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SUMMARY:Liquid-Vapour Interfaces of Patchy Colloids - Paulo Teixeira\, ISE
 L Lisbon
DTSTART:20190205T130000Z
DTEND:20190205T140000Z
UID:TALK116041@talks.cam.ac.uk
CONTACT:Professor Mike Cates
DESCRIPTION:We investigate the liquid-vapour interface of a model of patch
 y colloids. This model consists of hard spheres decorated with short-range
 d attractive patches of different types on their surfaces. We focus on a o
 ne-component fluid with two patches of type A and nine patches of type B\,
  which has been found to exhibit reentrant liquid-vapour coexistence curve
 s and very low-density liquid phases. We have used the density-functional 
 theory form of Wertheim’s first-order perturbation theory of association
  to calculate the surface tension\, and the density and degree of associat
 ion profiles\, at the liquid-vapour interface of our model. In re-entrant 
 systems\, where AB bonds dominate\, an unusual thickening of the interface
  is observed at low temperatures. Furthermore\, the surface tension versus
  temperature curve reaches a maximum. If BB attractions are also present\,
  competition between AB and BB bonds gradually restores the monotonic temp
 erature dependence of the surface tension. Lastly\, the interface contains
  a region where the average chain length is close to that in the bulk liqu
 id\,but where the density is that of the vapour. Sufficiently strong BB at
 tractions remove these features. We next show that the non-monotonic tempe
 rature dependence of the surface tension and interfacethickness in this mo
 del can be qualitatively reproduced by a local\, square-gradient type DFT\
 , with a density-dependent prefactor. This simpler theory is then applied 
 to colloids decorated with two patches of type A and ten patches of type B
  interactions chosen so as to exhibit a closed-loop phase diagram when onl
 y AA and AB bonds are present. As BB attractions are gradually switched on
 \, the lower critical point disappears and the surface tension vs temperat
 ure curve acquires a very deep minimum. On further increasing the strength
  of the BB attractions\, the surface tension becomes a monotonically decre
 asing function of the temperature\, as in atomic fluids. The very low surf
 ace tension at the minimum for weak BB attractions\, combined with the abi
 lity to form physical gels\, suggests that patch colloids might be exploit
 ed as temperature-controlled surfactants and foam stabilizers.
LOCATION:MR11\, CMS
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