Volume Fraction Of Polystyrene Research Articles

Effect of Composition Distribution on Microphase-Separated Structure from Diblock Copolymers

Microphase-separated structures of diblock copolymers with narrow molecular weight distributions but with various composition distributions were investigated. Monodisperse nine parent block copolymers composed of polystyrene and poly(2-vinylpyridine) having almost the same molecular weight but with different polystyrene volume fraction, φs, covering 0.1−0.9, were prepared. Successively they were blended variously to produce samples with various composition distributions but with constant average composition; that is, φs was kept constant at approximately 0.5. Structures from solvent-cast and well-annealed films were observed through transmission electron microscopy and small-angle X-ray scattering. It has been found that the blends with wide composition distributions show periodic alternating lamellar structure up to 1.7 in terms of Mw(S)/Mn(S), where Mw(S) and Mn(S) denote weight-average and number-average molecular weights of polystyrene block, respectively, and that the microdomain spacing increases with increase of polydispersity of each block. Further, it was clarified that the blend shows macrophase separation in between two kinds of regular microphase-separated structures if Mw(S)/ Mn(S) reaches approximately 1.8.

Singular value decomposition analysis of time-resolved small-angle X-ray scattering during morphological transition in a block copolymer

Time-resolved small-angle X-ray scattering (TR-SAXS) studies of the structural changes in a block copolymer after a temperature jump are reported. The sample used was a polystyrene-block-poly(ethylene-alt-butylene)-block-polystyrene (SEBS) triblock copolymer, which has a number-average molecular weight of 54000 g mol−1and a volume fraction of polystyrene of 0.227. The film specimen was prepared by the solution-cast method using a selective solvent. The as-cast specimen with lamellar microdomains underwent the temperature jump from 363 to 403 K and the morphological transition from lamellae to cylinders was observed as a function of time by the TR-SAXS technique. The singular value decomposition (SVD) analysis was performed on the scattering profiles. This analysis strongly suggested the existence of a third basis component of the X-ray scattering profiles, thus supporting that there is an intermediate state during the transition from lamellae to cylinders.

Phase Behavior of Lithium Perchlorate-Doped Poly(styrene-b-isoprene-b-ethylene oxide) Triblock Copolymers

We report on the phase behavior of a system of lithium perchlorate-doped poly(styrene-b-isoprene-b-ethylene oxide) (SIO) triblock copolymers. Two complete phase diagrams are described along the isopleth formed by equal volume fractions of polystyrene and polyisoprene and varying poly(ethylene oxide) contents at ether oxygen-to-lithium ratios of 48:1 and 24:1 between 70 and 200 °C. Our results, based primarily on small-angle X-ray scattering (SAXS) data, reveal four phases as a function of PEO and salt content: two-domain lamellae (LAM2), a pillared lamellar structure (PLS), core−shell cylinders (CSC), and three-domain lamellae (LAM3). Two microstructures present in the neat material, core−shell gyroid (CSG), and semiperforated lamellae (SPL), are replaced by the CSC phase in the doped systems. In addition, the order−disorder transition temperatures at low PEO content increase dramatically with the addition of salt. Within the CSC phase, LiClO4 can be dispersed up to a loading of 3:1 without inducing macr...

Macro- and Microphase Transitions in Binary Blends of Block Copolymers with Complementarily Asymmetric Compositions

A unique phase transition between the state of “two macrophase-separated disordered phases” at higher temperatures and that of “a single phase with only a local order” at lower temperatures was observed in a binary mixture of polystyrene (PS)-block-polyisoprene (PI) copolymers by using small-angle X-ray scattering, light scattering, transmission electron microscopy, and optical microscopy. The constituent block copolymers of the mixture have almost same molecular weights but complementary compositions: one component (designated as i-2K) has a number-average molecular weight (Mn) of 1.2 × 104 and its volume fraction of PS (fPS) is 0. 81, and the other component (designated as s-3K) is Mn = 1.3 × 104 and fPS = 0.21; both neat i-2K and neat s-3K are in disordered state at all temperatures covered in this experiment. The macrophase transition temperature for the i-2K/s-3K = 50/50(wt %/wt %) mixture was determined to be 130 °C, above which the mixture showed the two macrophase-separated disordered phases comp...

