MOLECULAR AND SUPRAMOLECULAR ORDERING IN CONFINED ENVIRONMENTS

Crystal and phase morphologies and structures determined by self-organization of crystalline-amorphous diblockcopolymers, crystallization of the crystallizable blocks, and vitrification of the amorphous blocks are reviewed through asystematic study on a series of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers. On the base ofcompetitions among these three processes, molecular and supramolecular ordering in confined environments can beinvestigated. In a concentration-fluctuation-induced disordered (D_(CF)) diblock copolymer, the competition between crystalli-zation of the PEO blocks and vitrification of the PS blocks is momtored by time-resolved simultaneous small angle X-rayscattering (SAXS) and wide angle X-ray diffraction (WAXD) techniques. In the case of T_c相似文献   

Orientation of platelets in multilayered nanocomposite polymer films

The orientation of platelets in micro-meter-thick polymer-clay nanocomposite films was investigated with small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD). The films with various clay contents (15–60% by mass fraction) were prepared by a layer-by-layer approach from polymer-clay solutions that led to the formation of a high degree of orientation in both polymer and clay platelets. Shear-induced orientation of polymer-clay solutions is compared with the orientation of polymer-clay films. SANS, SAXS, and WAXD, with beam configurations in and perpendicular to the spread direction of the film, were used to determine the structure and orientation of platelets. In all films, the clay platelets oriented preferentially in the plane of the film. The observed differences in semidilute solutions, with clay surface normal parallel to the vorticity direction, versus bulk films and with clay surface normal parallel to the shear gradient direction at clay mass fractions of 40 and 60%, were attributed to the collapses of clay platelet during the drying process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3237–3248, 2003     

Preparation of Oriented Liquid‐Crystalline/Isotropic Block Copolymer Films with Parallel or Perpendicular Arrangement of Smectic Layers and Lamellar Microdomains

Films of a symmetric liquid‐crystalline/isotropic block copolymer consisting of a smectic LC side‐chain polymer and polystyrene were prepared by solvent casting from solution and from the isotropic melt. By annealing the solvent‐cast film in the S_A phase an oriented microphase‐separated film of lamellar morphology was obtained in which both the lamellae of the block copolymer and the smectic layers of the LC block were oriented parallel to the film surface. A lamellar morphology with perpendicular orientation of lamellae and smectic layers was generated by cooling the block copolymer from the melt.     

Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

The crystallization behavior of isotactic propylene‐1‐hexene (PH) random copolymer having 5.7% mole fraction of hexene content was investigated using simultaneous time‐resolved small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques. For this copolymer, the hexene component cannot be incorporated into the unit cell structure of isotactic polypropylene (iPP). Only α‐phase crystal form of iPP was observed when samples were melt crystallized at temperatures of 40 °C, 60 °C, 80 °C, and 100 °C. Comprehensive analysis of SAXS and WAXD profiles indicated that the crystalline morphology is correlated with crystallization temperature. At high temperatures (e.g., 100 °C) the dominant morphology is the lamellar structure; while at low temperatures (e.g., 40 °C) only highly disordered small crystal blocks can be formed. These morphologies are kinetically controlled. Under a small degree of supercooling (the corresponding iPP crystallization rate is slow), a segmental segregation between iPP and hexene components probably takes place, leading to the formation of iPP lamellar crystals with a higher degree of order. In contrast, under a large degree of supercooling (the corresponding iPP crystallization rate is fast), defective small crystal blocks are favored due to the large thermodynamic driving force and low chain mobility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 26–32, 2010     

Reversible de-intercalation and intercalation induced by polymer crystallization and melting in a poly(ethylene oxide)/organoclay nanocomposite

Semicrystalline polymer/layered silicate nanocomposites were prepared by solution blending of a low molecular weight poly(ethylene oxide) (PEO) with an organically modified montmorillonite, Cloisite 10A (C10A). The intercalation morphology was studied by temperature-dependent synchrotron wide-angle X-ray diffraction (WAXD). Unlike PEO homopolymers, significant secondary crystallization was observed in the PEO/C10A nanocomposites. Reversible de-intercalation and intercalation processes were detected during secondary crystallization and subsequent melting of secondary crystals. On the basis of two-dimensional WAXD results on oriented samples, an interphase layer between the silicate primary particles and PEO lamellar crystals was proposed. Secondary PEO crystallization in the interphase regions was inferred to be the primary driving force for polymer chains to diffuse out of the silicate gallery. This study provided a useful method to investigate polymer diffusion in nanoconfined spaces, which can be controlled by PEO secondary crystallization and melting outside the silicate gallery.     

