Morphology of polyanhydride copolymers: Time‐resolved small‐angle X‐ray scattering studies of crystallization

Synchrotron small‐angle X‐ray scattering (SAXS) was used to study the isothermal crystallization kinetics of a family of polyanhydride copolymers consisting of 1,6‐bis(p‐carboxyphenoxy)hexane and sebacic acid monomers. In situ SAXS experiments permitted the direct observation of the crystallization kinetics. The structural parameters (the long period, lamellar thickness, and degree of crystallinity) were obtained from Lorentz‐corrected intensity profiles, one‐dimensional correlation functions, and interface distribution functions to form a comprehensive picture of the crystal morphology. The combination of these three analyses provided information not only on the lamellar dimensions but also on the polydispersity (nonuniformity) of these dimensions. Where possible, the crystallization kinetics were interpreted with a modified version of the Avrami equation. The results can be used to perform the rational design of controlled‐drug‐release formulations because crystallinity affects drug‐release kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 463–477, 2005     

Differential scanning calorimetry,small‐angle X‐ray scattering,and wide‐angle X‐ray scattering on homogeneous and heterogeneous ethylene‐α‐copolymers

The objective of this work was to use both X‐ray and differential scanning calorimetry techniques in a comparative study of the lamellar and crystalline structures of heterogeneous and homogeneous ethylene‐α‐copolymers. The samples differed in the comonomer type (1‐butene, 1‐hexene, 1‐octene, and hexadecene), comonomer content, and catalyst used in the polymerizations. Step crystallizations were performed with differential scanning calorimetry, and the crystallinity and lamellar thicknesses of the different crystal populations were determined. Wide‐angle X‐ray scattering was used to determine crystallinities, average sizes of the crystallites, and dimensions of the orthorhombic unit cell. The average thickness, separation of the lamellae, and volume fractions of the crystalline phase were determined by small‐angle X‐ray scattering (SAXS). The results revealed that at densities below 900 kg/m³, polymers were organized as poorly organized crystal bundles. The lamellar distances were smaller and the lamellar thickness distributions were narrower for the homogeneous ethylene copolymers than for the heterogeneous ones. Step‐crystallization experiments by SAXS demonstrated that the long period increased after annealing. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1860–1875, 2001     

Semidilute solution structure of cellulose in an ionic liquid and its mixture with a polar organic co‐solvent studied by small‐angle X‐ray scattering

Structural and thermodynamic properties of cellulose solutions in the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EMIMAc) and its binary mixtures with N,N‐dimethyl formamide (DMF) are studied by small‐angle X‐ray scattering (SAXS). These measurements indicate molecular dissolution of the cellulose chains without any significant aggregation. The power–law relationships of the evaluated correlation length and osmotic modulus to concentration exhibit exponents of ?0.76 and 2.06 for EMIMAc and ?0.80 and 2.14 for DMF/EMIMAc solvent mixture, respectively. Thus, these solvents can be considered to be good solvents for cellulose. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 888–894     

Deformation in lamellar and crystalline structures: in situ simultaneous small‐angle X‐ray scattering and wide‐angle X‐ray diffraction measurements on polyethylene terephthalate fibers

Changes in the lamellar and crystalline structures were followed as a function of applied stress to understand the influence of the interactions between the crystalline and amorphous domains on the fiber properties. We observed a reversible transformation from a structure giving a four‐point small‐angle pattern to a structure giving a two‐point pattern; these structures corresponded to the lamellae with oblique and normal lamellar surfaces, respectively. The characteristics of these two structures such as the stack diameter, stack height, and tilt angle were different and were determined by the processing conditions and did not change when the fiber was elastically deformed. The structure giving a two‐point pattern was probably the load‐carrying lamellar entity in these fibers. The diameter of the lamellar stacks, tilt angle of the lamellae, and the strain in the lamellar spacing appeared to have the most influence on properties such as tenacity and dimensional stability. The long‐spacing strain, which is about the same as the fiber strain, determined the modulus at low elongation as well as ultimate elongation. These indicate that the lamellar stacks have at least as much influence as the interfibrillar chains on fiber properties. Structural features that determine the performance in semicrystalline polymers were investigated by analyzing four generations of polyethylene terephthalate fibers. Some of the fiber properties correlate with changes in the crystalline domains such as the crystalline orientation, size, and unit cell dimensions. Fibers in which the crystalline strain was large because of their strong linkages to the amorphous chains, and better load transfer, had the highest modulus and lowest ultimate elongation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1538–1553, 2003     

