UV curing of organic–inorganic hybrid coating materials

The effect of UV-curing time on the mechanism of interaction between the various precursor phases in a novel sol–gel-derived organic–inorganic hybrid coating material and the resulting mechanical and thermal properties of this material when coated onto substrates in thin film form have been examined using a variety of chemical and physical characterisation methods. Microstructurally, the hybrid coating materials examined were all a single amorphous phase and were all optically transparent. The degree of interaction between the organic and inorganic phases, the scratch behaviour of the coating materials and the thermal stability of the coating materials were all found to depend strongly on the UV curing time. For the particular proportions of inorganic and organic components used to make up this hybrid coating material, an optimum UV curing time of 10 min under a UV intensity of 46.3 mW cm⁻² was found to produce transparent coatings which adhered well to the substrates and which were robust in scratch tests on aluminium and polycarbonate substrates and abrasion tests on polycarbonate substrates.     

Halogenometalates with N-containing organic cations structural chemistry and thermal behavior

The crystal structures, spectroscopic characterization, and thermal behavior of fluoro, chloro, and bromo complexes preferably of aluminium, iron and manganese formed with organic cations are reviewed. Compared with the structural chemistry of complexes with alkali metal cations, the use of quarternary ammonium or protonated N-containing base cations considerably extends the structural variety of halogenocomplexes and, in certain cases, allows the access to new modifications of metal fluorides if a suitable precursor compound is thermally decomposed.

For most of the described new compounds, the formation of the final structure is governed by the anionic part. Isolated anions [MF_{6 − n}(H₂O)_n]^{(3 − n)−} connected via hydrogen bridges are the predominant structure motifs. However, multi-nuclear units as well as chain structures can be prepared from aqueous HX solutions, too. Due to the hydrogen atoms provided by the organic cations, additional hydrogen bonds stabilize various novel structures. Some special structural features will be presented, e.g. the discrete tetrafluoroaluminate complex as well as pentacoordinated aluminium and iron(II).     

Simultaneous tailoring of surface topography and chemical structure for controlled wettability

Wettability was controlled in a rational manner by individually and simultaneously manipulating surface topography and surface chemical structure. The first stage of this research involved the adsorption of charged submicrometer polystyrene latex particles to oppositely charged poly(ethylene terephthalate) (PET) film samples to form surfaces with different topographies/roughness; adsorption time, solution pH, solution ionic strength, latex particle size, and substrate charge density are external variables that were controlled. The introduction of discrete functional groups to smooth and rough surfaces through organic transformations was carried out in the second stage. Amine groups (-NH(2)) and alcohol groups (-OH) were introduced onto smooth PET surfaces by amidation with poly(allylamine) and adsorption with poly(vinyl alcohol) (PVOH), respectively. On latex particle adsorbed surfaces, a thin layer of gold was evaporated first to prevent particle redistribution before chemical transformation. Reactions with functionalized thiols and adsorption with PVOH on patterned gold surfaces successfully enhanced surface hydrophobicity and hydrophilicity. Particle size and biomodal particle size distribution affect both hydrophobicity and hydrophilicity. A very hydrophobic surface exhibiting water contact angles of 150 degrees /126 degrees (theta(A)/theta(R)) prepared by adsorption of 1-octadecanethiol and a hydrophilic surface with water contact angles of 18 degrees /8 degrees (theta(A)/theta(R)) prepared by adsorption of PVOH were prepared on gold-coated surfaces containing both 0.35 and 0.1 microm latex particles. The combination of surface topography and surface-chemical functionality permits wettability control over a wide range.     

Electrical conductivity,electronic thermal conductivity,and thermo-EMF of an organic semiconductor

Kinetic coefficients are calculated on the assumption that the lifetime of an electron at a node is greater than the equilibration time in the phonon subsystem. It is found that this approximation is justified for a system with narrow bands and for not very weak coupling with the scattering subsystem.     

