Glass Microspheres in Medicine

 

Using Embolic Glass Microspheres to Target Chronic Disease

Sierra Kucko

•

February 5, 2025

Glass microspheres under magnification. Image source: MO SCI.

Glass Microspheres: The Tiny Superheroes of Glass Form Factors

Two main factors contribute to the properties of glass: composition and form factor. While emphasis is often placed on glass composition, the form factor is arguably equal in importance. Glass in the form of microspheres has permeated various industries, ranging from aerospace to medical sectors. MO SCI specializes in the production of precision glass microspheres that have become invaluable to these industries, and their usage is ever-evolving. Whether it be controlling gaps for adhesive bondline spacing, improving the visibility of road markings, or drug delivery devices, glass microspheres fit the bill.

Targeted Treatment with Embolic Glass Microspheres

Biocompatible (and in some cases biodegradable) microspheres are especially appreciated for medical applications, such as transarterial embolization (TEA) or musculoskeletal (MSK) embolization.^1,2

TEA refers to the blockage of blood supply, which may sound like a bad thing, but in many cases, these are lifesaving procedures. For example, a substantial driver for this technology is cancer treatment. One way to combat a tumor or abnormal tissue growth is to cut off its blood supply, which can be achieved through the precise application of appropriately sized microspheres to occlude the fine vasculature ‘feeding’ it.¹

Similarly, MSK embolic microspheres are sought after to prevent the abnormal overgrowth of blood vessels, a consequence of chronic inflammation. This kind of inflammation is part of a pathological loop, whereby the inflammation promotes the formation of new blood vessels that in turn, can feed nerve growth and contribute to chronic, debilitating pain.² Microsphere embolization can therefore be used as a pain management tool, as well. For applications with this level of weightiness, the microsphere size is a chief feature.

Together with the form factor, glass microspheres can be tailored through their composition. First and foremost, any implantable glass must be compatible with the body. Ancillary to this, the composition can be altered to offer additional functionality. Using TAE as an example to put this concept into context, the composition of glass used in this type of application is unique and important.

TAE is a procedure utilized by interventional radiologists. Interventional radiology (IR) is the diagnosing and/or treatment of cancer and other conditions while avoiding major surgery. To achieve this, small tools such as needles, catheters, or wires are utilized in conjunction with radiation like MRI, ultrasound, etc. to apply treatment precisely to the tissue site.^1–3 Personalization and optimization of outcomes is a clinical challenge of any medical intervention, making the accurate delivery and distribution of the embolic particles in real-time indispensable.

Due to the use of radiation to guide the placement, the embolic particle should be radiopaque (opaque to radiation) to ensure that guided delivery to the site can be realized. Compared with glass, this radiopacity is lacking or more difficult to achieve in microspheres derived from other material types.

Partner with MO SCI for Precision Glass Microspheres

Each application of glass is unique and therefore may require unique chemistries and form factors. Glass microspheres are becoming increasingly popular, since their form factor alone may improve the function of the glass (depending on the application) when compared to their powder or frit counterparts.

For applications that require precise microsphere size and composition, it is important to turn to trusted experts. MO SCI produces a wide range of glass microspheres in a variety of chemistries to suit nearly any need. Contact us today to learn how glass microspheres may be beneficial for your application.

References

1.  Pérez-López A., et al. (2022). Embolization therapy with microspheres for the treatment of liver cancer: state-of-the-art of clinical translation. Acta Biomaterialia. https://doi.org/10.1016/j.actbio.2022.07.019

2.  Gremen E., et al. (2022). Safety and efficacy of embolization with microspheres in chronic refractory inflammatory shoulder pain: a pilot monocentric study on 15 patients. Biomedicines. https://doi.org/10.3390/biomedicines10040744

3.  Kishore S, et al, (2021). Transarterial embolization for the treatment of chronic musculoskeletal pain: a systematic review of indications, safety and efficacy. ACR Open Rheumatology. https://doi.org/10.1002/acr2.11383

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Glass Surge Protectors

 "Surge arresters are the primary defense for electrical equipment against over-voltages. These essential devices house metal oxide varistors (MOVs), which act as rapid-response protectors against voltage spikes. To optimize the performance and ensure the safety of MOVs, effective insulation is required around their outer surfaces."

image source: iStock

Slumping Research

The following is an abstract of an article investigating the behaviour of glass in slumping (or as they term it - sagging).  They are using optical glass which has a much higher viscosity at its slumping temperature than fusing glass, but the principles are transferable.  They indicate quick firing to the strain point (which is about 500C/930F) is possible, but that best results come from progressing slowly to the slump soak temperature.  

