Papers by Keyword: Self-Assembling

Abstract: In this work we describe the studies of preparation and stability of liposomes formed by 1,1'-[(3,5-didodeciloxycarbonyl-4-phenyl-1,4-dihydropyridine-2,6-diil) dimethylebispyridinium dibromide, novel lipid-like compound. The influence of the amount of amphiphilic compound, solvent and sonication time was studied. Liposomes were prepared by dispersing of compound in the corresponding media at a selected concentration by sonication using a probe type sonicator and characterised by atomic force microscopy (AFM) and dynamic light scattering (DLS) methods.

Abstract: Self-assembling of 1O4Cd identical tetrahedral clusters resulting to nanoscale order in ZnTe:(Cd, O) is presented. Such co-doping transforms ZnTe into Cd_xZn_1-xO_yTe_1-y alloy. The decrease of the strain energy is a cause of this phenomenon. The self-assembling conditions are obtained by the minimum condition of the free energy of ZnTe:(Cd, O) at the Cd and oxygen in the dilute and ultra dilute limits, respectively. An occurrence of 1O4Cd clusters and completion of self-assembling (all oxygen atoms are in clusters) are results of the continuous phase transitions. The temperature of the occurrence of self-assembling does not depend on the oxygen content and it is a function of Cd concentration only. Cd_xZn_1-xO_yTe_1-y with all oxygen atoms in clusters may be obtained in temperature ranges from T = 270 °C (x = 0.002, y = 1×10^-4) to T = 620 °C (x = 0.02, y = 1×10^-4) and from T = 240 °C (x = 0.005, y = 0.001) to T = 580 °C (x = 0.02, y = 0.001).

Abstract: With the depth of space exploration and applications, the space robot self-assembling has become more and more important for space on-orbit service. Parameter analysis is an indispensable work of assembling process design. The dynamic model of the space robot with target is established firstly, then the Hertz model is introduced as the collision model between the docking link and the capturing cone, and the operational space control is applied to achieve the assembling operation control under the Cartesian space. Then the paper focuses on the discussion and analysis of the influences of the parameters such as the stiffness coefficient, friction coefficient, leading speed coefficient and vertical speed damping coefficient on the assembling characteristics. The simulation results would provide a basis for assembling control and parameter design and have an important academic value and engineering significance on space service.

Abstract: In the space robot self-assembling process, the assembling control becomes quite complicated and important for the nonlinear characteristics, which are caused by the dynamic coupling between the arm and the base, and the collision between the target and the assembling hole on the base. The dynamic model of the space robot with target is established firstly, then the Hertz model is introduced as the collision model between the docking link and the capturing cone, and the operational space control is applied to achieve the assembling operation control under the Cartesian space. Through simulating and analyzing the influence of the stiffness coefficient, the soft and hard behaviors during assembling are discovered, which would provide a basis for assembling control and parameter design. The results would have important academic value and engineering significance on space robot achieving on-orbit self-assembling.

Abstract: The aim of the study was to synthesize and characterize silsesquioxane-based hybrid nanocomposites with self-assembling properties to be used in monumental stone conservation. Through radical polymerization of 3-(trimethoxysilyl)propyl methacrylate, a monomer that contains both methacrylate and silica phases, in the presence of a primary amine surfactant, at different silica precursor:ethanol molar ratios, new types of hybrid nanocomposites, in which silica was dispersed as domains with typical sizes in the nanometer range, were obtained. The self-assembling properties of the synthesized composites have been ascribed to the supramolecular assembling abilities of the surfactants, as well as to the combination of linear, ladder, and cagelike fragments of silsesquioxane type. The incorporation of surfactant within the sol-gel derived matrix may also lead to the obtaining of compounds that avoid cracking of the hybrid gel while drying inside the stone.

Abstract: Citrate gold nanoparticles of 13.5 nm average diameters have been synthesized by Turkevich method and further functionalized by place exchange reaction using mercaptosuccinic acid (MSA), 1,4-benezenedimethanethiol (1,4BDMT) or mercaptoundecanoic acid (MUA) as the incoming ligands. In the first case, the functionalization of the gold clusters with MSA yielded solution of blue color and large aggregates on carbon grids. Moreover, after filtration and drying, any film formed by hydrogen bonding, could not be removed from the filter, being embedded into the filter texture. The second ligand used for the place exchange reaction, the 1,4BDMT, determined the change of the solution color from red to dark purple, and generation of a purple powder but no film formation. In the third case, the purification and drying of the MUA functionalized gold clusters yielded films of purple color with homogenous composition, robustness, soft topographies and remarkable optical properties which were dependent on their thicknesses. The Au-MUA NP films obtained are new, being generated by hydrogen bonding and having features which makes them very attractive for the fabrication of optoelectronic devices. The long alkyl chained thiol proved to be the adequate ligand for film synthesis.

