SANS from Pluronic P85 in d-water

Small-angle neutron scattering (SANS) has been used to investigate Pluronic P85 (EO₂₆PO₄₀EO₂₆) copolymer in deuterated water. A range of P85 fractions were measured for a wide sample temperature window. A rich phase behavior is reported. Unimers were observed below the critical micelle formation condition. At fixed P85 fraction, a number of micellar phases were observed upon increasing temperature; first spherical micelles, then cylindrical micelles, then lamellar micelles. At the highest temperature, a demixed lamellae phase was observed. Analysis of the SANS data consisted in fits to an empirical Guinier-Porod model that was appropriate for data fitting in the various phases at low P85 fractions. When the P85 fraction increased, an inter-particle structure factor was included to analyze SANS data from concentrated spherical micelles. At high P85 fractions, paracrystalline structures were observed as evidenced by an enhanced inter-particle interaction peak. A phase diagram for P85/d-water was obtained showing the various phases. Focusing on the spherical micelles phase for one sample composition, a core-shell model was used to fit SANS data and obtain sizes and scattering length densities. Using material balance equations, information such as the aggregation number (i.e., number of Pluronic macromolecules per micelle) and the number of hydration water molecules in the shell region are determined.     

Chain scission in polystyrene by impact fracture

The number of chain scissions n_s per unit fracture area by impact in high-molecular weight polystyrene is determined to be approximately 3.3 × 10¹⁴/cm² at room temperature. This is almost 20 times larger than would be expected if chain scissions took place only at, or very close to, fracture surfaces. This result was obtained by measuring the molecular weight decrease and the total fracture area of the impact fragments by using size exclusion chromatography and statistical particle size measurements, respectively. The large n_s strongly indicates that significant chain breakage occurs during crazing before the propagation of cracks. An average craze thickness before breakdown under impact is estimated from n_s to be around 2 μm. In a diluted polymer, n_s is found to be significantly lower than the extrapolated value, assuming a linear dilution of entangled chain crossings at the fracture surface. This low chain scission density, however, can be explained by taking into account the reduction of craze breakdown strain in the diluted polymers. Finally, the broken chain ends of polystyrene appear to be stable under ambient conditions. © 1992 John Wiley & Sons, Inc.     

SANS investigations of oxide gel formation in inverse micelle and lamellar surfactant systems

The mechanisms of oxide gel formation in inverse micelle and lamellar surfactant systems have been investigated by Small Angle Neutron Scattering (SANS). In the first of these processes colloidal particles and gels are formed by the controlled hydrolysis and condensation of metal alkoxides in a reversed microemulsion system (water in oil), where the water is confined in the microemulsion core. With this route the rate of formation and structure of the oxide gel can be controlled by appropriate choice of the surfactant molecule (e.g. chain length) and the volume fraction of the micelles dispersed in the continuous organic phase. Investigations have been made with the system cyclohexane/water/C₈E _x , where C₈E _x is the non-ionic surfactant octylphenyl polyoxyethylene. The influence of the size and structure of the microemulsion has been studied by contrast variation (using deuterated solvents) before and during the reaction to form zirconia gels, and the mechanism of gelation is analysed in terms of percolation of fractal cluster aggregates. The structure of gels formed in surfactant/water lamellar phase systems, using surfactants with greater chain length, has also been investigated by SANS. The application of contrast variation to study such anisotropic bilayer systems, in which oriented gel films can be formed, is illustrated.     

Effective interaction parameter between branched and linear polystyrene

Values of the effective interaction parameter (χ) between regular, long‐branched polystyrene chains and their linear analogues were measured with small‐angle neutron scattering for several star‐branched chains and one comb‐type polymer. The contribution to this interaction due to architecture alone increases monotonically with star functionality for the set of polymers studied here. The interaction appears to be less sensitive to variations in arm size than would be expected from fluctuation theory predictions by G. H. Fredrickson, A. Liu, and F. S. Bates (Macromolecules 1994, 27, 2503) for a purely entropic interaction due to architecture. The change in χ with the volume fraction of the star in the blend is in agreement with the theory, however. The magnitudes of the interaction in the star/linear blends are small enough that bulk phase separation is unlikely, whereas that in the comb/linear blend is about 20 times higher for the same number of arms. Thus, bulk phase separation can be readily expected for comb/linear blends at commercially relevant values of molecular weights. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2549–2561, 2001     

