V. Cech

Plasma surface treatment and modification of glass fibers

New helical coupling plasma system for continuous surface treatment and modification (surface processing) of fiber bundles has been developed and tested for glass fibers. The system enables surface processing of single filaments and flat substrates as well. Surface processed glass fibers and their bundles were examined as reinforcements for glass fiber/polyester composite systems. Processing of fibers comprised a surface treatment using argon gas and a surface modification using hexamethyldisiloxane and vinyltriethoxysilane monomers. Interfacial and interlaminar shear strengths of plasma processed glass fiber/polyester systems were compared with those of untreated and commercially sized fibers.

The influence of surface modifications of glass on glass fiber/polyester interphase properties

Unsized glass fibers and planar glass substrates were subjected to low temperature plasma or wet-chemical process to modify the fiber or substrate surface and thus influence the interphase properties of the glass/polyester system. Plasma-polymerized thin films (interlayers) of organosilicon monomers (hexamethyldisiloxane and vinyltriethoxysilane) were deposited in an RF helical coupling plasma system on the glass surface. Commercial silane coupling agent (vinyltriethoxysilane) was coated onto an unmodified glass surface from an aqueous solution. Bonding at the glass/interlayer interface was analyzed by employing a micro-scratch tester together with an optical polarizing microscope for the planar samples. The results revealed that the adhesion bonding could be controlled by plasma process parameters. Scanning electron and atomic force microscopies enabled characterization of the film surface morphology. Chemical composition and chemical structure of prepared interlayers were characterized using X-ray photoelectron and infrared spectroscopies. Microcomposites (macrocomposites) were tested to evaluate the interfacial shear strength (short-beam strength) of the glass fiber/polyester interphase using the microbond test (short-beam shear). Our study indicated that the most efficient interphase could be prepared by plasma polymerization or wet-chemical process using the vinyltriethoxysilane monomer. The short-beam strength was 110% higher than that for untreated fibers in both cases.

Plasma-polymerized organosilicones as engineered interlayers in glass fiber/polyester composites

The plasma polymerization technique was used to surface modify glass fibers in order to form a strong but tough link between the glass fiber and the polyester matrix, and enable an efficient stress transfer from the polymer matrix to the fiber. Plasma polymer films of hexamethyldisiloxane, vinyltriethoxysilane, and tetravinylsilane in a mixture with oxygen gas were engineered as compatible interlayers for the glass fiber/polyester composite. The interlayers of controlled physico-chemical properties were tailored using the deposition conditions with regard to the elemental composition, chemical structure, and Youngs modulus in order to improve adhesion bonding at the interlayer/glass and polyester/interlayer interfaces and tune the cross-linking of the plasma polymer. The optimized interlayer enabled a 6.5-fold increase of the short-beam strength compared to the untreated fibers. The short-beam strength of GF/polyester composite with the pp-TVS/O2 interlayer was 32% higher than that with industrial sizing developed for fiber-reinforced composites with a polyester matrix.

Plasma Polymer Film as a Model Interlayer for Polymer Composites

In this paper, a plasma-enhanced chemical vapor deposition process that is useful for the preparation of thin and ultrathin films of controlled mechanical properties is identified. Plasma-polymerized films of vinyltriethoxysilane were deposited on planar substrates and analyzed using nanoindentation measurements of the Youngs modulus of the films, adhesion bonding at the film/glass interface, chemical composition, and structure. The modulus of the plasma polymer film can be controlled simply by the effective power fed into the capacitive-coupled low-pressure plasma. The single film was tested as an interlayer in glass fiber (GF)/polyester composites. GF bundles were surface modified by plasma polymer in a unique technological system, enabling continuous processing of the bundle. GF/polyester composites in the form of short beams were manufactured using the coated fibers and tested according to the standard test method. By increasing the interlayer modulus, the short-beam strength was enhanced up to 112% compared with the untreated GFs, and this enhancement was also supported by an improvement in interfacial bonding

XPS study of siloxane plasma polymer films

Abstract Plasma polymer films were deposited from hexamethyldisiloxane (HMDSO), dichloro(methyl)phenylsilane (DCMPS) and vinyltriethoxysilane (VTEO) on polished silicon wafers using a RF helical coupling deposition system. The composition of elements in the surface region (top 6–8 nm) of the deposited films was studied by X-ray-induced photoelectron spectroscopy (XPS) on an ADES 400 VG Scientific photoelectron spectrometer using MgK α (1253.6 eV) or AlK α (1486.6 eV) photon beams at the normal emission angle. Aging effects of plasma-polymerized (PP) HMDSO and DCMPS films stored under standard laboratory conditions were investigated by employing XPS. Post-deposition contamination and oxidation of pp-DCMPS and pp-HMDSO film was carefully observed. An increase in oxygen atoms on the film surface over time is accompanied by changes in bulk atomic concentrations. Sequential sputtering with an Ar ion-beam, together with XPS analysis, was used to measure concentration depth profiles in pp-HMDSO and pp-DCMPS films.