热处理对尼龙6及其与聚酰胺嵌段共聚物共混体系晶体熔融行为和结晶结构的影响

采用溶液共混-共沉淀的办法获得尼龙6及聚酰胺嵌段共聚物/尼龙6共混体系粉末,样品在260℃下熔融之后经程序降温的方法得到非淬火样品,然后分别在190℃下高温退火不同时间(0~48 h),采用示差扫描量热仪(DSC)、广角X射线衍射仪(WAXD)、偏光显微镜(POM)等表征手段研究热处理对体系晶体熔融行为和结晶结构的影响.结果表明,(1)在相同的热历史条件下,嵌段共聚物的存在影响了尼龙6的结晶行为及结晶结构;(2)退火处理对两种样品有着不同的影响,对于尼龙6体系,退火处理促进了非晶相向晶相的转变,大大提高样品的结晶完善程度和结晶度;对于共混体系,退火处理同样促进了非晶相向晶相的转变,同时形成新的α型和γ型结晶,体系的结晶完善程度明显提高,退火48 h后,结晶度比原始样品提高约84%.     

Solubilization and location of phenethylalcohol, benzaldehyde, and limonene in lamellar liquid crystal formed with block copolymer and water

Three fragrances, phenethylalcohol, benzaldehyde, and limonene (that differ in their polarity), were solubilized in lamellar liquid crystal using the polyethylene oxide-polypropylene oxide-polyethylene oxide, (EO27PO61EO27), P104 triblock copolymer, and water. The interlayer spacing of the lamellar liquid crystal were established using small angle X-ray scattering (SAXS). The SAXS data are used to calculate the interfacial area per polyethylene oxide (PEO) block and to determine the location of each fragrance in the association structure. The results show the presence of phenethylalcohol at the interface while part of benzaldehyde contributing to the interface and the other part being located inside the polar/apolar domains. The third fragrance, limonene, did not participate in the formation of the interface and is located inside the apolar domain.     

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     

Structural evolution of melt-drawn transparent high-density polyethylene during heating and annealing: Synchrotron small-angle X-ray scattering study

The morphological development of melt-drawn transparent high-density polyethylene during heating was investigated employing in-situ synchrotron small-angle X-ray scattering (SAXS) technique. The results confirm that at lower temperatures only meridional scattering peaks aligned perpendicular to the extensional flow direction can be observed, indicating a highly oriented lamellar crystallite structure; whereas at higher temperatures an equatorial streak additional to the layer-like meridional scattering pattern develops, reflecting the presence of shish-kebab-like objects in the specimen under investigation. Upon heating, the average thickness of the kebab crystals remains essentially unaffected below 110 °C, and subsequently the selective melting of the less stable kebabs proceeds yielding thicker layered lamellar crystals. When the temperature is raised to 131 °C, the shish-like formation and the thermally stable kebab crystals melt simultaneously. In addition, the microstructure of the melt-drawn specimen subjected to annealing at elevated temperatures was probed at room temperature. As opposed to the SAXS patterns registered at high temperatures, the SAXS diagram measured after annealing shows no equatorial streak, suggesting that the cylindrical structures could be re-formed. This observation can be explained by assuming that the plate-like kebab crystals with their normal parallel to the stretching direction grow and impinge during cooling to room temperature due to secondary crystallization, which can be verified by in-situ SAXS experiments during annealing and subsequent cooling.     

Thickness-dependent molecular chain and lamellar crystal orientation in ultrathin poly(di-n-hexylsilane) films