Molecular dimensions and chain conformation in glassy syndiotactic polystyrene

For the first time the small-angle neutron scattering (SANS) from mixtures of protonated and totally deuterated syndiotactic polystyrene (sPS) has been studied. Two amorphous samples with similar molecular weights have been measured at various concentrations of the protonated part. All measurements were performed at room temperature using the scattering equipment of two different laboratories. The molecular weight M_w evaluated from SANS data agreed with those obtained by gel permeation analysis (GPC). In the Kratky representation the scattering contribution due to the contrast scattering shows a plateau behavior up to q = 0.45 Å^?1, where q is magnitude of the scattering vector. This observation is in evident contrast to what is expected from the rotational isomeric state (RIS) model. In addition the characteristic ratios C_∞, derived either from the plateau height or from radii of gyration of the Zimm regime and being in reasonable agreement with each other, show strong deviations from the predictions of the RIS model. © 1994 John Wiley & Sons, Inc.     

Small‐Angle Neutron Scattering from Elastomeric Networks in which the Junctions Alternate Regularly in their Functionality

We compute scattering form factors for SANS from labeled paths in Gaussian phantom networks in which junctions alternate regularly in their functionality (the number of chains emanating from a junction). Our calculations are based on the James‐Guth model of rubber‐like elasticity, which assumes that fluctuations are strain independent, while mean vectors transform affinely with the applied strain. Kratky plots for scattering from isotropic and uniaxially stretched bifunctional networks are computed and compared with corresponding plots for the simpler unifunctional networks. The results show the effects of the length of the labeled path, extent of deformation, direction of scattering with respect to the principal axis of the deformation and the functionalities of the network junctions.

     

Structural Characterization of Biomaterials by Means of Small Angle X-rays and Neutron Scattering (SAXS and SANS), and Light Scattering Experiments

Scattering techniques represent non-invasive experimental approaches and powerful tools for the investigation of structure and conformation of biomaterial systems in a wide range of distances, ranging from the nanometric to micrometric scale. More specifically, small-angle X-rays and neutron scattering and light scattering techniques represent well-established experimental techniques for the investigation of the structural properties of biomaterials and, through the use of suitable models, they allow to study and mimic various biological systems under physiologically relevant conditions. They provide the ensemble averaged (and then statistically relevant) information under in situ and operando conditions, and represent useful tools complementary to the various traditional imaging techniques that, on the contrary, reveal more local structural information. Together with the classical structure characterization approaches, we introduce the basic concepts that make it possible to examine inter-particles interactions, and to study the growth processes and conformational changes in nanostructures, which have become increasingly relevant for an accurate understanding and prediction of various mechanisms in the fields of biotechnology and nanotechnology. The upgrade of the various scattering techniques, such as the contrast variation or time resolved experiments, offers unique opportunities to study the nano- and mesoscopic structure and their evolution with time in a way not accessible by other techniques. For this reason, highly performant instruments are installed at most of the facility research centers worldwide. These new insights allow to largely ameliorate the control of (chemico-physical and biologic) processes of complex (bio-)materials at the molecular length scales, and open a full potential for the development and engineering of a variety of nano-scale biomaterials for advanced applications.     

Energy-consuming micromechanisms in the fracture of glassy polymers. I. Chain scission in polystyrene

The number of chain scissions per unit area that occur during the fracture of partially annealed latex films from M_n ? 180,000 g/mol polystyrene particles of about 275 Å radius were measured and correlated to annealing times. A curve with four regimes was found. At short annealing times the curve is nearly flat, in what is called the chain pull-out regime. In the second regime, the number of chains broken per unit area increases with a 0.8 power of annealing time as entanglement of the diffusing polymer chains increases in neighboring host particles. This is in good agreement with Wool's theory which predicts a 0.75 power dependence. Then, after reaching a peak, the number of scissions decreases in the third regime, indicating a change in fracture mechanism. The number of chain scissions increases again in the fourth regime, as final healing of the film interface takes place. Fracture surface analysis reveals a rough surface for short annealing times and a smooth surface for longer annealing times. The number of polymer chain scissions per unit area of fracture surface showed no dependence on initial molecular weights for t ? τ_r where t and τ_r are annealing and relaxation times, respectively. The number of chain bridges crossing a unit area of interface was suggested as the basic molecular property. © 1992 John Wiley & Sons, Inc.     

