Structural characterization of semicrystalline polymer blends by small-angle neutron scattering

A series of phase-separated polyethylene-polypropylene blends, which have undergone different thermal treatments, have been analysed by small-angle neutron scattering (SANS). The coherent scattering from normal hydrogenated blends is virtually zero, but strong contrast may be induced by partial or complete deuteration (labelling) of either phase. Here, the scattering from blends with complete labelling of the polyethylene phase was analysed to provide the domain dimensions by means of a theory due to Debye using an exponential correlation function. By this means the mean chord intercept lengths of both phases were shown to be in the range 1000–10000Å. The scattering from blends with partial labelling of the polyethylene was analysed to give the radius of gyration of the molecules in the polyethylene domains, which was found to be close to that measured in the homopolymer. For melt-quenched blends the deuterated polyethylene was shown to be statistically distributed in the polyethylene phase, whereas for slow-cooled blends, partial segregation of the labelled molecules occurred.     

Conformation of polymer molecules at solid-liquid interfaces by small-angle neutron scattering

A wide variety of physical-chemical phenomena depend on the behavior of the polymer at solid-liquid interfaces. The feature that distinguishes such phenomena from their small-molecule counterparts is the long-chain structure of the polymer molecules. Just as in solution and the bulk, the conformational statistics of the polymer molecules in the interface is an important determinant of interfacial properties. Conformational statistics of interfacial polymer is expressed in terms a function called the polymer density profile ϕ(Z), which is just the volume fraction of polymer as a function of Z, the distance from the solid surface out into the continuum liquid. There is only one experimental technique that is purported to be able to determine polymer density profiles of polymers confined to the interface between finely divided substrate and dispersant, and that technique is small-angle neutron scattering (SANS). In this paper we present a protocol for the analysis of SANS data on spherical particles with adsorbed polymer for the determination of ϕ(Z). We give an example for nearly-monodisperse chains of poly(n-butyl methacrylate) with a molecular weight of 45,000 tethered to silica spheres with a diameter of 2150 Å. The polymer density profile demonstrates a deep depletion layer next to the surface with a maximum in ϕ(Z) of about 0.7 at about Z = 40 Å. Our experimental ϕ(Z) is compared with various theoretical predictions.     

Thermodynamics of polyolefin blends: small-angle neutron scattering studies with partially deuterated chains

Small-angle neutron scattering is used to evaluate the binary interaction parameter χ in molten blends of polyethylenes having different levels of ethyl branching along the backbone. The labelled chains were partially deuterated to minimize the isotope effect on χ. The present results for equal-volume-fraction binary blends at 150°C can be summarized as χ=0.4×10⁻⁴+0.014ΔX²_br. The first term is from the hydrogen-deuterium isotope effect for chains labelled with about 33% deuterium. The second term is due to chemical composition differences, expressed here as the difference in X_br, the fraction of four-carbon repeat units having an ethyl branch. The observed contributions to χ are in reasonable accord with calculated estimates.     

Persistence length of cellulose tricarbanilate by small-angle neutron scattering

Small-angle neutron scattering measurements were made on cellulose tricarbanilate in dioxane at different temperatures. The persistence length evaluated from the Kratky plot was found to be 110 Å at room temperature. A decrease in persistence length with increasing temperature was observed.     

Morphology of syndiotactic polystyrene as examined by small-angle X-ray scattering

Small Angle X-Ray scattering (SAXS) studies have been carried out on injection molded syndiotactic polystyrene (SPS) at room temperature and at elevated temperatures up to 290°C. Features indicating lamellar crystallinity were weak or entirely absent at room temperature, becoming increasingly intense above the glass transition temperature (T_g) for this material. A background scattering whose intensity was roughly proportional to q^?2, where q is the scattering momentum transfer, was present throughout the temperature range. We suggest that these results indicate that SPS materials formed in this way are three-phase systems, with an amorphous phase, a crystalline phase, and a grain boundary phase.     

Chain conformation of polystyrene in bulk by small-angle X-ray scattering

Small-angle x-ray scattering from solid solutions of different molecular weight fractions of partially brominated polystyrene in polystyrene has been studied. The results of this study indicate that polymer chains in bulk have a radius of gyration proportional to the square root of molecular weight, which is consistent with the random coil model. However, these radii are approximately 20% larger than the unperturbed radii deduced by light scattering in dilute solutions.     

