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.     

Small angle neutron scattering of partially segregated polymer blends

Small angle neutron scattering (SANS) has been used extensively to investigate the conformation of macromolecules. However, the scattered intensity has been found to be extremely sensitive to the segregation of the isotopic labelled species. The segregation has resulted in enormous increases in both the radius of gyration and the molecular weight. A theoretical treatment based on the Zernicke-Prins equation with a modified pair correlation function has been developed in this work; the size and the degree of segregation can be calculated from the scattering data using the equations obtained herein.     

Structure of polymer within the coating: an atomic force microscopy and small angle neutrons scattering study

Synthetic latex is widely used as a binder in waterbased paints. Upon dehydration of the dispersion, latex particles are brought into contact with mineral pigments: this process results in coating structuration and consolidation. This composite layer is described as a porous mineral structure, whose pores are covered by latex particles. Therefore, it is of fundamental interest to study the ordering of binder particles in the coating, and the wetting of pigments by polymer particles, toward understanding properties of coating such as: optical properties, adhesion, cohesion, sensitivity to water, etc. In this regard, we have used small angle neutron scattering and atomic force microscopy to study the ordering, the spreading, and the adhesion of latex particles on calcium carbonate within the coating. We discuss the structure of the coating.     

Small angle neutron scattering study of deuterated sodium dodecylsulfate micellization in dilute poly((2-dimethylamino)ethyl methacrylate) solutions

Poly((2-dimethylamino)ethyl methacrylate) with 60,000 g/mol and a narrow polydispersity (1.12) was synthesized using group transfer polymerization in order to investigate the structure of poly((2-dimethylamino)ethyl methacrylate)/sodium dodecylsufate complexes in water. The synthesized polymer chain conformation in water was studied as a function of deuterated sodium dodecylsulfate concentration using small angle neutron scattering. We found three transitions of the poly((2-dimethylamino)ethyl methacrylate) chain conformation induced by the added deuterated sodium dodecylsulfate. The transitions resulted from interactions between the polymer and the surfactant, so that micelles are formed along the polymer backbone above the critical aggregation concentration. The structure of micelles in a poly((2-dimethylamino)ethyl methacrylate)/deuterated sodium dodecylsulfate solution was analyzed through model fitting of the small angle neutron scattering data measured at the condition where the poly((2-dimethylamino)ethyl methacrylate) was contrast-matched with a mixture of 80% H₂O and 20% D₂O.     

Small angle neutron scattering from ionomer gels

Small angle neutron scattering intensities for sols and gels of the physically associating ionomer 1.39 mol% sodium sulphonated polystyrene with molecular weight 10⁵ g/mole in xylene have been obtained over a broad wavevector (q) and concentration range. In the low q and concentration range the scattering behaviour of this ionomer/solvent system can quite readily be interpreted using the open association aggregation model. In more concentrated solutions and at higher q, however, interpretation of the scattering behaviour for polymers associating via an open association mechanism (OAM) is more difficult, particularly if, as in this investigation, the single chains and aggregates have varying densities and fractal parameters. In this study various methods have been developed to interpret the low and high q scattering from systems whose extent of aggregation can be modelled using the OAM. Using these methods it has been possible to confirm that the open association model can be used to interpret the extent of aggregation of the above ionomer in xylene even after the solutions appear to be gelled. Single ionomer chains within both the dilute solutions and gels were found via modelling to have a radius of gyration of 60 Å, which compares with dimensions of 25 Å and 93 Å calculated for a solid sphere of polystyrene or an unperturbed polystyrene Gaussian coil, respectively. The aggregates, however, all had radii of gyration comparable with what would be expected for polystyrene of the aggregate molecular weight in an unperturbed state. These results suggest that gelation of ionomer solutions at particular concentration thresholds is not due to an abrupt change in the aggregate structures at some critical concentration but occurs as a result of interactions between the very large aggregates that the OAM predicts should gradually form as the ionomer concentration increases.     

