Transparent assemblies with ormosil aerogels

Abstract

The invention provides reinforced aerogel monoliths as well as fiber reinforced composites thereof for a variety of uses. Compositions and methods of preparing the monoliths and composites are also provided. Application of these materials in transparent assemblies is also discussed.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application is a continuation-in-part of U.S. Utility patent application Ser. No. 11 / 030,395 and claims benefit of priority from U.S. Provisional Patent Applications 60 / 594,165 (filed on Mar. 15, 2005) and 60 / 739,748 (filed on Nov. 23, 2005), both which are hereby incorporated in its entirety as if fully set forth.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] This invention was partially made with Government support under Contract DE-FC26-03NT41950 awarded by the Department of Energy (DOE.) The Government may have certain rights in parts of this invention.FIELD OF THE INVENTION [0003] The inventions described herein relate to producing solvent filled, nanostructured gel monolith and flexible blanket composite sheet materials. These materials become nanoporous aerogel bodies after all mobile phase solvents are extracted via a process such as hypercritical solvent extraction (supercritical fluid drying). For...

AI Technical Summary

Benefits of technology

[0013] The present invention provides methods for producing solvent filled, nanostructured gel monolith as well as flexible blanket composite sheet materials produced therefrom via fiber reinforcement. The composite sheets result after all mobile phase solvents are extracted using a hypercritical solvent extraction (supercritical fluid drying). This novel organically modified silica (sometimes referred to as an “ormosil”) formulation can lead to the improvement of various physical and mechanical properties in the resulting aerogel monolith and aerogel composite.

[0014] The ormosil matrix materials described in this invention are best derived from sol-gel processing, preferably composed of polymers (inorganic, organic, or inorganic / organic hybrid) that define a structure with very small pores (on the order of billionths of a meter). Fibrous materials added prior to the point of polymer gelation reinforce the matrix materials described in this invention. The preferred fiber reinforcement is preferably a lofty fibrous structure (batting or web), but may also include individual randomly oriented short microfibers, and woven or non-woven fibers. More particularly, preferred fiber reinforcements are based upon either organic (e.g. thermoplastic polyester,high strength carbon, aramid, high strength oriented polyethylene), low-temperature inorganic (various metal oxide glasses such as E-glass), or refractory (e.g. silica, alumina, aluminum phosphate, aluminosilicate, etc.) fibers. Thus in a first aspect, the invention provides ormosil aerogels containing a linear polymer as a reinforcing component within the structure of the aerogel. The preferred embodiment is to have the polymer covalently bonded to the inorganic structures. The present invention is thus based on the linear polymer reinforcement concept. A number of different linear polymers have been incorporated into the silica network to improve the mechanical properties of the resulting ormosils.

[0015] Transparent monoliths more compliant than silica aerogels have been produced. They are strong enough to resistant the tendency of cracking during wet gel handling and extraction. The improvement in elasticity of these ormosil materials also improve the flexibility and reduce its dustiness in its fiber-reinforced composite. The formulation describe in this invention thus improves the flexibility of the gel monolith, which will lead to the improvement on the handling of monolith during aerogel productions. The invention thus provides for the incorporation of flexible nano-reinforcement component into silica network to improve the tensile properties of the resulting aerogel monolith. This reduces the chance of cracking caused by the brittleness of silica. The improvement of the elasticity of silica aerogel will also reduce its tendency to break apart from the fiber in the fiber reinforcement composite aerogel, leading to the reduction of dustiness of the aerogel composite material.

[0016] In another aspect, the present invention provides a method for co-condensation of trialkoxysilyl end capped linear polymer with a silica precursor, such as (but not limited to) hydrolyzed tetraalkoxysilane, via a sol-gel process. The flexible linear polymeric chain is thus covalently bonded into the rigid silica network, as illustrated in FIG. 1. The introduction of the organic polymeric phase will not lead to phase separation in the resulting ormosil gel. Unlike most ormosil materials, this ormosil gel with low polymer content (<20%) will remain optically transparent after CO2 supercritical extraction. The improved flexibility of the family of ormosil gels provided by the present invention will improve the ease of handling their monolith counterparts during the preparation process, and reduce to tendency of cracking during CO2 extraction.

[0017] In a further aspect, the invention also provides a method for making a linear polymer bonded ormosil fiber reinforced flexible composite. The introduction of silicon bonded linear polymers further increases the flexibility of the resulting aerogel composite. The dustiness of the silica aerogel composite caused by the brittleness of silica material can also be reduce significantly in this case, without sacrificing other inherent properties of the aerogel materials, such as low thermal conductivity and low density. Thus the invention provides an organically modified silica (ormosil) aerogel composition comprising an ormosil aerogel reinforced with linear polymer (or linear polymer chains). Such a composition has a linear polymer covalently bonded at one or both ends to the silica network of the aerogel through a C—Si bond between a carbon atom of the polymer and a silicon atom of the network. The polymer may be covalently bonded at both ends to one silicon containing molecule of the network, and thus be intramolecularly linked, or covalently bonded at the two ends to two separate silicon containing molecules of the network, and thus be intermolecularly linked. The invention of course includes compositions with both intramolecularly and intermolecularly linked polymers. An aerogel of the invention preferably has a density from about 0.01 to about 0.3 g / cm3, preferably about 0.02, or about 0.05, or about 0.1, or about 0.15 or about 0.2, or about 0.25 g / cm3.

[0025] Non-limiting examples of the silica precursor include alkoxysilanes and partially hydrolyzed alkoxysilanes. The alkoxysilane may be selected from tetraethoxylsilane, tetramethoxysilane, and tetra-n-propoxysilane as non-limiting examples. Partially hydrolyzed alkoxysilanes include, but are not limited to, hydrolyzed polysilicate formulations; Dynasil 40 and its family product. The highly transparent material has up to 90% or more transmittance in the visible spectrum for thicknesses between 0.5 and 1.5 cm. The composition would include a linear polymer as described herein without decreasing the optical quality of the resulting aerogel. Preferably, the weight % of linear polymer should be less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, or less than about 5% in the composition. The resultant highly transparent monolith may have high recovery strain up to 95% or more (or up to about 90% or more, or up to about 85% or more) under 20% compression. The improved compressive and flexural resilience of the gel compositions described by the invention allow for creation of larger crack free monolithic structures compared to pure silica aerogel produced under the same processing conditions. This improvement offers a significant advantage for producing crack-free transparencies such as insulated window inserts between support memebers and the like. Preferably, such an aerogel of the invention has thermal conductivity between about 10 and about 16 mW / m·K under ambient conditions

Problems solved by technology

Yet it is inherently impossible to produce transparent aerogel composite, due to the presence of macro scale phase separation in these materials.

This results in the collapse of the filigrane, the highly porous inorganic network of the wet gels.

Stated differently, the solutions or mixtures generally used to prepare a xerogel cannot be used to prepare an aerogel simply by altering the drying conditions because the resultant product will not automatically have a density of an aerogel.

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