The molecular chain and lamellar crystal orientation in ultrathin films (thickness < 100 nm) of poly-(di-n-hexylsilane) (PDHS) on silicon wafer substrates have been investigated by using transmission electronic microscopy, wide-angle X-ray diffraction, atomic force microscopy, and UV absorption spectroscopy. PDHS showed a film thickness-dependent molecular chain and lamellar crystal orientation. Lamellar crystals grew preferentially in flat-on orientation in the monolayer ultrathin films of PDHS, i.e., the silicon backbones were oriented along the surface-normal direction. By contrast, the orientation of lamellar crystals was preferentially edge-on in ultrathin films thicker than ca. 13 nm, i.e., the silicon backbones were oriented parallel to the substrate surface. We interpret the different orientations of molecular chain and lamellar crystal as due to the reduction of the entropy of the polymer chain near the substrate surface and the particularity of the crystallographic (001) plane of flat-on lamellae, respectively. A remarkable influence of the orientations of the silicon backbone on the UV absorption of these PDHS ultrathin films was observed due to the one-dimensional nature of sigma-electrons delocalized along the silicon backbone. With the silicon backbones perpendicular or parallel to the surface of the substrate, the UV absorbance increased or decreased with an increase of the angle between the incident UV beam direction and direction normal to the thin film, respectively.     

偏氟乙烯/三氟氯乙烯无规共聚物的结晶

用示差扫描量热法(DSC)、广角X射线衍射(WAXD)和傅里叶红外光谱(FTIR)研究了偏氟乙烯/三氟氯乙烯单体摩尔比为1:4的无规共聚物的结晶与晶体结构.结果表明,该无规共聚物属于半结晶型聚合物.在333～353K温度范围内退火,片晶逐渐完善、增厚,熔点和结晶度均随着退火时间的延长而升高.于353K退火时,由DSC结果计算得到片晶厚度约4.68nm.在333K退火时得到共聚物的最大结晶度约为14%.WAXD测试结果表明,沿晶粒(101)晶面的面间距为0.55nm,垂直于(101)衍射晶面方向上的晶粒平均尺寸为5.86nm.     

Influence of initial order on the microscopic mechanism of electric field induced alignment of block copolymer microdomains

We investigate the mechanism of microdomain orientation in concentrated block copolymer solutions exposed to a dc electric field by in situ synchrotron small-angle X-ray scattering (SAXS). As a model system, we use concentrated solutions of a lamellar polystyrene-b-polyisoprene block copolymer in toluene. We find that both the microscopic mechanism of reorientation and the kinetics of the process strongly depend on the initial degree of order in the system. In a highly ordered lamellar system with the lamellae being aligned perpendicular to the electric field vector, only nucleation and growth of domains is possible as a pathway to reorientation and the process proceeds rather slowly. In less ordered samples, grain rotation becomes possible as an alternative pathway, and the process proceeds considerably faster. The interpretation of our finding is strongly corroborated by dynamic self-consistent field simulations.     

The Influence of Ethyl Branch on Formation of Shish-Kebab Crystals in Bimodal Polyethylene under Shear at Low Temperature

Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight(HMW)component with different ethyl branch contents was investigated.In situ small-angle X-ray scattering(SAXS)and wide-angle X-ray diffraction(WAXD)techniques were used to monitor the formation and evolution of shish-kebab structure sheared at low temperature in simple shear mode and low rate.Only the bimodal PE with no branch formed shish-kebab crystals at the shear temperature of 129℃,and the shish length increased with the crystallization time,while bimodal PE with branch has no observable shish under the same conditions.The degree of crystallization for bimodal PE with no branch increased with time up to above 7％,while those with ethyl branch increased continually up to above 23％.Furthermore,bimodal PE's Hermans orientation factor with no branch increased to 0.60,while those with ethyl branch only increased to a value below 0.15.This study indicated that the shish-kebab crystal formed at the low temperature of 129℃is due to the stretch of entangled chains under shear for the bimodal PE with no branch.Only partly oriented lamellar crystals were formed for the bimodal PE with ethyl branch.All the results at the shear temperatures higher,closed to,and lower than the melting point,the modulation of shish crystals formation owing to different mechanisms of the coil-stretch transition and the stretched network by changing shear temperature was achieved in the bimodal PE samples.     