Adhesion forces in liquid media: effect of surface topography and wettability

This work was motivated by the unexpected values of adhesion forces measured between an atomic force microscopy tip and the hydrophobic surface of ultra-high-molecular-weight polyethylene. Two types of samples with different roughness but similar wettability were tested. Adhesion forces of similar magnitude were obtained in air and in polar liquids (water and Hank's Balanced Salt Solution, a saline solution) with the rougher sample. In contrast, the adhesion forces measured on the smoother sample in air were much higher than those measured in water or in the aqueous solution. Those experimental results suggested the presence of nanobubbles at the interface between the rough sample and the polar liquids. The existence of the nanobubbles was further confirmed by the images of the interface obtained in noncontact tapping mode. The adhesion forces measured in a nonpolar liquid (hexadecane) were small and of the same order of magnitude for both samples and their values were in good agreement with the predictions of the London-Hamaker approach for the van der Waals interactions. Finally, we correlate the appearance of nanobubbles with surface topography. The conclusion of this work is that adhesion forces measured in aqueous media may be strongly affected by the presence of nanobubbles if the surface presents topographical accidents.     

Synthesis, curing kinetics and thermal properties of bisphenol-AP-based benzoxazine

A novel bisphenol-AP-aniline-based benzoxazine monomer (B-AP-a) was synthesized from the reaction of 4,4′-(1-phenylethylidene) bisphenol (bisphenol-AP) with formaldehyde and aniline. The chemical structures were identified by FT-IR, ¹H and ¹³C NMR analyses. The polymerization behavior of the monomer and the types of hydrogen bonding species were monitored by differential scanning calorimetry (DSC) and FT-IR. The curing kinetics was studied by isothermal DSC and the isothermal kinetic parameters were determined. The thermal properties of cured benzoxazine were measured by DSC and thermogravimetric analysis (TGA). The bisphenol-AP-aniline-based polybenzoxazine (poly(B-AP-a)) exhibited higher glass transition temperature (T_g) and better thermal stability than corresponding bisphenol A-aniline-based polybenzoxazines (poly(BA-a)). The T_g value of poly(B-AP-a) is 171 °C. The temperatures corresponding to 5% and 10% weight loss is 317 and 347 °C, respectively, and the char yield is 42.2% at 800 °C. The isothermal curing behavior of B-AP-a displayed autocatalysis and diffusion control characteristics. The modified autocatalytic model showed good agreement with experimental results.     

How changes in computer technology are revolutionizing the practice of chemistry

During the early 1980s, two major developments in computer technology changed the way chemists approached their science. The advent of the micropressor and then the PC changed experimental chemistry, while the availability of two classes of computer, the superminicomputer and supercomputer, greatly influenced computational chemistry. In the past two years, graphics workstation computers have begun to affect the practice of chemistry by combining fast, high-resolution, multiwindow graphics with superminicomputer power. In 1988, the advent of a new class of computer--the graphics supercomputer--offers extraordinary promise to both theoretician and experimentalist. In these systems, near-Cray compute power is combined with ultrahigh-speed 3-dimensional graphics for unparalleled visualization of molecular processes and other complex events. This is made practical not just by computing and graphics power but by use of ultrahigh internal bandwidths inside the graphics supercomputers. Another major development in scientific computing is the evolving concept of the laboratory computer network. Current network designs include hierarchical configurations incorporating various levels of computers--through supercomputers--either locally or via national or regional networks. New software methods are also having impact on chemical research, allowing, for example, the scientist to better abstract information from noisy or incomplete experimental data. Use of parallelism (multiple CPUs) in new design workstation computers will extend their power, by the early 1990s, past that of current supercomputer mainframes. Within five years the chemist will have $10 million of 1985 computer power on his desk, for considerably less than $100,000, along with visualization tools and software only dreamed of in 1985.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nanostructuring of a polymeric substrate with well-defined nanometer-scale topography and tailored surface wettability

This study demonstrates a simple and highly reproducible method for fabricating well-defined nanostructured polymeric surfaces with aligned nanoembosses or nanofibers of controllable aspect ratios, showing remarkable structural similarity with interesting natural biostructures such as the wing surface of Cicada orni and the leaf surface of Lotus. Our studies on the present biomimetic surfaces revealed that the wetting property of the nanostructured surface of a given chemical composition could be systematically controlled by rendering nanometer-scale roughness. The nanofabricating method we developed can be readily extended to other thermoplastic polymeric materials (e.g., light-emitting polymers, conducting polymers, block copolymers, liquid crystalline polymers), and it could be applied to developing a new generation of optical and electronic devices.     