Nanocavitation around a crack tip in a soft nanocomposite: A scanning microbeam small angle X‐ray scattering study

We explore nanocavitation around the crack tip region in a styrene‐butadiene random copolymer filled with typical carbon black (CB) particles used in the rubber industry for toughening the rubber. Using quasistatic loading conditions and a highly collimated X‐ray microbeam scanned around the crack tip, we demonstrate the existence of a damage zone consisting of nanovoids in a filled elastomer matrix. The existence of voids near the crack tip is demonstrated by a significant increase of the scattering invariant Q/Q₀ in front of both fatigued and fresh cracks. The size of the zone where cavities are present critically depends on the macroscopic strain ε_m, the loading history, and the maximum energy release rate G applied to accommodate the crack. Our findings show that nanovoiding occurs before fracture in typical CB‐filled elastomers and that realistic crack propagation models for such elastomers should take into account a certain level of compressibility near the crack tip. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 422–429     

Lamellar structural changes in miscible crystalline polymer blends during melting and crystallization processes,as studied by real‐time small‐angle X‐ray scattering measurements

Real‐time small‐angle X‐ray scattering (SAXS) measurement using synchrotron radiation was applied to study the lamellar structural changes in miscible crystalline polymer blends of poly(1,4‐butylene succinate) (PBSU) and poly(vinylidene fluoride) (PVDF) during melting and crystallization processes. The lamella of PBSU is either included in the interlamellar region of PVDF (interlamellar inclusion structure), or rejected from the interlamellar region of PVDF (interlamellar exclusion structure). The two lamellar structures coexists in the melt‐quenched samples of the PBSU/PVDF = 30/70 blend. Only the interlamellar exclusion structure exists in the drawn films of the PBSU/PVDF = 30/70 blend. The real‐time SAXS results show that the interlamellar exclusion structure in these samples is irreversibly transformed into the interlamellar inclusion structure by heating the sample above the melting temperature of PBSU and that the PBSU chains are crystallized between the lamellae of PVDF during the cooling process. The factors controlling the lamellar structural changes are possibly a balance of the miscibility and the chain exclusion by tie‐molecules and/or the chain diffusion under confinement by the lamellae of PVDF with higher melting temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1959–1969, 2007     

Small‐angle X‐ray scattering study of a weak polyelectrolyte in water

Small‐angle X‐ray scattering (SAXS) was used to obtain solution parameters of a weak polyelectrolyte in water in the absence of any additives, such as neutralizing agents or salt. Poly(acrylic acid) (PAA) was used as a weak polyelectrolyte from which SAXS data were obtained in the dilute region of 1–10 mg cm^?3. An intrinsic viscosity of 15.7 dL g^?1 was obtained from a plot of reciprocal reduced viscosities versus the concentration. The application of the SAXS data, that is, the contour length (L = 1.97 × 10⁴ Å), the persistence length (a* = 58.5 Å), and the molecular weight (M = 5.9 × 10⁵ Da), to the Yamakawa–Fujii equation suggested that PAA in water at 25 °C could be described as a wormlike chain having a cylindrical body of d = 6 Å. An end‐to‐end distance (r = 1.6 × 10³ Å) was calculated from r = 2a*L ? 2(a*)². The nonisotropic expansion factor (α = 2.9) was calculated for PAA expanding from the random coil in dioxane at 30 °C (Θ temperature) to the wormlike chain in water at 25 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1263–1272, 2003     

Small‐angle X‐ray scattering investigation of carbon nanotube‐reinforced polyacrylonitrile fibers during deformation

