Solute structure function scattering experiments

The solute structure function H(q) is determined experimentally by radiation scattering. The interval gmin, m in which H(q) is measured depends upon the nature of the radiation used in the experiment [see (15.1.22) and (15.1.23)]. The choice of such a radiation is imposed by the choice of the interval which best suits the study of the observed structure. 

A first measurement of the function H(q) for solutions with overlap was made in 1966 by Benoit and Picot,19 using light scattering. Systematic measurements of the function H(q) for solutions with overlap have been made by the Strasacol group (Daoud et al. 197520) using neutron scattering. 

There is a relationship between the solute structure function H(q) at q = 0 and the osmotic pressure. Nevertheless, H(q) reveals the structure of the solution in more detail than does the osmotic pressure, because q is an arbitrary vector. 

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The reduced intensity observed in an X-ray diffraction experiment corresponds to the sum over the different partial structure functions, each weighted by the product of the scattering factors for the two atomic species involved. In an aqueous solution of a salt MX, which contains four atomic species M, X, O, and H, the number of different pair interactions is ten and the reduced intensity function can be written ... 

The quantities measured during a scattering experiment are the intensities I(q) of the scattered radiation, for various transfer vectors q (see Chapter 6). From these quantities, we can deduce the structure function of the solutes. 

Numerous light-scattering experiments have been performed with polymer solutions in the vicinity of the critical demixtion point in order to determine the structure function fi(q). 

There are data available on dose rate and dose tolerances. Doses of 109rad destroy the structure of organic molecules and 106rad kill living cells (Bordas and Mandelkow 1983). These authors discuss the case of microtubule polymerisation levels of 30 000-50 000 rad delivered at rates of 2000 rad min-1 with medical X-ray sources impair this function whereas on DORIS in solution scattering experiments 1.5x 106rad delivered at a rate of 60 000 rad min-1 are needed, i.e. an increase of 30 in... 

Figure 2.13 shows the result of a light scattering experiment on the same system, a dilute solution of polystyrene (Mn = 8.79 10 ) in cyclohexane. The measurement was conducted exactly at the theta-point. As we have learned, ideal chains scatter according to the Debye-structure function, with the asymptotic limit Sd The data display the product... 

The existence of the cluster has also been proposed from dynamic light scattering experiments the time corrdation function obtained for solutions of some ionic polymers at low salt concentrations showed two or three dynamic modes, fast and slow. The very slow mode was first reported by Lin, Lee, and Schurr, who coined the term ordinary-extraordinary transition for its appearance at low salt concentrations [11]. Several authors have also observed essentially the same phenomena by DLS [bb-TO]. The slow mode has been attributed to the translational diffusion of (temporal) cluster by Schmitz [66], or of multi-chain domains (dusto s) by Sedlak [68,70]. We also observed two modes for polystyrenesulfonate solutions we attributed the slow mode to the translational diffusion of the localized ordered structures [71]. 

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