A Small-Angle X-ray Scattering Study of the Phase Behavior of Diblock Copolymer/Homopolymer Blends

The order−disorder transition (ODT), microdomain morphology, and phase behavior in mixtures of polystyrene-block-polyisoprene (SI) diblock blended with homopolystyrene (HPS) were investigated. SI with a total molecular weight of 2.0 × 104 and volume fraction of polystyrene (PS) of 0.51 (designated SI-11/9) was blended with a homopolystyrene of molecular weight 6.1 × 103 (designated S-6). Binary mixtures of diblock copolymer and homopolymer were prepared by solvent casting. The ODT was quantitatively identified using the discontinuity observed in a plot of the reciprocal of the peak small-angle X-ray scattering (SAXS) intensity, Im-1, as a function of the reciprocal of the absolute temperature, 1/T, except for the mixtures showing the disordered sphere morphology for which we determined the temperature of the demicellization/micellization transition (DMT) instead of the ODT by the disappearance of the form factor peak with increasing temperature. We systematically measured the ODT or DMT temperature as a f...

Lattice Disordering/Ordering and Demicellization/Micellization Transitions in Highly Asymmetric Polystyrene-block-Polyisoprene Copolymers

Two kinds of transitions involving a change in molecular assembly, lattice disordering/ordering transition (LDOT) and demicellization/micellization transition (DMT), in highly asymmetric polystyrene-block-polyisoprene (SI diblock) copolymers were investigated using oscillatory shear rheometry, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). For the study, three highly asymmetric SI diblock copolymers having the volume fractions of polystyrene (PS) block of 0.11, 0.13, and 0.16, respectively, were synthesized using anionic polymerization. In highly asymmetric block copolymer, LDOT is defined as a transition where the long-range order of microdomains is lost during heating, giving rise to a disordered arrangement of spheres with short-range liquidlike order (termed disordered spheres or micelles), and DMT is defined as a transition where all microdomains disappear during heating and are transformed into the micelle-free homogeneous state in which the component polymers are mixed on a molecular level and only thermally induced composition fluctuations may exist. DMT may be regarded as a pseudo-phase transition, involving effectively a finite number of molecules and hence occurring over a finite range (possibly a narrow range) of temperatures. It was found that the three highly asymmetric SI diblock copolymers underwent, during heating, first lattice disordering and then demicellization transitions. The values of LDOT temperature (TLDOT) and DMT temperature (TDMT) for the highly asymmetric SI diblock copolymers were determined by careful analysis of SAXS results, and the value TDMT determined by oscillatory shear rheometry was found in good agreement with SAXS results. The LDOT determined from SAXS was confirmed by TEM, showing the existence of disordered spheres at thermal equilibrium at TLDOT ≤ T < TDMT.

Factors controlling surface morphology of porous polystyrene membranes prepared by thermally induced phase separation

A special device for preparing porous polymer membranes through a thermally induced phase separation (TIPS) process was designed and machined; it included a solution container, a membrane-forming platform, a coldplate, a temperature-decreasing system and a temperature-supervising system. Polystyrene was selected as the model polymer from which to prepare porous membranes using the device due to its better understood TIPS and good biocompatibility with cells. The major factors controlling surface morphology and cell size, ie volume fraction of polystyrene (ϕ2), quench rate and solvent-removing methods, were studied. Fixing the coldplate temperature, when ϕ2 is as low as 0.045, provokes the formation of round pores on both the bottom and top surfaces of the membrane; when ϕ2 = 0.16 no pores are formed on either surface; when ϕ2 = 0.087 pores form on the top surface, but not on the bottom surface. When ϕ2 = 0.087 the cell size is very small or no pores are formed on the bottom surface, whereas the top surface shows a regular decrease of the pore sizes and an increase of the pore number and pore area, along with a decrease of the coldplate temperature. The side near the coldplate is dense, and the dense layer aligns along the coldplate, while the side away from the coldplate is like a porous foam, the shape of which is isotropic and the surfaces are interconnected with each other three dimensionally. On the top surface of a membrane obtained by ethanol extraction, the cell size is enlarged and the cell number reduced, but the surface morphology and the whole area remained almost the same when compared to samples obtained by freeze drying in the same membrane-forming conditions. The isotropic, uniformly distributed and round pores suggest that the mechanism of phase separation is a spinodal liquid–liquid decomposition under our research conditions. © 2000 Society of Chemical Industry

Mechanical properties of weakly segregated block copolymers 2. The influence of phase behaviour on tensile properties of poly(styrene-b-butylmethacrylate) diblock copolymers

The tensile properties of poly(styrene-b-butylmethacrylate) diblock copolymers (PS-b-PBMA) were investigated depending on volume fraction of polystyrene (with a constant molecular weight of M ̄ n ≈100 kg/mol) and overall molecular weight (constant volume fraction of 65–70% PS). Diblock copolymers in the composition range 37–57% PS show lamellar structures and a partial miscibility due to their weakly segregated phases. In contrast, samples with other compositions are disordered. A transition from ductile to brittle properties was observed at a PS-content of 57%. Using different molecular weights, it was possible to correlate the different states of segregation (disordered, weak and intermediate segregation) with tensile properties where a change from brittle to ductile properties can be found with increasing molecular weight due to the transition from disordered to an ordered state. At higher molecular weights the phases are intermediately segregated and a maximum in tensile strength as well as strain-at-break can be observed.