Structural changes during deformation in solution‐ and gel‐spun polyacrylonitrile (PAN) fibers with multi‐ and single‐wall carbon nanotubes (CNTs), and vapor‐grown carbon nanofibers were investigated using synchrotron X‐ray scattering. Previously published wide‐angle X‐ray scattering (WAXS) results showed that CNTs deform under load, alter the response of the PAN matrix to stress, and thus enhance the performance of the composite. In this article, we find that the elongated scattering entities that give rise to the small‐angle X‐ray scattering (SAXS) in solution‐spun fibers are the diffuse matrix‐void interfaces that follow the Porod's law, and in gel‐spun fibers these are similar to fractals. The observed smaller fraction of voids in the gel‐spun fibers accounts for the significant increase in the strength of this fiber. The degree of orientation of the surfaces of the voids is in complete agreement with those of the crystalline domains observed in WAXS, and increases reversibly upon stretching in the same way as those of the crystalline domains indicating that the voids are integral parts of the polymer matrix and are surrounded by the crystalline domains in the fibrils. The solution‐spun composite fibers have a larger fraction of the smaller (<10 nm) voids than the corresponding control PAN fibers. Furthermore, the size distribution of the voids during elongation changes greatly in the solution spun PAN fiber, but not so in its composites. The scattered intensity, and therefore the volume fraction of the voids, decreases considerably above the glass transition temperature (T_g) of polymer. Implications of these observations on the interactions between the nanotubes and the polymer are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2394–2409, 2009     

Transport and time dependent small angle X‐ray morphology in metal cation and polymer modified perfluorocarbon ionomers

Transport and absorption in metal cation exchanged and polyvinylpyrrolidone (PVP) modified Nafion® films were studied by various techniques. To understand the microscopic basis for permeation, time resolved small angle X‐ray scattering (SAXS) was used to characterize the ionic domain morphology while films were exposed to vapors of water, dimethyl methylphosphonate (DMMP), or triethyl phosphate. Macroscopic weight uptake studies of DMMP vapor into PVP‐Nafion® were also used to help explain the SAXS absorption studies and DMMP permeation properties. The SAXS results were correlated with macroscopic permeation rates of DMMP, Soman, and water through several different membranes. To provide additional basis for the SAXS derived morphologies, tapping‐mode AFM was also used to image the 3–5 nm diameter ionic domains. A goal for protective suit applications is to find films with a balance of high moisture permeation rate for comfort, and low DMMP permeation. The best balance of properties in this context was found with PVP‐ and zirconyl‐modified films. In another extreme, the permeation rates of both water and DMMP through cesium‐modified Nafion® were low. SAXS studies were used to explain this where the ionic domains of cesium‐modified Nafion® did not “expand” when exposed to DMMP or water vapor. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 284–298, 2009     

Capillary flow behavior of worm‐like micelles studied by small‐angle X‐ray scattering and small angle light scattering

A novel capillary flow device has been developed and applied to study the orientation of worm‐like micelles, among other systems. Small‐angle X‐ray scattering (SAXS) data from micelles formed by a Pluronic block copolymer in aqueous salt solution provides evidence for the formation of worm‐like micelles, which align under flow. A transition from a rod‐like form factor to a less persistent conformation is observed under flow. Flow alignment of worm‐like micelles formed by the low molar mass amphiphile system cetyl pyridinium chloride+sodium salicylate is studied for comparative purposes. Here, inhomogenous flow at the micron scale is revealed by streaks in the small‐angle light scattering pattern perpendicular to the flow direction. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of preparation method on nanoscopic structure of conductive SBS/PANI blends: Study using small‐angle X‐ray scattering

Small‐angle X‐ray scattering (SAXS) studies of electrically conductive blends based on polyaniline–dodecylbenzenesulfonic acid (PANI–DBSA)/styrene–butadiene–styrene (SBS) triblock copolymer were performed to investigate the influence of the blend preparation procedure on the nanoscopic structure of the blends. The blends were prepared by mechanical mixing (MM) procedure and by in situ polymerization (ISP) of aniline in the presence of SBS. The results indicate that pure PANI–DBSA presents an extended phase consisting of crystalline islands of nanometric size, with a good spatial correlation between them, embedded into an amorphous PANI phase. This feature was not observed in SBS/PANI–DBSA blends prepared by MM or ISP. In MM blends, the PANI phase is constituted by smaller domains, containing poorly spatially correlated crystalline islands, whereas in ISP blends with low or medium amount of PANI, there is no SAXS peak which could be related to a spatial correlation between PANI crystalline islands. The conductivity of the ISP blends is higher when compared to MM blends because of the higher homogeneity at nanometric scale. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3069–3077, 2007     