The article is as follows|: 

Numerical and Experimental Investigation of the Heating Process of Glass Thermal Slumping

• Author: Zhao Dachun, Liu Peng, He Lingping, Chen Bo

• Publish: Journal of the Optical Society of Korea Volume 20, Issue2, p314~320, 25 Apr 2016

https://oak.go.kr/central/journallist/journaldetail.do?article_seq=20778

The abstract of the article follows.

“Simulations performed for different heating rates resulted in different sag variation between glass and mold; higher heating rate caused larger sag variation. Therefore, to save time in manufacturing, the furnace should be heated to about 500℃ quickly, but then to the soaking temperature slowly. According to the simulation, the maximum sag variation decreased with higher soaking temperature. Considering the temperature-dependent viscosity of glass, the optimal soaking temperature was about 800℃.

Based on the optimized experimental conditions, glass samples of thickness 0.5 mm were formed in a furnace with a concave parabolic mold made of steel. Slumped glass was produced and tested. Comparison between surface profiles of the formed glass, theoretical data, and mold suggested that the quality of the slumped glass can be significantly improved by optimizing the shape of the mold. The RMS and PV sag deviations between formed glass and mold were 2.3 and 4.7 μm respectively, along the axial direction.

On the other hand, with a soaking temperature of 800℃ the formed glass was still not fully slumped at the edges, according to the radial deviation seen in experimental results, which meant that the glass was not making full contact with the mold. The experimental results agreed with the numerical predictions. Therefore, trimming the edges is necessary to achieve a better surface profile. Based on the simulated and measured results, improvements can be made in future research, and new mold materials or manufacturing processes should be adopted to improve the shape accuracy of the mold.”

Devising Slumping Schedules

A while ago Bob Leatherbarrow gave a presentation to Lunch With A Glass Artist (LWAGA) on slumping schedules. You can follow a recording of the Zoom meeting after joining the facebook group Lunch With A Glass Artist – Larry Pile.

The most important point for thinking about the process he follows is the order of slumping factors. They are:

• span

• thickness

• viscosity

How big is the unsupported part of the glass?   Glass on larger span moulds will begin slumping at lower temperatures than on smaller spans.

The thickness has an effect. With the same ramp rate thicker glass will need higher temperature or longer time.

The viscosity of the glass also affects the temperature of the slump. Low viscosity glass will slump at lower temperatures than higher ones, e.g., black vs. white.

Then you can begin to think about temperature and time. The objective is to use the lowest temperature to get the slump done in 30 minutes to avoid marking of the glass touching the mould, leaving a smooth shiny back.

There is a lot more in the presentation to LAWAGA. Join the facebook page to get access.

There is even more information about fusing principles and practices in his book Firing Schedules for Kilnforming, Just Another Day at the Office.

https://www.leatherbarrowglass.com/purchase/firing-schedules-for-kilnformed-glass

This inexpensive eBook is worth much more than the purchase price!

Glass in Electronics

"Glass, a highly functional material integral to modern technology, plays an active role in the world of electronics and energy. From the screens of our smartphones to the fibers that carry internet signals across oceans, glass is at the heart of many technologies that rely on its unique electrical properties. " 

Image generated with the assistance of AI

Glass, a highly functional material integral to modern technology, plays an active role in the world of electronics and energy. From the screens of our smartphones to the fibers that carry internet signals across oceans, glass is at the heart of many technologies that rely on its unique electrical properties.

This article aims to shed light on these properties—from dielectric constants to electrical resistivity—exploring how they are influenced by glass composition. We will delve into the science behind these properties and their diverse applications in today’s technology-driven world. This journey will reveal not just a material but a versatile and essential component of countless electrical and electronic innovations.

The Relationship Between Composition and Electrical Properties

Dating back to 1845, glass was initially chosen for its insulating capabilities in telegraph communications. Fast forward to today, over 360,000 different compositions of glass have been documented, each engineered for specific electrical, mechanical, and thermal properties to meet diverse technological needs. This broad spectrum of compositions is a testament to the material’s adaptability in electrical applications.