Synthesis, curing behavior and thermal properties of fluorene containing benzoxazines

A series of difunctional fluorene-based benzoxazine monomers were synthesized from the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with formaldehyde and primary amines including aniline, o-toluidine, n-butylamine, and n-octylamine. Their chemical structures were confirmed by FT-IR, ¹H and ¹³C NMR analyses. The curing behaviors of the precursors were monitored by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polymers were evaluated with DSC and thermogravimetric analysis (TGA). The fluorene-based polybenzoxazines show the typical curing characteristic of oxazine ring-opening for difunctional benzoxazines centred at 231-250 °C, and remarkably higher glass transition temperature and better thermal stability ascribed to the high rigidity, high aromatic content, and intermolecular and intramolecular hydrogen bonding. The thermal decomposition temperature and char yield of aromatic amine-fluorene-based polybenzoxazines are much higher than those of aliphatic amine-based polybenzoxazines.     

Radiation curing of intelligent coating for controlled release and permeation

Intelligent membranes for pH and temperature-responsive drug releases were developed by coating and curing of polymer-drug composite film with electrolyte or N-isopropyl acrylamide curable mixture. It was proved that those intelligent membranes showed the stimule-sensitive and responsive release functions and could be produced efficiently by radiation curing prosessing with a conveyer system.     

Kinetic analysis of the thermal degradation of an epoxy-based intumescent coating

The aim of this work is to analyse and to simulate the kinetics of pyrolysis of an intumescent formulation designed to protect steel in the case of hydrocarbon and jet fires. The coating is based on a thermoset epoxy-amine resin system into which two fire retardant agents, boric acid and ammonium polyphosphate derivative have been incorporated. Industrial tests (jet fire tests) are usually used to evaluate the degradation mode of an intumescent coating. But these tests are quite expensive, and as the heating rates are extremely high (between 500 and 800 °C/min), it is not possible to evaluate the thermal degradation behaviour of the intumescent coating directly by thermogravimetric analyses. That is why it is necessary to develop predictive models of kinetics of degradation of these intumescent coatings. In this work, the coating has been pyrolyzed at different heating rates and a predictive model of its kinetics of degradation has been developed.     

Study of the curing of an acetylene-terminated polyphenylene resin with thermal expansion measurements

The curing of an acetylene-terminated polyphenylene resin (Hercules H-Resin) was followed by thermal expansion measurements. This approach proved useful in optimizing the curing conditions of the resin. Curing the polymer in air led to the formation of carboxyl groups, whereas curing under nitrogen did not. The thermal expansion coefficient is a minimum (32 ppm deg^?1) for a cure cycle of 250°C for 30 min, followed by 350°C for 30 min. Heating at temperatures above 350°C led to degradation of the crosslinked polymer and an increase in the thermal expansion coefficient.     

Surface chemistry and annealing-driven interfacial changes in organic semiconducting thin films on silica surfaces