Fold recognition aided by constraints from small angle X-ray scattering data

We performed a systematic exploration of the use of structural information derived from small angle X-ray scattering (SAXS) measurements to improve fold recognition. SAXS data provide the Fourier transform of the histogram of atomic pair distances (pair distribution function) for a given protein and hence can serve as a structural constraint on methods used to determine the native conformational fold of the protein. Here we used it to construct a similarity-based fitness score with which to evaluate candidate structures generated by a threading procedure. In order to combine the SAXS scores with the standard energy scores and other 1D profile-based scores used in threading, we made use both of a linear regression method and of a neural network-based technique to obtain optimal combined fitness scores and applied them to the ranking of candidate structures. Our results show that the use of SAXS data with gapless threading significantly improves the performance of fold recognition.     

Computer-aided experiment of using real-time small angle light scattering image processing technique for visual characterization flow field of polymer melts

The phenomenon of small angle light scattering (SALS) has been applied to the actual extrusion molding process. The current study utilizes a self-designed mold with built-in windows for observation of polymer melts within a slit die. A high-speed charge-coupled-device (CCD) camera is used to record the SALS images in real-time with different process conditions for subsequent analysis. Modification algorithm has been proposed to eliminate the effect of multiple scattering. Flow behavior of polymer melts is simulated and analyzed by real-time SALS image processing technique. Visualization is performed via a high-performance computer-aided analysis software which allows on-line data acquisition and characterization the flow field of polymer melts.     

Multiple scattering in small-angle neutron scattering measurements on polymers

Multiple scattering corrections in small-angle neutron scattering experiments on polymers have been examined. Numerical calculations show that, for typical experimental conditions, the second-order scattering is less than 2% of the first-order scattering for QR_g up to 10.0. An approximate expression is also given for obtaining a rough estimate of the second-order scattering without numerical calculation.     

The quantitative analysis of nano-clay dispersion in polymer nanocomposites by small angle X-ray scattering combined with electron microscopy

The main objective of this work is to propose a new approach for the quantitative analysis of the degree of dispersion of clay particles in the polymer matrix by small angle X-ray scattering (SAXS) combined with electron microscopy. Due to the low temperature processibility and good thermal stability, poly[(butylene succinate)-co-adipate] (PBSA) was chosen as a model polymer matrix for this study. The nanocomposites of PBSA with four different weight percentages of organically modified montmorillonite (OMMT) loadings were prepared via melt-blending method. The dispersed structure of the clay particles in the PBSA matrix was studied by SAXS. Results show that the clay particles are nicely dispersed in the case of all nanocomposites. However, with a systematic increase in clay loading, the dispersed clay structure of the nanocomposites changes from a highly delaminated to a flocculated and then to a stacked intercalated one. The probability of finding neighboring clay particles in the PBSA matrix as well as their thickness was calculated using the Generalized Indirect Fourier Transformation technique developed by Glatter and the modified Caillé theory proposed by Zhang. The morphology of the nanocomposites was also extensively studied by scanning transmission electron microscopy (STEM). In the case of all nanocomposites, SAXS results were in good agreement with STEM observations. Finally, a correlation between the predicted morphology of nanocomposites and their melt-state rheological properties is reported.     

Quantification of organoclay dispersion and lamellar morphology in poly(propylene)-clay nanocomposites with small angle X-ray scattering

Intensity profiles of small angle X-ray scattering (SAXS) curves were analyzed to simultaneously gain quantitative information on nanoclay dispersion as well as lamellar ordering in polypropylene-clay nanocomposites. Different types of PP nanocomposites prepared with PP homopolymer (HPP), random propylene-ethylene copolymer (RCP) and a high impact polypropylene-ethylene propylene rubber (ICP) were analyzed. Various one-dimensional models for stacked structures were applied on Lorentz corrected SAXS spectra to derive long period, thicknesses of alternating high and low electron density layers and their distributions, and the number of stacks for both nanoclay and PP lamellae. We applied a mixed thickness distribution model comprising combined Gaussian and exponential for a simple stack of finite thickness, which was found to explain the experimental data better for both nanoclay tactoids and lamellar stacks, compared to simple Gaussian and exponential thickness distributions. Long period X and number of stacks N were derived as important parameters signifying changes in levels of nanoclay exfoliation in PP. Among the three types of polypropylenes studied, better nanoclay exfoliation was obtained for the high impact ICP grade compared to HPP and RCP. Complete exfoliation of nanoclay was achieved in ICP matrix, employing a masterbatch processing route. Moreover, role of nanoclay as a γ nucleating agent was evident from small and wide angle X-ray analyses, and was seen strongly in RCP. Changes in lamellar structure of PP as a result of nanoclay incorporation, double population consisting of both α and γ polytypes in the nanocomposites from that of a primarily α population in neat polymer matrices, were also analyzed in detail with the mixed thickness distribution model, thereby demonstrating its usefulness.     