Structure of Waterborne Organic Composite Coatings

The mechanical properties and structure of composite films made of high-Tg polystyrene (PS) nodules dispersed in a low-Tg poly(butyl acrylate) (PBuA) matrix were studied by means of dynamic mechanical spectrometry and small-angle neutron scattering. At temperatures between the Tg of PS and PBuA, the mechanical properties depend drastically on the spatial distribution of the glassy PS domains. For films cast from mixtures of PS and PBuA latexes, an aggregation of PS particles into dense clusters dispersed in the PBuA matrix was observed. As a consequence, a large density of contacts between PS particles in the dry films ensured a strong mechanical reinforcement above a percolation threshold of 30% PS volume fraction. Extensive coalescence of PS particles occurred at their contacts upon annealing the films above the Tg of PS, leading to further mechanical reinforcement. For films cast from core−shell particles, the aggregation phenomenon was prevented, depending on the coverage of the PS core by the PBuA shell. An efficient core encapsulation in the core−shell morphology led to poor contact between PS cores, the elastic moduli were then close to that of the PBuA matrix, and the PS coalescence upon annealing was prevented.

Lattice Disordering and Domain Dissolution Transitions in Polystyrene-block-poly(ethylene-co-but-1-ene)-block-polystyrene Triblock Copolymer Having a Highly Asymmetric Composition

The lattice disordering transition (LDT) and the domain dissolution transition (DDT) of a highly asymmetric polystyrene-block-poly(ethylene-co-but-1-ene)-block-polystyrene (SEBS-8) triblock copolymer with a volume fraction of polystyrene (PS) block of 0.084 have been investigated by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and rheology. The PS spheres formed in the SEBS-8 sample exhibited a body-centered cubic (bcc) lattice at lower temperatures and underwent disordering in the bcc lattice (so-called LDT) at ∼150 °C. Above this temperature (TLDT), spheres in liquidlike short-range order (LSO) with relatively thin interface between the PS domain and the poly(ethylene-co-but-1-ene) (PEB) matrix were detected up to ∼210 °C, above which the spherical domains started to dissolve into the PEB matrix. Finally, the spherical domains were completely dissolved into a homogeneous state at ∼232 °C. The starting and the final dissolution temperatures are referred to as the TDDT and ...

Ordered Structure in Blends of Block Copolymers. 4. Location of the Short Diblock

We used small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to examine a blend of two polystyrene-block-polyisoprene polymers with different molecular weights (6.73 × 104 and 1.0 × 104) and volume fractions of polystyrene (0.81 and 0.52, respectively), i.e., a blend of the type (A−B)α/(A−B)β. The results show that the junctions of the short diblock copolymer are localized at the interface in the lamellar microdomains at low temperatures with a relatively strong segregation and that more of the short diblock copolymer is delocalized with their junctions moving away from the interface with increasing temperature. The domain spacing is seen to decrease with the addition of the short diblock to the long diblock copolymer at a given temperature. The domain spacing of blends with a large amount of the short diblock is seen to increase or stay constant with increasing temperature, which is radically different from the behavior of pure diblock copolymers or their blends with homopolymer....

Morphology of Model Graft Copolymers with Randomly Placed Trifunctional and Tetrafunctional Branch Points

The morphologies of two series of model graft copolymers were studied using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Both series of materials have monodisperse polybutadiene (PB) backbones and monodisperse polystyrene (PS) graft blocks. In one series there are on average five trifunctional junction points randomly distributed along the PB backbone. Each junction point grafts one PS block to the backbone. In the other series there are on average four tetrafunctional junction points randomly distributed along the PB backbone. Each junction point grafts two PS blocks to the backbone. A range of overall PB and PS volume fractions was investigated for both series. These materials simulate a controlled and known degree of architectural disorder. Current theory cannot rigorously predict the morphological behavior for these complex molecular architectures. However, it is found that an approximate extension of existing theory utilizing the constituting block copolymer (fundam...