The following discussion will detail some of the commonly measured electrical properties of glass,² examine the effects of compositional variations on these properties, and provide insight into the role of different components in enhancing or moderating these properties for advanced technological applications.

The Dielectric Constant

The dielectric constant is a critical factor in a material’s ability to store electrical charge under an electric field. As a dielectric material, glass acts as an electrical insulator, meaning that electric charges do not flow through it as they do in conductors like metals. Instead, when exposed to an electric field, the positive and negative charges within the glass are displaced—positive charges move towards the field, while negative charges move away. This charge separation, or polarization, reduces the internal electric field in the glass, enabling it to store charge.³

This dielectric behavior can be observed when glass is inserted between the plates of a parallel-plate capacitor. This augments the capacitance value, enhancing its ability to store opposing charges on each plate.³

The relationship between the composition of glass and its dielectric constant is an active research area. This relationship is complex, requiring an understanding of how the various elemental components within glass contribute to polarization.

Generally, glasses with higher dielectric constants tend to contain alkalis, alkaline earth, and heavy-metal cations like lead, bismuth, and tungsten,⁴ and research has revealed that altering the composition of glass can impact its dielectric constant. For instance, replacing silicon with aluminum in sodium aluminosilicate glasses, increasing tungsten oxide in sodium germanium borosilicate glasses, and adjusting copper oxide levels in borate zinc-fluoride glasses can raise the dielectric constant. On the other hand, adding rare earth oxides to alkali-free aluminoborosilicate glass can lower its dielectric constant.^4,5,6,7

By manipulating the elemental makeup of glass, researchers and engineers can tailor its electrical characteristics to meet specific technological needs, paving the way for advanced and specialized uses in various industries.

Loss Tangent

When glass is exposed to an alternating electric field, a portion of the electrical energy is stored in line with its dielectric constant. However, not all energy is efficiently stored; some is inevitably lost, predominantly as heat, a phenomenon known as dielectric loss. The dielectric loss tangent of glass relates to this dissipation of electrical energy and can result from various physical processes, including electrical conduction, dielectric relaxation, and dielectric resonance.^8,9

For applications like high-frequency electronic circuits, where minimizing energy dissipation is crucial, the composition of the glass must be meticulously tailored to achieve a low loss tangent. This careful adjustment ensures that the glass performs optimally, avoiding unnecessary energy waste.

While it has been observed that the levels of impurities in glass can impact dielectric loss, in the case of borosilicate (BRS) glass-reinforced PTFE composites used for microwave substrate applications, researchers found that decreasing BRS filler size can reduce the loss tangent.^10,11 This finding underscores the importance of material composition and structure in achieving desired electrical properties for specific technological applications.

Conductivity and Resistivity

Conductivity and resistivity are also fundamental properties, especially with regard to electronic applications. Put simply, electronic conductivity involves the transmission of electrical charge by electrons, which are negatively or positively charged electron holes. Glass, characterized by its covalent and ionic bonding structure, typically shows conductivity levels far lower than those in metals, making it an ideal insulator.

Notably, two glass families exhibit significant electronic conduction:

1. Oxide glasses containing high amounts of transition metal oxides exhibit enhanced conductivity. These oxides introduce unpaired electrons, facilitating electron flow.
2. Chalcogenide and tetrahedral glasses, where the inherent covalent bonding contributes to their conductive properties.¹²

By adjusting specific elements within the glass, such as incorporating elements with free electrons or modifying the bonding structures, manufacturers can tailor glass to have specific conductivity and resistivity characteristics. This ability to customize glass properties makes it versatile for various electronic applications, from insulators to conductive components.

Applications

Glasses with low dielectric constants are crucial in applications where minimizing electrical losses, signal distortion, or interference is essential. For this reason, they are used in high-performance microelectronic systems, such as substrates in semiconductor packaging and in thick-film resistors. On the other hand, glasses with high dielectric constants are important for high-magnitude capacitors and multilayer dielectrics.^4,14

The exploitation of electronic conductivity in glass has also opened up a realm of opportunities in modern technology. Notably, the photoconductivity of selenium and arsenic-selenium glasses, driven by electronic conduction, has been pivotal in revolutionizing the photocopying process.

