Molecular dipoles at substrate/film interfaces influencing surface energy of Langmuir-Blodgett films

Langmuir and Langmuir-Blodgett (LB) films of novel rigid Schiff base amphiphiles with different polar groups on aromatic rings have been studied at air/water interfaces and on solid substrates. The local surface potentials for the different substituents on the aromatic groups of the amphiphiles are correlated to the surface energy of LB films on solid substrates. Their contributions are probed on high-surface-energy (hsfe) quartz and hydrophobically modified low-surface-energy (lsfe) quartz. Using theoretical estimates, the long-range effects of the substituents of the polar groups on the alkyl chains have been studied from charge on the carbon and hydrogen atoms of the alkyl tails. The calculations indicate that a substituted carbon atom has a charge that is directly dependent on the nature of the atoms to which it is attached rather than on the charges of any other atoms of the substituents. This work shows that the polar substituents on the head group clearly influence the distal methylene groups of the tail. Thus, any treatment, either theoretical or experimental, of these films in contact with solid substrates should include the local relative permitivities of the polar moieties, which seem to play an important role in determining macroscopic properties such as surface energy.     

Adhesion and friction properties of molecularly thin perfluoropolyether liquid films on solid surface

The adhesion and friction properties of molecularly thin perfluoropolyether (PFPE) lubricant films dip-coated on a diamond-like carbon (DLC) overcoat of magnetic disks were studied using a pin-on-disk-type micro-tribotester that we developed. The load and friction forces were simultaneously measured on a rotating disk surface under an increasing/decreasing load cycle and slow sliding conditions. Experiments were performed using two types of PFPE lubricants: Fomblin Z-tetraol2000S with functional end-groups and Fomblin Z-03 without any end-group. The curves of the friction force as a function of the applied load agree with the curves estimated using the Johnson-Kendall-Roberts (JKR) model. The friction forces on the Z-03 films having different thicknesses were not found to decrease drastically; however, the friction forces on the Z-tetraol film were found to decrease drastically when the film thickness is more than ~1.2 nm. This drastic change in the case of the Z-tetraol film is estimated to be affected by the coverage of the lubricant film.     

Autophobic dewetting of Z-tetraol perfluoropolyether lubricant films on the amorphous nitrogenated carbon surface

The thermodynamic stability of thin films of the perfluoropolyether (PFPE) Z-Tetraol, as a function of molecular weight, on amorphous nitrogenated carbon, CNx, is investigated. An optical surface analyzer is used to image the autophobic dewetting of the Z-Tetraol films. Film dewetting results when the PFPE film thickness applied to the CNx surface exceeds a critical value. This critical dewetting thickness is identified as the monolayer thickness of the adsorbed PFPE film via measurements of the changes in the surface energy as a function of lubricant film thickness. The observed dewetting coincides with the film thickness at which the disjoining pressure goes to zero. The critical dewetting thickness is dependent on the PFPE molecular weight.     

The stability of ultra-thin perfluoropolyether mixture films on the amorphous nitrogenated carbon surface

The thermodynamic stability of boundary lubricant films based upon mixtures of liquid perfluoropolyethers (PFPEs) is reported. Mixtures of A20H-2000 with Zdols 2000, 2500, and 4000 and Zdol-TX 2200 on amorphous carbon nitride films are investigated. An optical surface analyzer is used to image the autophobic dewetting of the mixture PFPE films. The critical dewetting thickness coincides with the monolayer thickness of the adsorbed mixture PFPE films as determined by the changes in the surface energy as a function of lubricant film thickness. The critical dewetting thickness varies linearly with mixture concentration.     

3-三氟甲基联苯的合成

以3-三氟甲基苯胺为原料,叔丁醇亚硝酸酯为重氮化试剂,铜粉为催化剂,采用改良的Gomberg反应合成了3-三氟甲基联苯。最佳的反应条件为：3-三氟甲基苯胺20mmol,叔丁醇亚硝酸酯的用量为3-三氟甲基苯胺摩尔数的两倍,Cu的用量为3-三氟甲基苯胺摩尔数的0．6倍,于在40℃反应5h,其结构经^1H NMR,^13C NMR和IR表征。     

Peroxidic perfluoropolyether for the covalent binding of perfluoropolyether chains on carbon black surface

