Neutron scattering studies

The technique of neutron scattering has been used in the study of macromolecules for several years. A previous review in this series outlined the early contributions to the field up to 1978. The aim of this report is to review the work that has been published from that date up to the present time. 

To retain continuity with the earlier report, this review will be split into five sections Amorphous and Molten Polymers, Semi-crystalline Polymers, Solutions and Polyelectrolytes, Biological Materials, and Dynamical Studies of Macromolecules. 

The basic theory of neutron scattering from macromolecules has been given earlier and will not be repeated here. 

Traditionally, low concentrations of tag (i.e., deuteriated) molecules have been used in neutron scattering. This practice was a continuation of light scattering procedures, where it was necessary to extrapolate to zero concentrations to obtain meaningful results because of interactions between the polymer and solvent. However, if the only difference between a tagged molecule and matrix is the degree of deuteriation the necessity of using low tag concentrations is removed. 

It has been shown that the coherent scattering intensity can be written as  

Important developments have occurred in the use of the large incoherent scattering cross-section of protons to study the dynamics of the chain motion of a polymer in bulk and in solution. 

Initial SANS studies of poly(methyl methacrylate) and polystyrene in the solid state were used to test the credibility of the technique. These studies have since been extended to include poly(dimethyl siloxane) (see ref. 12) and poly(vinyl chloride). In each case Rw = aM where a varies between 0.26 and 0.41 depending on the polymer and in each case was close to the value obtained from the measurements in solution in a 0-solvcnt. Similarly the melts of the crystalline 

Some interesting results have been obtained for mixtures of glassy polymers which are similar in type and described in the literature as compatible. The coil dimensions of the copolymer of acrylonitrile and styrene (PSAN) dispersed in deuteropoly(methyl methacrylate) have been measured in those compositions in which the copolymer forms molecularly disperse mixtures. The coils are expanded as compared with the unperturbed coil dimensions. Measurements of the second viral coefficient at different temperatures show that the system is exothermic and has a negative excess entropy of mixing. Measurements of the coil dimensions in mixtures of poly(dimethyl siloxane) with the deuteriated polymer also show that the coil of the former expands compared to the 0-value as the 

Ti = 110 °C) non-linear behaviour is observed in and dependence on scattering intensity. The radii of gyration cannot, therefore, be measured. This behaviour is explained by the formation of voids or cracks. As n reaches a value of 0.1 A a slope emerges from the graph which is comparable to that which a purely affine deformed coil would give. A model was fitted to the observed longitudinal data which contains affine and non-affine mechanisms of deformation of the coil. The contribution of the former was found to decrease with temperature, whereas the contribution of the latter increases. 

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Kjems J K, Passell L, Taub H, Dash J G and Novaco A D 1976 Neutron scattering study of nitrogen adsorbed on basal plane-oriented graphite Rhys. Rev. B 13 1446-62... 

Hamley I W, Garnett S, Luckhurst G R, Roskilly S J, Pedersen J S, Richardson R M and Seddon J M 1996 Orientational ordering in the nematic phase of a thermotropic liquid crystal A small angle neutron scattering study J. Chem. Phys. 104 10 046-54... 

The early Hartley model [2, 3] of a spherical micellar stmcture resulted, in later years, in some considerable debate. The self-consistency (inconsistency) of spherical symmetry witli molecular packing constraints was subsequently noted [4, 5 and 6]. There is now no serious question of tlie tenet tliat unswollen micelles may readily deviate from spherical geometry, and ellipsoidal geometries are now commonly reported. Many micelles are essentially spherical, however, as deduced from many light and neutron scattering studies. Even ellipsoidal objects will appear... 

Mortensen K 1996 Structural studies of PEO-PPO-PEO triblock copolymers, their micellar aggregates and mesophases a small-angle neutron scattering study J. Phys. Condens Matters A103-A104... 

Recently, this observation has been confirmed experimentally through neutron scattering studies, making use of isotopic substitution . These studies have revealed that the water molecules in the... 

M. Zulauf, K. Weckstrom, J. B. Hayter, V. Degiorgio, M. Corti. Neutron scattering study of micelle structure in isotopic aqueous solutions of poly(oxy-ethylene) amphiphiles. J Phys Chem 29 3411-3417, 1985. 

