@misc{oai:ir.soken.ac.jp:00000259,
author = {林, 久史 and ハヤシ, ヒサシ and HAYASHI, Hisashi},
month = {2016-02-17, 2016-02-17},
note = {Aqueous solutions of small organic molecules often show anoma-
lous behavior in various transport and thermal properties. The formation of
some kind of molecular aggregates or microinhomogeneity has generally
been invoked for explaining these peculiarities. However, details of the
microinhomogeneity are not clear as yet.
The small angle X-ray scattering (SAXS) method is one of the most
direct ones to study microinhomogeneity. In the analysis, SAXS intensity
curve (I(s)) is expanded as follows:
I(s)=r0-r2s2+r4s4-r6s6+ ... ...(1)
where
r2i=(1/(2i+1)i)<Δρe(O)Δρe(r)>r2i 4πr2dr. . . . (2)
Here s is the scattering parameter(s=4πsinθ/λ,where 2θ is the scattering
angle and λ is the wavelength of X-rays), Δρe(r) is the difference in the
electron density from the average at position r, and < > denotes the
ensemble average. The 'moment' determined through a SAXS measure-
ment (r2i) reflects various properties of the solution. The zero-angle scat-
tering intensity (I(O)), which relates to the square of the number of mole
cules concerning the microinhomogeneity, is equal to r0 . The mean square
fluctuation is concentration ((ΔC1)2>) is derived from I(O). The correla-
tion length (ξ), which indicates the average size of the microinhomogenei-
ty, is calculated as (r2/r0)0.5. These two (r0 and r2 ) have been chief concern
in the previous SAXS studies.
Higher order coefficients in eq. (1), which have not been employed
in previous SAXS studies, have a possibility to give additional information
about microinhomogeneity as long as accurate enough SAXS data can be
accumulated. To understand the complicated mixing state of the molecular
aqueous solutions, it is required to use as many kinds of indicators of
microinhomogeneity as possible. Thus, in this thesis, the author has
attempted to apply the higher order coefficients to studying the mixing
state.
A point-focusing diffractometer with a double-bent LiF crystal
monochromator as well as a position-sensitive proportional counter has
been constructed to obtain accurate SAXS data. With this diffractometer,
small-angle resolution of better than 0.42 is achieved. To evaluate the
performance of the diffractometer, SAXS data on several pure liquids and
aqueous solutions were measured. The results showed that this diffrac-
tometer produced incident beams intense enough to measure SAXS on
solutions, making a collimation effect negligible simultaneously.
With the diffractometer mentioned above, it is possible to accurately
determine the higher order coefficients. Accordingly, the following new
parameter (χ) is proposed:
χ=r0 r4/r22 . . (3)
Being related with r4 , this dimensionless parameter reflects the shape of
I(s). Several theoretical SAXS functions were examined in order to under-
stand the physical meaning of χ further, and χ has been interpreted to
represent the size dispersion of fluctuating clusters formed in solution: a
large/small χ corresponds to a large/small size dispersion.
To examine whether or not an analysis in terms of χ is meaningful
in understanding the mixing state, the SAXS curve shape of 2-butoxyeth-
anol (BE) and 1-propanol (abbreviated to NPA) aqueous solution has
been extensively studies. The behavior of χ for the two aqueous solutions
shows marked contrast.
BE aqueous solution has a lower critical solution temperature near
room temperature, and its correlation length (ξ) and concentration fluctua-
tion (<(ΔC1)2>) showed very large variations with temperature and
concentration. In accordance with <(ΔC1)2> and ξ,χ markedly
changed with both concentration and temperature.
On the other hand, NPA mixes with water at any concentration and
at any temperature. ξ changed gradually with concentration but showed
almost no change with temperature. The χ of NPA aqueous solution
changed smoothly with concentration but varied only slightly with tempera-
ture; modest/immodest local structure change with temperature and
concentration of NPA/BE aqueous solution is reflected on χ. Thus, it has
been experimentally proved that χ is very sensitive to the mixing state and
is accordingly available as a useful parameter.
In terms of the obtained χ's, a new piece of information about clus-
ters formed in the two aqueous solutions can be discussed. In BE aque-
ous solution, χ is the smallest and is about 0.8 near the critical composi-
tion (around BE 5 mole%) at all the temperature studied and near the<
miscibility curve in phase diagram. In NPA aqueous solution, χ takes a
minimum value and is about 1.1 around NPA 15 mole% at all the tempera-
ture studied. Because χ is small, it is predicted that clusters having a fairly
well-defined size are dominant in these regions. This interesting sugges-
tion should be ascertained in future work.
A use of the diffractometer constructed in this work has also made
it possible to obtain SAXS data within a short time. Hence, the growth of
nickel and iron silicates in the mixed solution of metal ethylene glycolates,
water, and tetraethoxysilane has been monitored with SAXS. At an early
stage of polymerization, the fractal dimension (D) increases, reaching a
constant value while the reaction is still in progress. The D value suggests
that the structure of the gels containing metals is different from that made
without metals. Useful catalysts are prepared by the calcination of the
gels. A relationship between the structures of the gel and of the catalyst is
discussed., application/pdf, 総研大甲第14号},
title = {Ｘ線小角散乱法による水溶液の不均一性の研究},
year = {}
}