Liquid-like Short-range Order Research Articles

Lipid vesicle pools studied by passive X-ray microrheology

Vesicle pools can form by attractive interaction in a solution, mediated by proteins or divalent ions such as calcium. The pools, which are alternatively also denoted as vesicle clusters, form by liquid-liquid phase separation (LLPS) from an initially homogeneous solution. Due to the short range liquid-like order of vesicles in the pool or cluster, the vesicle-rich phase can also be regarded as a condensate, and one would like to better understand not only the structure of these systems, but also their dynamics. The diffusion of vesicles, in particular, is expected to change when vesicles are arrested in a pool. Here we investigate whether passive microrheology based on X-ray photon correlation spectroscopy (XPCS) is a suitable tool to study model systems of artificial lipid vesicles exhibiting LLPS, and more generally also other heterogeneous biomolecular fluids. We show that by adding highly scattering tracer particles to the solution, valuable information on the single vesicle as well as collective dynamics can be inferred. While the correlation functions reveal freely diffusing tracer particles in solutions at low CaCl2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document} concentrations, the relaxation rate Γ(q)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma (q)$$\\end{document} shows a nonlinear dependence on q2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q^2$$\\end{document} at a higher concentration of around 8 mM CaCl2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}, characterised by two linear regimes with a broad cross-over. We explain this finding based on arrested diffusion in percolating vesicle clusters.Graphic

Highly Ordered Structure Formation in RAFT-Synthesized PtBOS-b-P4VP Diblock Copolymers.

Linear poly(4-tert-butoxystyrene)-b-poly(4-vinylpyridine) (PtBOS-b-P4VP) diblock copolymers are synthesized using reversible addition-fragmentation chain transfer polymerization. The self-assembly of four different PtBOS-b-P4VP diblock copolymers is studied using small-angle X-ray scattering and transmission electron microscopy and a number of interesting observations are made. A tBOS62 -b-4VP28 diblock copolymer with a weight fraction P4VP of 0.21 shows a disordered morphology of P4VP spheres with liquid-like short-range order despite an estimated value of χN of the order of 50. Increasing the length of the 4VP block to tBOS62 -b-4VP199 results in a diblock copolymer with a weight fraction P4VP of 0.66. It forms a remarkably well-ordered lamellar structure. Likewise, a tBOS146 -b-4VP120 diblock copolymer with a weight fraction P4VP of 0.33 forms an extremely well-ordered hexagonal structure of P4VP cylinders. Increasing the P4VP block of this block copolymer to tBOS146 -b-4VP190 with a weight fraction P4VP of 0.44 results in a bicontinuous gyroid morphology despite the estimated strong segregation of χN≅150. These results are discussed in terms of the architectural dissimilarity of the two monomers, characterized by the presence of the large side group of PtBOS, and the previously reported value of the interaction parameter, χ≅0.39, for this polymer pair.

BCC Grain Formation Triggered by Miscibility Jump on Temperature Drop

Formation of a body-centered cubic (BCC) structure and grain growth process triggered by segregation-power jump on a temperature drop was studied by small-angle X-ray scattering (SAXS), rheology, and differential scanning calorimetry (DSC). Polystyrene-block-poly(ethylene-alt-propylene) (SEP) was dissolved in tridecyl-2,2,4-trimethyl hexanoate (salacos913) that was a practically neutral good solvent for both of polystyrene (PS) and PEP block chains at temperature above 84 °C (Tsol), while it was highly selective (good for PEP) below Tsol. Spherical microdomains in a short-range liquid-like order were formed above Tsol; the system was in the so-called “lattice disordered state”, designated as disordered sphere. The solution was annealed at a temperature (130 °C) above Tsol for 10 min and successively subjected to a temperature drop across Tsol. The system stayed in the lattice-disordered state for a certain induction period. During this induction period, stronger segregation power at the lower temperature ...

