Rt

TAF

a

ARR2AA

KPL

1

cotcibm[ltsguttstebota[

0d

Colloids and Surfaces A: Physicochem. Eng. Aspects 395 (2012) 32– 37

Contents lists available at SciVerse ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l h omepa g e: www.elsev ier .com/ locate /co lsur fa

ing patterns in liquid crystals aligned by phase-separatedwo-component monolayers

anmay Bera, Wenlang Liang, Jiyu Fang ∗

dvanced Materials Processing and Analysis Center and Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando,L 32826, United States

r t i c l e i n f o

rticle history:eceived 18 September 2011eceived in revised form

a b s t r a c t

We investigate the alignment of 4′-pentyl-4-cynobiphenyl (5CB) liquid crystal on phase-separated two-component organosilane monolayers that consist of the protruding islands surrounded by a continuousphase. The molecular disordering at the protruding island edge locally perturbs the homeotropic align-

9 November 2011ccepted 30 November 2011vailable online 8 December 2011

eywords:

ment of the 5CB induced the phase-separated monolayers, leading to the formation of ring patterns.The edge effect on the 5CB alignment decreases with the decrease of the height difference between theprotruding islands and the surrounding monolayer and increases with the decrease of the size of theprotruding islands.

hase-separated organosilane monolayersiquid crystal alignments

. Introduction

Interfacial properties of liquid crystals have been a subject ofonsiderable studies since the discovery of liquid crystals at the endf 19th century [1,2]. It is known that the alignment of liquid crys-als can be achieved by the chemical treatments of the substrate inontact with the liquid crystals. Recently, there have been interestsn aligning liquid crystals with self-assembled organic monolayersecause their surface properties and orientational ordering can beanipulated by varying the nature of self-assembling molecules

3–9]. For example, Gupta and Abbott reported the alignment ofiquid crystals on the self-assembled monolayers of alkanethiolshat differ by a single methylene. They found that the change in thepatial orientation between odd and even numbers of methyleneroups could cause a 90◦ rotation in the azimuthal director of liq-id crystals [3–4]. Evans and coworkers aligned liquid crystals withhe patterned thiol monolayer presenting CH3, CF3, OH, and COOHerminal groups [5,6]. The CH3- and CF3-terminated regions (lowurface energy) generated a homeotropic alignment in liquid crys-als, whereas the COOH and OH terminal regions (higher surfacenergy) gave rise to a planar alignment. The optical pattern formedy the different alignments of liquid crystals reflects the patternf the different chemical regions in the thiol SAMs. We showedhat the long-range tilted monolayers of fatty acids could align the

zimuthal orientation of liquid crystals into star and stripe patterns8,9].

∗ Corresponding author. Tel.: +1 407 882 1182; fax: +1 407 882 1462.E-mail address: jfang@mail.ucf.edu (J. Fang).

927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2011.11.035

© 2011 Elsevier B.V. All rights reserved.

The self-assembly of organosilanes has been widely used inengineering the surface of oxidized substrates, in which organosi-lanes bind covalently to the hydroxyl groups of the substratesurface and then cross-link to form a robust monolayer [10]. Theself-assembled organosilane monolayers have been used to alignliquid crystals [11–19]. For example, Lee and Clark showed thatthe boundary lines of silane monolayer stripes, which were formedby photolithography, could be used to align liquid crystals withoutthe need of molecular level anisotropy [14]. Price and Schwartzreported the alignment of liquid crystals on silane monolayerswith a wettability gradient and found a homeotropic-to-tilted ori-entation transition as the decrease of surface wettability [18].Phase-separated organosilane monolayers are attractive becausethey allow us to locally control the structure and propertiesof engineered surfaces. Due to the difference in the reactionkinetics of organosilanes, the direct control of the phase separa-tion in organosilane monolayers by the coassembly of differentorganosilanes still remains challenge [20–23]. Langmuir–Blodgett(LB) assisted assembly of organosilanes has been developedfor forming the phase-separated organosilane monolayers atthe microscale [24–26]. Here, we report the alignment of 4′-pentyl-4-cynobiphenyl (5CB) liquid crystal on the phase-separatedtwo-component monolayers that contain the protruding islandssurrounded by a continuous monolayer. The protruding islandsare formed by the LB assembly of an organosilane, while the sur-rounding monolayer is formed by the self-assembly of anotherorganosliane. Both parts of the phase-separated monolayers are