Thermally induced morphological transition from lamella to gyroid in a binary blend of diblock copolymers

We report an experimental result of the thermally induced morphological transition from lamellar to gyroid phase in a binary blend of polystyrene-block-polyisoprene (SI) diblock copolymers. Two SI copolymers employed in this study have almost the same molecular weights but different volume fractions of polystyrene (PS) block (φPS=0.26 and 0.65). The blend was prepared by these two SI diblock copolymers and the overall volume fraction of PS block in the blend, φPS¯, was 0.58. Time-resolved small-angle x-ray scattering (SAXS) experiments were conducted to reveal morphological structures as a function of temperature from 120 to 205 °C during the heating with a rate of 2 °C/min. It was observed from SAXS results that the lamellar phase (L) was found below 164 °C, the gyroid phase (G) above 188 °C, and the coexistence of L and G phases between these temperatures. The gyroid phase was confirmed by transmission electron micrograph. The transition from L to G phase is different from a thermally induced transition of kinetically locked morphology formed by the vitrification of the PS matrix, because it was also found by a separate SAXS experiment for the specimen annealed for long times in which the lamellar phase was stable up to 140 °C, which is well above the glass transition temperature of the PS block. A temperature sweep of SAXS experiment with a smaller heating rate was a useful method to roughly estimate the transition temperature. Moreover, it was found from this experiment that the position of the first-order peak does not change remarkably upon the transition. Although the thermoreversibility of the transition between L and G phases has not yet been confirmed, it does not necessarily mean that the lamellar morphology is not stable at lower temperatures.

Phase Behavior of Polystyrene/Polybutadiene and Polystyrene/Hydrogenated Polybutadiene Mixtures: Effect of the Microstructure of Polybutadiene

The effect of the microstructure on the phase behavior of mixtures of polybutadiene (PB) and poly(ethylene-co-1-butene) (PEB) with polystyrene (PS) has been investigated. A series of PBs with 1,2-addition content ranging from 7 to 93% were synthesized by anionic polymerization, and a portion of each was subsequently hydrogenated to yield PEB. Polymer pairs with blend compositions from 10 to 90 wt % were cast from toluene for each of the 16 PS/PB pairs and 7 PS/PEB pairs. Laser light scattering was used to obtain cloud point measurements, which were then used to construct phase diagrams. It was found that, for constituent components with equivalent degrees of polymerization, PS/PEB pairs give rise to higher upper critical solution temperatures than PS/PB pairs, indicating that PS/PEB pairs are less miscible than PS/PB pairs. Experimental phase diagrams were curve-fitted to theoretical phase diagrams predicted from the Flory−Huggins theory with the expression for the interaction parameter α: α = a + b/T + cφPS/T, where α is related to the Flory−Huggins interaction parameter χ by χ = αVr, where Vr is the molar reference volume, T is the absolute temperature, and φPS is the volume fraction of PS in the mixture. α values for PS/PB mixtures increase with increasing 1,2-addition (miscibility decreases) while α values for PS/PEB mixtures decrease (miscibility increases) with increasing 1-butene content. Using these α values, the Helfand−Wasserman theory was applied to predict the order−disorder transition temperatures of PS-block-PB and PS-block-PEB copolymers with varying 1,2-addition and 1-butene content, respectively.

STUDIES ON MORPHOLOGIES AND MECHANICAL PROPERTIES OF POLYSTYRENE-BLOCK-POLYETHYLENEBUTYLENE-BLOCK-POLYSTYRENE TRIBLOCK COPOLYMERS

We report the effects of morphologies on mechanical properties of polystyrene-block-polyethylenebutylene-block-polystyrene (SEBS) triblock copolymers using SEBS samples with various compositions. The morphologies and the mechanical properties were examined by the small-angle X-ray scattering (SAXS) technique and the tensile stress-strain measurements, respectively. It is well known that the morphology of microphase-separated structures can be controlled by composition. We found that a border composition dividing spherical and cylindrical phases and that dividing cylindrical and lamellar phases shifted towards smaller values of φPS (in the case of φPS≤0.5) upon hydrogenation (from SEBS to SBS), where φPS denotes the volume fraction of polystyrene and SBS stands for polystyrene-block-polybutadiene-block-polystyrene. Namely, for example, an SEBS sample forms lamellar morphology even at a composition where an SBS sample forms cylinders. It is also confirmed that the mechanical properties were well correlated with change of the morphologies with composition or upon thermal annealing.

