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IRTG / Soft Matter Science
Freiburger Materialforschungszentrum
Stefan-Meier-Str. 21
79104 Freiburg, Germany

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You are here: Home Events Prof. Wiebke Drenckhan & Dr. Manish Kaushal "Outstanding stability of free-standing co-polymer films above the glass transition"

Prof. Wiebke Drenckhan & Dr. Manish Kaushal "Outstanding stability of free-standing co-polymer films above the glass transition"

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Laboratoire de Physique des Solides, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay Cedex & Institut Charles Sadron, UPR22, Strasbourg, France

What
  • Seminar
When Jan 18, 2017
from 02:15 PM to 03:00 PM
Where Seminarraum A, FMF, Stefan-Meier-Str. 21, Freiburg
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Thin films of polymer melts - wherein the flow occurs under the confinement of submicrometric dimension - span a broad range of industrial processes as well as natural phenomena. The stability and drainage dynamics of such films involve many fundamental questions and has been investigated extensively in last few decades. Most polymer melts make very unstable films above their glass transition. However, in a recent work we have discovered that certain statistical PDMS-g-PEG-PPG block-copolymer (DBP) melts can make large (> 10 cm²) and extremely stable, free-standing thin films (15 – 100 nm thickness) far above the glass transition and without the addition of stabilising agents.[1] Figure 1 shows the temporal evolution of the interference pattern of a vertical film draining under gravity. The film reaches a thickness of roughly 30 nm before rupture.  Interestingly, we also observe a layer-by-layer thinning (stratification) for vertical as well as horizontal films (Figure 2), which can be correlated with a characteristic length scale of ~15 nm of the isotropic bulk melt, as shown in Figure 2.

This observation suggests that structural forces play a major role, and puts forward many questions concerning the influence of the molecular architecture (backbone and side chain lengths, chemical composition and statistical distribution of the side chains, chain flexibility etc.) and the organisation of the polymers at the air/film interface. In collaboration with EVONIK we have therefore synthesised 12 different derivatives of DBP where the structural parameters are systematically varied keeping the chemical architecture same. We investigate the underlying stability mechanisms using various complementary experimental techniques, such as time-dependent vertical and horizontal film-pulling experiments, interfacial rheology or interfacial tension. These are combined with bulk characterisation of the melt (rheology, x-ray, DSC, …).

The combination of our different observations leads us to think that we are dealing with an interfacially-driven micro-phase separation of the amphiphilic block-copolymer. We have planned to do more direct characterization of the interfacial organisation by conducting high-quality X-ray reflectivity and grazing-incidence X-ray diffraction at small-angles (GISAXS) test at SOLEIL. We are also interested in theoretical modelling which can account for such interfacial organisation and can explain this long-term stability and the associated drainage dynamics via stratification. We believe that our investigations will provide insight into the stability of polymeric thin films, foams, and emulsions without the use of stabilizing agents.

[1] T. Gaillard et al., ACS Macro Letters 4, 1144 (2015).

 

invited by Jörg Baschnagel

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