Double-Polyelectrolyte, Like-Charged Amphiphilic Diblock Copolymers: Swollen Structures and pH- and Salt-Dependent Lyotropic Behavior

We consider a symmetrical poly(styrene- stat-(acrylic acid))- block-poly(acrylic acid), i.e., PSAA- b-PAA, diblock copolymer, with a molar fraction phi AA = 0.42 of acrylic acid, in the more hydrophobic PSAA statistical first block. We investigate its structural behavior at constant concentration in water using small-angle neutron scattering (SANS) by varying (i) the ionization of its acrylic acid motives via the pH by adding NaOH and (ii) the ionic strength of the solution by increasing the NaCl salt concentration c S. We present the resulting morphological phase diagram {pH, c S}, in which we identified two different lamellar phases presenting a smectic long-range order at small-to-intermediate ionizations and a spherical phase with a liquid-like short-range order at larger ionization. In the low-ionization regime, the first lamellar phase comprises a water-free PSAA lamellar core surrounded by a dense poly(acrylic acid) brush swollen with water. Its mostly hydrophobic core still being glassy, this phase is unable to reorganize and is frozen in. A detailed analysis of the SANS data shows the osmotic nature of the polyelectrolyte brush, in which the Na+ counterions are confined so that local electroneutrality is satisfied. Above the pH at which the PSAA statistical block starts ionizing, the PSAA lamellar core melts. The second lamellar phase identified then comprises a PSAA core thinner than that of the frozen-in previous phase, implying a significant increase of the core/water interface and a decrease of the brush surface density. The transition from the first lamellar phase to the second one can be quantitatively shown to result from the balance between the two contributions: (i) the extra interfacial cost between the thinner core and water and (ii) the associated gain in entropy of mixing for the counterions confined inside the brush. At even higher ionization, the diblocks finally form spherical objects with a very small, pH-dependent aggregation number and reach an apparent onset of self-association. When the highest ionization investigated is reached, the cores of these final spherical core-shell objects are found to contain a significant amount of water. We thereby demonstrate that at constant concentration, pH, and ionic strength both trigger a transition from frozen to molten hydrophobic phases as well as unexpected morphological transitions.

Thermotropic Ionic Liquid Crystals via Self-Assembly of Cationic Hyperbranched Polypeptides and Anionic Surfactants

This work describes the dilute solution and solid-state structure of polyelectrolyte complexes generated from hyperbranched polylysine (HBPL) and various anionic, sodium alkyl sulfate surfactants. In dilute solution, the radius of gyration (Rg) of the HBPL and HBPL-surfactant complexes was determined in the Guinier regime in good solvent conditions by means of small-angle X-ray scattering (SAXS). With increasing molecular weight of the HBPL, an increase in Rg up to a maximum of 3.7 and 4.2 nm was observed for the HBPLs and HBPL-surfactant complexes, respectively. In the solid state, HBPL-surfactant complexes were found to form liquid crystalline (LC) phases, whose thermal stability and structure depended both on the molecular weight of the HBPL as well as on the nature of the anionic surfactant. Depending on the surfactant alkyl chain length, liquid crystalline phases with short range liquid-like order, columnar hexagonal packing or lamellar ordering were observed. By combination of small-angle X-ray scattering, differential scanning calorimetry (DSC), and cross-polarized light optical microscopy (CPOM), the exact structure of the LC phases, as well as their region of thermal stability, could be identified. HBPL-sodium dodecyl sulfate LC phases showed thermotropic behavior and underwent two transitions with increasing temperature. First, at lower temperatures, an order-nematic transition was observed. Upon further temperature increase, a second transition from a nematic to an isotropic phase was observed. Structural models for these different LC phases are proposed. © 2007 American Chemical Society.

Asymmetric swelling and self-assembly of poly( N-isopropyl-acrylamide)- block-poly(ethylene glycol) in water

This investigation focused on the self-assembly of poly( N-isopropylacrylamide)- block-poly(ethylene glycol) (PNIPA- b-PEG) in water. We distinguish four regions in the phase diagram: a transparent sol, opaque sol, opaque gel, and syneresis. Small-angle neutron scattering measurements revealed that microphase separation occurs above 17 ∘ C to form disordered micelles, which includes a range of states from (i) asymmetric swelling to (ii) micelle formation with only short-range liquid-like order. This result may be attributed to the action of water, which starts to behave as a selective solvent for PEG blocks; the PEG chains are more swollen with water than are the PNIPA chains.

