Phase transitions in mixed Langmuir films of 8CB and stearic acid

Enderle, Th.; Meixner, A. J.; Zschokke‐Gränacher, I.

doi:10.1063/1.467487

Cited by 25 publications

(13 citation statements)

References 26 publications

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“…72 The linear and nonlinear optical properties of the nCB films have been extensively studied as model systems for understanding of the structure and phase transitions of the LCs with theoretical importance and potential technological use. [73][74][75][76] Studies on the structure and film stability of the nCB and nCT monolayers, and the binary monolayers with a mixture of the nCB or the nCT with other surface active molecules at the air/water interface have also been pursued using surface second harmonic generation (SHG) techniques 7,77,78 and surface pressure and Brewster angle microscopy (BAM). 7,[63][64][65][66][67][68][69][70][71] The phase diagram and phase behaviour of the 8CB or 5CB and the 5CT Langmuir monolayes are significantly different.…”

Section: Resultsmentioning

confidence: 99%

“…The molecular detail of the orientational order of the 8CB Langmuir monolayer before and after the transition between Regions I and II was quantitatively analyzed with a surface second harmonic generation (SHG) measurement in different polarization combinations. 58,77 It was found that a continuous orientational distribution narrowing (ODIN) process started before Region II and ended at just the transition point of the surface pressure, where a closely packed homogeneous monolayer was finally formed to give a steep rise of the surface pressure under further compression. 58 Using BAM, Inglot and co-workers studied the nCB Langmuir monolayers and found that for 4 r n r 12 their phase diagram and phase behaviour were both similar to those of the 8CB monolayer.…”

Section: Resultsmentioning

confidence: 99%

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Water penetration/accommodation and phase behaviour of the neutral langmuir monolayer at the air/water interface probed with sum frequency generation vibrational spectroscopy (SFG-VS)

Zhang

Dong

Guo

et al. 2009

Phys. Chem. Chem. Phys.

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A strong and broad hydrogen bonded O-H band around 3520 cm(-1) is observed in the insoluble monolayer of the neutral liquid crystal molecules of 4''-n-pentyl-4-p-cyanobiphenyl (5CB) and 4''-n-octyl-4-p-cyanobiphenyl (8CB) throughout the whole surface density range, but not in the 4-pentyl-4'-cyanoterphenyl (5CT) monolayer, at the air/water interface. This novel spectral feature suggests the existence of an oriented water cluster species which has penetrated or accommodated into the Langmuir monolayer of the 8CB and 5CB molecules. This finding provided a molecular level mechanism for the stark difference in the phase behaviour between the CB and CT insoluble Langmuir monolayers at the air/water interface. It also calls for attention to the details of the specific water-surface interaction in mediating the structure and the phase behaviour of the molecular assemblies at the heterogeneous aqueous interfaces.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Water penetration/accommodation and phase behaviour of the neutral langmuir monolayer at the air/water interface probed with sum frequency generation vibrational spectroscopy (SFG-VS)

Zhang

Dong

Guo

et al. 2009

Phys. Chem. Chem. Phys.

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“…The components of the dielectric tensor then follow from ε ∥ = = 2.86 and ε ⊥ = = 2.34. We also set φ equal to − 71° and the monolayer thickness (to which the results are not very sensitive) d 1 to 1.2 nm. Computed images of the splay−bend structure 27 of the defects in the 10CB monolayers were generated for a range of values of ε x ‘ , which is related to ε y ‘ through eq 16.…”

Section: Experimental Methodsmentioning

confidence: 99%

Determination of the Thickness and Optical Properties of a Langmuir Film from the Domain Morphology by Brewster Angle Microscopy

Mul

Mann

1998

Langmuir

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A method employing Brewster angle microscopy was developed to measure the relative thickness of monolayers and multilayers at the air−water interface. Results proved that multilayers in ultrathin films of 8CB (4‘-n-alkyl[1,1‘-biphenyl]-4-carbonitrile; nCB, n = 8) are built up from one or two stacked bilayers on top of a monolayer at the air−water interface covered by a continuous bilayer. In addition, the fan texture of the mixed splay-bend disclination defects, which are formed in 10CB monolayers on reverse collapse of a continuous trilayer, was used to obtain estimates for the components of the anisotropic dielectric constant of the monomolecular film. This estimate was made by comparing experimental images with computationally generated model images based on an assumed director distribution around the defect. The results support the validity of the folding mechanism of multilayer generation and reverse collapse as opposed to the condensation mechanism. Finally, comparison of the experimental and theoretical values of the ratio of the multilayer thickness and the monolayer thickness indicates that at this level the water−film interface cannot be assumed to be sharp or well defined.

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“…A number of papers have described the application of SHG for studies of the tilt angle of 8CB and related molecules in monolayers including Langmuir films at the air/water interface. − In most cases, a simplified analysis has been used in which it is assumed that β zzz is the only nonzero element of β (2) . In the simplified analysis, the ratio of susceptibility elements χ ZXX /χ ZZZ is obtained from measurements of SHG using selected plane-polarized states of fundamental and second harmonic radiation. ,, The tilt angle, θ o , of the chromophore relative to the surface normal, Z , is then obtained by using eq 2.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear Susceptibility of a Cyanobiphenyl Derivative at the Air/Water Interface: Improved Measurement of Molecular Orientation by Optical Second Harmonic Generation

2005

J. Phys. Chem. B

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The nonlinear susceptibility tensor, chi(2), for second harmonic generation (SHG) by a monolayer of the cyanobiphenyl derivative 4-n-octyl-4'-cyanobiphenyl (8CB) at the air/water interface has been measured with the fundamental frequency variant Planck's over 2piomega=1.55 eV (lambda=800 nm). The contribution of the water subphase was estimated by measuring the magnitudes and relative phases of the nonlinear susceptibilities of the bare and monolayer-covered water surfaces. All nonzero elements of chi(2) are placed on an absolute scale by comparison with SHG in reflection from a z-cut quartz crystal. The experimental measurements for the 8CB monolayer are compared with computed susceptibilities derived by using standard time-dependent perturbation theory in conjunction with a semiempirical electronic structure model. Good agreement has been found between experimental and computational results when the average tilt angle of the cyanobiphenyl chromophore of 8CB is in the range 60-70 degrees relative to the surface normal. A critique is given of an alternative, simplified measurement procedure of the tilt angle in which only the dominant element of the molecular hyperpolarizability tensor is considered. It is shown that the simplified procedure is invalid for 8CB monolayers when the tilt angle is greater than approximately 70 degrees.

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Phase transitions in mixed Langmuir films of 8CB and stearic acid

Abstract: Articles you may be interested inAnalysis of linear and quadratic optical response of mixed Langmuir-Blodgett films of stearic acid and 5-CT Effects of surface tension of substrate on annealing of evaporated stearic acid film

Cited by 25 publications

References 26 publications

Water penetration/accommodation and phase behaviour of the neutral langmuir monolayer at the air/water interface probed with sum frequency generation vibrational spectroscopy (SFG-VS)

Water penetration/accommodation and phase behaviour of the neutral langmuir monolayer at the air/water interface probed with sum frequency generation vibrational spectroscopy (SFG-VS)

Determination of the Thickness and Optical Properties of a Langmuir Film from the Domain Morphology by Brewster Angle Microscopy

Nonlinear Susceptibility of a Cyanobiphenyl Derivative at the Air/Water Interface: Improved Measurement of Molecular Orientation by Optical Second Harmonic Generation

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