Strain induced nanocavitation and crystallization in natural rubber probed by real time small and wide angle X‐ray scattering

The concomitant appearance of crystallites and nanocavities under uniaxial strain is investigated by X‐ray scattering in a model natural rubber system. The nanocavities appear after crystallization and only when the true stress is above a critical cavitation stress σ_Cav. The presence of crystallites alone does not influence the calculation of the void volume fraction ?_void. The nanocavities formed are 20–50 nm in size with a constant aspect ratio. The presence of filler shifts the critical crystallization extension ratio λ_Cry, λ_Cav, and σ_Cav to lower values. The clear correlation between σ_Cav and the crystallinity at the onset of cavitation χ_C(λ_Cav) implies that the crystallites take most of the mechanical loading thus delaying the cavitation in the amorphous phase. Under cyclic loading, nanocavitation is significant only in the first loading and in the successive loadings if the extension ratio is above its maximum historical value. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1125–1138     

Oriented lamellar structures in uniaxially drawn films of poly(vinylidene fluoride) and poly(3‐hydroxybutyrate) blends studied by small‐angle X‐ray scattering measurements

The lamellar structures in uniaxially drawn films of miscible crystalline/crystalline polymer blends of poly(vinylidene fluoride) (PVDF) and poly(3‐hydroxybutyrate) (PHB) were investigated by static and time‐resolved measurements of small‐angle X‐ray scattering (SAXS). Intense SAXS in the low angle range of the meridian was interpreted as originating from the interlamellar inclusion structure, in which the PHB chains were included between the lamellae of PVDF. The interlamellar inclusion was induced for the uniaxially drawn films of PVDF/PHB = 30/70 blend with a draw ratio (DR) of 2.8–4.5, whereas the lamellae of the PVDF and PHB components were mutually excluded from each other forming their own lamellar stacks (interlamellar exclusion) in the blend with a higher DR (5.0–5.7). When the highly drawn film with the interlamellar exclusion structure was heat treated at 154–165 °C, the interlamellar inclusion structure was partially induced by the heat treatment. The time‐resolved SAXS measurements indicated that the interlamellar inclusion structure was developed by melting and recrystallization of PVDF during the heat treatment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 381–392, 2009     

Multiaxial deformation of polyethylene and polyethylene/clay nanocomposites: in situ synchrotron small angle and wide angle X‐ray scattering study

A unique in situ multiaxial deformation device has been designed and built specifically for simultaneous synchrotron small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) measurements. SAXS and WAXS patterns of high‐density polyethylene (HDPE) and HDPE/clay nanocomposites were measured in real time during in situ multiaxial deformation at room temperature and at 55 °C. It was observed that the morphological evolution of polyethylene is affected by the existence of clay platelets as well as the deformation temperature and strain rate. Martensitic transformation of orthorhombic into monoclinic crystal phases was observed under strain in HDPE, which is delayed and hindered in the presence of clay nanoplatelets. From the SAXS measurements, it was observed that the thickness of the interlamellar amorphous region increased with increasing strain, which is due to elongation of the amorphous chains. The increase in amorphous layer thickness is slightly higher for the nanocomposites compared to the neat polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Multi‐scaled microstructures in natural rubber characterized by synchrotron X‐ray scattering and optical microscopy

Multi‐scaled microstructures induced by natural impurities (i.e., proteins, phospholipids, carbohydrates) in natural rubber (NR) were investigated by synchrotron small‐angle X‐ray scattering (SAXS), wide‐angle X‐ray diffraction (WAXD), and optical microscopy using several kinds of untreated and chemically treated un‐vulcanized samples. These microstructures include large aggregates (size less than 50 μm), well‐defined crystals (size less than a few 10 μm), and micelles (size much less than 10 μm). In un‐vulcanized NR samples, even though the concentrations of natural impurities are relatively low, the dispersion of these microstructures significantly affects the mechanical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2456–2464, 2008     

Removal of poly(methyl methacrylate) in diblock copolymers films studied by grazing incidence small‐angle X‐ray scattering