Moreover, certain glasses exhibiting electronic conductivity can dynamically switch between insulator and semiconductor states. This unique property has been applied in the development of computer memory devices, showcasing the versatility of glass in electronic applications. The photovoltaic characteristics of amorphous hydrogenated silicon, a product of its electronic conduction, also form the cornerstone of solar cell technology.¹²  

Overall, the applications of glass with electrical properties are diverse and continually expanding, driven by ongoing research. This progress highlights the pivotal role that the electronic conductivity of glass plays across multiple high-tech industries, showcasing its versatility and importance in shaping modern technology.

How can Mo-Sci help?

Meticulous calibration and consideration of glass composition are crucial for accurate and meaningful measurements of the aforementioned electrical properties. Mo-Sci specializes in creating high-performance sealing glasses suited for a wide range of applications. Our expertise extends to customizing solutions, including the production of specialized glass substrates and ultra-pure glass frit.

For inquiries on sealing solutions or custom development services, contact the Mo-Sci team today.

References and Further Reading

1. Chen, J., et al. (2017) Generation of shock lamellae and melting in rocks by lightning-induced shock waves and electrical heating. Geophysical Research Letters. doi.org/10.1002/2017GL073843
2. Jones, R. (2010) An Incomplete History and Timeline of the Electric Telegraph and the CD 731 Compromise Insulator. Available at: https://www.insulators.info/shows/handouts/cd_731.pdf
3. Al-Amoudi, M.A. (2020) Determining Dielectric Constants of Glass and Thin Film Using a Parallel Plate Capacitor. International Journal of Applied Science and Engineering Review. ISSN: 2582-6271.
4. Hsieh, C., et al. (1996) Correlation between dielectric constant and chemical structure of sodium silicate glasses. Journal of Applied Physics. doi.org/10.1063/1.363824
5. Mundher, M. (2023) Tungsten oxide effects on conductivity, dielectric parameters, and density of sodium germanium borosilicate glass. Journal of Materials Science: Materials in Electronics. doi.org/10.1007/s10854-023-10280-6
6. Shaaban, S.M., et al. (2023) Influence of Copper Ions on the Structural, Mechanical, Radiation Shielding and Dielectric Properties of Borate Zinc-Fluoride Glasses. Journal of Electronic Materials. doi.org/10.1007/s11664-023-10564-x
7. Zhang, L., et al. (2020) Influence of rare earth oxides on structure, dielectric properties and viscosity of alkali-free aluminoborosilicate glasses. Journal of Non-Crystalline Solids. doi.org/10.1016/j.jnoncrysol.2020.119886
8. Poplavko, Y.M. (2019) Chapter 7 – Dielectrics. Electronic Materials: Principles and Applied Science. doi.org/10.1016/B978-0-12-815780-0.00007-4
9. Sebastian, M.T. (2008) Chapter Two – Measurement of Microwave Dielectric Properties and Factors Affecting Them. Dielectric Materials for Wireless Communication. doi.org/10.1016/B978-0-08-045330-9.00002-9
10. Rodriguez-Cano, R., et al. (2023) Broadband Characterization of Silicate Materials for Potential 5G/6G Applications. IEEE Transactions on Instrumentation and Measurement. doi.org/10.1109/TIM.2023.3256463
11. Alhaji, I.A., et al. (2021) Effects of Particle Size on the Dielectric, Mechanical, and Thermal Properties of Recycled Borosilicate Glass-Filled PTFE Microwave Substrates. Polymers. doi.org/10.3390/polym13152449
12. Varshneya, A.K., et al. (2019) Chapter 16 – Electronic Conduction. Fundamentals of Inorganic Glasses (Third Edition). doi.org/10.1016/B978-0-12-816225-5.00016-X
13. Mo Sci. (2022) Applications of Thin and Thick Glass Films. Available at: https://mo-sci.com/applications-of-thin-and-thick-glass-films/ (Accessed on 17 November 2023).
14. Li, J.C., et al. (2012) Characterization of Semiconductor Surface Conductivity by Using Microscopic Four-Point Probe Technique. Physics Procedia. doi.org/10.1016/j.phpro.2012.03.568

Annealing temperatures by colour

 It has been suggested that there are different annealing temperatures for different colour groups. This is not so.

