Thermo-responsive nanogel dispersions: dynamics and phase behaviour

The self assembly of nano or sub-micron sized particles into ordered structures have gained wide spread recognition due to their importance in fundamental studies as well as their practical applications in a wide range of disciplines. Deionised suspensions of charged polystyrene nanospheres exhibit...

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Bibliographic Details
Published in:International journal of advances in engineering sciences and applied mathematics 2013-12, Vol.5 (4), p.240-249
Main Authors: Tata, B. V. R., Brijitta, J., Joshi, R. G.
Format: Article
Language:English
Subjects:
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Engineering
Mathematical and Computational Engineering
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Summary:The self assembly of nano or sub-micron sized particles into ordered structures have gained wide spread recognition due to their importance in fundamental studies as well as their practical applications in a wide range of disciplines. Deionised suspensions of charged polystyrene nanospheres exhibit long-range order at very dilute conditions (volume fraction ϕ  ~ 0.001) whereas in hard-sphere colloids the crystallization occurs at much higher values ( ϕ  ~ 0.5). In these dispersions the particle size is fixed and temperature is not a controllable parameter to investigate the phase behaviour, whereas aqueous dispersions of thermo-responsive poly( N -isopropylacrylamide) (PNIPAM) nanoparticles exhibit rich phase behaviour upon varying the temperature due to the variation in particle size as well as inter-particle interactions. This paper discusses the static/dynamic light scattering and confocal laser scanning microscopy studies on aqueous suspensions of PNIPAM nanogel particles having different particle number densities as a function of temperature. We report here our recent observations: (a) A liquid-like ordered PNIPAM nanogel dispersion exhibiting a fluid to fluid transition as a function of temperature (b) Violation of the dynamical criterion of freezing in PNIPAM nanogel liquid undergoing freezing (c) Dependence of crystal structure on the method of re-crystallization and (d) A split second peak in three-dimensional pair-correlation function of PNIPAM nanogel crystals. Present results are discussed in the light of those reported for hard-sphere and charged colloidal suspensions.
ISSN:0975-0770
0975-5616
DOI:10.1007/s12572-010-0016-5