Abstract: In order to immobilize enzyme to multi-wall nanotube (MWNT), the MWNT was coated by the electrochemical polymerization of aniline. The horseradish peroxide (HRP) was immobilized on the surface of the polyaniline (PANI)-coated MWNT (PANI-MWNT film) by using gold nanoparticle (physical immobilization). The HRP was also immobilized on the surface of PANIMWNT film by using 2-aminothiophenol and Au nanoparticle (self-assembling immobilization). HRP was immobilized on the surface of PANI-MWNT electrode by using glutaric dialdehyde (covalent immobilization). The sensing efficiency of HRP-MWNT electrodes for H2O2 was evaluated by amperometric method. The sensing efficiency of HRP-MWNT electrodes for H2O2 was as following order; physical immobilization > covalent immobilization > self-assembling immobilization.

Abstract: The mechanism and conditions of meso-tetra (4-sulfonatophenyl) porphine (TPPS₄) molecular aggregate formation and their geometrical structure are investigated by methods of molecular mechanics and quantum chemistry. J- type aggregates are formed of zwitterionic forms of TPPS₄ via interaction of their positively charged porphyrin rings and negatively charged SO₃ - groups. According to ab initio and PM3 calculations it was found that TPPS₄ zwitterion has asymmetrical structure (parts of porphyrin ring are asymmetrically bent out of plane), although the porphyrin ring of TPPS₄ molecule in neutral aqueous solution (at pH 7) is flat and the planes of phenyl rings are nearly perpendicular to the porphyrin plane. We propose that asymmetrical porphyrin rings are able to form bent threads. The thread is bent approx. 5° for each monomer, so approximately 60 monomers should form the loop (diameter ~20 nm).

Abstract: An understanding of both the interactions between the adsorbate molecules and the interactions between adsorbates and the surface is a prerequisite to eventually controlling the selfassembly process in supramolecular aggregation. Here we report the formation of supramolecular structures (J-aggregates) whose size and aggregation pattern are controlled by changing the number of polar sulfonic groups of meso-tetra (4-sulfonatophenyl) porphine. Using atomic force microscopy we show that substituted porphyrin molecules (5,10,15,20-tetrakis(4-sulfonatophenyl) porphine (TPPS₄), 5,10,15-tris(4-sulfonatophenyl)-20-phenyl porphine (TPPS₃), 5,15-bis(4-sulfonatophenyl)- 10,20-diphenyl porphyne (TPPS_2op) - SO₃ groups are opposite each other, and 5,20-bis(4- sulfonatophenyl)-10,15-diphenyl porphyne (TPPS2a) . SO₃ groups are adjacent each other) form different spatial structures. Our findings suggest that placement of functional groups that are participating in direct noncovalent interactions will allow design and construction of different supramolecular structures adsorbed to surfaces.

Abstract: The adsorption of organic molecules on solid surfaces is one of the fundamental processes for the development of molecular-based nanodevices. Here we focus on the adsorption and ordering of the TPPS₄-based J-aggregates on silicon and gold as well as on self-assembled monolayer (SAM) surfaces. The SAMs used for the experiments were based on the chemisorption of thiol containing compounds onto gold. Long ω-substituted alkanethiols are spontaneously assembled on gold to form highly ordered and densely packed layers with controllable chemical and physical properties. TPPS₄ J-aggregates were dispersed on SAM surfaces, and on plain gold and silicon substrates for comparison. The dimensions of aggregates, measured by means of atomic force microscopy, varied depending on the type of substrate. Long stripe-like aggregates were flattened on the substrate surface, and the height and width of aggregates highly correlated with the polarity of surface groups. For example, the J-aggregates were narrower on hydrophobic substrates (with non-polar groups) and wider on hydrophilic substrates (with polar groups). These observations support the hypothesis, that TPPS₄ forms .soft. cylindrical aggregates, that appear flattened on the substrate.