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

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.

Wetting morphologies on substrates with striped surface domains

“…Striped domains in the millimeter range can be created using screen printing technology 4 or printed circuit board technology. 5 In order to obtain stripes with a width in the micrometer range, one may use elastomer stamps, [6][7][8][9][10] vapor deposition through grids, 2 photolithography of amphiphilic monolayers, 11 domain formation in Langmuir-Blodgett monolayers, 12,13 electrophoretic assembly of colloids, 14 or anisotropic rupture of polymer films. 15 Finally, stripes in the nanometer range could be produced using lithography with colloid monolayers, 16 atomic beams modulated by light masks, 17 microphase separation in diblock copolymer films, 18 or local oxidation of silicon surfaces induced by atomic force microscopy.…”

Polymer nanodroplets forming liquid bridges in chemically structured slit pores: A computer simulation

“…In the context of the emerging technology of microscale processing the use of surface substrates with micropatterns has become increasingly important for microfluidics applications. Chemically structured surfaces that exhibit lateral patterns of varying wettability can be produced by techniques such as photolithography 1,2 , microcontact printing [3][4][5] , vapor deposition through grids 6 , domain formation in Langmuir-Blodgett monolayers 7,8 , electrophoretic colloid assembly 9 , lithography with colloid monolayers 10 , microphase separation in diblock copolymer films 11 , etc. For patterned surfaces in the micrometer range, on which liquid droplets or thin liquid films are adsorbed, fascinating wetting morphologies have been predicted [12][13][14][15][16][17][18][19] (including "morphological wetting transitions" 12,16,17 ) and observed 6 .…”

Silica‐supported biomimetic membranes

“…An outline of the system is summarized in Figure 2. It is a very early example of the SAM/LB combination done in the middle of 1980s, and this cencept is currently widely used by many researchers 34–50…”

“…Matsumoto and colleageus studied similar phase separation structure and component exchange 50. Wang and colleagues reported that formation in a Langmuir monolayer of alkylsilane formed a nonequilibrium pattern of ring‐in‐a‐ring morphology in its liquid expanded phase 45. Knobler and colleagues reported phase‐separated, two‐component self‐assembled organosilane monolayers and their use in selective adsorption of a protein 40.…”