Browsing by Author "Song, KJ"

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Molecular conformation and nanomechanics of self-assembled alkylsiloxane monolayers
(1997-01-08)
Huang, JY
;
Song, KJ
;
Lagoutchev, A
;
Yang, PK
;
Chuang, TJ
We have studied the chain conformation and nanomechanical properties of pure alkylsiloxane monolayers and the mixed films with fluorine-containing species using scanning force microscopy (SFM) and infrared-visible sum-frequency generation spectroscopy (IV-SFG). Our IV-SFG spectra yield information about the chain ordering and surface density of specific species in the pure and mixed monolayers. A film formation process involving preferential adsorption of the fluorinated species from solution was observed. On the basis of the SFM measurements, the stiffness of alkylsiloxane monolayers under load was found to increase with the chain length, changes of chain conformation, and alkyl chain fluorination.
Molecular conformation and nanomechanics of self-assembled alkylsiloxane monolayers
(1997-01-08)
Huang, JY
;
Song, KJ
;
Lagoutchev, A
;
Yang, PK
;
Chuang, TJ
We have studied the chain conformation and nanomechanical properties of pure alkylsiloxane monolayers and the mixed films with fluorine-containing species using scanning force microscopy (SFM) and infrared-visible sum-frequency generation spectroscopy (IV-SFG). Our IV-SFG spectra yield information about the chain ordering and surface density of specific species in the pure and mixed monolayers. A film formation process involving preferential adsorption of the fluorinated species from solution was observed. On the basis of the SFM measurements, the stiffness of alkylsiloxane monolayers under load was found to increase with the chain length, changes of chain conformation, and alkyl chain fluorination.
Self-assembly of alkylsiloxane monolayers on fused silica studied by XPS and sum frequency generation spectroscopy
(1998-01-15)
Lagutchev, AS
;
Song, KJ
;
Huang, JY
;
Yang, PK
;
Chuang, TJ
Infrared-visible sum frequency generation (SFG) vibrational spectroscopy in the C-H stretching region was used to study a set of self-assembled monolayers, formed from octyltrichlorosilane [CH3(CH2)(7)SiCl3], its partially fluorinated analog, (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-trichlorosilane [CF3-(CF2)(5)(CH2)(2)SiCl3] and their mixtures. SFG measurements were complemented with transmission-absorption FTIR spectroscopy and X-ray photoemission spectroscopy. Simultaneous self-assembly of both chlorosilanes results in preferential deposition of the fluorinated compound. The major reason for this behavior is the alkyl chain fluorination. There is a strong spectroscopic evidence of close coadsorption of fluorinated and non-fluorinated molecules in mixed monolayers. It follows that the species in self-assembled monolayers of binary composition do not segregate into different phases as it is observed for similar Langmuir-Blodgett films. Distinct differences found in SFG spectra of fluorinated and non-fluorinated samples indicate that SFG spectroscopy is much more sensitive than FTIR in detection of symmetry distortions in the alkyl chain of the amphiphiles. Both SFG and FTIR spectroscopic data show the presence of hydrocarbon residue in fluorinated and mixed films that is very likely due to hexadecane used as a solvent during monolayer deposition. (C) 1998 Elsevier Science B.V.
Sum-frequency vibrational spectroscopic study of mixed alkylsiloxane monolayers self-assembled on fused silica surface
(1997-10-01)
Lagutchev, AS
;
Song, KJ
;
Huang, JY
;
Yang, PK
;
Chuang, TJ
Self-assembled monolayers of fluorinated and non-fluorinated alkylsiloxanes were prepared on fused silica substrates and studied by both conventional IR and nonlinear sum-frequency vibrational spectroscopy complemented with XPS. Simultaneous self-assembly of the two alkylsiloxanes results in preferential adsorption of the fluorinated compound and formation of the mixed monolayer. Different species are found to be closely coadsorbed in the mixed monolayers which distinguishes self-assembly from Langmuir-Blodgett deposition where the similar species tend to separate into different phases. Nonlinear sum-frequency spectroscopy of C-H stretching region detects symmetry perturbations of the alkyl chain induced by trans-cis defects and partial fluorination and clearly distinguishes between them. All three characterization methods consistently indicate the presence of a hydrocarbon residue in all deposited monolayers, which is ascribed to the hexadecane used as a solvent during the self-assembly process. (C) 1997 Elsevier Science S.A.