Reflectometry neutron

Neutron refleetometry is one of the most versatile techniques used to analyze very aecurately the interfaces between immiscible polymers [78]. This technique provides 

The d-PS-g-MA with an MA content of 0.3 wt% can only give rise to structurally very simple graft copolymers compared to the complex graft copol)miers resulting from high functional SMA types. This also means that the low interfacial thickness of the bi-layer PA-6I/d-PS-g-MA (NR data) does not a priori exclude the large interfacial thickness of the bilayers PA12/SMA [102] (measured with ellipsometry). 

Reflection of X-rays and neutrons from a surface responds to the variation of electron density and scattering-length density, respectively. Penetration depths can be several thousand angstroms and resolution 10A. Hence, in principle these techniques should be ideal for providing information on the nature, composition and size of polymer surfaces and interfaces. However, a direct description of the surface is not provided the predictions of a model have to be compared with literature data, and in many cases finding a unique solution may be difficult. Only neutron reflectometry is dealt with here, since this has been applied to a wider range of polymer systems than X-ray reflectometry. 

From eqn (8.24) we note that since p 1 for most materials, then n and total reflection will take place when the incident angle satisfies Snell s Law  

If the medium 2 is a layer of finite thickness on a thick substrate layer of scattering-length density, then, for Q 2c- 

Surface roughness will give the surface some diffuse character and the reflectivity will be suitably modified to  

Reflectivity can also be described as the motion of the neutron in one dimension subjected to a pseudopotential whose magnitude is related to the scattering-length density of the medium. Using the Schrodinger equation to describe the perpendicular component of the motion eventually results in the 

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The monotonic increase of immobilized material vith the number of deposition cycles in the LbL technique is vhat allo vs control over film thickness on the nanometric scale. Eilm growth in LbL has been very well characterized by several complementary experimental techniques such as UV-visible spectroscopy [66, 67], quartz crystal microbalance (QCM) [68-70], X-ray [63] and neutron reflectometry [3], Fourier transform infrared spectroscopy (ETIR) [71], ellipsometry [68-70], cyclic voltammetry (CV) [67, 72], electrochemical impedance spectroscopy (EIS) [73], -potential [74] and so on. The complement of these techniques can be appreciated, for example, in the integrated charge in cyclic voltammetry experiments or the redox capacitance in EIS for redox PEMs The charge or redox capacitance is not necessarily that expected for the complete oxidation/reduction of all the redox-active groups that can be estimated by other techniques because of the experimental timescale and charge-transport limitations. 

By variation of the contrast between the structural imits or molecular groups, complex systems may be selectively studied. In particular, the large contrast achieved by isotopic substitution of hydrogen - one of the main components of polymers - by deuterium constitutes the most powerful tool for deciphering complex structures and dynamic processes in these materials. Neutron reflectometry constitutes a imique technique for the investigation of surfaces and interfaces in polymeric systems. 

Another example showing unique properties of high-density brushes concerns the miscibility of the polymer brush with a chemically identical polymer matrix [154]. Neutron reflectometry was applied to a series of deuter-ated PMMA (PMMAj) brushes with a constant chain length (Mn = 46000, Mw/Mn = 1.08) and differing graft density (a 0.7 and 0.06 chains nm ). 

Neutron reflectometry (NR) has been employed to study the structure and... 

Probing Surfactant Adsorption at the Solid-Solution Interface by Neutron Reflectometry... 

In the last 10-15 years, neutron reflectometry has been developed into a powerful technique for the study of surface and interfacial structure, and has been extensively applied to the study of surfactant and polymer adsorption and to determine the structure of a variety of thin films [14, 16]. Neutron reflectivity is particularly powerful in the study of organic systems, in that hydrogen/deu-terium isotopic substitution can be used to manipulate the refractive index distribution without substantially altering the chemistry. Hence, specific components can be made visible or invisible by refractive index matching. This has, for example, been extensively exploited in studying surfactant adsorption at the air-solution interface [17]. In this chapter, we focus on the application of neutron reflectometry to probe surfactant adsorption at the solid-solution interface. 

The scope of the chapter will include an introduction to the technique of neutron reflectometry, and how it is applied to the study of surfactant adsorption at the planar solid-solution interface, to obtain adsorbed amounts and details of the structure of the adsorbed layer. The advantages and limitations of the technique will be put in the context of other complementary surface techniques. Recent results on the adsorption of a range of anionic, cationic and nonionic surfactants, and surfactant mixtures onto hydrophilic, hydrophobic surfaces, and surfaces with specifically tailored functionality will be described. Where applicable, direct comparison with the results from complementary techniques will be made and discussed. 