able to induce a homeotropic alignment of 5CB. The edge of theprotruding islands locally perturbs the homeotropic alignment of5CB, leading to the formation of ring patterns. The edge effect on the5CB alignment decreases with the decrease of the height difference

Physicochem. Eng. Aspects 395 (2012) 32– 37 33

ba

2

ctstmpwtaGa

iscws

wawsa

osm4itpa

3

altt[iHdOoAmoostTtewbtT

T. Bera et al. / Colloids and Surfaces A:

etween the protruding islands and the surrounding monolayernd increases with the decrease of the size of the protruding islands.

. Experimental

Octadecyltrichlorosilane (OTS) (Aldrich, 95% purity), tetrade-yltrichlorosilane (TTS) (Lancaster, 98% purity), and dodecyl-richlorosilane (DTS) (PCR, 97%) were used as received. Bovineerum albumin (BSA) was purchased from Aldrich. Chloroform andoluene (Fisher, >99%) were used as solvents which were dried with

olecular sieves prior to use. Water used in the experiments wasurified by Easypure II system (18 M� and pH 5.7). Mica substratesere freshly cleaved with an adhesive tape. To enhance the forma-

ion of siloxane bonds, the cleaved mica was treated with 0.5 Mqueous HCl solution for 2 h, followed by drying with nitrogen.lass substrates were cleaned in a solution of 70% H2SO4/30% H2O2t 100 ◦C for 60 min and then rinsed thoroughly with water.

Langmuir monolayers of OTS were prepared at the air–waternterface in a NIMA trough at 18 ◦C. The temperature of the waterubphase was controlled by water flow from a thermostat that cir-ulates through the base plate of the trough. The OTS monolayersere transferred from the air–water interface onto mica and glass

ubstrates with Langmuir–Blodgett (LB) technique.Atomic force microscopy (AFM) measurements were carried out

ith a Dimension 3100 (Veeco Instruments) in contact mode inir at room temperature. A silicon nitride cantilever (Nanosensors)ith a spring constant of 0.051 N/m was used for the scans. The

ize of the cantilever tips (radius of curvature) was about 15 nmccording to the manufacturer.

Liquid-crystal cells were constructed with a phase-separatedrganosilane monolayer-covered glass slide and a bare glasslide with a 25 �m Mylar spacer to image the phase-separatedonolayers with liquid crystals. Liquid crystal 5CB (4′-pentyl-

-cynobiphenyl) was filled into the cells by capillary action ints isotropic phase (above 35 ◦C) and then cooled down to roomemperature (22 ◦C). The anchoring transition of the 5CB on thehase-separated organosilane monolayers was characterized withn Olympus BX40 microscope with crossed polarizers.

. Results and discussion

It is known that the phase of Langmuir monolayers at their–water interface can be controlled by changing the molecu-ar area, pH, and temperature [27]. Previous studies have shownhat the monolayer behavior of octadecyltrichlorosilane (OTS) athe air–water interface depends on the pH of the water subphase28,29]. If the subphase pH is ∼2, the OTS molecules at the air–waternterface rapidly crosslink to form a densely packed monolayer.owever, the polymerization rate of OTS at the air–water interfaceecreases with the increase of subphase pH. In our experiments,TS was spread from chloroform with a concentration of 0.2 mg/mLnto the water subphase with pH 5.7 in Langmuir trough at 18 ◦C.fter chloroform was allowed to evaporate for 5 min, the OTSonolayer at the air–water interface was compressed at a speed

f 1.5 A/min. Fig. 1a shows the surface pressure-area isothermf an OTS monolayer at the air–water interface. The isothermhows a plateau at ∼16 mN/m. The plateau suggests the coexis-ence between a liquid-expended and a liquid-condensed phase.he existence of different phases provides an opportunity to controlhe density of OTS monolayers. The OTS monolayer in the liquid-xpended phase was transferred onto mica and glass substrates

ith the LB technique at a dipping speed of 5 mm/min and then

aked in an oven at 70 ◦C for 30 min. As can be seen from Fig. 1b,he transferred OTS monolayer on mica consists of micron islands.he height of the micron OTS islands is ∼27 A, which is close to