Ultraslow dynamics in asymmetric block copolymers with nanospherical domains

Low shear rate and low frequency measurements focused on the extremely slow dynamics of a three-dimensional body-centered cubic (BCC) structure of an asymmetric block copolymer under nanophase-separated conditions. The material studied was poly(styrene-b-ethylene-co-butylene-b-styrene) swollen in a hydrocarbon oil selective for the midblock. Transient viscosities during start-up of shear flow at extremely low shear rates are governed by very long relaxation times and by a modulus that is nearly the same as the plateau modulus obtained from oscillatory shear experiments. Only at extremely low shear rates a zero shear viscosity could be attained. Its very high value is close to the viscosity calculated from stress relaxation experiments. The steady shear viscosity decreases by several orders of magnitude when increasing the shear rate. SAXS experiments on samples sheared even at very low rates indicated loss of the BCC order that was present in the annealed samples before shearing. The SAXS profile recorded on such a sample showed a first-order maximum followed by a broad shoulder indicating a liquid-like short-range order of PS nanospheres in the swollen EB matrix.

Time-resolved SAXS studies on ordering kinetics of block copolymers: Further investigation of two-step ordering from disorder-sphere to hex-cylinder

We have conducted the systematical investigations for the ordering process and kinetics of both hexagonally packed cylindrical microdomains (hex-cylinder) and spheres in a body-centered cubic lattice (bcc-sphere) from spherical microdomains with a short-range liquid-like order (disorder-sphere) over a wide range of quench depth for a polystyrene-block-polyisoprene-block-polystyrene triblock copolymer, having order–order transition (OOT) temperature, TOOT, at 190°C between hex-cylinder and bcc-sphere, by using time-resolved small-angle X-ray scattering. As a result, we clearly assessed a range of temperature over which the two-step ordering from disorder-sphere to hex-cylinder occurs. A possible interpretation for the two-step ordering process was proposed in the text. The following three kinds of ordering processes are observed. (i) The single-step ordering of hex-cylinder: when the system is quenched into the temperature below 183.2°C, hex-cylinder is directly transformed from disorder-sphere via the nucleation and growth process. The incubation time for the nucleation and the transition rate largely depend on the quench depth. (ii) The ordering of bcc-sphere: when the system is quenched into the temperature above 190°C in the bcc-sphere phase, bcc-sphere is formed from disorder-sphere via the nucleation and growth process. The quench-depth dependence of the incubation time is very small, compared with that for hex-cylinder, and the transition rate is independent of the quench depth. (iii) The two-step ordering of hex-cylinder: when the system is quenched into the temperature range from 183.2 to 190°C, the volume-filling metastable bcc-sphere is first developed by nucleation and growth, followed by the OOT from metastable bcc-sphere to hex-cylinder via the nucleation and growth process. The incubation time for the formation of metastable bcc-sphere is very close to that for the formation of equilibrium bcc-sphere, and the transition rate for the formation of metastable bcc-sphere is independent of the quench depth. Thus, the ordering pathways for the volume-filling of metastable bcc-sphere are almost identical to that for the volume-filling equilibrium bcc-sphere. The incubation time for the OOT from metastable bcc-sphere to hex-cylinder is longer than that for the formation of metastable bcc-sphere, and the transition rate for the former is also slower than that for the latter. Moreover, the incubation time for the OOT from metastable bcc-sphere to hex-cylinder is longer than that for that from equilibrium bcc-sphere to hex-cylinder, and the transition rate for the former is also slower than that for the latter, because metastable bcc-sphere is considered to be more distorted than the equilibrium bcc-sphere, which suppress the epitaxial growth of hex-cylinder along a [111] direction of bcc-sphere.