Yager K, Tanchak O, Godbout C, Fritzsche H, Barrett C. (2006) Photomechanical effects in azo-polymers studied by neutron reflectometry. Macromolecules 39 9311-9319... 

Due to the wave-particle duality of neutrons, they can be reflected and refracted in a manner similar to light. Reflected neutron beams can interfere with each other to produce a reflected beam intensity that is characteristic of the reflecting material (Lekner, 1987). Detailed analysis of the reflectivity is able to able to provide information on the structural organization normal to the surface on which the beam is incident. Neutron reflectometry is particularly useful (vis a vis x-ray reflectometry), since selective isotopic labeling can be used to highlight particular regions of interest in a surface structure. This is especially valuable for monolayers on surfaces. 

Neutron reflectometry has been applied to the study of a variety of surfaces, including solid polymeric films, ferromagnetic films, and pure liquid surfaces (Penfold and Thomas, 1990). The technique has also been used in conjunction with Langmuir film balance apparatus to study the adsorption of compounds at the air-water interface, e.g., alkyl trimethylammonium bromide surfactants (Lee et al., 1989), fatty acids (e.g., Grundy et al., 1988), and a variety of polymeric compounds (e.g., Henderson et al., 1991 Henderson, 1993). 

Recently, the investigation of monolayer models of biological membranes by neutron reflectometry has received some attention. For example, the changes in the structure of monolayers of dimyristoylphosphatidylglycerol (DMPG) and dimyristoylphosphatidylcholine (DMPC), which accompany the transition from an expanded to a condensed state, were reported by Bayerl et al. (1990). Monolayers composed of a mixture of perdeuterated DMPC and DMPG in the ratio 7 3 were deposited on D2O and ACMW subphases to... 

The studies just outlined indicate that neutron reflectometry has considerable potential for studying the mode of actions of skin penetration enhancers at a molecular level. Of particular interest in the field of percutaneous absorption... 

Neutron reflectometry studies on mixed DPPC/oleic acid monolayers have been conducted using the CRISP reflectometer at RAL. First, the stmcture of DPPC monolayers was determined by measuring reflectivity profiles from three different isotopic forms of the DPPC monolayer system. This was achieved using hydrogenated (h-DPPC) and chain perdeuterated (d-DPPC) phospholipids and two different subphases of D2O and ACMW. The monolayers were studied at three surface coverages of approximately 50, 60, and 70 A /molecule. Examination of the surface pressure-area isotherm reveals that the main LE/LC phase transition for DPPC monolayers occurs over this range of molecular area (Lewis and Hadgraft, 1990). 

The preliminary results just reported for DPPC/OA monolayers illustrate the way in which neutron reflectometry can be used to study the interaction of components in model membrane systems. In particular, the technique has been shown to be useful in the study of the water associated with lipid headgroups. Data analysis by the partial stmcture factor method offers the potential to study complex multicomponent membrane systems, which have more relevance to the behavior of biological membranes in vivo. 

Henderson, J. A., Richards, R. W., Penfold, J., Shackelton, C. and Thomas, R. K. (1991). Neutron reflectometry from stereotactic poly (methylmethacrylate) monolayers spread at the air-water interface. Polymer 32 3284-3293. Hoogstraate, A. J., Verhoef, J., Brusse, J., Ijzerman, A. P, Spies, P. and Bodd6, H. E. (1991). Kinetics, ultrastructural aspects and molecular modelling of transder-mal peptide flux enhancement by A-alkylazacycloheptanones. Int. J. Pharm. 76 31-41. 

The use of neutron scattering techniques, both small angle neutron scattering (SANS) and neutron reflectometry, have been central to the development of our understanding of polymers at a microscopic level in bulk (solutions and melts), and at interfaces and in thin films. The power of these techniques and their extensive application stems primarily from the vastly different scattering powers of hydrogen and deuterium. Through this difference, H/D isotopic substitution provides a selectivity and sensitivity at an atomic scale resolution, which is more difficult to obtain with other techniques. 

Figure 2 The height of a polymer brush as a function of temperature, as revealed by neutron reflectometry. The brush is composed of end-grafted deuterated polystyrene, and the environment ispoly(vinyl methyl ether). As the temperature is increased the interaction between polystyrene and poly( vinyl methyl ether) becomes increasingly unfavourable and the brush height decreases reversibly...

Numerous trials for the mean field approach have been performed. Most of them have been focused on testing whether real profiles c )(z) of the surface segregated layer follow Eq. (30). Neutron reflectometry (NR, with a depth resolu-... 

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