Small angle neutron scattering studies of composite latex film structure

The mechanical properties and structure of composite films made of high T g polystyrene (PS) nodules dispersed in a low T g polybutylacrylate (PBuA) matrix were studied by means of dynamic mechanical spectrometry and small angle neutron scattering. For films cast from mixtures of PS and PBuA latexes, film mechanical reinforcement was obtained above a percolation threshold of about 30% PS volume fraction. A segregation of PS particles into dense clusters in the PBuA continuous matrix, reminiscent of a phase separation, was observed. For films cast from core-shell particles, this segregation phenomenon may be prevented, depending on the coverage of the PS core by the PBuA shell. An efficient core encapsulation in the core-shell morphology leads to poor contact between PS cores, and the elastic moduli are then close to that of the PBuA matrix. Upon annealing the films above the T g of PS, extensive coalescence of PS particles occurred when large contacts were already present in the dry film at room temperature, and a percolating network of coalesced PS domains provides large elastic moduli at temperatures between the T g of PBuA and PS. The coalescence was prevented when PS particles were taken apart by the PBuA shell.

Dynamics of polyisoprene in star block copolymers confined in microstructures: A dielectric spectroscopy study

Dielectric spectroscopy has been employed to study selectively the local and global dynamics of polyisoprene (PI) in three microphase separated star diblock copolymers (SI)4, where PI and polystyrene (PS) form the core and corona, respectively. The thermally induced order-to-disorder transition (ODT) has been identified by rheology and small-angle x-ray scattering (SAXS). All dielectric measurements were made at temperatures well below the ODT and the polystyrene glass transition temperatures, where the four PI chain ends are tethered by the glassy polystyrene domains. The ordered state morphology, studied by SAXS, revealed the formation of PS spheres (fPS=0.25, where fPS is the polystyrene volume fraction), polyisoprene cylinders (fPS=0.68), and a lamellar structure (fPS=0.41) in the three copolymers. In contrast to the local segmental motions, the chain orientational dynamics associated with the amplitude and the characteristic relaxation time are strongly influenced by the spatial confinement. The main effects are the suppressed amplitude and the enhanced chain mobility, which are predicted and found to be stronger if the star topology is accompanied by topological (entanglement) effects of the PI block, irrespective of the ordered star morphology.

Order−Disorder Transition, Microdomain Structure, and Phase Behavior in Binary Mixtures of Low Molecular Weight Polystyrene-block-polyisoprene Copolymers

Order-disorder transition, microdomain structure, and phase behavior in binary mixtures of low molecular weight polystyrene-block-polyisoprene (SI diblock) copolymers were investigated. For the study, four SI diblock copolymers were synthesized, namely (i) SI-Q having a weight-average molecular weight (Mw )o f 2.810 4 and polystyrene volume fraction (f) of 0.186, (ii) SI-R having Mw ) 1.5 10 4 and f ) 0.508, (iii) SI-S having Mw ) 1.76 10 4 and f ) 0.372, and (iv) SI-M having Mw ) 1.55 10 4 and f ) 0.626. Then binary mixtures of SI-Q and SI-R and binary mixtures of SI-M and SI-S, with various compositions, were prepared via solvent casting. The order-disorder transition of the binary mixtures was investigated using rheology and small-angle X-ray scattering (SAXS), respectively. Also investigated was the microdomain structure of the binary mixtures using SAXS and transmission electron microscopy (TEM). Experimentally determined phase diagrams are compared with predictions based on a self- consistent mean-field theory.

Photonic band structure of bcc colloidal crystals

Self-ordering colloidal systems are being recognized as possible candidates for optical photonic crystals. Such structures exhibit three-dimensional periodicity in refractive index, and possess lattice dimensions comparable to optical wavelengths. Recently, fcc colloidal crystals of water-suspended polystyrene microspheres were investigated in the context of photonic band structure. At lower polystyrene volume fractions, these colloidal suspensions crystallize in the bcc crystal lattice. This work extends our investigation of this system to cover the bcc phase and reiterates the use of Kossel lines in mapping the underlying photonic band structure. Along certain crystal directions, numerous Kossel lines intersect, giving rise to unusually large optical stop bands.

Asymmetric diblock copolymers-phase behaviour and kinetics of structure formation

The structure of a series of three molecular weights of diblock copolymers polystyrene/b-isoprene with 11% volume fraction of polystyrene and low polydispersity has been investigated using small angle X-ray scattering (SAXS). In between the disordered and the BCC ordered state a micellar state with liquid-like order was found. The transition between these states was investigated in a temperature-driven experiment. Whereas the micelles appear gradually with lowering temperature the formation of the BCC ordered state occurs discontinuously at a well-defined temperature. Detailed analysis of the scattering profiles provides access to the micellar size and distance in the liquid-like as well as in the BCC state. The kinetics of the ordering transition was studied using time-resolved SAXS after temperature jumps from the liquid-like to the BCC state. The growth of the micelles and their ordering on the periodic lattice were found to occur on clearly separated time scales.