Characterization of pore distribution in activated carbon fibers by microbeam small angle X-ray scattering

In the present work, the results corresponding to the first experiments done with single activated carbon fibers (ACFs) at the microfocus beamline (ID13) in the ‘European Synchrotron Radiation Facility’ (Grenoble) are presented. The experiments done with CO₂ and steam ACFs have demonstrated the suitability of this technique to characterize a single ACF. The experiments show that scattering intensity increases with the burn-off degree, which agrees with SAXS experiments carried out using bigger amounts of fibers. Moreover, the two-dimensional scattering patterns show that, in this type of ACFs, the porosity development during the activation process is isotropic. In addition, it has been demonstrated that the use of an X-ray microbeam of 2 μm diameter allows the characterization of different regions of the same fiber with microscopic position resolution. The scans across the fiber diameter are the first direct proof for the previous results obtained by our research group. Thus, in the case of CO₂ ACFs, the scattering is high in different regions across the fiber diameter, confirming that CO₂ activation takes place within the fibers, generating a quite homogeneous development of porosity. On the other hand, in the case of steam ACFs, the scattering is much higher in the external zones of the fibers than in the bulk, which means that steam focuses the activation in the outer parts of the fibers.     

Small angle neutron scattering study of the structure and formation of MCM-41 mesoporous molecular sieves

The nanoscale structure and synthesis mechanisms of the MCM-41 class of inorganic mesoporous materials have been investigated by small angle neutron scattering (SANS). SANS measurements with solvents imbibed in the pores to vary the scattering contrast demonstrate that the low angle diffraction peaks from these materials are entirely due to the pore structure and that the pores are fully accessible to both aqueous and organic solvents. Static and shear flow SANS measurements on the concentrated cationic surfactant and silicate precursor solutions typically used in the synthesis of the mesopore materials indicate that the existence of preassembled supramolecular arrays that mimic the final pore structure is not essential for the synthesis of these materials.     

Effect of silane functionalization of montmorillonite on epoxy/montmorillonite nanocomposite

Mechanical and dynamic mechanical properties of various montmorillonite (MMT)/epoxy nanocomposites were investigated. 3-aminopropyltriethoxysilane functionalized MMT was compared with commercial pristine MMT and ammonium salt substituted MMT. Qualitative evidence of silane functionalization was confirmed by FT-IR. XRD and TEM were used to characterize the degree of intercalation of MMT in epoxy nanocomposite. Tensile stress and elongation of MMT/epoxy nanocomposite were improved significantly by the silane functionalization of MMT. Dynamic mechanical analysis showed that silane functionalization of MMT resulted in active interactions between MMT and epoxy.     

Enhanced thermal properties of PS nanocomposites formed from montmorillonite treated with a surfactant/cyclodextrin inclusion complex

We have prepared polystyrene/clay nanocomposites using an emulsion polymerization technique. The nanocomposites were exfoliated at 3 wt% content of pristine clay relative to the amount of polystyrene (PS). We employed two surfactants for the montmorillonite: cetylpyridinium chloride (CPC) and the CPC/α-CD inclusion complex. Prior to polymerization, each surfactant intercalates into the layers of the pristine clay dispersed in water. The inclusion complex was characterized by X-ray diffraction, ¹³C CP/MAS NMR spectra, and ¹H NMR spectroscopy, and TGA. X-ray powder patterns of the CPC/α-CD complex indicate that the α-CDs units form channels. The ¹³C CP/MAS NMR spectrum of the complex suggests that a CPC chain is included in the channel formed by the α-CDs. The ¹H NMR spectra of the complexes indicate that the stoichiometry of the complexes is 1:2 (i.e. one CPC molecule and two α-CD units). The TGA reveals that the inclusion complex has higher thermal stability relative to the virgin CPC. We employed both X-ray diffraction (XRD) and transmission electron microscopy (TEM) to characterize the structures of the nanocomposites. The value of T_g of the PS component in the nanocomposite is 6 °C higher than that of the virgin PS and its thermal decomposition temperature is 33 °C higher. The CPC/α-CD-treated clay is more effective than is virgin CPC-treated clay at enhancing the thermal stability of polystyrene.     

