Nonequilibrium Pattern Formation in Langmuir-Phase Assisted Assembly of Alkylsiloxane Monolayers

Rong Wang, Atul N. Parikh, Jaime D. Beers, Andrew P. Shreve, Basil Swanson

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Abstract

Prepolymerized n-octadecyltrichlorosilane (OTS) monolayers were deposited onto oxidized silicon substrates from precursor Langmuir monolayers (at an air-water interface) in two-dimensional liquid expanded (LE), liquid condensed (LC), or mixed (LE/LC coexistence phase) states at four different pulling rates. Morphologies of the transferred monolayers have been investigated using atomic force microscopy (AFM). The OTS monolayers formed from the LE phase precursor reveal an incipient condensation transition exhibiting a novel ring-in-a-ring morphology, wherein uniformly distributed circular domains consisting of two concentric walls of ordered OTS molecules in a high density phase both sandwich and encapsulate disordered OTS molecules in a reduced density phase. On the other hand, the monolayers formed from the LC/LE phase precursor implicate a complete condensation transition, evidenced in the AFM images showing a uniform tiling of near-circular domains composed of ordered OTS molecules in a dense monolayer phase. The monolayers derived from the 2D solid or LC precursor state reveal near-complete surface coverages and uniform film structures, comparable to those obtained by adsorption from a dilute organic solution of OTS molecules (conventional self-assembly process). These structural reconstructions at the substrate surface, namely lateral redistribution into 2D domains, condensation transitions and film coverages, are discussed in terms of the competition between short range and long range interactions. The most dominant effect of increasing pulling rates is the appearance of coalesced domain structures, presumably due to drainage of the water layer at the substrate surface as well as occasional substrate pinning. These results substantiate the idea that templating surface self-assembly of monolayers by using their Langmuir-phase precursors provides a useful alternative to classical solution-phase self-assembly approaches, and affords a wide range of control over film structures and surface morphologies.

Original languageEnglish (US)
Pages (from-to)10149-10157
Number of pages9
JournalJournal of Physical Chemistry B
Volume103
Issue number46
StatePublished - Nov 18 1999
Externally publishedYes

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Wang, R., Parikh, A. N., Beers, J. D., Shreve, A. P., & Swanson, B. (1999). Nonequilibrium Pattern Formation in Langmuir-Phase Assisted Assembly of Alkylsiloxane Monolayers. Journal of Physical Chemistry B, 103(46), 10149-10157.