Main-chain smectic liquid-crystalline polymers as randomly disordered systems

We report a high-resolution X-ray lineshape study of main-chain smectic polymers. The results indicate that the layer ordering differs fundamentally from the algebraic decay typical for other smectic liquid-crystalline systems. The lineshapes are best described by broad squared Lorentzians indicating some form of short-range correlations. However, several higher harmonics are observed, which excludes simple liquid-like short-range order. This behaviour is tentatively attributed to a random field of defects associated with entangled hairpins in the main-chain polymer structure.

Transitions of domain ordering and domain size in a spherical-forming polystyrene- block-poly(ethylene oxide) copolymer and its composites with colloidal cadmium sulfide quantum dots

With specific annealing schemes applied to a neat polystyrene- block-poly(ethylene oxide) (SE) and its composites with cadmium sulfide quantum dots (CdS QD), we have observed microdomain structures and phase transitions in the system using temperature-resolved small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Both TEM images and SAXS results show clearly that incorporation of surfactant-tethered CdS QD preferentially into PEO blocks leads to increases in thermal stabilities of both bcc-packed lattice (referred as long-range order) and microdomains themselves in the sphere-forming SE/CdS composites. The bcc-packed lattice in the SE/CdS composites sustains better than that in the neat SE, during a temperature elevation to ∼160 °C, at which the bcc-packed SE/CdS spheres start to transform into micelles with a short-range liquid-like order. Quantitative model analysis shows that the PEO/CdS micelles can retain their size in the SE/CdS composites up to 200 °C, whereas the PEO micelles shrink after the softening of the PS matrix around 100 °C, and disassociate largely into the PS matrix of the neat SE at 160 °C.

Thermosensitive Diblock Copolymer of Poly(N-isopropylacrylamide) and Poly(ethylene glycol) in Water: Polymer Preparation and Solution Behavior

This investigation focused on the self-assembly of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) (PNIPA-block-PEG) in water. A quasi-living radical polymerization technique including a Ce(IV) ion redox system enabled us to prepare block copolymers with relatively narrow molecular weight distributions. We distinguish five regions in the phase diagram: a transparent sol, opaque sol, transparent gel, opaque gel, and syneresis. By examining the extent of changes in the spectroscopic properties of a fluorescence probe, pyrene, as a function of block polymer concentration and/or temperature, we determined the critical association concentration as well as the partition coefficient Kv for pyrene. The spectroscopic properties indicate that the hydrophobicity around the probe starts to increase far below the demixing line of the PNIPA-block-PEG, a remarkable finding which suggests that even in the temperature region below the LCST temperature of a PNIPA block (∼32 °C), this block copolymer provides more space for a preferential transfer of pyrene molecules than a bulk water medium at a higher temperature. This result may be attributed to the action of water, which starts to behave as a selective solvent for PEG blocks; the PEG chains are more swollen with water than are the PNIPA chains. Dynamic light scattering measurements also indicate that contraction of the PNIPA block starts to occur around 18 °C, which is consistent with results obtained by fluorescence measurements. By employing small-angle neutron scattering, it is also confirmed that microphase separation occurs above 17 °C to form disordered micelles, which includes a range of states from (i) asymmetric swelling to (ii) micelle formation with only short-range liquidlike order. Above 30 °C, network domains are formed as a result of macrophase separation due to dehydration of PNIPA blocks. As the temperature increased up to 40 °C, the network domain is collapsed along a direction parallel to PNIPA-block-PEG interface, leading to increase in interfacial thickness and to macroscopic syneresis.