Peroxidic perfluoropolyethers (PFPEs) are suitable tools for the covalent linkage of fluorinated groups on substrates containing aromatic moieties. Thus the thermal decomposition process of such fluorinated peroxides allowed the covalent linkage of PFPE radicals to the polycyclic aromatic structure of a graphitic carbon black. Contact angle measurements on molded pellets made with modified carbon black powders revealed a gradual enhancement of the hydrophobicity, which follows the increase of the fluorine content on the surface according to XPS experiments. BET analyses also revealed variations of the surface area of carbonaceous samples. Products and by-products were also evaluated by mass balances of decomposed portions of PFPE residues, respectively, PFPE chains bonded on carbon black and PFPE fluids obtained by homocoupling side-reactions. Modified carbonaceous materials were analyzed by solid state ¹⁹F-MAS NMR and the results are in agreement with the proposed radical mechanism.     

1-[2′,4′-二氟-(1,1′-联苯)-4-基苯基甲基]-咪唑的合成

以2,4-二氟联苯为起始原料,经酰化反应制得2′,4′-二氟-(1,1′-联苯)-4-基苯基甲酮(2);2经NaBH4还原得2′,4′-二氟-(1,1′-联苯)-4-基苯基甲醇(3);3经氯代得2′,4′-二氟-(1,1′-联苯)-4-基苯基氯甲烷(4);4与咪唑发生亲核取代反应合成了1-[2′,4′-二氟-(1,1′-联苯)-4-基苯基甲基]-咪唑(5). 2～5为新化合物,其结构经1H NMR, IR, MS和元素分析确证.     

Molecular dynamics and residual entropy in the soft crystal, SmE phase, of 4-butyl-4'-isothiocyano-1,1'-biphenyl

Molecular dynamics and resulting disorder in the soft crystal, smectic E (SmE) phase, were studied in detail for the title compound, 4-butyl-4'-isothiocyano-1,1'-biphenyl (4TCB), by (1)H NMR spectroscopy and adiabatic calorimetry. The ordered crystal phase of 4TCB was realized for the first time under ambient pressure after long two-step annealing and used as the reference state in the analysis of the experimental results. Four motional modes were identified in the SmE phase through the analysis of the (1)H NMR T(1). The residual entropy was determined as ca. 6 J K(-1) mol(-1). This magnitude implies that most of the disorder in the SmE phase at high temperatures is removed on cooling except for the head-to-tail disorder of the rod-shaped 4TCB molecule. Standard thermodynamic functions are tabulated below 375 K.     

Langmuir-Blodgett films of diazobenzene molecules

Langmuir-Blodgett (LB) films from diazobenzene Sudan III have been investigated using surface potential measurements as a function of number of layers and deposition pressures, with the surface potential data being related to molecular dipole moments obtained from theoretical electronic structure calculations. The surface potential increased with the number of layers for SIII LB films, and then tended to saturate. Results from density functional theory (DFT) and UV-vis spectroscopy indicated that the increase is due to addition of layers with oriented molecular dipoles, with the saturation tendency being attributed to a decrease in the amount of material deposited in each layer. The surface potential increased with the surface pressure used for deposition, probably owing to a higher contribution from the vertical component of the dipole moment as a closer molecular packing, which is associated with decreasing conformational entropy, was reached.     

4-{[Mono/dimethyl(1,1'-biphenyl)-4-yl]oxy}phthalonitriles and Phthalocyanines Based on Them

4-{[Mono/dimethyl(1,1'-biphenyl)-4-yl]oxy}phthalonitriles have been obtained by nucleophilic substitution of nitro group in 4-nitrophthalonitrile. The prepared phthalonitriles have been used for the synthesis of tetra-4-{[mono/dimethyl(1,1'-biphenyl)-4-yl]oxy}phthalocyanines and their complexes with copper, cobalt, and zinc. Spectral characteristics and thermal stability of the prepared compounds have been investigated.     