Fig. 1. (a) Surface pressure-area isotherm of an OTS monolayer at the air–waterinterface at 18 ◦C. The position for the OTS monolayer transfer is marked with anarrow. (b) AFM image of an OTS monolayer transferred on acid-treated mica.

the length of a fully extended OTS molecule. This suggests that thehydrocarbon chains of OTS molecules are oriented perpendicularto the substrate surface. The formation of the micron OTS islandsis believed to be a result of the breakup of the liquid-expendedphase after being transferred onto the substrates since the micronOTS islands was not observed at the air–water interface [30]. Thebreakup of the liquid-expended phase into small islands was alsoreported in the transferred monolayers of lipids and fatty acids[31–35].

By backfilling the OTS island-covered substrate with theself-assembly of dodecyltrichlorosilane (DTS) and tetradecyl-trichlorosilane (TTS), we formed phase-separated OTS/DTS andOTS/TTS monolayers with the same terminated group (CH3). Inour experiments, the OTS island-covered substrate was immersedin a 2.0 vol% solution of DTS, TTS, and OTS in toluene for 30 min,respectively. Finally, the phase-separated monolayer was bakedin an oven at 100 ◦C for 30 min. Fig. 2 shows AFM images of theOTS/DTS and OTS/TTS monolayers on mica. The phase-separationis observed in both the OTS/DTS and the OTS/TTS monolayers.The height difference between the protruding OTS islands andthe surrounding phase is ∼9.2 A for the phase-separated OTS/DTSmonolayer (Fig. 2a), which agrees with the chain length differ-ence between OTS and DTS. The height difference is ∼6.1 A for thephase-separated OTS/TTS monolayer (Fig. 2b), consisting with thechain length difference between OTS and TTS. The phase-separatedtwo-component silane monolayers are highly stable during AFM

multiscans at a loading force of 20 nN. On the phase-separatedOTS/DTS monolayers, the alignment of 5CB is homeotropic on boththe protruding micron OTS islands and the surrounding DTS mono-layer. Interestingly, the edge of the protruding micron OTS islands

34 T. Bera et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 395 (2012) 32– 37

F n acids al mic(

iipstossbO

Fi

ig. 2. AFM images of phase-separated OTS/DTS (a) and OTS/TTS (b) monolayers ourrounding DTS and TTS monolayers were formed by self-assembly. Polarizing opticd) monolayers. The arrows indicate the direction of polarizer and analyzer.

s lighted up as a bright ring in the polarizing optical microscopymage shown in Fig. 2c. The ring patterns around the edge of therotruding micron OTS islands are also observed for the phase-eparated OTS/TTS monolayers (Fig. 2d). However, the contrast ofhe ring patterns on the OTS/TTS is low, compared to that observedn the OTS/DTS monolayer. By backfilling the OTS island-covered

ubstrate with the self-assembly of OTS for 30 min, we form amooth OTS monolayer, in which the initially formed OTS islandsy the LB method are not distinguishable from the surroundingTS monolayer by the self-assembly technique (Fig. 3a). On the

ig. 3. (a) AFM image of a completed OTS monolayer. (b) Polarizing optical microscopy imndicate the direction of polarizer and analyzer.

