Langmuir-Blodgett Film Method Research Articles

Hydrodynamic Process in the Langmuir-Blodgett Film Method.

Preparing organic coatings in a very controlled manner through the spreading of organic molecules on the water surface is one of the emphases for research in Langmuir-Blodgett (LB) technology. For preparing a homogeneous film and improving the quality of the film, it is our concern to have a deeper understanding of the dynamic process involved in spreading. Here, we present an overview of the hydrodynamic process under the influence of assisting the spreading solvent, which mainly focuses on the mechanical mechanisms of related phenomena. A typical spreading experiment of two-component mixed droplets on water substrate for the purpose of preparing LB films was carried out in this research. We perform the spreading of a liquid of silicone oil and oleic acid mixture on the horizontal surface of another immiscible deep water substrate, where the volatile silicone oil is the assisting spreading solvent with low viscosity. We find that it needs to exceed a certain critical value (60% in our experiment) to achieve a uniform and centrosymmetric spreading process, which is a key factor for getting a homogeneous film. We observe that the evolution of a large droplet into liquid film and then into small droplets under the action of surface tension gradient in experiments. Gravity-viscous and surface tension-viscous dominate successively in the whole spreading process, with its spreading radius r(t) ∝ t1/4 and r(t) ∝ t3/4, respectively. However, we also obtain singular values of scaling exponents -0.033 and -0.180, which is attributed to nonuniform distribution of the Laplace pressure caused by different curvatures near the capillary wave.

Organization of amphiphiles, part XIV: Studies on the interaction of a novel organic molecule with surfactant in solution and at air–water interface

The interaction between a novel organic molecule (3E, 5E)-bis(4-butyloxy)benzylidene-8-(4-butyloxy)phenyldicyclopentano[2,3-b:3,2-e]pyridine(BP4) independently with a cationic surfactant, cetyltrimethylammonium bromide (CTAB) as well as with a nonionic surfactant, Triton-X-100 (TX-100) has been investigated through a number of analytical techniques such as conductivity, spectral analyses (fluorescence, UV–visible absorbance) and area/molecule measurements (Langmuir–Blodgett film method) in solution and at air–water interface. Both CTAB and TX-100 aggregate at lower concentration in the presence of BP4 compared to the absence of later, indicating the generation of synergism in the solution mixture. The hydrocarbon chain of BP4 interacts with the cetyl chain of CTAB or 1,1,3,3-teramethyl butyl chain of TX-100 through hydrophobic interaction thereby enhancing the surface activity of the mixture. Subsequently, CMC decreases. On the contrary, CMC of BP4 increases upon addition of both CTAB and TX-100 due to the inefficiency of BP4 to interact aptly with the CTAB/TX-100 to form hydrophobic complex (U. Dash, P. K. Misra, JCIS, 357(2011)407-418). But both the surfactants and BP4 adsorb as monomer in the presence of each other and form a mixed monolayer at the air–water interface by associating through lateral interaction of their hydrocarbon chain. This leads to an increase of the cooperative effect as evidenced by the decrease in area per molecule at the air–water interface.

Gas sensitivity of poly (3, 4-ethylene dioxythiophene) prepared by a modified LB film method

An arachidic acid/poly (3, 4-ethylene dioxythiophene) (AA/PEDOT) multilayer Langmuir-Blodgett (LB) film was prepared by a modified LB film method. The theories were utilized to explain the effects between HCl molecule and LB film. The gas sensitivity mechanism of poly (3, 4-ethylene dioxythiophene) (PEDOT) multilayer film can be explained by the charge transfer between p system of PEDOT and oxidization HCl system. The gas sensitivity of PEDOT LB film deposited interdigital electrode to HCl was tested. The results showed that film thickness, treating temperature, deposition speed had different influence on film gas sensitivity. The AA/PEDOT film deposited device exhibited nonlinear behavior to HCl gas at lower concentration (20–60 ppm) and linear response behavior at higher gas concentration was observed. The time of the compound LB film of the AA/PEDOT responding to the 30 ppm HCl gas is about 20 seconds, which is far quicker than the time of the film to the PEDOT-PRESS film(about 80 seconds). It is not higher film press to better film. When the film press attains 45 mNs/m, the sensitivity of the AA/PEDOT film on the contrary descends.

Fabrication of Nanosilicon Ink and Two-Dimensional Array of Nanocrystalline Silicon Quantum Dots

An assembly of nanoparticles using a colloidal solution is promising for the fabrication of future highly integrated electron and photoelectronic devices because of low manufacturing cost, flexible substrates, and alternative methods that can overcome the limitation of top-down technology. We have successfully prepared two-dimensional arrays of nanocrystalline silicon (nc-Si) quantum dots with a uniform size of 10 nm. However, the area of two-dimensional arrays has been limited because of the problems of dissolution in water and agglomeration of nc-Si due to a high surface reactivity. The key issue is the surface modification of nc-Si particles. In this study, we have demonstrated the evaluation of surface modification states of nc-Si QDs by zeta potential and particle size distribution measurements. As a result of the optimization of the surface modification process, we have successfully obtained a well-dispersed nc-Si QD solution, namely, nanosilicon ink. Furthermore, we have successfully fabricated a two-dimensional array of nc-Si QDs using the Langmuir-Blodgett film method in the entire 1 ×1 cm2 silicon substrate.

Bioelectronic device consisting of self-assembled biomolecules

Abstract Bioelectronic device based on photoinduced electron transfer such as the biomolecular photodiode consisting of protein-adsorbed hetero film was investigated. Three kinds of functional molecules in biomolecular photodiode were used as a sensitizer, a first electron acceptor, and a second electron acceptor. The hetero-film was fabricated subsequently depositing functional molecules onto the pretreated conducting substrate using self-assembly method and Langmuir–Blodgett film method. The metal/insulator/metal structured bioelectronic device was constructed by depositing the metallic electrode onto the surface of the hetero-films. Based on the photoelectric response properties, the rectifying property in the current–voltage characteristic and the photoswitching effect of the proposed bioelectronic device were observed. The charge separation of molecular interface was verified in time-resolved fluorescent measurement by the time-correlated single photon counting method. The charge shift in the device was analyzed by the measurement of transient photocurrent of the device and thus the efficient directional flow of photocurrent through the redox potential difference was observed.