A convenient neutron scattering method for studying monomer correlations in homopolymer melts

Small angle neutron scattering data are compared with given expressions of scattering cross section for isotropic and uniaxially stretched melts containing a large fraction ø_D of deuterated chains. An expression of the cross section as ø_D(1 ? ø_D)f(q), where f(q) is the correlation function of one chain, fits the data for equal molecular weights of hydrogenated and deuterated species. For different molecular weights in the case of isotropic melts an expression is given, which agrees well with the data. The data lie in a scattering vector range of 7.10^?2, 10^?1 Å; seven values of ø_D were used for each mixture; the following deuterated and hydrogenated weights¹⁹ were mixed: 138 000 and 155 000, 105 000 and 155 000, 620 000 and 675 000. Both the Guinier range and the intermediate range are explored. Possible technical artefacts of high deuteration are discussed, especially multiple scattering which is not observed under normal conditions, and void scattering which is more difficult to avoid.     

Dynamic light scattering and small-angle neutron scattering studies on phenolic resin solutions

Solution properties of unfractionated phenolic resins prepared by polycondensation of phenol and formaldehyde using oxalic acid as a catalyst were investigated by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The hydrodynamic radius, obtained by DLS experiments with 1 vol % solution in acetone, and the correlation length, ξ, of the Ornstein-Zernike equation, obtained by SANS experiments with 10 vol % solution in tetrahydrofuran, obey a power-law relation as a function of z-average molecular weight estimated by gel permeation chromatography, with scaling exponents of 0.57 and 0.27, respectively. These behaviors are unaffected by polymerization conditions, such as initial phenol-to-formaldehyde molar ratio in the range from 0.9 to 1.5, catalyst concentration with oxalic acid-to-phenol molar ratio from 0.01 to 0.1, and reaction time within the period in which the polymer remains soluble. SANS curves for polymers prepared under different conditions are sufficiently superimposed onto a single curve with the reduced variables, ξ⁻²I(q) and ξq. These results indicate that unfractionated phenolic resins have a self-similar structure with respect to the molecular weight.     

Small-angle neutron scattering from branched epoxide resins

Small-angle neutron scattering experiments in the range of q² from 0.01 to 25 nm⁻² have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble (q=(4π/λ) sin(θ/2)). Measurements were made with six samples in the range of M_W from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship S²_z=4.69×10⁻⁴M^1.20_W (nm²). (ii) In all cases fairly large second virial coefficients A₂ are obtained which, however, decrease strongly with molecular weight. Above M_W=2500, the virial coefficient follows the relationship A₂=1.6M^−0.85_W (mol cm³g⁻²). (ii) The reciprocal particle scattering factor as a function of q² exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the S²_z versus M_W dependence are briefly discussed.     

环氧树脂/蒙脱土纳米复合材料的制备及性能

实验采用长链烷基胺对原始蒙脱土进行有机化处理，再利用环氧树脂对有机蒙脱土插层，制得环氧树脂，蒙脱土纳米复合材料。实验表明，改性环氧树脂的冲击强度有所提高。     

Small angle neutron scattering study of the structure of a triblock copolymer of styrene and isoprene during extension

A triblock copolymer with a styrene weight fraction of 0.41, has been examined at various extension ratios using small angle neutron scattering. The original ‘polycrystalline’ material with a face centred cubic arrangement of styrene domains acquires orientation as the extension ratio increases. Affine deformation is not obeyed at the supramolecular level and there is some evidence for non-uniform stress at this level.     

Assessment of branching in polymers from small angle X-ray scattering (SAXS): SAXS from model comb-branched polystyrenes

Comb-branched polystyrenes having both fixed backbone length and number of branches but variable branch lengths were prepared anionically. Small angle X-ray scattering of the model polystyrenes from methyl ethyl ketone (MEK) solutions at 25°C was examined and it is shown that the mass per unit length and cross-sectional radius of gyration increase with increasing branch length. A maximum appears in the Kratky plot for the branched polymers. While the linear polymer displays an essentially Gaussian segment distribution in solution, the branched polymers deviate considerably from the behaviour of the linear polymer under the same conditions.