Wetting Instability Driven Stripe
Formation In Monolayers
Atul N. Parikh
Los Alamos National Laboratory
CST-1, MS G755
Los Alamos, NM 87545
(505) 667-7017
(505) 667-8021 FAX
Dewetting instabilities characterized by the competition between short-range attractive and long-range repulsive interactions in amphiphilic molecules lead to the formation of spatially modulated or stripe architectures.
In a recent study, performed under the auspices of a Los Alamos DR initiative on ÒCompeting Interactions In Soft, Hard, and Bio Matter (P.I. David Whitten)Ó we have shown an emergence of such a stripe phase during the spontaneous dewetting of the single molecular monolayers of long-chain trifunctional silanes at an air-water interface. Specifically, we have shown that upon extraneously-imposed compression, the initial equilibrium phase of the silane monolayer, characterized by long banded and circular ÒbubbleÓ phases, is replaced by a featureless homogeneous phase. Upon stepped expansion of the latter compressed state, the monolayer morphology was found to evolve into a spatially modulated architecture shown below.
We interpret this observation to corroborate the dewetting model based on competition between short range attractive interactions between the aliphatic chains and the long-range pairwise repulsive interactions between the polar head-groups. The former favors macroscopic phase separation (to minimize the line tension due to domain walls), while the latter imparts the competing propensity for the continuous sub-division of domains.