-treated mica. The protruding OTS islands were prepared by the LB technique. Theroscopy images of the 5CB aligned by the phase-separated OTS/DTS (c) and OTS/TTS

OTS/OTS monolayer, 5CB shows a homeotropic alignment acrossthe entire monolayer (Fig. 3b). It is clear that the appearance ofthe ring patterns is a result of the disruption of the homeotropicalignment of 5CB by the edge of the protruding OTS islands. Fig. 4ais a height profile across a protruding OTS island in the phase-separated OTS/DTS monolayer. The height of the protruding OTS

island slightly decreases near its edge, which suggests that the pro-truding segments of OTS molecules at the edge of the island aretilted and/or bent to form a disordered boundary since they areexpected to have large freedom (Fig. 4b). It has been shown that

age of the 5CB aligned by the completed OTS monolayer. The arrows shown in (b)

T. Bera et al. / Colloids and Surfaces A: Physic

Fig. 4. (a) Height profile along the dashed line across a protruding OTS island in aphase-separated OTS/DTS monolayer. AFM image of the protruding OTS island wasiO

toibt2ooaodm

c

erature although the mechanism of the preferential adsorption has

Fi

nset in (a). (b) Schematic of the molecular disordering at the edge of the protrudingTS island in the phase-separated OTS/DTS monolayer.

he alignment of liquid crystals is sensitive to the packing densityf self-assembled monolayers [36,37]. Therefore, it is reasonable tonfer that the observed ring patterns in the aligned 5CB are inducedy the disordering of the OTS molecules near the edge of the pro-ruding islands. The width of the rings is measured to be about00 nm, which is larger than the disorder region near the edgef the protruding OTS islands (Fig. 4a). It is likely that the dis-rdered region around the edge of the protruding OTS islands ismplified by the orientational correlation of 5CB. The edge effectn the 5CB alignment decreases with the decrease of the heightifference between the protruding islands and the surrounding

onolayer.The organization in phase-separated silane monolayers can be

ontrolled by changing the condition under which they are formed.

ig. 5. (a) AFM image of a phase-separated monolayer containing densely packed OTS islanmage of the 5CB aligned by the phase-separated OTS monolayer. The arrows shown in (b

ochem. Eng. Aspects 395 (2012) 32– 37 35

We filled the OTS island-coated substrate with a self-assembledOTS monolayer with different packed densities by controlling theadsorption time. Fig. 5a shows a phase-separated monolayer con-taining the micron OTS islands surrounded by a loosely packedOTS monolayer. The loosely packed OTS monolayer was formed byimmersing the OTS island-coated substrate in a 2.0 vol% solution ofOTS in toluene for 5 min and then baked at 100 ◦C for 30 min. As canbe seen from Fig. 5a, the micron OTS islands have a smooth surface,while the small grains are clearly visible in the surrounding OTSmonolayers. We find that the alignment of the 5CB is homeotropicon the OTS islands and planar on the loosely packed OTS mono-layer (Fig. 5b). This result further confirms that the formation ofbright ring patterns on the OTS/DTS and OTS/TTS monolayers is aresult of the locally disruption of the 5CB alignment induced by thedisordering at the edge of the protruding OTS islands.

In addition, the formation of the OTS islands from the liquid-expended phase is due to the dewetting of the water film thatis transferred to the substrate. As the water film dewets, its sur-face decreases, which compresses the adsorbed OTS molecules intothe densely packed islands. Based on the hydrodynamic mech-anism of dewetting, the size of the densely packed OTS islandsdepends on the transfer speed [30]. The submicron OTS islands canbe formed by carrying out the LB transfer from the liquid-expendedphase at the dipping speed of 1 mm/min. By backfilling the sub-micron OTS island-covered substrates with a DTS monolayer, weform a phase-separated OTS/DTS monolayer in which the heightdifference between the protruding submicron OTS islands and thesurrounding DTS monolayer is ∼8.7 A (Fig. 6a). In this case, the edgeeffect on the alignment of the 5CB is overwhelming. Due to the ori-entation correlation of 5CB, the edge-induced disruption of the 5CBalignment extends to the top of the submicron OTS islands. The sub-micron OTS islands appear as bright dots in the polarizing opticalmicroscopy image shown in Fig. 6b. The brightness of these dotschanges when the sample is rotated in the plane.

