SYNOPSISThe transmittance, flexure strength, Young's modulus, and Vickers hardness of poly (methyl methacrylate) ( PMMA ) , filled with fumed silica, was measured. Transmittance decreased with increasing content of filler. At 2 vol % filler content, composites had a higher transmittance with a lower surface area of fumed silica (larger primary particle size) because the lower surface area filler was better dispersed. At 4 vol % filler content, composites had a higher transmittance with a higher surface area fumed silica (smaller primary particle size). Flexure strength and Young's modulus of the composites was measured using three point bending. Addition of fumed silica led to a decrease of strength. Also, addition of fumed silica led to a n increase of Young's modulus and Vickers hardness. I NTRODU CTl O NIn recent years, a variety of highly transparent oxide /polymer composite materials have been investigated. One class of these transparent composites has received names such as ormocers (organically modified ceramics ) and ormosils (organically modified silicates) .'p2 A second class of transparent oxide /polymer composite materials is poly ( methyl methacrylate) ( PMMA ) impregnated silica gel^.^,^ These composites often possess high transparency because the scale of the individual phases is on the molecular or nanometer level.Transparent oxide /polymer composite materials often combine useful attributes of both the oxide and polymer constituents. For example, ormosils are both transparent and hard. Ormosil coatings, applied on polycarbonate lenses, have been shown to provide abrasion resistance.' Another possible application of these composites is as a host for an organic dye molecule. Like polymers, these composites can be processed at or near room temperature, allowing incorporation of organic dye molecules. Yet these composites have improved thermal properties with * To whom correspondence should be addressed. respect to polymers due to the ceramic phase. When used as hosts for organic dyes, transparent oxide/ polymer composite materials often improve the photostability and thermal stability of the dye molecules, in comparison to polymer hosts. For example, organic laser dyes incorporated in ormosils showed improved ph~tostability.~ Also, an electro-optically active aniline dye showed improved thermal stability when incorporated in PMMA-silica gel composites? Over the years, a number of polymers have been filled with submicron fumed or precipitated silica to yield transparent composites. Filled polymers are typically not nearly as transparent as the new classes of transparent composites described above. Nevertheless, one outstanding advantage of filled polymers is that they can easily be prepared in very large size. Like ormosils and PMMA-silica gel composites, filled polymers show improvement in thermal properties over bulk polymers. For instance, acrylicfumed silica composites show an increase in the glass transition temperat~re.~ This effect has been attributed to a boundary layer surrounding the fille...
To calculate elastic constants, longitudinal and tranverse acoustic wave velocities were measured for silica xerogels as a function of relative humidity (rh). The silica xerogels studied are microporous with open porosity of 53 ~01%. The longitudinal wave velocity exhibits a minimum at about 35% rh. The transverse wave velocity decreases to a constant value for 235% rh. Consequently, Young's modulus is a minimum at about 35% rh, whereas the shear modulus decreases to a constant value at 35% rh. The bulk modulus and Poisson's ratio exhibit minimum values at about 15% rh. Young's modulus decreases from 4.91 to 3.42 GPa at 35% rh and then increases to 3.60 GPa at 55% rh. Poisson's ratio decreases from 0.184 to 0.164 at 15% rh and then increases to 0.272 at 55% rh. Below 35% rh, silica xerogels adsorb a monolayer of hydroxyls, whereas above 35% rh silica xerogels show pore filling. [
To calculate elastic constants, longitudinal and tranverse acoustic wave velocities were measured for silica xerogels as a function of relative humidity (rh). The silica xerogels studied are microporous with open porosity of 53 ~01%. The longitudinal wave velocity exhibits a minimum at about 35% rh. The transverse wave velocity decreases to a constant value for 235% rh. Consequently, Young's modulus is a minimum at about 35% rh, whereas the shear modulus decreases to a constant value at 35% rh. The bulk modulus and Poisson's ratio exhibit minimum values at about 15% rh. Young's modulus decreases from 4.91 to 3.42 GPa at 35% rh and then increases to 3.60 GPa at 55% rh. Poisson's ratio decreases from 0.184 to 0.164 at 15% rh and then increases to 0.272 at 55% rh. Below 35% rh, silica xerogels adsorb a monolayer of hydroxyls, whereas above 35% rh silica xerogels show pore filling. [
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.