Conformation of isotactic polystyrene (IPS) in the bulk crystallized state as revealed by small-angle neutron scattering

Neutron scattering experiments have been performed on isotactic polystyrene (IPS) samples in the bulk crystallized state (T_{crystallization} = 185°C). The determination of the conformation of tagged chains ranging from 2.5 × 10⁵ to 7 × 10⁵ has been undertaken on two different hydrogenated IPS matrices. A matrix of usual molecular weight (M_w = 4 × 10⁵) leads to results which do not agree with Flory's model. In this case, measurements on radius of gyration R_g show on the one hand an important increase of this parameter (40%) with increasing crystallinity for the highest molecular weight tagged chains and on the other hand a variation with molecular weight like M^0.78. These results are interpreted with a schematic model involving a long crystalline sequence incorporated in the monocrystal along the 110 plane and two amorphous wings. Such an assumption is confirmed by the scattering behaviours in the intermediate range. On the other hand, by using an IPSH matrix of very high molecular weight (M_w = 1.75 × 10⁶), and the same tagged chains previously considered, a very weak variation of R_g with increasing crystallinity is observed. This leads to consider in this case Flory's conformation which is corroborated by data obtained in the intermediate range.     

Crosslink distribution of epoxy networks studied by small-angle neutron scattering

Crosslink distribution of epoxy networks of diglycidyl ether of bisphenol A (DGEBA) cured with stoichiometric amounts of meta-phenylene diamine (mPDA) was examined by small-angle neutron scattering (SANS). A monodisperse DGEBA resin with the smallest molecular weight was used to enhance the crosslink density and to simplify the network structure for deuterium-labelling. Meta-phenylene-d₄ diamine (mPDAd₄) was applied to label definitively the crosslinks. SANS measurements covered a reciprocal space range from 0.016 to 0.220 Å^?1 or, equivalently, real-space distances from 400 to 30 Å. Application of SANS on the deuterium-labelled epoxy networks consistently produces a constant excess intensity over the unlabelled epoxy networks. Since the scattering intensity from total correlation of the network was negligible, as evident from measurements of SANS on the unlabelled epoxy networks and small-angle X-ray scattering on the epoxy networks, the constant excess SANS intensity can only be attributed to a uniform spatial distribution of the amine curing agent. In other words, the crosslinks are distributed uniformly throughout the epoxy network.     

Evidence of polyion hydration from X-ray and neutron small-angle scattering experiments

Summary The recently published small-angle scattering curves of semidilute solutions of poly (methacrylic acid) indicate some differences in neutron and X-ray data. At high degree of neutralization (>0.6), with increasing the neutron intensity decreases and X-ray intensity increases. A new series of experiments confirms this apparent discrepancy. We suggest an explanation of the observed phenomenon, based on a simple model which considers hydration of macroions. Using the proposed model, about one water molecule is estimated to be in excess in the hydration shell.     

Analysis of C-S-H gel and cement paste by small-angle neutron scattering

The role of small-angle X-ray and neutron scattering (SAXS and SANS) in the characterization of cement is briefly reviewed. The unique information obtainable from SANS analysis of C-S-H gel in hydrating cement is compared with that obtainable by other neutron methods. Implications for the nature of C-S-H gel, as detected by SANS, are considered in relation to current models. Finally, the application of the SANS method to cement paste is demonstrated by analyzing the effects of calcium chloride acceleration and sucrose retardation on the resulting hydrated microstructure.     

Molecular conformation and interactions in oligomeric mixtures of polystyrene with polybutadiene: a small-angle neutron scattering study

In this preliminary study we report values of the interaction parameter determined from small angle neutron measurements at two temperatures and three concentrations for two blends of oligomeric polystyrene with polybutadiene. One blend contained labelled (deuterated) polystyrene with hydrogenous polybutadiene and the other deuterated polybutadiene with hydrogenous polystyrene. The results from the latter are compared with predicted values.     