Furthermore, we find that the preferential adsorption ofBSA on the protruding micron OTS islands of the phase-separated OTS/DTS monolayers can erase the homeotropicalignment of 5CB on the micron islands. In our experiments,the adsorption of BSA was carried out by exposing the phase-separated OTS/DTS monolayer to 0.04 �g/mL solution of BSA ina phosphate buffer (pH 7.0) for 10 min and then rinsed withwater. The BSA adsorbs preferentially on the protruding OTSislands (Fig. 7a), which agrees with the previous report in the lit-

not been fully understood [24]. However, at higher concentrationsor longer adsorption time, BSA was found to adsorb on all regionsof the phase-separated OTS/DTS monolayer. It is known that BSA is

ds surrounded by a loosely packed OTS monolayer. (b) Polarizing optical microscopy) indicate the direction of polarizer and analyzer.

36 T. Bera et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 395 (2012) 32– 37

Fig. 6. (a) AFM image of a phase-separated OTS/DTS monolayer containing submicron OTS islands surrounded by a continuous DTS monolayer. (b) Polarizing opticalmicroscopy image of the 5CB aligned by the phase-separated OTS/DTS monolayer. The arrows shown in (b) indicate the direction of polarizer and analyzer.

F b) Polm r.

astsotmstItm

soBtptaitsnae

ig. 7. (a) AFM image of BSA adsorbed on a phase-separated OTS/DTS monolayer. (onolayer. The arrows shown in (b) indicate the direction of polarizer and analyze

trimer that has the form of an equilateral triangle, 80 A on eachide and 30 A in height [38]. It is clear from Fig. 7a that most ofhe adsorbed BSA aggregate on the protruding OTS islands. Fig. 7bhows a polarizing optical microscopy image of the 5CB alignmentn the phase-separated OTS/DTS monolayer with the preferen-ially adsorbed BSA. The alignment of 5CB on the surrounding DTS

onolayer remains unchanged. However, the adsorption of BSA isufficient to erase the homeotropic alignment of 5CB on the pro-ruding OTS islands, leading to the formation of bright domains.n other word, the anchoring transition of 5CB allows us to detecthe preferential adsorption of BSA on the phase-separated OTS/DTS

onolayers.In summary, we report the alignment of 5CB on the phase-

eparated two-component organosilane monolayers that consistf the protruding islands surrounded by a continuous monolayer.oth parts of the phase-separated silane monolayers have the CH3erminated surface. The molecular disordering at the edge of therotruding islands locally abrupts the alignment of 5CB, leadingo the formation of ring patterns. The edge effect on the 5CBlignment depends on the height difference between the protrud-ng islands and the surrounding monolayer as well as the size ofhe protruding islands. Our results also suggest that the phase

eparation of the organosilane monolayers with the same termi-al group can be imaged by using liquid crystals as an opticalmplification probe without the need for complex and expensivequipments.

arizing optical microscopy image of the 5CB aligned on the BSA-adsorbed OTS/DTS

Acknowledgment

This work was supported by the National Science Foundation(CBET 0931778).

References

[1] P.G. De Gennes, The Physics of Liquid Crystals, Clarendon, Oxford, 1974.[2] B. Jerome, Surface effects and anchoring in liquid crystals, Rep. Prog. Phys. 54

(1991) 391–451.[3] V.K. Gupta, N.L. Abbott, Design of surfaces for patterned alignment of liquid

crystal from odd and even alkanethiols, Phys. Rev. E 54 (1996) R4540–R4543.[4] V.K. Gupta, N.L. Abbott, Design of surfaces for patterned alignment of liquid

crystals on planar and curved substrates, Science 276 (1997) 1533–1536.[5] S.D. Evans, H. Allinson, N. Boden, T.M. Flynn, J.M. Henderson, Surface plasmon

resonance imaging of liquid crystal anchoring on patterned self-assembledmonolayers, J. Phys. Chem. B 101 (1997) 2143–2148.

