Hatharasinghe, Henegama Liyanage Mallika; (2001) Studies of clay-polymer interactions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The clay-polymer interactions have been investigated by experiments on a four-component system consisting of n-butylammonium vermiculite clay, n-butylammonium chloride, polyethylene oxide (PEO) and water. The inter-platelet distance, d was studied by neutron diffraction as a function of the clay volume fraction r, the salt concentration c and the molecular weight Mw and volume fraction of the PEO v in the system. The most conspicuous results is that PEO addition only brings about a contraction in the d spacing when the mean end-to-end distance l of PEO is greater than or equal to daq (d spacing in the clay-salt-water system). The structure of the gel phase was studied using H/D isotope substitution of polymer. The results indicate that a significant part of the polymer chains are directly bound to the clay surfaces. With r, c, v constant, d is independent of Mw, ruling out the depletion mechanism. The results fitted well to a model of bridging flocculation. The strength of the bridging force was determined by mapping d vs. v data onto previously determined d vs. p (uniaxial stress) data obtained for the same clay-salt-water system without added polymer. The drawing force depends on knowing v inside the gel, which was determined to be 45% of added PEO by refractometry and chemical analyses. Using this value gave a drawing force per bridge of 0.6pN and this finding represents a new challenge in colloid and polymer science. Previous studies of the three-component system showed that a phase transition from gel to tactoid occurred as the temperature increases. In our studies a gel to tactoid transition was found to occur when the temperature was decreased through the freezing point of solution. These both upper and lower phase transitions have been studied as a function of Mw, v and c by diffraction techniques and interestingly they were found to be completely reversible and sharp even with added polymer. Neither the transition temperature nor the d spacing of the clay tactoid phase was affected by the addition of PEO.

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