Non-aqueous polymer dispersions: dimensions of adsorbed AB block copolymers of polystyrene and poly(dimethyl siloxane) by small-angle neutron scattering

Poly(methyl methacrylate) and polystyrene particles stabilized in n-heptane, Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane) and silicone fluid by AB block copolymers of polystyrene and poly(dimethyl siloxane) have been studied using small angle neutron scattering. Particle sizes calculated from the scattering intensity are in reasonable agreement with particle diameters estimated from electron micrographs. The intensity of scattering from poly(methyl methacrylate) particles stabilized with copolymers containing A blocks prepared from perdeuterostyrene was much higher than from polystyrene particles stabilized with the same block copolymers. It is proposed that the polystyrene blocks are molecularly dispersed in polystyrene particles and cluster into domains in poly(methyl methacrylate) particles. Scattering arising from the poly(dimethyl siloxane) blocks has been detected but could not be simply interpreted.     

The thermal response of the polyether soft segment chain conformation in a polyurethane block copolymer measured by small-angle neutron scattering

The conformation of the soft segment chains in a pair of polyether polyurethanes was studied as a function of temperature using small angle neutron scattering. The samples were synthesized from 3 moles of methylene bis(p-phenyl isocyanate), 2 moles of butanediol, and one mole of a poly(tetramethylene oxide) (PTMO) blend. The PTMO blend was composed of 0.325 moles of deuterated PTMO (d-PTMO) and 0.675 moles of hydrogenous PTMO. This degree of deuterolabelling was chosen so that there would be no interphase scattering in the final sample; only intrachain scattering from the labelled soft segments comprised the coherent part of the total scattering. At room temperature, the average soft segment was found to be in an extended conformation. As the temperature was raised from room temperature, the radius of gyration of the soft segments decreased. This was attributed to the stress exerted by the extended soft segments on the adjoining hard segments increasing as the temperature was increased. The increased stress causes some of the hard segments to pull out of the hard domain into the soft phase, thereby allowing the soft segments adjacent to the extracted hard segment to relax to a more compact conformation. As the temperature was increased above 160°C, the soft segment radius of gyration increased slightly. This behaviour is ascribed to an increased degree of mixing between the phases. The presence of substantial amounts of hard segment material in the soft phase causes the increase in the soft segment R_g due to the greater compatibility between the soft and hard segments in the soft phase at these elevated temperatures. This effect is similar to a homopolymer being swollen by a small amount of a good solvent, where the chain conformation is a random coil, but the radius of gyration is larger than that measured for the pure material.     

Interaction of nanogel with cyclodextrin or protein: Study by dynamic light scattering and small-angle neutron scattering

The structure of hydrogel nanoparticles (CHP nanogels), formed by self-aggregation of cholesterol-bearing pullulan (CHP) was studied by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The interactions between the CHP nanogel and methyl-β-cyclodextrin (CD) or protein (hen egg white) were also investigated. It was revealed by SANS that the nanogels were spherical in shape with a radius of 6.7 nm. The following two functions were disclosed. (1) CHP nanogels were dissociated by the addition of CD and formed inclusion complexes with cholesteryl groups, leading to suppression of hydrophobic interaction between the cholesteryl groups. (2) The nanogel behaved as a molecular chaperone (heat shock protein-like activity) when CHP nanogel was mixed with hen egg white and heated up to 75 °C. The egg white aqueous solutions with CHP nanogel remained transparent while the egg white without CHP nanogel became opaque.     

On the deformation of poly(methyl methacrylate) poly(ethylene oxide) blends: A molecular characterization by small-angle neutron scattering

The deformation behavior of miscible amorphous/amorphous PMMA/PEO poly(methyl methacrylate)/poly(ethylene oxide) blends was compared with that of pure PMMA. Small-angle neutron scattering experiments were performed on labeled systems made of PEO + D-PMMA + HPMMA. Characteristic molecular parameters such as radius of gyration, Rg, molecular weight, M_w, and interaction parameter, X, were extracted from the coherent scattering cross sections, Molecular anisotropy was measured on the solid state coextruded samples, and the observed drawing efficiency is compared with, the results of shrinkage tests. In the case of PMMA/PEO blends, anomalous scattering behavior precludes any quantitative Interpretation of the scattering patterns, but revealed important structural changes upon drawing, namely a deformation-induced phase separation.     