All the colours in a single fusing compatible range are annealed at the same temperature. It is true that there are variations in the viscosities of different colours, but these are designed by the makers to be minor. Also relevant is that annealing can occur over a range, making concern about different viscosities within a fusing compatible line of glass less important. The anneal soak gives time for all the glass to reach the same temperature differential of ∆T = 5°C, where the viscosity differences will be so small as to be insignificant.

There are precautions that should be observed when combining strongly contrasting colours or contrasting styles. In general, hot and dark colours are less viscous than light and cool colours at slumping and above temperatures. There are also contrasting viscosities between opalescent and transparent colours. A cautious approach to these differences in viscosities is to anneal them as for one layer thicker than that for the profile of the finished item.

The annealing temperature remains the same for all the glass in a fusing compatible line, regardless of colour or style. The length of the anneal soak and cool rates may be altered for these contrasts, but not the anneal temperature.

Glass vs Ceramics

 Glass and ceramics have distinct differences, but can be combined into a fine-grained microstructure that uniformly disperses crystalline phases within an amorphous glass matrix.

Image source: CILAS

Glass and ceramics have similar material properties, including high strength and hardness. However, at the microscopic level, there are many differences in the structures of glasses and ceramics, which ultimately influence their suitability for particular applications.

Key Characteristics of a Glass

Glass is a solid characterized by its amorphous or non-crystalline microscopic structure.¹ Typically transparent to visible light, many glasses are valued for their chemical inertness and hardness, allowing them to withstand highly corrosive environments, including extreme pH levels and biological conditions.²

In contrast, crystalline materials possess a high degree of regularity in their atomic structure, featuring a periodic crystal lattice. The planes of atoms present in crystalline materials can easily slip past one another, which helps relieve internal stresses. This regularity is absent in glasses, contributing to their typically brittle nature. An important characteristic of glass is the glass transition temperature, which is the point where glass transitions from a hard, brittle state to a molten state. This temperature significantly influences the thermal properties and behavior of the glass.³

Commonly, glasses are composed of network formers such as SiO₂, B₂O₃, P₂O₅; and network modifiers designed to achieve specific properties. For optical fibers, minimizing unwanted dopants is crucial to prevent the formation of color centers and radiation damage. However, dopants can also enhance the optical and optoelectronic properties of glasses for other applications.⁴

Bioactive glasses form a distinct category, designed for medical devices and technologies. These materials are biologically safe and promote healing or treatment processes, often through ion release.⁵ Typically made from a mixture of SiO₂, calcium oxide, sodium oxide, and phosphate (P₂O₅), bioactive glasses can be engineered with specific degradation kinetics to enable drug release or to create dissolvable scaffolds for wound healing.

Key Characteristics of a Ceramic

Ceramic materials are renowned for their high thermal resistance. They belong to a diverse family that includes inorganic materials, metallic oxides, nitrides, and carbides. The microstructure of ceramics is made up of small crystalline areas called grains, which can vary in size.

The size and composition of grains significantly influence the material properties of ceramics, and the interfaces between these grains are crucial for optimizing hardness and durability.⁷

Ceramics can be very brittle and have poor resistance to shearing and tension forces. However, like many glasses, they exhibit excellent resistance to chemical erosion. With the appropriate chemical composition, ceramics can be engineered into semiconductors and electrical components, with many capacitors being made from ceramic materials due to their superb thermal and electrical resistance.

Ceramics are now extensively used across various industries, and the development of composite ceramics has broadened their applications, including in the medical field for creating devices like dental implants.⁸

Glass-Ceramics

While a vast array of glass and ceramic materials exists, the ideal material properties for a specific application sometimes require merging the best attributes of both. Glass-ceramics are such a hybrid, possessing the chemical compositions of glasses but differing in their microstructure. Unlike purely glassy materials, which are entirely amorphous, glass-ceramics typically exhibit a predominantly crystalline structure interspersed with amorphous characteristics. This is typically achieved through a fine-grained microstructure that uniformly disperses crystalline phases within an amorphous glass matrix.

This hybrid microstructure makes glass-ceramics stronger than their purely glass counterparts and allows them to retain some of the beneficial electrical properties associated with ceramics, while still remaining transparent.⁹

Glass-ceramics are particularly valued as bioactive materials, with variants like Bioglass 4555 receiving FDA approval for medical device applications. The ability to further refine their properties through controlled crystallization processes during manufacturing enhances their adaptability for complex uses.