A. Nagasawa and Y. Morii, Recent neutron scattering studies on the premartensitic state of bcc-based metals... 

T.R. Finlayson and H.G. Smith, Neutron scattering studies of premartensitic indium-thallium alloys. Met. Trans A 19A 193 (1988). 

Wignall, G.D. (1999) Neutron scattering studies of polymers in supercritical carbon dioxide. Journal of Physics Condensed Matter, 11 (15), R157-R177. 

Additional neutron scattering studies on different polymer systems could prove very important. Strobl [31,32,47,103] provides evidence that, for some polymers, lamellar crystallization is preceded by pre-ordering of the melt followed by formation of planar arrays of blocks. Investigating crystallization from the melt, Kaji and coworkers [25] find pre-ordering phenomena relating to orientational fluctuations of stiff polymer segments which, under appropriate conditions, determine phase separation prior to crystallization. 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

Saul Oseroff and Pieter H. Keesom, Magnetic Properties Macroscopic Studies T. Giebultowicz and T.M. Holden, Neutron Scattering Studies of the Magnetic Structure and Dynamics of Diluted Magnetic Semiconductors J. Kossul, Band Structure and Quantum Transport Phenomena in Narrow-Gap Diluted Magnetic Semiconductors... 

Polybutadiene in the Melt. A Quasielastic Neutron-Scattering Study. 

G. D. Smith, W. Paul, M. Monkenbusch, and D. Richter, Chem. Phys., 261, 61 (2000). A Comparison of Neutron Scattering Studies and Computer Simulations of Polymer Melts. 

While a high-resolution inelastic neutron scattering study has attempted... 

Beaufils, J.P., Heimion, M.C., and Rosset, R., Neutron scattering study of alkyl chain motion on reversed phase liquid chromatographic packings. Anal. Chem., 57, 2593, 1985. 

The question can be raised as to whether the structure of the proteins within the ribosomal particle is the same as in the isolated state. The only direct evidence we have that the structures of proteins are not changed upon incorporation into the subunit is provided by the neutron-scattering studies of Nierhaus et al. (1983b). They showed that individual proteins in solution had radii of gyration indistinguishable from those obtained from their counterparts on the ribosomal subunits in the same buffers and under identical preparation conditions. 

For both the 30 S and 50 S subunits, additional neutron-scattering studies have been made to determine the distribution of the protein and the RNA within the subunits. It has been shown in both cases that the... 

Fig. 11. Map of proteins within the E. coli 30 S ribosomal subunit as determined by neutron scattering studies (Moore, 1980 Moore et al., 1984). Reproduced with permission from Wittmann (1983).

Parker, S.F., Taylor, J.W., Albers, R, Lopez, M., Sextl, G., Lennon, D., Mclnroy, A.R., Sutherland, I.W. 2004. Inelastic neutron scattering studies of hydrogen on fuel cell catalysts. Vibration Spectrosc 35 179-182. 

This finding implies a sublinear increase of (r (t)) with time. Thus, the incoherent neutron scattering studies qualify the motion of the hydrogens as an anomalous diffusion involving a sublinearly increasing (r (t)). 

Ruffle, S. V. Michalarias, I. Ei, ].-C. Ford, R. C. Inelastic Incoherent Neutron Scattering Studies of Water Interacting with Biological Macromolecules. /. Am. Chem. Soc. 2002, 124, 565-569. 

T. Giebultowicz and T M. Holden, Neutron Scattering Studies of the Magnetic Structure and... 

Chen W-R, Porcar L, Liu Y, Butler PD, Magid LI. Small angle neutron scattering studies of the counterion effects on the molecular conformation and strucmre of charged G4 PAMAM dendrimers in aqueous solutions. Macromolecules 2007 40 5887-5898. 

Huang QR, Dubin PL, Lai J, Moorefield CN, Newkome GR. SmaU-angle neutron scattering studies of charged carboxyl-terminated dendrimers in solutions. Langmuir 2005 21 2737-2742. 

Robinson BH, Toprakcioglu C, Dore JC, Chieux P (1984) Small-Angle Neutron-Scattering Study of Microemulsions Stabilized by Aerosol-Ot.l. Solvent and Concentration Variation. J Chem Soc Faraday Trans 1 80 13-27... 

Simmons BA, Irvin GC, Agarwal V, Bose A, John VT, McPherson GL, Balsara NP (2002) Small Angle Neutron Scattering Study of Microstructural Transitions in a Surfactant-Based Gel Mesophase. Langmuir 18 624-632... 

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