Vibrational sum frequency generation (VSFG) spectroscopy was used in conjunction with steady-state IR spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry to characterize organic semiconductor thin films that were vapor deposited on silica- and trimethoxy(octadecyl)silane (ODTMS)-functionalized silica surfaces. The growth of perylene derivative N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C(8)) was found to proceed differently on simple glass slides relative to that of native oxide on silicon and fused quartz slides. VSFG was applied to these samples to isolate structural changes that occurred specifically at the buried interface between the organic semiconductor and the silica dielectric upon thermal annealing. A model was introduced to globally fit the imide carbonyl symmetric and asymmetric interfacial spectra that included contributions from both inner and outer interfaces. The fits to the VSFG data and AFM topographic images revealed significant reordering at the outer interface on all substrates upon thermal annealing. Within the model, the spectroscopic data reported that the inner interfacial PTCDI-C(8) monolayer reoriented to a more reclined phase on bare substrates after annealing but remained essentially unchanged on ODTMS monolayers. Electrical characterization of PTCDI-C(8) field-effect transistors indicated that electron mobilities were higher on bare substrate devices but could be improved by a factor of 2 on both surface types by thermal annealing. The mobility effects were attributed to the annealing-driven coalescence of PTCDI-C(8) grain boundaries. Consistent with previous structural reports, the molecular rearrangements of the first monolayer of PTCDI-C(8) on bare substrates that were reported by VSFG spectroscopy had a noticeable impact on the device performance.     

Understanding the role of clay silicate nanoparticles with organic modifiers in thermal curing of cyanate ester resin

The catalytic effect of montmorillonite clay nanoparticles containing organic modifiers such as quaternary phosphonium salts on cure mechanism of cyanate ester resin (RS-9D) was studied by differential scanning calorimetry (DSC) measurements, FT-IR and NMR spectroscopy as well as mass-spectrometry. The results show that the net catalytic effect arises from the presence of moisture associated with nanoclay particles where organic modifiers act as moisture transport agents. Possible mechanisms for cure pathways are discussed.     

Improved thermal stability of an organic zeolite by fluorination

The thermal stability of an organic zeolite material, namely 2,4,6-tris(4-bromo-3,5-difluorphenoxy)-1,3,5-triazin (Br-3,5-DFPOT), was improved by fluorination of 2,4,6-tris(4-bromophenoxy)-1,3,5-triazin (BrPOT). The open pore structure (van der Waals diameter of 10.5 Å) of the modified zeolite was observed up to 110 °C in comparison to 70 °C for BrPOT. Nitrogen sorption at low temperature showed a type I isotherm and derived pore volumes thereof are in agreement with structural data. It was observed here that Br-3,5-DFPOT crystals preserving the open pore structure could only be obtained below a typical size of about 50 μm. The improved thermal stability of the fluorinated system is attributed to an enhancement of the strength of the Br₃-synthon.     

Structural, thermal and optical characterization of an organic NLO material--benzaldehyde thiosemicarbazone monohydrate single crystals

Single crystals of the organic NLO material, benzaldehyde thiosemicarbazone (BTSC) monohydrate, were grown by slow evaporation method. Solubility of BTSC monohydrate was determined in ethanol at different temperatures. The grown crystals were characterized by single crystal X-ray diffraction analysis to determine the cell parameters and by FT-IR technique to study the presence of the functional groups. Thermogravimetric and differential thermal analyses reveal the thermal stability of the crystal. UV-vis-NIR spectrum shows excellent transmission in the region of 200-1100 nm. Theoretical calculations were carried out to determine the linear optical constants such as extinction coefficient and refractive index. Further the optical nonlinearities of BTSC have been investigated by Z-scan technique with He-Ne laser radiation of wavelength 632.8 nm. Mechanical properties of the grown crystal were studied using Vickers microhardness tester. Second harmonic generation efficiency of the powdered BTSC monohydrate was tested using Nd:YAG laser and it is found to be ～5.3 times that of potassium dihydrogen orthophosphate.     

Synthesis, crystal growth, structural, thermal and optical properties of naphthalene picrate an organic NLO material

Crystalline substance of naphthalene picrate (NP) was synthesized and single crystals were grown using slow evaporation solution growth technique. The solubility of the naphthalene picrate complex was estimated using different solvents such as chloroform and benzene. The material was characterized by elemental analysis, powder X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and fourier transform-infrared (FT-IR) techniques. The electronic absorption was studied through UV-vis spectrophotometer. Thermal behavior and stability of the crystal were studied using thermogravimetric (TG) and differential thermal analysis (DTA) techniques. The second harmonic generation (SHG) of the material was confirmed using Nd:YAG laser.