[6] Y.L. Cheng, D.N. Batchelder, S.D. Evans, J.R. Henderson, J.E. Lydon, S.D. Ogier,Imaging of micropatterned self-assembled monolayers with adsorbed liquidcrystals, Liq. Cryst. 27 (2000) 1267–1275.

[7] J.P. Bramble, D.J. Tate, D.J. Revill, K.H. Sheikh, J.R. Henderson, F. Liu, X. Zeng,G. Ungar, R.J. Bushby, S.D. Evans, Planar alignment of columnar ciscotic liquidcrystals by isotropic phase dewetting on chemically patterned surfaces, Adv.Funct. Mater. 20 (2010) 914–920.

[8] J.Y. Fang, U. Gehlert, R. Shashidar, C.M. Knobler, Imaging the azimuthal tilt

order in monolayers by liquid crystal optical amplification, Langmuir 15 (1999)297–299.

[9] W. Liang, T. Bera, X. Zhang, A.J. Gesquiere, J.Y. Fang, Boojum and stripe tex-tures in long-range orientationally ordered monolayers on solid substrates,Langmuir 27 (2011) 1051–1055.

Physic

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

T. Bera et al. / Colloids and Surfaces A:

10] J. Sagiv, Organized monolayers by adsorption. I. Formation and structure ofoleophobic mixed monolayers on solid surfaces, J. Am. Chem. Soc. 102 (1980)92–98.

11] J. Cognard, Alignment of nematic liquid crystals and their mixtures, Mol. Cryst.Liq. Cryst. Suppl. 78 (1982) 1–75.

12] J. Naciri, J.Y. Fang, D. Shenoy, C. Dulcey, R. Shashidhar, Photosensitive tri-ethoxysilane derivatives for alignment of liquid crystals, Chem. Mater. 12(2000) 3288–3295.

13] J.Y. Fang, G. Whitaker, M.S. Chen, J. Naciri, R. Shashidhar, Synthesis andphotodimerization in self-assembled monolayers of 7-(8-trimethoxysilylo-ctyloxy)coumarin, J. Mater. Chem. 12 (2001) 2992–2995.

14] B.W. Lee, N.A. Clark, Alignment of liquid crystals with patterned isotropic sur-faces, Science 291 (2001) 2576–2580.

15] D.M. Walba, C.A. Liberko, R. Shao, N.A. Clark, Ferroelectric liquid crystal align-ment using self-assembled monolayers, Liq. Cryst. 29 (2002) 1015–1024.

16] J.G. Fonseca, J. Hommet, Y. Galerne, Surface structure and anchoring prop-erties of modified self-assembled monolayers, Appl. Phys. Lett. 82 (2003)58–60.

17] D.M. Walba, C.A. Liberko, E. Körblova, M. Farrow, T. Zurtak, B.C. Chow, D.K.Schwartz, A.S. Freeman, K. Douglas, S.D. Williams, A.F. Klittnick, N.A. Clark, Self-assembled monolayers for liquid crystal alignment: simple preparation on glassusing alkyltrialkoxysilanes, Liq. Cryst. 31 (2004) 481–489.

18] A.D. Price, D.K. Schwartz, Anchoring of a nematic liquid crystal on a wettabilitygradien, Langmuir 22 (2006) 9753–9759.

19] S.M. Malone, D.K. Schwartz, Polar and azimuthal alignment of a nematic liquidcrystal by alkylsilane self-assembled monolayers: effects of chain-length andmechanical rubbing, Langmuir 24 (2008) 9790–9794.

20] D.A. Offord, J.H. Griffin, Kinetic control in the formation of self-assembled mixedmonolayers on planar silica substrates, Langmuir 9 (1993) 3015–3025.

21] R. Banga, J. Yarwood, A.M. Morgan, B. Evans, J. Kells, FTIR and AFM studiesof the kinetics and self-assembly of alkyltrichlorosilanes and (perfluo-roalkyl)trichlorosilanes onto glass and silicon, Langmuir 11 (1995) 4393–4399.