Non-metallic materials, such as glass, ceramics, and glass-ceramics, exhibit a broad range of properties influenced by the degree of crystallinity in their microstructure. Generally, a higher degree of crystallinity results in harder materials, but it can also increase light scattering, which is why specialized processing is required to render ceramic materials transparent.

Mo-Sci Solutions

At Mo-Sci, we are experts in the development and creation of glass, ceramic, and glass-ceramic materials, no matter what the application. Whether you need very high-purity silicon dioxide or a more complex custom-made bioactive material, contact us today to see how our services and capabilities could benefit you and help you find the perfect material solution to your product needs.

References and Further Reading

1. Doremus, R. H. (1972). Structure of inorganic glasses. Annual Review of Materials Science, 2(1), 93-120. https://doi.org/10.1146/annurev.ms.02.080172.000521
2. Axinte, E. (2011). Glasses as engineering materials: A review. Materials & Design, 32(4), 1717-1732. https://doi.org/10.1016/j.matdes.2010.11.057
3. Tanguy, A. (2021). Elasto-plastic behavior of amorphous materials: a brief review. Comptes Rendus. Physique, 22(S3), 117-133. https://doi.org/10.5802/crphys.49
4. Griscom, D. L. (2013). A Minireview of the Natures of Radiation-Induced Point Defects in Pure and Doped Silica Glasses and Their Visible / Near-IR Absorption Bands , with Emphasis on Self-Trapped Holes and How They Can Be Controlled. Physics Research International, 379041. http://dx.doi.org/10.1155/2013/379041
5. Jo, W., Kim, D., & Hwang, N. (2006). Effect of Interface Structure on the Microstructural Evolution of Ceramics. Journal of the American Ceramic Society, 8, 2369–2380. https://doi.org/10.1111/j.1551-2916.2006.01160.x
6. Cannio, M., Bellucci, D., Roether, J. A., & Cannillo, V. (2021). Bioactive Glass Applications : A Literature Review of Human Clinical Trials. Materials, 14, 5440. https://doi.org/10.3390%2Fma14185440
7. Jo, W., Kim, D., & Hwang, N. (2006). Effect of Interface Structure on the Microstructural Evolution of Ceramics. Journal of the American Ceramic Society, 8, 2369–2380. https://doi.org/10.1111/j.1551-2916.2006.01160.x
8. Vallet-Regí, M. (2001). Ceramics for medical applications. Dalton Perspective, 97–108. https://doi.org/10.1039/b007852m
9. So, M., Górny, A., Pisarska, J., & Pisarski, W. A. (2018). Electrical and optical properties of glasses and glass-ceramics. Journal of Non-Crystalline Solids, 498, 352–363. https://doi.org/10.1016/j.jnoncrysol.2018.03.033

Notes on Kiln wash

 

Composition

Kiln wash generally is made up of a mix of aluminium hydrate and kaolin, although some contain vegetable extracts instead of the kaolin (china clay).

Application

The kiln wash mix should be applied in at least four directions with a soft brush, such as a hake, one immediately after the other. The object is to have all the layers incorporating into one smooth layer. There are fuller descriptions elsewhere in this blog.

Drying of layers

Some people suggest drying after each direction of application. This is not recommended because the following layers of kiln wash drag at the dry layers and create an uneven surface. A full description is given here.  

Air drying the shelf before use reduces the amount of moisture introduced to the kiln and extends the life of the metal structure of the kiln. This can be done by air drying on top of the heated kiln if you have two sets of shelves, or simply by leaving in a ventilated room for 6 – 8 hours.  Drying in the kiln could be done more efficiently with the glass on the prepared shelf – the moisture will be driven out before the glass has reached its strain point., so the glass will not be affected by a damp shelf.

Performance

A Bullseye video suggests the kiln wash should be completely removed and renewed every time it is fired over 730°C/1350°F. The reason for this is that the kaolin in kiln wash changes its form – with added heat – from its slippery platelets to a crystalline structure. It is the crystalline form of kaolin that sticks to the glass on a second fuse.  Removal involves cleaning all the kiln wash off, down to the bare shelf before applying the new layers. Continual painting over old kiln wash builds up the thickness of exhausted kiln wash and risks cracking and flaking which is mirrored on the back of the glass.

Freshly applied kiln wash prevents it sticking to the glass. However even fresh kiln wash is prone to stick to opalescent glass at full fuse temperatures.  It is easy to remove the adhered kiln wash by using a solution of citric acid.

