matrix of sulfonated poly(ether ether ketone) (SPEEK) were investigated with anomalous small‐angle X‐ray scattering (ASAXS) and electron microscopy. ASAXS revealed that ZrO₂ was distributed in the SPEEK matrix in the form of nanoparticles smaller than 13 Å. A decrease in the conductivity suggested that the sulfonic groups were bound to the zirconium oxo species at the particle surface. Furthermore, two kinds of membranes containing zirconium phosphate were investigated. In one case, the phosphate was directly dispersed in the polymer solution for the casting of the membrane. In the other case, the phosphate was previously treated with n‐propyl ammonium and polybenzimidazole. From ASAXS data, the fractal dimension could be estimated. Mass‐fractal behavior was confirmed for the SPEEK membrane containing previously exfoliated zirconium phosphate, with aggregates of 6.3–165 Å. Surface‐fractal behavior was detected for membranes with untreated phosphates, with aggregates of 6.4–185 Å. The untreated phosphates caused an increase in the permeability, without changing the proton conductivity much. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 567–575, 2004     

Effect of Hydrophilic/Hydrophobic Block Ratio and Temperature on the Surface and Associative Properties of Oxyethylene and Oxybutylene Diblock Copolymers in Aqueous Media

Recent development in dispersion science and technology demands block copolymers with a variable block length and composition. To highlight that purpose, the surface active, associative, colloidal, and thermodynamic behavior of three diblock copolymers having different hydrophilic to hydrophobic ratio is reported here. Using surface tension and light scattering measurements, the micellization and adsorption behavior of polyoxyethylene and polyoxybutylene diblock copolymers of the type E_mB_n have been analyzed. Critical micelle concentration (CMC) and related thermodynamic parameters like free energy (ΔG_mic), enthalpy (ΔH_mic), and entropy (ΔS_mic) of micellization were calculated from CMC value using the closed association model. Likewise, the surface active parameters, like surface excess concentration (Γ₂), area per molecule (A₂), and thermodynamic parameters such as free energy (ΔG_ads), enthalpy (ΔH_ads), and entropy (ΔS_ads) of adsorption of polymer at the air/water interface, were also calculated at various temperatures. Static and dynamic light scattering techniques were employed for the determination of the weight-average molar (M_w), association number (N_w), polymer–water interaction (A₂), and micellar size in terms of hydrodynamic radii (R_h) of copolymer micelles. The effect of block length and solution temperature on the surface and micellar properties of these copolymers was also investigated.     

Combinatorial Mapping of Substrate Step Edge Effects on Diblock Copolymer Thin Film Morphology and Orientation

We have used a combinatorial gradient technique to map precisely how the terrace structure and microdomain lattice alignment in a thin film of a sphere‐forming diblock copolymer are affected by both the thickness of the copolymer film and the height of a series of parallel step edges fabricated on the substrate. We find that for film thicknesses slightly incommensurate with integer numbers of sphere layers, the step edges act as nucleation sites for regions with one more or one fewer layers of spheres. We also find that for our system, the hexagonal lattice formed by a single layer of spheres on the low side of a step edge is aligned along the direction of the step edge only where the film on the high side is sufficiently thin to support only a wetting layer of copolymer material. This work will guide the tuning of film thickness and step height in future studies and applications of graphoepitaxy in block copolymer films.

     

Cure temperature influence on natural rubber—A small angle X‐ray scattering study

To analyze the natural rubber behavior during vulcanization under different cure treatments, an experimental investigation using small angle X‐ray scattering was performed. To achieve this, a set of samples were prepared using sulfur and N‐t‐butyl‐2‐benzothiazole sulfenamide as accelerator and then cured at temperatures between 403 and 463 K reaching their optimum mechanical properties considering rheometer tests. The crosslink density of the samples was evaluated by means of the swelling technique in solvent. In the usual Lorentz corrected representation of the X‐ray scattered intensity, a maximum was observed in the plots corresponding to the cured samples, revealing a highly correlated structure. This maximum shifted toward higher values of the scattering vector when the cure temperature of the samples increased. This behavior is discussed in terms of the crosslinks type present in the vulcanized rubber network at different cure temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2966–2971, 2007     

Effect of Polydispersity on the Phase Behavior of Polymer Blends

Summary: The effect of polydispersity on polymer blend phase behavior is studied by in situ small‐angle X‐ray scattering. In a polydisperse polyethylene (PE)/isotactic poly(propylene) (iPP) blend, the enthalpic portion of the interaction parameter is greater than that of a corresponding blend with lower polydispersity. This is attributed to the presence of long chains, which provide a higher interaction energy and packing constraint, reducing the system miscibility. As expected, the radius of gyration is higher in the system with higher polydispersity.

Comparison of phase diagrams of the iPP/PE system used in this study (thin lines) with that obtained from the literature (thick lines). The solid lines represent binodals and the dashed lines are spinodals.     

New evidences of glass transitions and microstructures of soy protein plasticized with glycerol

Soy protein isolate (SPI) and glycerol were mixed under mild (L series) and severe (H series) mixing conditions, respectively, and then were compression-molded at 140 degrees C and 20 MPa to prepare the sheets (SL and SH series). The glass transition behaviors and microstructures of the soy protein plasticized with glycerol were investigated carefully by using differential scanning calorimetry and small-angle X-ray scattering. The results revealed that there were two glass transitions in the SPI/glycerol systems. When the glycerol contents ranged from 25 to 40 wt.-%, all of the SL- and SH-series sheets showed two glass transition temperatures (T(g1) and T(g2)) corresponding to glycerol-rich and protein-rich domains, respectively. The T(g1) values of the sheets decreased from -28.5 to -65.2 degrees C with an increase of glycerol content from 25 to 50 wt.-%, whereas the T(g2) values were almost invariable at about 44 degrees C. The results from wide-angle X-ray diffraction and small-angle X-ray scattering indicated that both protein-rich and glycerol-rich domains existed as amorphous morphologies, and the radii of gyration (R(g)) of the protein-rich domains were around 60 nm, a result suggesting the existence of stable protein domains. The results above suggest that protein-rich domains were composed of the compact chains of protein with relatively low compatibility to glycerol and glycerol-rich domains consisted of relative loose chains that possessed good compatibility with glycerol. The significant microphase separation occurred in the SPI sheets containing more than 25 wt.-% glycerol, with a rapid decrease of the tensile strength and Young's modulus. [illustration in text].