TY - JOUR

T1 - Effect of nanometer-scale phase separation on wetting of binary self-assembled thiol monolayers on Au(111)

AU - Imabayashi, Shin Ichiro

AU - Gon, Narutoshi

AU - Sasaki, Takayuki

AU - Hobara, Daisuke

AU - Kakiuchi, Takashi

PY - 1998/4/28

Y1 - 1998/4/28

N2 - The advancing contact angle of water has been measured on three types of the binary self-assembled monolayers (SAMs) on Au(111) with known surface structure at nanometer scale: a homogeneously mixed SAM of undecanethiol (UDT) and 11-mercaptoundecanoic acid (MUDA) (1), a SAM of hexadecanethiol (HDT) and 3-mercaptopropionic acid (MPA) phase-separated into nanometer-scale domains with different heights (2), and a SAM of UDT and MUDA artificially phase-separated into nanometer-scale domains having approximately equal heights (3). The homogeneously mixed SAM, 1, shows a linear variation of the cosine of the contact angle, cos θ, with the surface mole fraction of COOH-terminated thiol, xsurfCOOH, while in the case of 2 the cos θ versus xsurfCOOH plot is strongly concave; the cos θ depends little on xsurfCOOH for xsurfCOOH < 0.5 and abruptly increases with xsurfCOOH for xsurfCOOH > 0.5. In contrast, the phase-separated SAM, 3, shows a linear variation of cos θ with xsurfCOOH, as is the case of 1, indicating that the contact angle does not reflect the phase separation in nanometer scale. The difference in the height of the domains of the two thiols is the primary factor for the nonlinear cos θ versus xsurfCOOH plot for 2. The Young-Laplace equation explains the nonwetting of the lower domains of 2.

AB - The advancing contact angle of water has been measured on three types of the binary self-assembled monolayers (SAMs) on Au(111) with known surface structure at nanometer scale: a homogeneously mixed SAM of undecanethiol (UDT) and 11-mercaptoundecanoic acid (MUDA) (1), a SAM of hexadecanethiol (HDT) and 3-mercaptopropionic acid (MPA) phase-separated into nanometer-scale domains with different heights (2), and a SAM of UDT and MUDA artificially phase-separated into nanometer-scale domains having approximately equal heights (3). The homogeneously mixed SAM, 1, shows a linear variation of the cosine of the contact angle, cos θ, with the surface mole fraction of COOH-terminated thiol, xsurfCOOH, while in the case of 2 the cos θ versus xsurfCOOH plot is strongly concave; the cos θ depends little on xsurfCOOH for xsurfCOOH < 0.5 and abruptly increases with xsurfCOOH for xsurfCOOH > 0.5. In contrast, the phase-separated SAM, 3, shows a linear variation of cos θ with xsurfCOOH, as is the case of 1, indicating that the contact angle does not reflect the phase separation in nanometer scale. The difference in the height of the domains of the two thiols is the primary factor for the nonlinear cos θ versus xsurfCOOH plot for 2. The Young-Laplace equation explains the nonwetting of the lower domains of 2.

UR - http://www.scopus.com/inward/record.url?scp=0032045417&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0032045417&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0032045417

VL - 14

SP - 2348

EP - 2351

JO - Langmuir

JF - Langmuir

SN - 0743-7463

IS - 9

ER -