Self‐assembly of diblock copolymers (BCP) into periodic arrays is a promising route to generate templates for the fabrication of nanoscopic elements, when one block is selectively removed. In cylindrical morphology polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) copolymer (BCP) films, the efficiency of different processes for removing the PMMA from cylinders is studied using grazing incidence small angle X‐ray scattering (GISAXS), x‐ray reflectivity and critical dimension scanning electron microscopy. The detailed analysis of the GISAXS patterns leads to the determination of the depth of cylindrical holes left by removal of the PMMA. It is found that the combination of a preliminary UV exposure followed by a wet treatment allows to remove totally the PMMA blocks. Furthermore, the optimization of both UV exposition time and solvent allows to preserve the PS matrix and interestingly for nanolithographic applications to decrease the process costs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1137–1144     

Time‐resolved crystallization study of absorbable polymers by synchrotron small‐angle X‐ray scattering

Changes in the lamellar morphology that occurred during the quiescent isothermal crystallization of absorbable poly(p‐dioxanone) (PDS) and PDS/poly(glycolide) block copolymer were studied by synchrotron small‐angle X‐ray scattering. Important morphological parameters such as the lamellar long period, the thicknesses of the crystal and amorphous phases, and the scattering invariant were estimated as a function of time, and trends observed over a wide range of experimental conditions are discussed. Thicker but more perfect lamellae were detected at higher crystallization temperatures. The breadth of the normalized semilog Lorentz‐corrected intensity peak systematically decreased with increasing temperature. In addition, the values of the crystallization half‐time and the Avrami exponent (n = 2.5), determined from the real‐time changes in the lamellar development, showed superb agreement with the bulk crystallinity data generated from other experimental techniques, such as calorimetry and dielectric relaxation spectroscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 153–167, 2001     

Small‐angle X‐ray scattering and polymer melting: A model study

Small‐angle X‐ray scattering (SAXS) gives information on lamellar stacks in semicrystalline polymers. SAXS experiments have been used to follow the melting transition that occurs over a temperature range of 10 °C or more. One common feature is the increase in the average period by 50–100% during the melting process, a change that is often attributed to sequential melting of crystals in the lamellar stack. A quantitative treatment shows that the scattering experiment indicates only the original period, not the average period that increases throughout sequential melting. With this model, I discuss the relation between structural parameters of the melting structure and quantities derived from the SAXS intensity, the correlation function, and the interface distribution function. Uncertainties persist in our understanding of polymer melting. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2454–2460, 2001     

Crystallization and chain conformation of semicrystalline and amorphous polymer blends studied by wide‐angle and small‐angle scattering

We examine the crystallization and chain conformation behavior of semicrystalline poly(ethylene oxide) (PEO) and amorphous poly(vinyl acetate) (PVAc) mixtures with wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and small‐angle neutron scattering (SANS) experiments. For blends with PEO weight fractions (wt_PEO) greater than or equal to 0.3, below the melting point of PEO, the WAXD patterns reveal that crystalline PEO belongs to the monoclinic system. The unit‐cell parameters are independent of wt_PEO. However, the bulk crystallinity determined from WAXD decreases as wt_PEO decreases. The scattered intensities from SAXS experiments show that the systems form an ordered crystalline/amorphous lamellar structure. In a combination of WAXD and SAXS analysis, the related morphological parameters are assigned correctly. With the addition of amorphous PVAc, both the average amorphous layer thickness and long spacing increase, whereas the average crystalline layer thickness decreases. We find that a two‐phase analysis of the correlation function from SAXS, in which the scattering invariant is linearly proportional to the volume fraction of lamellar stacks, describes quantitatively the crystallization behavior of PEO in the presence of PVAc. When wt_PEO is close to 1, the samples are fully spaced‐filled with lamellar stacks. As wt_PEO decreases from 1.0 to 0.3, more PVAc chains are excluded from the interlamellar region into the interfibrillar region. The fraction outside the lamellar stacks, which is completely occupied with PVAc chains, increases from 0 to 58%. Because the radius of gyration of PVAc with a random‐coil configuration determined from SANS is smaller than the average amorphous layer thickness from SAXS, we believe that the amorphous PVAc chains still persist with a random‐coil configuration even when the blends form an ordered structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2705–2715, 2001