Papers by Keyword: Gels

Abstract: Dentine hypersensitivity (DH) is a common issue among humans caused by the erosion of tooth enamel as a result of chewing and brushing incorrectly. The most effective treatment method is occluding the exposed dentine tubules. Because calcium phosphate is an important mineral and the most common mineral for dentine and orthopaedic application, this study focuses on the synthesis of bioactive gels containing calcium phosphate nanoparticles. The synthesis is performed using water-in-oil emulsion and characterized by the use of TGA, Rheological, TEM, and SEM techniques. This method used oleic fatty acids as an external phase and Tween 20 as surfactant to form water-in-oil nanodroplets. Gelatine was used to form the substance into a gel and increase its stability. The resulting nanoparticles had the same spherical shape and a similar size. Therefore, the varying amounts of gelatin do not affect the particle size. However, viscoelastic properties of gels were found to be changed. The ability of the gel for dentine tubule occlusion was investigated using SEM techniques. After 1 day, it was found that the gels can occlude dentine tubules.

Abstract: The CDB-spectrometer at NEPOMUC enables spatially resolved Doppler Broadening Spectroscopy of the electron-positron annihilation line with a lateral resolution of up to 200~$\mu$m (FWHM). We have applied this technique for studying single particles of silica gel dependent on loading with an altering amount of the ionic liquid [C2MIM][NTf2]. Our results reveal a strong correlation between the observables of DBS and the loading factor which presumably arises from a smaller inner surface of voids in loaded silica gel.

Abstract: . A polishing process, which is the final process in manufacturing optical elements, takes a long time and often depends on the experience and special skills. Development of a skill-less polishing technology and automation of its process, therefore, has been required. One of the most promising polishing technologies is Field-assisted Fine Finishing (FFF). In this study, an Electro-rheological Gel (ERG) polishing pad with one-sided patterned electrodes is developed to polish insulator materials and, moreover, a novel electric-field-assisted polishing technology for glass polishing is proposed applying this pad. The ERG polishing pad can change the polishing performance according to applied electric field due to “electro-adhesion effect”. Results of several polishing tests show that the performance of polishing a blue glass can be controlled by applying electric field to the ERG pad.

Abstract: Acoustic cavitation effects in sol-gel liquid processing permits to obtain nanostructured materials, with size-dependent properties. The so-called “hot spots” produce very high temperatures and pressures which act as nanoreactors. Ultrasounds force the dissolution and the reaction stars. The products (alcohol, water and silanol) help to continue the dissolution, being catalyst content, temperature bath and alkyl group length dependent. Popular choices used in the preparation of silica-based gels are tetramethoxysilane (TMOS), Si(OCH3)4, and tetraethoxysilane (TEOS), Si(OC2H5)4. The resultant “sonogels” are denser gels with finer and homogeneous porosity than those of classic ones. They have a high surface/volume ratio and are built by small particles (1 nm radius) and a high cross-linked network with low –OH surface coverage radicals. In this way a cluster model is presented based on randomly-packed spheres in several hierarchical levels that represent the real sonoaerogel. Organic modified silicates (ORMOSIL) were obtained by supercritical drying in ethanol of the corresponding alcogel producing a hybrid organic/inorganic aerogel. The new material takes the advantages of the organic polymers as flexibility, low density, toughness and formability whereas the inorganic part contributes with surface hardness, modulus strength, transparency and high refractive index. The sonocatalytic method has proven to be adequate to prepare silica matrices for fine and uniform dispersion of CdS and PbS quantum dots (QDs), which show exciton quantum confinement. We present results of characterization of these materials, such as nitrogen physisorption, small angle X-ray/neutrons scattering, electron microscopy, uniaxial compression and nanoindentation. Finally these materials find application as biomaterials for tissue engineering and for CO2 sequestration by means the carbonation reaction.

Abstract: Consolidants are sols or solutions that are used to restore the strength of weathered stone. The liquids are drawn into the pores of stone by capillary suction, then they harden by gelation and/or drying. In this chapter, we discuss the requirements that such a material must fulfill, and demonstrate the effectiveness of consolidants based on alkoxysilanes and alkylalkoxysilanes.

Abstract: We have developed polymer and gels with an autonomous self-oscillating function by utilizing the Belousov-Zhabotinsky (BZ) reaction. Under the coexistence of the substrates, the polymer undergoes spontaneous cyclic soluble-insoluble changes or swelling-deswelling changes (in the case of gel) without any on-off switching of external stimuli. By using microfabrication technique, ciliary motion actuator or self-walking gel have been demonstrated. Further, in order to realize nano-actuator, the linear polymer chain and the submicrometer-sized gel beads were prepared. By grafting the polymers or arraying the gel beads on the surface of substrates, we have attempted to design self-oscillating surface as nano-conveyer. For application to biomaterials, it is necessary to cause the self-oscillation under biological condition without using non-biorelated BZ substrates. So we attempted to introduce pH-control site and oxidant-supplying site into the polymer. By using the polymer, self-oscillation only in the existence of biorelated organic acid was actually achieved.

Abstract: Dielectric elastomers, a class of electroactive polymers, are specially promising due to their proven high actuation strain and energy density. Their electromechanical response is described by the Maxwell stress, where the level of strain reached depends mostly on the dielectric constant, elastic modulus and applied electric field. Since a decrease in modulus can enhance the elastomer response, swelling in appropriate solvents, transforming them into gels may enhance actuation. Tri-block copolymer gels offer a large range of possibilities since the mechanical properties and electroactive behaviour of these physically crosslinked materials can be adjusted by varying the polymer concentration, morphology and molecular weigh between crosslinks. In this work efforts were undertaken in reducing the elastic modulus by selective swelling of the elastomer midblocks with an organic oil. Strain responses to static and dynamic electrical stimuli were considered and, in particular, the effect of the frequency on the mechanical efficiency was investigated in detail. A simple theoretical model describing the frequency response was formulated.

Abstract: There is a current need for the localized delivery of antibiotics in order to treat implant based infections. In this study, the efficacy of hydroxyapatite (HA) gels, HA cements, and silica gels in the delivery of vancomycin have been investigated and compared. Vancomycin release was monitored at set time points using a UV/VIS spectrophotometer (288 nm). The activity of the vancomycin released from the cements and gels was assessed using an agar diffusion test with Staphylococcus aureus. Vancomycin was released rapidly from both HA matrices, and the silica gel in the first day of the experiment, but the release rate was slowed considerably after 3 days for the HA gels. Following ten days of aging, 70% of the vancomycin remained in the HA gel matrix and the quantity released from the gel was shown to retain its effectiveness against Staphylococcus aureus.

Abstract: Non-aggregated nanoscale α-Al2O3 powders with average size ranging from 7 to 20 nm were prepared successfully at various conditions with the use of the hydrated aluminum sulfate extracted from kaolin by polyacrylamine (PAA) gel method. The calcination temperature was relatively lower about 100°C, compared to conventional solid-state reaction. It revealed that PAA worked as a chelating agent to disperse the Al3+ ions homogeneously, and the size of alumina nanoparticles could be controlled by varying the concentration of crosslinking agent.

Abstract: The development of lead-free piezoelectric materials has been required from the viewpoint of environmental preservation. We focused the lead-free KNbO3-based systems, and used a chemical solution deposition (CSD) process to obtain their precursor. (Na1-xKx)NbO3 precursor solutions were prepared from metal alkoxides and solvents such as absolute ethanol and 2-methoxyethanol. Crystallization behavior of the precursor gels obtained from the above solutions was investigated by the thermogravimetry differential thermal analysis (TG-DTA) measurement.