Phase Transition from Disordered Sphere to Hex-Cylinder via Transient Ordering into Bcc-Sphere in SIS Triblock Copolymer

We have investigated the ordering processes from the disordered-sphere phase (designated hereafter disordered sphere), where spherical microdomains exist but they have only a short-range liquidlike order, to the phase of hexagonally packed cylindrical microdomains (designated hereafter hex-cylinder), induced by the temperature drop (T-drop). The block copolymer studied is a compositionally asymmetric polystyrene-block-polyisoprene-block-polystyrene triblock copolymer and forms disordered sphere above the order−disorder transition temperature involving the lattice disordering−ordering transition temperature, TODT or TLDOT, spheres in a body-centered-cubic lattice (designated hereafter bcc-sphere) below TLDOT but above the order−order transition (OOT) temperature, TOOT, and hex-cylinder below TOOT. The ordering processes induced by T-drop were explored in situ and at a real time by using time-resolved small-angle X-ray scattering, and the transient microdomain structures developed during the ordering processes were observed by a transmission electron microscope and a polarized optical microscope for specimens rapidly frozen below the glass transition temperature at particular times in the ordering processes. We confirmed that the freeze-in process does not change the long-range order of the system. When the specimen is deeply quenched into the temperature range below TOOT, hex-cylinder is directly formed from disordered sphere. However, when the specimen is shallowly quenched below TOOT, bcc-sphere is first formed from disordered sphere and fills the whole sample space. Then bcc-sphere is transformed into hex-cylinder. This striking ordering process first involves the ordering into a metastable structure followed by the OOT into a stable structure.

Phase Transitions in Sphere-Forming Polystyrene-block-polyisoprene-block-polystyrene Copolymer and Its Blends with Homopolymer

Phase transitions in sphere-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and its blends with polystyrene (PS) were investigated using oscillatory shear rheometry, transmission electron microscopy, and small-angle X-ray scattering (SAXS). For the investigation, a commercial grade of high-molecular-weight SIS triblock copolymer (Vector 4113, Dexco Polymers) and a low-molecular-weight SIS triblock copolymer (SIS-100) synthesized in our laboratory were used. It is found from oscillatory shear rheometry and SAXS that both Vector 4113 and SIS-100 undergo order−disorder transition (ODT) having a characteristic feature of lattice disordering/ordering transition (LDOT) of spheres, giving rise to a phase consisting of micelles with short-range liquidlike order at thermal equilibrium above ODT and demicellization/micellization transition (DMT), as a pseudo phase transition, giving rise to a micelle-free phase with only thermal composition fluctuations. The LDOT temperature (TLDOT...

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.

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 ...

Ordering Dynamics of Cylindrical and Spherical Microdomains in Polystyrene-block-Polyisoprene-block-Polystyrene. 1. SAXS and TEM Observations for the Grain Formation

We have investigated the ordering dynamics of a triblock copolymer of a polystyrene-block-polyisoprene-block-polystyrene with asymmetric composition from the disordered sphere phase, where spherical microdomains exist but they have only a short-range liquidlike order, to the cylindrical and spherical microdomains with a long-range order. The ordering process was explored in situ by time-resolved small-angle X-ray scattering (SAXS), and the microdomain structures during the ordering process were observed by transmission electron microscopy (TEM) on specimens frozen at particular times in the ordering process. The SAXS observations show that there is an incubation period before the formation of the cylindrical and spherical microdomains with a long-range order. The coexistence of the ordered grains and the disordered spheres was observed in the TEM pictures taken during the ordering of both cylinders and spheres. The coexistence of the ordered grains and disordered spheres together with the existence of the incubation period suggests that this ordering proceeds via a nucleation and growth process. Moreover, it is revealed that the shape of the ordered grains in the matrix of the disordered spheres highly depends on the microdomain structures.

Assessment of Spatial Order in Dried Latexes by Small-Angle X-ray Scattering

The spatial order present in a dried latex consisting of poly(styrene) (PS) particles (diameter: 106 nm) is investigated by small-angle X-ray scattering (SAXS). The process of drying is conducted below the glass transition temperature of PS to avoid deformation of the particles when going from the concentrated latex to a system of close-contact particles. The assessment of spatial order rests on the analysis of the structure factor S(q) (q = (4π/λ) sin(θ/2); θ = scattering angle; λ = wavelength) of the dry latex. S(q) has been obtained by SAXS measurements of the particles in the dilute latex and in the dried system. Special attention is paid to the different contrast between the particles and the surrounding medium when going from the waterborne latex particles to the dry film. It is demonstrated that the system under consideration here exhibits no true long-range order but a more liquidlike short range order. The data show furthermore that the deformation of the particles during the process of drying m...

