این پایان نامه به زبان انگلیسی، مربوط به دپارتمان شیمی دانشگاه گلاسگو (University of Glasgow) میباشد که در سال 2012 انجام و با رتبه عالی مورد تایید قرار گرفته است است.
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این پایان نامه به زبان انگلیسی، مربوط به دپارتمان شیمی دانشگاه گلاسگو (University of Glasgow) میباشد که در سال 2012 انجام و با رتبه عالی مورد تایید قرار گرفته است است.
این پایان نامه به زبان انگلیسی، مربوط به دپارتمان شیمی دانشگاه گلاسگو (University of Glasgow) میباشد که در سال 2012 انجام و با رتبه عالی مورد تایید قرار گرفته است است.
Abstrsct
This project was concerned with observing the
process of nucleation of crystalline species during the cooling
crystallisation of supersaturated solutions prepared from both
ionic salt and small organic solutes. Cooling crystallisation
induces a steady temperature-dependant destabilisation of the
supersaturated liquid phase where the chemical potential of the
liquid state increases and so becomes less thermodynamically
stable. This decrease in stability triggers the onset formation of
the corresponding solid state, which has a lower chemical
potential. This driving force permits the spontaneous formation of
critical nuclei and their subsequent growth into larger crystalline
structures. Desire to understand the processes occurring at the
earliest stages of crystal nucleation have attracted much interest
over the years. Dynamic light scattering experiments were employed
to closely observe the precursors to crystal nucleation. More
specifically the phenomenon of molecular clustering and their
consequent dispersion to form solute-rich regions within solution,
where the generation of viable critical nuclei would be most likely
occur, according to current theory. The pre-nucleation mechanism
for cooling crystallisation was observed to involve large
nano-droplet sized molecules of non-specific composition, for
solutions of urea and glycine and almost micron-sized droplets for
solutions of sodium chloride and sodium nitrate. Interestingly,
there was evidence that clustering of larger aggregates was a
phenomenon not wholly restricted by supersaturation as they were
found in undersaturated solutions of all prepared samples. The
relative size of particle radii formed in pre-crystalline solution
tended to depend on the extent of the supersaturation i.e., the
concentration of the solute present within the solution. This is
not true in all cases though as supersaturated glucose indicated.
This may suggest an alternate pathway in the route of nucleation of
crystals than was previously assumed. The theory of a metastable
phase forming within the bulk solution, where critical nuclei are
thermodynamically more stable and hence are able to grow once
formed might not hold true for all crystallising solutions or
another factor may need to be better understood and manipulated in
order to claim more control over the desired process. Further
understanding of this could give an increased degree of control
over yield and quality of products in pharmaceuticals and other
material producing industries