The use of kiln wash is cheaper, simpler and easier than many people suggest.

Glass Bonding

 This post may help with choosing high performance fastenings to glass objects.  Glass bonding with silane and polymer coatings.

Although glasses are often valued for their chemical inertness, this property also presents challenges when attempting to form strong chemical bonds with other materials. Silanes and polymer coatings offer effective solutions by enhancing the bond between a glass and other materials in a composite.

The Challenge

The challenge of bonding glass to polymers spans across several industries, including industrial, automotive, and healthcare. In biomaterial applications, polymer carriers are often used to deliver glass or ceramic particles to specific treatment sites. However, bioactive glasses, commonly used in treatment delivery and bone regeneration, face a similar issue: the mismatch in critical surface tension and adhesion properties between the materials in the composite.¹ This mismatch is primarily driven by differences in hydrophobicity and hydrophilicity, making it difficult to create strong, stable bonds.

The key question, then, is how to improve and strengthen the bonds between glass and polymer materials to create stable composites that benefit from the properties of both material types.

The Solution

Fortunately, there are several approaches to improving the bonding characteristics of glass. One such solution is the use of silane or polymer materials as adhesive treatments. These materials help bypass the challenges of forming direct chemical bonds between the surface oxide groups on the glass and the substrate of interest.

Silanes

Silanes are particularly effective in improving the bonding between glass and other materials due to their ability to form highly stable siloxane bonds. These strong covalent bonds enhance the compatibility between glass and various organic or inorganic surfaces, creating a stronger interface than unmodified glass. Silanes are an excellent choice for composites, retaining the properties of glass while significantly improving surface chemistry and wettability.

One challenge in forming glass-bonded materials is the introduction of a new surface type, which can create potential regions of weakness and shear. Silanes act as effective coupling agents by forming strong covalent bonds with both the glass and the substrate, reducing these weak points and enhancing the overall stability and durability of the material.²

While physical abrasion and etching with hydrofluoric acid can improve adhesion by roughening the surface, chemical modification using silanes is often preferable. Chemical bonds offer superior grafting properties compared to physical methods, resulting in stronger, more durable connections between glass and other substrates.

Polymers

Polymer materials are widely used for bonding to glass due to their flexibility, which is highly advantageous in adhesive applications. While silicone-based materials can bond to glass, they are generally not as strong as many polymer adhesive options.

One such polymer adhesive, polyurethane, is a popular choice for bonding glass in various industries. This popularity is due to its flexibility, which helps absorb and mitigate vibrations induced by movement, enhancing the durability and integrity of the bonded structure. Similarly, acrylic adhesives are the ideal choice for oily or corrosive environments or for use in high-temperature applications. Epoxy adhesives also offer similar benefits, with excellent chemical and electrical resistance.

While many polymers show good adhesion to glass surfaces, their bonding interactions tend to be weaker than the covalent bonds formed with silanes, relying instead on intermolecular forces.³

Polymer adhesion is sufficient for many applications, especially where motion or substrate deformation is likely, as flexibility in the bonding is beneficial. However, for applications that demand the highest levels of adhesion, combining silane treatment with polymer bonding provides a superior solution. This approach significantly enhances bond strength, making it ideal for situations requiring both flexibility and durability.

MO SCI Solutions

MO SCI has a long history of developing custom glass solutions for even the most challenging applications. We can help you find innovative and effective ways to overcome the challenges of glass bonding and adherence to create devices that not only have the properties for peak application performance but are also stable and resistant to environmental degradation.

Contact us today to discuss your application.

References and Further Reading

1. Brauer, D. S. (2015). Bioactive Glasses — Structure and Properties Angewandte. Angewandte Chemie – International Edition, 54, 4160–4181. https://doi.org/10.1002/anie.201405310
2. Yavuz, T., & Eraslan, O. (2016). The effect of silane applied to glass ceramics on surface structure and bonding strength at different temperatures. Journal of Advced Prosthodontics, 75–84. https://doi.org/10.4047%2Fjap.2016.8.2.75
3. Park, H., & Lee, S. H. (2021). Review on Interfacial Bonding Mechanism of Functional Polymer Coating on Glass in Atomistic Modeling Perspective. Polymers, 13, 2244. https://doi.org/10.3390/polym13142244

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