Pressure induced changes in fractal structure of detonation nanodiamond powder by small-angle neutron scattering

The results of the experiments on small-angle neutron scattering from the industrial detonation nanodiamond powder under a pressure in the range of up to 1000 MPa are reported. It is shown that at a scale of 10–100 nm the scattering is determined by the fractal pore structure within aggregates of nanodiamonds. Its fractal dimension monotonously decreases with pressure from 1.8 to 1.2, which indicates the recombination of pores as a result of mobility of nanodiamonds in the powder under pressure. The mean pore size under the highest pressure (6 nm) is close to the characteristic size of nanodiamonds in the sample (5 nm) found from the width of X-ray diffraction peaks. The difference can be explained by the existence of a non-diamond carbon shell around diamond crystallites.     

Morphology of blends containing high concentrations of POSS nanoparticles in different polymer matrices

This article reports an investigation into the miscibility and morphology of octaisobutyl‐substituted polyhedral oligomeric silsesquioxane (ibPOSS) nanocages over a wide concentration range (25–75 wt%) in polymer matrices, produced by solution blending. Three different, strategically chosen polymers were used: polystyrene (PS), poly(isobutyl methacrylate) (PIBMA), and poly(methyl methacrylate) (PMMA), to allow the effect of matrix structure and polarity on miscibility to be investigated. Differential scanning calorimetry, dynamic mechanical analysis, X‐ray diffraction, and scanning electron microscopy were used to characterize the composite systems. The T_g of PMMA and PIBMA were found to increase with introduction of ibPOSS, whereas PS did not show any significant change of T_g with increasing POSS content, indicating differing degrees of interaction. The phase separation has been found and a cubic POSS crystal structure has been observed in all blends with different size. The glass transition increased with concentration, even though all compositions were predominantly phase‐separated, and we suggest that this is due to the influence of the external face of the crystalline units on the polymer chains, and possibly some polymer contained within the crystalline POSS phase. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

The interfacial properties and porous structures of polymer blends characterized by synchrotron small-angle X-ray scattering

Microvoids are induced upon uniaxial drawing of films made from immiscible polypropylene (PP)/polystyrene (PS) binary blends and ternary blends of PP, PS, and a block copolymer SEEPS. The shape of the uniaxially oriented microvoids is rod- or slit-like with a high aspect ratio. Synchrotron small-angle X-ray scattering (SAXS) is used to characterize the dimensions of these microvoids. Their scattering image is an intense azimuthally narrow equatorial streak on a two-dimensional SAXS pattern. This streak is analyzed to obtain the diameter, length and misorientation of the microvoids. The microvoids length is identified as an effective measure of the interfacial adhesion and strength between phase domains. Drawn films of binary blends of PP/PS are found to have the longest microvoids. The initial addition of the block copolymer SEEPS as a compatibilizer enhances the interfacial adhesion and shortens the length of microvoids. Further addition of compatibilizer induces the formation of aggregates of a composite PS/SEEPS dispersed phase, and this leads to reduced interfacial adhesion and a longer microvoids. Interfacial properties are also dependent on the mixing protocol used to produce the blends.

The transport property of the films is determined by porosity and the degree of interconnectivity. A convenient measure of the degree of interconnectivity is proposed. The degrees of interconnectivity of these films are in accordance with the interfacial adhesion and strength. Non-equatorial streaks are observed and attributed to the microvoids with a complex orientation and geometry, which are responsible for the interconnectivity among microvoids.     

Small-angle neutron scattering from polystyrene—DVB networks containing a delta fraction of deuterated polystyrene: Evidence for aggregation during polymerization

Homopolymer polystyrene-divinylbenzene, PS-DVB, networks were made by free radical chemistry u.v. photopolymerization techniques, and characterized by small-angle neutron scattering (SANS). The networks contained a delta fraction of chains labelled with deuterium. Two different series of samples were made: Method A in which the insertion was made centrally or at the end of the polymerization; Method B in which the delta fraction of deuterated primary chains was inserted at the beginning of the polymerization. Method B samples yielded a molecular weight of about 70,000 g/mole and a radius of gyration of about 120 Å, values in the range expected for single primary chains. Method A samples, however, gave molecular weights of 1–2 million and radii of gyration ranging from 350 to 400 Å. Intrinsic viscosity and gel permeation chromatography (g.p.c.) studies on parallel fractions yielded weight-average molecular weights near 72,000 g/mole for most of the polymerization. These results strongly suggest the existence of aggregation of primary chains synthesized in the same conversion period within the network. A new method of characterizing crosslinking between network chains is proposed, since these experiments count the probability of a chain crosslinking with a chain polymerized immediately before in time.