Order and orientation control of mesoporous silica films on conducting gold substrates formed by dip-coating and self-assembly: a grazing angle of incidence small-angle X-ray scattering and field emission scanning electron microscopy study

Grazing-angle of incidence small-angle X-ray scattering (GISAXS) and high-resolution field emission scanning electron microscopy have been used to characterize the mesophase symmetry, orientation, and long-range order in PEO20-PPO70-PEO20 (Pluronic P123) templated mesoporous silica thin films on conducting gold substrates as a function of silica-to-ethylene oxide (Si/EO) block ratio and relative humidity (RH). The films are formed by dip-coating followed by evaporation-induced self-assembly under tightly controlled RH. The general evolution of the mesophase follows the trends that are expected based on shape factors due to swelling of the PEO block. However, changes in orientation of the nanostructure relative to the substrate and the degree of long-range order are found to depend on Si/EO ratio. These effects are likely due to the dynamics of evaporation and self-assembly. Generally, at Si/EO ratios lower than 3.29, the films contained regions where the nanostructure was not oriented relative to the plane of the substrate. However, for Si/EO ratios greater than 3.62, conditions were found where the nanostructure of the film was highly oriented relative to the plane of the substrate. This is true over the range of RH studied, independent of the nanostructure symmetry. For low Si/EO ratios at the highest RH levels, the films were composed of a mixture of spherical and cylindrical pores. At high Si/EO ratios and high RH levels, the films had a highly oriented R-3m nanostructure but displayed streaking perpendicular to the substrate in the Bragg spots on GISAXS patterns. This streaking is interpreted as faulting along planes parallel to the substrate.     

Lamellar orientation in thin films of symmetric semicrytalline polystyrene-b-poly(ethylene-co-butene) block copolymers: effects of molar mass, temperature of solvent evaporation, and annealing

Orientation of the lamellar microdomains in thin films of three symmetric polystyrene-b-poly(ethylene-co-butylene) block copolymers (S65E155, S156E358, and S199E452) on mica was investigated via atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). The results show that lamellar orientation in the SxEy block copolymers greatly depends on the molar mass of the block copolymers, the temperature of solvent evaporation, and annealing. The nascent thin film of the low molar mass block copolymer, S65E155, shows a multilayered structure parallel to the mica surface with the PS block at both polymer/mica and polymer/air interfaces, but the high molar mass block copolymers, S156E358 and S199E452, exhibit a structure with lamellar microdomains perpendicular to the mica surface. When the solvent is evaporated at a lower temperature, the crystallization rate is fast and a two-dimensional spherulite structure with the lamellar microdomains perpendicular to the mica surface is observed. Annealing of all the thin films with lamellar microdomains perpendicular to the mica surface leads to morphological transformation into a multilayered structure parallel to the mica surface. In all SxEy thin films on mica, the stems of PE crystals are always perpendicular to the interface between the lamellar PE and PS microdomains. A mechanism is proposed for the formation of different microdomain orientations in the thin films of semicrystalline block copolymers. When the thin film is prepared from a homogeneous solution, microdomains perpendicular to the substrate surface are formed rapidly for strongly segregated block copolymers or at a lower crystallization temperature and kinetically trapped by the strong segregation strength or solidification of crystallization, while for weakly segregated block copolymers or at slower crystallization rate, the orientation of the microdomains is dominated by surface selectivity.     

Brill transition of nylon-6 in electrospun nanofibers

Electrospun nylon-6 fibers were prepared from its polyelectrolyte solution in formic acid with different concentrtaions. In situ Fourier transform infrared (FTIR), wide-angle X-ray diffraction and small-angle X-ray scattering (SAXS) were performed on the nylon-6 fibers heated to various temperatures until melting. For comparison, stepwise annealing of the solution-cast film having exclusively the α-form was also carried out to elucidate the structural evolution. Our results showed that Brill transition in the electrospun fibers occurs at a lower temperature than that in the solution-cast film due to the crystal size difference. Differential scanning calorimetry heating traces on the as-spun fibers exhibited a unique crystalline phase with a melting temperature of ～235?°C, higher than the equilibrium melting temperature of nylon-6. The content of high melting temperature (HMT) phase increased with increasing nylon-6 concentration; a maximum of 30?% of the fiber crystallinity was reached for fibers obtained from the 22?wt.% solution regardless of the heating rates used. Based on the SAXS and FTIR results, we speculated that the HMT phase is associated with thick α-form crystals developed from the highly oriented nylon-6 chains that are preserved in the skin layer of the as-spun fibers. A plausible mechanism for the formation of the skin/core fiber morphology during electrospinning was proposed.     