Entropically driven phase separation of highly branched/linear polyolefin blends

Small‐angle neutron scattering (SANS) was used to examine the melt phase behavior of a heavily branched comb PEE polymer blended separately with two linear PEE copolymers. In this case, PEE refers to poly(ethylene‐r‐ethylethylene) with 10% ethylene units; therefore, the molecular architecture was the only difference between the two components of the blends. The molecular weights of the two linear random copolymers were 60 and 220 kg/mol, respectively. The comb polymer contained an average of 54 long branches, with a molecular weight of 13.7 kg/mol, attached to a backbone with a molecular weight of 10 kg/mol. Three different volume compositions (25/75, 50/50, and 75/25) were investigated for both types of blends. SANS results indicate that all the blends containing the lower molecular weight linear polymer formed single‐phase mixtures, whereas all the blends containing the high molecular weight linear polymer phase‐separated. These results are discussed in the context of current theories for polymer blend miscibility. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2965–2975, 2000     

Small-angle neutron scattering of polymer blends of polyvinylmethylether at dilute concentration in deuterated polystyrene

Small-angle neutron scattering was used to measure the radius of gyration and thermodynamics of blends of poly(vinylmethylether) (PVME) at dilute concentration in deuterated polystyrene (PSD). The data were analyzed using the Zimm equation and the random phase approximation theory. For PVME with a weight-average molecular weight of 38,400 the value of the radius of gyration, R_g, was found to be 47 Å in the limit of the concentration of PVME extrapolated to zero. Analysis of the temperature dependence of the Flory interaction parameter, χ/v₀, indicates that phase separation should occur at approximately 300°C for a sample with ϕ_PVME ≅ 9%. No significant temperature dependence of R_g was found over the experimental range studied. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 1–9, 1998     

The response of microstructure to processing in a series of poly(siloxaneimide) copolymers

Poly(siloxaneimide) (PSI) segmented copolymers exhibit organized microdomains if the blocks are sufficiently incompatible. As with neat diblock and triblock copolymers, the processing route employed to prepare films of PSI materials is expected to influence the dimensions and/or morphology of the resultant microstructure. In this work, small-angle neutron scattering (SANS) is utilized to characterize the disordered microstructure found in films of a series of PSI copolymers which are subjected to solvent casting and various thermal treatments. Microstructural dimensions such as the periodicity and correlation length are deduced from the Teubner-Strey (TS) model for disordered microemulsions. The scattering intensity of each copolymer up to q = 5.0 nm^?1, where q is the scattering vector, is found to scale as q^?2.8+?0.1. Results indicate that processing the materials as cast films or as melt-pressed films allowed to cool slowly has a small, but discernible, effect on microstructural characteristics. SANS profiles of films quenched from elevated temperatures reveal a clear transition in microdomain periodicity, which correlates well with the glass transition temperature of the imide microphase in these and other materials of similar chemical structure. © 1993 John Wiley & Sons, Inc.     

The in situ reactive compatibilization of nylon-6/polystyrene blends using anhydride functionalized polystyrenes

Nylon-6/polystyrene (PS) blends were reactively compatibilized by addition of various anhydride functionalized polystyrenes. The morphology of the blends was examined using a scanning electron microscopy (SEM) technique. The particle size of the dispersed styrenic phase was about 3.2 μm for the uncompatibilized 8/2 Nylon-6/PS blend while those of the compatibilized blends were decreased by as much as two orders of magnitude depending on the amount and type of the functionalized polystyrene (FPS) added. Several low-molecular weight polystyrenes with terminal anhydride groups, prepared by two different functionalization methods, were examined. The effect of molecular weight on particle size reduction depended on the basis of comparison, mass of additive, or moles of anhydride units. A high-molecular weight random copolymer of styrene and maleic anhydride was most effective when compared on a mass basis. The increase in adhesion between the Nylon-6 and the styrenic phases caused by the in situ reaction was evaluated by a lap shear technique. The free polystyrene, Nylon-6, and Nylon-FPS copolymer formed were separated by solvent extraction technique using formic acid and toluene. The extent of coupling reaction between the functionalized polystyrenes and Nylon-6 ranged from 25 to 43%. © 1992 John Wiley & Sons, Inc.     

Miscibility and phase behavior in atactic polystyrene and poly(o-chlorostyrene-co-p-chlorostyrene) blends: Effect of polystyrene molecular weight and copolymer composition

Miscibility in blends of random copolymers of o-chlorostyrene and p-chlorostyrene [P(oClSy-co-pClS_1-y)] with 8 atactic polystyrene (aPS) fractions has been studied at temperatures ranging from 150°C to 300°C. Miscibility windows whose size depends on the molecular weight of the PS and on the copolymer composition, y, were observed for each blend. From these data, the temperature dependence of the three segmental interaction parameters required to describe this system were obtained.     