22] Y. Tong, E. Tyrode, M. Osawa, N. Yoshida, T. Watanabe, A. Nakajima, S. Ye, Prefer-ential adsorption of amino-terminated silane in a binary mixed self-assembled

monolayer, Langmuir 27 (2011) 5420–5426.

23] L. Patrone, V. Gadenne, S. Desbief, Single and binary self-assembled mono-layers of phenyl- and pentafluorophenyl-based silane species, and theirphase separation with octadecyltrichlorosilane, Langmuir 26 (2010) 17111–17118.

[

[

ochem. Eng. Aspects 395 (2012) 32– 37 37

24] J.Y. Fang, C.M. Knobler, Phase-separated two-component self-assembledorganosilane monolayers and their use in selective adsorption of a protein,Langmuir 12 (1996) 1368–1374.

25] J.Y. Fang, C.M. Knobler, M. Gingery, F.A. Eiserling, Imaging bacteriophage T4on patterned organosilane monolayers by scanning force microscopy, J. Phys.Chem. B 101 (1997) 8692–8695.

26] K. Kojio, A. Takahara, T. Kajiyama, Molecular aggregation state and molecu-lar motion of organosilane monolayers prepared at the air/water interface,Langmuir 16 (2000) 9314–9320.

27] C.M. Knobler, Seeing phenomena in flatland: studies of monolayers by fluores-cence microscopy, Science 249 (1990) 870–884.

28] S.W. Barton, A. Goudot, F. Rondelez, X-ray structural study of polymerizedoctyldecyltrichlorosilane on water, Langmuir 7 (1991) 1029–1030.

29] I. Bourdieu, J. Daillant, D. Chatenay, A. Brasiau, D. Colson, Buckling of polymer-ized monomolecular films, Phys. Rev. Lett. 72 (1994) 1502–1505.

30] J.Y. Fang, C.M. Knobler, Control of density in self-assembled organosilanemonolayers by Langmuir–Blodgett deposition, J. Phys. Chem. 99 (1995)10426–10429.

31] L.F. Chi, M. Anders, H. Fuchs, J.J. Johnston, H. Ringsdorf, Domain-structures inLangmuir–Blodgett films investigated by atomic force microscopy, Science 259(1993) 213–215.

32] J.M. Mikrut, P. Dutta, J.B. Ketterson, R.C. MacDonald, Atomic-force andfluorescence microscopy of Langmuir–Blodgett monolayers of l-alpha-dimyristoylphosphatidic acid, Phys. Rev. B 48 (1993) 14479–14487.

33] H.D. Sikes, J.T. Woodward, D.K. Schwartz, Pattern formation in a substrate-induced phase transition during Langmuir–Blodgett transfer, J. Phys. Chem.100 (1996) 9093–9097.

34] J.Y. Fang, E. Teer, C.M. Knobler, K.K. Loh, J. Rudnick, Boojums and the shapes ofdomains in monolayers, Phys. Rev. E 56 (1997) 1859–1868.

35] U. Gehlert, J.Y. Fang, C.M. Knobler, Relating the organization of the molecular tiltazimuth to lateral-force images in monolayers transferred to solid substrates,J. Phys. Chem. B 102 (1998) 2614–2617.

36] M. Barmentlo, F.R. Hoekstra, N.R. Willard, R.W.J. Hollering, Optical 2nd-harmonic-generation study of the interaction of silane-covered surfaces withliquid crystal layers, Phys. Rev. A 43 (1991) 5740–5743.

37] W.J. Miller, V.K. Gupta, N.L. Abbott, M.W. Tsao, J.F. Rabolt, Comparison of theanchoring of nematic liquid crystals on self-assembled monolayers formedfrom semifluorinated thiols and alkanethiols, Liq. Cryst. 23 (1997) 175–184.

38] X.M. He, D.C. Carter, Atomic structure and chemistry of human serum albumin,Nature 358 (1992) 209–215.