Composition fluctuation and domain spacing of low molar weight PEO–PPO–PEO triblock copolymers in the melt, during crystallization and in the solid state

We have studied a series of PEO–PPO–PEO triblock copolymers (Pluronics) in their melt and solid state mainly using static and time-resolved small-angle X-ray scattering (SAXS). In the melt state, composition fluctuations were observed. Their temperature variation was in accordance with mean-field theory. A crossover from the mean-field regime to the fluctuation regime was observed for samples with high molar mass. To check the overall conformation of molecules in the disordered state, composition fluctuations during crystallization were investigated by time-resolved SAXS. Detailed analysis on the time dependent intensity and peak position indicate that molecules remaining in the disordered state adopt a stretched overall conformation. In the solid state, crystallization of PEO blocks induced phase separation, resulting in an alternating crystalline/amorphous lamellar structure. Samples with short PEO block formed a simple lamellar structure with extended-chain conformation. The domain spacing increased with crystallization temperature due to the swelling of the amorphous domain by uncrystallized molecules. Samples with long PEO block formed a mixed lamellar structure. Structures with once-folded and extended PEO block coexisted in a large temperature range and their relative fraction changed with crystallization temperature. This mixed structure was reduced to a simple lamellar structure with once-folded crystalline structure at low crystallization temperatures.     

Improving the softness of BOPP films: From laboratory investigation to industrial processing

Young's modulus of biaxially oriented polypropylene (BOPP) films prepared with homemade film stretcher was investigated,which can be used to indicate the softness of fihns.It was found that the modulus of films was decreased by about 69％ as the content of polyethylene (PE) added into polypropylene (PP) reached 30％.Also,increasing draw temperature can induce lower stress level during stretching,which may lead to the formation of crystals with low orientation level and thus decreased modulus of films.Based on laboratory study,BOPP films produced on commercial line were studied by differential scanning calorimetry (DSC),wide and small-angle X-ray scattering (WAXS,SAXS) with varying contents of PE.SAXS results show that the crystals are oriented in both machine direction (MD) and transverse direction (TD),and the crystals are more oriented in TD than MD according to the WAXS results for all films.Also,the orientation parameter of crystal along TD increases from 0.68 to 0.83 as the contents of PE increase from 0％ to 25％.Meanwhile,the modulus of films in MD declines with increase of PE contents generally,improving the film softness.Orientation of crystals is thus an effective structure parameter to adjust the film softness.The relationship of processing-structure-property is also established.     

Orientation of LDPE crystals from microscale to nanoscale <Emphasis Type="Italic">via</Emphasis> microlayer or nanolayer coextrusion

The microlayer or nanolayer coextrusion of hundreds or thousands of alternating low density polyethylene (LDPE)/polystyrene (PS) microlayers or nanolayers were used to study the orientation of LDPE crystals in the confined quasi-two-dimensional or two-dimensional space. The clear and continuous layer structures from microscale to nanoscale can be found in SEM images. The morphology evolution of LDPE crystals in the confined microlayer or nanolayer can be varied from 3D spherulites, 2D spherulites, stacked edge-on lamellar, to single edge-on lamellar. Due to the orientation of the LDPE crystals, the tensile strength of the films increases obviously when the layer thickness reduces to nanoscale. The 2D small angle X-ray scattering (SAXS) patterns can reflect the average degree of orientation of LDPE in the confined layers. The stacking of LDPE lamellae is suppressed in interlamination and oppositely in parallel to the extrusion direction. The specific orientation function f can be calculated from the patterns. The infrared dichroism further confirms the mutation of the orientation of LDPE crystals from microscale to nanoscale in the confined space.     

Controlled melting of individual,nano‐meter‐sized,polymer crystals confined in a block copolymer mesostructure

We demonstrate a possibility to create custom‐made surface patterns on multiple length scales by melting selected nano‐meter‐sized polymer crystals confined in a highly ordered, spherical mesostructure of a hydrogenated poly(butadiene‐block‐ethylene oxide) (PB_h‐b‐PEO) block copolymer. With heatable probes of an atomic force microscope as a heat source, we succeeded to provide highly locally the thermal energy necessary to individually melt such crystals. Besides this possibility for modification of surface properties, we performed detailed in situ studies of thermally induced reorganization processes and subsequent melting of polymer crystals in confined volumes of a block copolymer mesostructure. Close to the melting point, the stability of the confined crystals could be improved by annealing. In addition, the crystal size increased at the expense of already‐molten crystals, indicating diffusion of PEO blocks across the highly incompatible PB_h matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1312–1320, 2004