Langmuir-Blodgett thin films of quantum dots: synthesis, surface modification, and fluorescence resonance energy transfer (FRET) studies

We describe herein studies on as-prepared hydrophobic ZnS-CdSe quantum dots (QDs) at the air-water interface. Surface pressure-area (pi-A) isotherms have been used to study the monolayer behavior. Uniform, lamellar multilayer thin films of QDs were deposited by the Langmuir-Blodgett (LB) technique. The role of two different surfactant systems commonly employed in the synthesis of these QDs (trioctylphosphine oxide-octadecylamine (TOPO-ODA) system and trioctylphosphine oxide-tetradecylphosphonic acid (TOPO-TDPA) system) on the monolayer behavior and the quality of thin films produced has been investigated. The thin films were characterized by quartz crystal microgravimetry (QCM), contact angle measurements, fluorescence spectroscopy, and transmission electron microscopy (TEM). These QD films were further modified by an amphiphilic polymer, poly(maleic anhydride-alt-1-tetradecene) (PMA). The hydrophobic interaction between the polymers and the surfactants attached to the QDs drove the self-assembly process. The carboxylic acid functional groups in the polymer were also used to immobilize avidin. We have demonstrated a proof of concept for the biosensing strategy wherein the avidin-coated QD films attracted biotinylated gold nanoparticles, resulting in fluorescence resonance energy transfer (FRET) quenching of the thin films.     

Photocurrent amplification by an energy/electron transfer cascade in polymer Langmuir-Blodgett films

Effective photocurrent generation by visible light irradiation on hetero-deposited polymer Langmuir-Blodgett (LB) films containing tris(bipyridine) ruthenium(II) (Ru(bpy)3(2+)) and anthracene derivatives was observed. The photocurrent amplification was found to be assisted by the photoinduced energy/electron transfer cascade, which consists of the interlayer triplet-triplet energy transfer process from photoexcited Ru(bpy)3(2+) to anthracene, and then electron transfer processes from the triplet anthracene to a viologen acceptor, from Ru(bpy)3(2+) to the oxidized anthracene and from the electrode to Ru(bpy)3(3+).     

Equivalent anchoring energy formula of a NLC on a grating surface and VCT effect

The voltage-controlled twist (VCT) effect shows that a grating surface, with its particular anchoring properties, has the potential to become a new surface anchoring for liquid crystal devices. In order to describe these properties an equivalent anchoring energy is introduced. The alignment of a nematic liquid crystal (NLC) on such a grating originates from two mechanisms, so each produces a term in the equivalent anchoring energy. One is the interaction potential between NLC molecules and the molecules on the substrate surface, from which we derive the expression of the corresponding term. The other is the increased elastic strain energy, for which we adopt the result of Berreman. The equivalent anchoring energy obtained is a function of pitch λ and amplitude δ of the grating surface. Both the corresponding strength parameter and the easy direction are functions of λ and δ. The hybrid aligned nematic cell proposed by. Bryan-Brown et al. is studied by the use of our formula, and the distribution of the director, the saturation state and the saturation voltage are calculated in detail. The results are consistent with experimental data, especially the values of λ and δ. The VCT effect can therefore be explained.     

Excimer laser ablation of Langmuir-Blodgett films

Photoablation of several Langmuir-Blodgett (LB) films on Silicon substrates was performed at the excimer laser wavelength of 248 nm. This is a fast, solvent-free, one-step method for structuring thin organic films. Structures were produced both by projection of a mask and also using direct writing of the laser beam, yielding feature sizes on the order of microns. Spectral analysis of the remaining material showed no change compared to the unexposed material, suggesting that no degradation has occurred. This technique appears to be viable for use in the lithography of LB films.     

Synthesis and Properties of Tetra-4-{[(1,1'-biphenyl)-4-yl]oxy}phthalocyanines and Their Sulfonic Acid Derivatives

The template condensation of 4-{[(1,1'-biphenyl)-4-yl]oxy}phthalonitrile with cobalt, copper, and magnesium acetate resulted in the synthesis of metal phthalocyanines. Sulfochlorination of the latter followed by hydrolysis gave the corresponding sulfonic acid derivatives. The spectral characteristics and chemical properties of the synthesized compounds were studied.     