Ordering kinetics of cylindrical and spherical microdomains in an SIS block copolymer by synchrotron SAXS and rheology

The ordering kinetics of cylindrical and spherical microdomains in a polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer were studied using synchrotron small-angle X-ray scattering (SAXS) and rheology upon quenching the sample from a disordered state to an ordered state having either spherical or cylindrical microdomains. The SIS exhibits an order to order transition at ≈181°C, a lattice disordering transition at ≈210°C and becomes disordered at higher temperatures. Higher order peaks in the SAXS profiles corresponding to hexagonally packed cylindrical (HEX) microdomains appeared after less than 1 h when the sample was quenched from 235°C to 170°C. When quenched from 235°C to 200°C. a broad higher order peak at ≈1.65 qm, corresponding to spheres with liquid-like short-range order, was persistent up to 4 h before higher order peaks corresponding to body-centered cubic (BCC) microdomains appeared. We repeated this experiment by changing temperature from one ordered state with BCC microdomains to another with HEX microdomains, and vice versa. The BCC microdomains were attained within 1 h when heating from 170°C to 200°C. The transition between HEX and BCC is thermoreversible. The time evolution of dynamic storage modulus G′ is in good agreement with that of SAXS intensity.

Ordering kinetics of cylindrical and spherical microdomains in an SIS block copolymer by synchrotron SAXS and rheology

The ordering kinetics of cylindrical and spherical microdomains in a polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer were studied using synchrotron small-angle X-ray scattering (SAXS) and rheology upon quenching the sample from a disordered state to an ordered state having either spherical or cylindrical microdomains. The SIS exhibits an order to order transition at 181°C, a lattice disordering transition at =210°C and becomes disordered at higher temperatures. Higher order peaks in the SAXS profiles corresponding to hexagonally packed cylindrical (HEX) microdomains appeared after less than 1 h when the sample was quenched from 235°C to 170°C. When quenched from 235°C to 200°C, a broad higher order peak at =1.65 q m , corresponding to spheres with liquid-like short-range order, was persistent up to 4 h before higher order peaks corresponding to body-centered cubic (BCC) microdomains appeared. We repeated this experiment by changing temperature from one ordered state with BCC microdomains to another with HEX microdomains, and vice versa. The BCC microdomains were attained within 1 h when heating from 170°C to 200°C. The transition between HEX and BCC is thermoreversible. The time evolution of dynamic storage modulus G' is in good agreement with that of SAXS intensity.

Ordering kinetics of cylindrical and spherical microdomains in an SIS block copolymer by synchrotron SAXS and rheology

The ordering kinetics of cylindrical and spherical microdomains in a polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer were studied using synchrotron small-angle X-ray scattering (SAXS) and rheology upon quenching the sample from a disordered state to an ordered state having either spherical or cylindrical microdomains. The SIS exhibits an order to order transition at ≈181°C, a lattice disordering transition at ≈210°C and becomes disordered at higher temperatures. Higher order peaks in the SAXS profiles corresponding to hexagonally packed cylindrical (HEX) microdomains appeared after less than 1 h when the sample was quenched from 235°C to 170°C. When quenched from 235°C to 200°C. a broad higher order peak at ≈1.65 qm, corresponding to spheres with liquid-like short-range order, was persistent up to 4 h before higher order peaks corresponding to body-centered cubic (BCC) microdomains appeared. We repeated this experiment by changing temperature from one ordered state with BCC microdomains to another with HEX microdomains, and vice versa. The BCC microdomains were attained within 1 h when heating from 170°C to 200°C. The transition between HEX and BCC is thermoreversible. The time evolution of dynamic storage modulus G′ is in good agreement with that of SAXS intensity.