SANS studies, structure

A pronounced influence of pH and added electrolyte on the charge interactions between dendrimers with ionizable groups is expected in aqueous solution. Briber et al. ° investigated the intermolecular interactions between PAMAM dendrimers in concentrated solutions using SANS and SAXS techniques. They showed that the molecules develop large scale interactions which can be screened by the addition of excess acid or electrolyte. SANS studies of the structural... 

In addition to giving information about the shape and internal structure of colloidal aggregates, SANS studies can also be used profitably to determine the thickness and conformation of polymer layers adsorbed onto the surface of colloidal particles such as latex nanoparticles, and in some special cases, the surface of emulsion droplets. ° In such studies, the particles on which the polymer is adsorbed must generally be very accurately contrast matched to the solvent so as to allow information to be obtained only about the adsorbed layer. SANS studies have also been recently used in combination with differential scanning calorimetry and visual inspection of the solutions, to draw up a (simplified) partial phase diagram of the aggregation behavior of a polymeric surfactant in water.t ... 

A liquid crystal is a general term used to describe a variety of anisotropic structures formed by amphiphilic molecules, typically but not exclusively at high concentrations. Hexagonal, lamellar, and cubic phases are all examples of liquid crystalline phases. These phases have been examined as drug delivery systems because of their stability, broad solubilization potential, ability to delay the release of encapsulated drug, and, in the case of lamellar phases, their ability to form closed, spherical bilayer structures known as vesicles, which can entrap both hydrophobic and hydrophilic drug. This section will review SANS studies performed on all liquid crystalline phases, except vesicles, which will be considered separately. Vesicles will be considered separately because, with a few exceptions, generally mixed systems, vesicles (unlike the other liquid crystalline phases mentioned) do not form spontaneously upon dispersal of the surfactant in water and because there have been many more SANS studies performed on these systems. 

As PAA exist in the form of a salt, it is important to determine, prior to use as endosomolytic agents, which, if any salt, exhibits the most appropriate pH-membrane perturbation properties. A SANS study was therefore initiated to investigate systematically the effects of pH and counterion on the molecular structure (as assessed by Rg) of the PAA, ISA 23 when dispersed in D2O, and to correlate molecular structure with its hemolytic activity. Fig. 10 shows the normalized... 

The above study is noteworthy for a few reasons. Firstly, the data were obtained using only one partially deuterated form of the amphiphilic molecules of interest. Secondly, while SANS studies of polymers at a contrast-matched interface are common, the work of Riley et al. is unique owing to the small size of the core particle and the fact that it was the off-contrast match data that provided the more detailed structural information via solvent contrast variation. 

Vogtle, F. Lindner, P. Distribution of end groups within a dendritic structure a SANS study including contrast variation. Macromolecules 2002, 35, 8098-8105. 

Small-angle neutron scattering (SANS) studies of polyradical 50 in THF-dg at 170 K (slightly above melting point of the solvent) revealed the molecular structure (Fig. 31), which was analogous to that obtained from conformational searches.94 Since SANS is a relatively low-resolution technique and the information content of the data is rather low, the structure of 50 might be best described as dumbbell-like with overall dimensions of 2 x 3 x 4nm. Also, this result confirms that polyradical 50 existed as a monomer in solution at low temperatures. 

Karino T, Okumura Y, Zhao C, Kataoka T, Ito K, Shibayama M. (2005) SANS studies on deformation mechanism of slide-ring gel. Macromolecules 38 6161-6167 Haraguchi K, Takehisa T. (2002) Nanocomposite hydrogels a unique organic-inorganic network structure with extraordinary mechanical, optical, and swel I ing/de-swelling properties. Adv Mater 10 1120-1124... 

Some information about the internal structure of the aggregates can be obtained from SANS studies. Of the systems mentioned above, it is only PCMA-SDS mixtures that have been studied with this technique, and at much higher polyelectrolyte concentrations than used during measurements of the turbidity (1000 ppm compared to 20 ppm). Some data, obtained using deuterated SDS in a solvent (80% H20 and 20% D20) where the polyelec-... 

A systematic SANS study of the PS-PA block copolymer has been achieved. The PS-PA co-polymers were obtained through thermal annealing of the diblock precursor PS-PPVS (polyphenylsulfoxide), a detailed description of the synthesis and preparation of the PA sequence free from defect can be found in references [54-55], To get a perfectly dispersed micelle structure in solution, the PA must be short and so the study was devoted to the diblock PS64-PA1 [56-58], The contrast factor of the PS unit is about 95 x 10 cm , while the contrast of the PA chain is negligible. As given in Section 1.2.2 the structure factor of a particle varies as a function of its geometrical shape. For instance, a... 

The formation of extended bilayer structures (lamellar micelles) is believed to be energetically unfavorable due to edge effects [98]. Indeed, evidence for such structures in either the water (Li) or nonpolar (L2) media is scarce [346]. On the basis of SANS studies of the structure of hydrated micelles formed from the C (EO)w surfactants in oil media [347,348], it was concluded that the extent of solubilization of water (Wm x) in the L2 phase did not exceed the maximum hydration requirement of the hydrophilic EO groups. The scattering spectral analysis is also consistent with the formation of small bilayer structures that become thicker and more extended as IFincreases. At low W, the thickness of the bilayer micelles ( hanks ) was found to be less than twice the fully extended conformation of the surfactant, suggesting that the EO chains of the surfactant were interdigitated (or coiled)... 

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