How the Aggregates Determine Bound Rubber Models in Silicone Rubber? A Contrast Matching Neutron Scattering Study

The correlation between aggregates and bound rubber structures in silicone rubbers(S(phr)) with various silica fractions(ΦSi) has been investigated by contrast matching small-angle neutron scattering(SANS), swelling kinetics, and low-field nuclear magnetic resonance(NMR).Mixed solvents with deuterated cyclohexane fractions of 4.9% and 53.7% were chosen to match the scattering length densities of the matrix(SMP(phr)) and the filler(SMS(phr)), respectively. All the data consistently suggest that:(i) There is a critical threshold ΦSic between 10 and 30 phr;below ΦSic, the isolated aggregates are dominant, while beyond ΦSic, some rubber fraction is trapped among the agglomerate;(ii) ΦSiindependent thicknesses around 7.5 nm(NMR) and 8.6 nm(SANS) suggest that the bound rubber formation is determined by inherent properties of the components, and the power-law around 4.2 suggests an exponential changed gradient density of the bound rubber;(iii) SMS(80) presents a bicontinuous bound rubber with three characteristic lengths of 41, 100, and 234 nm. The expanded correlation length, a 20 nm smaller aggregate sizes suggest that such existent bicontinuous network in dry samples with less ΦSi is kind of impacted by swelling. With the obtained bound rubber models, the reinforcing mechanism of filled silicone rubber is elucidated.     

Dynamic light scattering from bulk poly(n-hexylmethacrylate) near and above the glass transition

Photon correlation spectra of polarized scattered light from poly(n-hexylmethacrylate) PHMA (M_w = 1.6·10⁵, T_g = ?5°C) have been studied in the temperature range of ?2–25°C. The experimental time correlation functions over the time range 10^?6?10² s were represented by the Kohlrausch-Williams-Watts (KWW) function exp{?(t/τ)^β} with a virtually temperature-independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass-rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass-rubber or α-relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10^?6 s near T_g. © 1992 John Wiley & Sons, Inc.     

Orientation and relaxation of polymer–clay solutions studied by rheology and small-angle neutron scattering

The influence of shear on viscoelastic solutions of poly(ethylene oxide) (PEO) and clay [montmorillonite, i.e., Cloisite NA+ (CNA)] was investigated with rheology and small-angle neutron scattering (SANS). The steady-state viscosity and SANS were used to measure the shear-induced orientation and relaxation of the polymer and clay platelets. Anisotropic scattering patterns developed at much lower shear rates than in pure clay solutions. The scattering anisotropy saturated at low shear rates, and the CNA clay platelets aligned with the flow, with the surface normal parallel to the gradient direction. The cessation of shear led to partial and slow randomization of the CNA platelets, whereas extremely fast relaxation was observed for laponite (LRD) platelets. These PEO–CNA networklike solutions were compared with previously reported PEO–LRD networks, and the differences and similarities, with respect to the shear orientation, relaxation, and polymer–clay interactions, were examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3102–3112, 2004     

Peptide meets membrane: Investigating peptide-lipid interactions using small-angle scattering techniques

Peptide–lipid interactions play an important role in defining the mode of action of drugs and the molecular mechanism associated with many diseases. Model membranes consisting of simple lipid mixtures mimicking real cell membranes can provide insight into the structural and dynamic aspects associated with these interactions. Small-angle scattering techniques based on X-rays and neutrons (SAXS/SANS) allow in situ determination of peptide partition and structural changes in lipid bilayers in vesicles with relatively high resolution between 1-100 nm. With advanced instrumentation, time-resolved SANS/SAXS can be used to track equilibrium and nonequilibrium processes such as lipid transport and morphological transitions to time scales down to a millisecond. In this review, we provide an overview of recent advances in the understanding of complex peptide–lipid membrane interactions using SAXS/SANS methods and model lipid membrane unilamellar vesicles. Particular attention will be given to the data analysis, possible pitfalls, and how to extract quantitative information using these techniques.     

Brillouin scattering study of a polymer hydrogel

Brillouin light-scattering measurements of H₂O imbibed in hydrogels of poly(2-hydroxyethyl methacrylate) of two cross-linking densities have been made at 294 K. Increase in the amount of water imbibed in 19-30 Å size pores of the cross-linked network causes the velocity of sound to decrease monotonically from a value, which differs for the two pure polymers, to a limiting value for pure water. The absorption coefficient reaches a maximum at about 30% water content and then decreases toward that for pure water. The velocity and absorption coefficient of both pure polymer and hydrogel containing 32% water were measured from 110 to 300 K. The former decreases and the latter increases with increasing temperature, and both show a change in the slope at about 160 K for the hydrogel, which agrees with the calorimetric glass transition temperature of the hydrogel. The effect of the water on the velocity and absorption coefficient of the polymer increases with temperature. © 1992 John Wiley & Sons, Inc.