Effects of surface morphology on the anchoring and electrooptical dynamics of confined nanoscale liquid crystalline films

The orientation and dynamics of two 40-nm thick films of 4-n-pentyl-4'-cyanobiphenyl (5CB), a nematic liquid crystal, have been studied using step-scan Fourier transform infrared spectroscopy (FTIR). The films are confined in nanocavities bounded by an interdigitated electrode array (IDA) patterned on a zinc selenide (ZnSe) substrate. The effects of the ZnSe surface morphology (specifically, two variations of nanometer-scale corrugations obtained by mechanical polishing) on the initial ordering and reorientation dynamics of the electric-field-induced Freedericksz transition are presented here. The interaction of the 5CB with ZnSe surfaces bearing a spicular corrugation induces a homeotropic (surface normal) alignment of the film confined in the cavity. Alternately, when ZnSe is polished to generate fine grooves along the surface, a planar alignment is promoted in the liquid crystalline film. Time-resolved FTIR studies that enable the direct measurement of the rate constants for the electric-field-induced orientation and thermal relaxation reveal that the dynamic transitions of the two film structures are significantly different. These measurements quantitatively demonstrate the strong effects of surface morphology on the anchoring, order, and dynamics of liquid crystalline thin films.     

X-ray studies on Langmuir-Blodgett films of novel amphiphilic oligothiophenes

A new type of amphiphilic thiophene, oligo[n-alkyl-3-(3-thienyl) glutaric acid], was synthesised (with n = 8, 12 or 18). These molecules form a stable monolayer at the air/water interface. Successful Langmuir-Blodgett (LB) deposition was achieved by vertical dipping. The LB films of Y-type exhibit well-defined layered structures, as determined by X-ray diffraction measurements, with a regular molecular arrangement within the layers.     

Characterization of IgG Langmuir-Blodgett films immobilized on functionalized polymers

The bioactivity of anti-human IgG Langmuir-Blodgett (LB) films, the non-specific adsorption of protein and the topography of anti-IgG LB films have been studied for application in immunosensors. The antibody (AB) LB films were horizontally deposited on glass and functionalized polymers, such as carboxy-poly(vinyl chloride) (PVC-COOH), chloropropyl and aminopropyl sol-gel. The LB films were characterized by means of ellipsometry, atomic force microscopy (AFM) and bicinchoninic acid (BCA) protein test. The interpretation of ellipsometric data was performed using a one-layer model. Non-specifically adsorbed protein was desorbed by washing the IgG film in 0.5 M NaCl, 2 M NaCl and 1% N-cetyl-N,N,N-trimethylammoniumbromide detergent solution resulting in a 50% reduction of the film thickness. The mean thickness of an anti-IgG film on glass measured by ellipsometry, PVC-COOH and aminopropyl sol-gel was 9+/-2, 11+/-1 and 23+/-8 nm, respectively. According to the BCA test 6-8 mug antibody (AB) per slide was bound to the functionalized polymers, but only 3 mug AB per slide was adsorbed on glass. The average distance of anti-IgG granules as indicated by AFM measurements on PVC-COOH, chloropropyl and aminopropyl sol-gel was 42+/-20, 34+/-3 and 23+/-4 nm. The average distance of granular AB structures on glass, however, was 150+/-50 nm.     

Characterization of Langmuir and Langmuir-Blodgett films of a thiomacrocyclic ionophore by surface pressure and AFM

The new synthesized thiomacrocyclic ionophore 4-phenyl-4-sulfide-11-(1-oxodecyl)-1,7-dithia-11-aza-4-phosphacyclotetradecane has proven to form Langmuir and Langmuir-Blodgett (LB) films. This ionophore shows a large affinity for copper(II) ions. Thus, the influence of the subphase composition on the surface pressure-area isotherms has been studied. The LB films have been observed by AFM and the effect of the subphase composition and the deposition surface pressure on the LB films is discussed. AFM image morphology has been correlated to the ionophore molecular structure. Surface pressure-area isotherms and AFM images show that the presence of copper(II) ions has an important role in the film structure.     

On the validity of the elastic model for the nematic surface anchoring energy

The intrinsic uniform and non-uniform contributions to the anisotropic part of the surface energy are considered. Our analysis shows that the uniform part can be separated into an intrinsic and an extrinsic term. The first one is due to the nematic-nematic interaction only, whereas the second one is due to the nematic-substrate interaction. They are found to be of the same order of magnitude (≈1 erg cm²). The non-uniform part takes its origin from the spatial variation of the elastic constants. By means of a semi-microscopic model it is shown that, in the framework of perfect nematic order, the extrapolation length of the elastic origin is microscopic. On the contrary, if the spatial variation of the scalar order parameter is taken into account, simple calculations indicate that the extrapolation length is of the order of the coherence length in the nematic phase.