Thin plasma-polymerized films of dichloro(methyl)phenylsilane

Thin plasma polymer films were deposited from a mixture of dichloro(methyl)phenylsilane (DCMPS) vapour and gaseous hydrogen in a r.f. (13.56 MHz) capacitive coupling deposition system on pieces of silicon wafers. Some samples were annealed in vacuum at the temperature ranging from 450 to 700°C. Chemical composition, structure and surface morphology of annealed samples and those stored in air at room temperature were studied by FTIR, XPS, SEM, and optical microscopy. Thermal stability and a decomposition of the plasma polymer with increasing temperature were characterized by thermogravimetry together with mass spectrometry. The plasma polymer was stable up to a temperature of 300°C. Above that temperature the material started to decompose together with additional cross-linking due to incorporation of extra oxygen atoms forming new siloxane bonds. The plasma polymer was tough at room temperature but much more brittle at elevated temperatures.

Modeling of the I–V characteristics in amorphous silicon n+-i-n+ devices

Both model and experimental results of electron injection in amorphous silicon n+-i-n+ devices with heavily doped n+ layers are presented using a realistic model of such a structure, developed by the author. Spatial profiles of transport parameters were calculated changing the undoped layer (i layer) thickness and the energy and spatial distributions of the density of localized states in undoped film. Simulated current–voltage (I–V) characteristics were compared with space-charge-limited current (SCLC) dependences given by the drift currents. The effect of diffusion currents on the I–V characteristics was studied to determine the criteria for a correct application of the SCLC technique. As follows from numerical simulations, only the characteristics measured on a device with a sufficiently “thick” i layer can be used to apply the SCLC technique. The effect of contacts on the I–V dependence can be checked by the scaling law.

A Fiber-Bundle Pull-out Test for Surface-Modified Glass Fibers in GF/Polyester Composite

The development of high-performance polymer composites is tightly bound with the functional surface modification of reinforcements. A new method, based on the principle of the fiber-bundle pull-out test, is proposed to analyze the interfacial properties between the long fibers in the form of a bundle and the polymer matrix. Specimen geometry and a test fixture were designed using finite element analysis. The method was verified for unsized and sized glass fibers embedded in polyester resin to demonstrate its applicability for a wide range of adhesion between fibers and the polymer matrix. The pull-out test can be used for a relative comparison of different surface modifications if the bundle geometry is unknown. The results of high reproducibility and sensitivity for interfacial properties make the method attractive.

Functional interlayers in multiphase materials

Properties of a three-dimensional interlayer formed between the reinforcement (fiber) and the matrix are final properties of composite materials. It means that surface properties, chemistry of the coated fiber and the matrix play a very important role for achieving good adhesion (a primary factor for stress transfer from the matrix to the fiber) and strong bonding between the fiber and the matrix (to gain the best possible composite mechanical properties). The aim of this work was to prepare thin films with siloxane structure by glow discharge polymerization technique, and the film serves in the end as an adhesion interlayer between the glass fiber and the polyester resin. Plasma polymerized dichloro(methyl)phenylsilane, hexamethyldisiloxane and vinyltriethoxysilane thin films were deposited on the surface of glass slides, silicon wafers and glass fibers. Chemical composition of the plasma polymers on planar substrates was examined by Fourier transform infrared and X-ray photoelectron spectroscopies, surface morphology was studied by atomic force microscopy and surface properties were evaluated by contact angle measurements as the free surface energy. Adhesion between the plasma polymerized film and the glass slide was tested using fully PC-controlled scratch tester with the Rockwell diamond tip. Performance of glass fiber/polyester composite was assessed using a short beam shear and the test revealed that the plasma-polymerized vinyltriethoxysilane interlayer was the best and the interlaminar shear strength was 75% higher than that for untreated fibers.

NEW PROGRESS IN COMPOSITE INTERPHASES: A USE OF PLASMA TECHNOLOGIES

A development of high-performance composites is tightly bound with a designing of composite interphases. The interphase is a region intermediate to the fibre and the matrix which are in a contact. In fact this region includes the fibre coating and a part of the matrix affected by the presence of the coated fibre. Theoretical and experimental studies have showed that the properties of fibre reinforced composites are given by the coating material with its thickness and modulus, by the interaction at interfaces with the fibre and the matrix, and by the reinforcement and matrix materials. Therefore, sophisticated interphases can lead to higher strength and higher toughness of the specific composite system. Low temperature plasma technology is the new technique used for surface modification of reinforcements. This technology is able to prepare controlled interphases. Actual possibilities and achievements of the plasma technology are outlined.