Technology created by researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) is literally shedding light on some of the smallest particles to detect their presence – and it’s made from tiny glass bubbles.

The technology has its roots in a peculiar physical phenomenon known as the “whispering gallery,” described by physicist Lord Rayleigh (John William Strutt) in 1878 and named after an acoustic effect inside the dome of St Paul’s Cathedral in London. Whispers made at one side of the circular gallery could be heard clearly at the opposite side. It happens because sound waves travel along the walls of the dome to the other side, and this effect can be replicated by light in a tiny glass sphere just a hair’s breadth wide called a Whispering Gallery Resonator (WGR).



A magnified photograph of a glass Whispering Gallery Resonator. The bubble is extremely small, less than the width of a human hair.




When light is shined into the sphere, it bounces around and around the inner surface, creating an optical carousel. Photons bouncing along the interior of the tiny sphere can end up travelling for long distances, sometimes as far as 100 meters. But each time a photon bounces off the sphere’s surface, a small amount of light escapes. This leaking light creates a sort of aura around the sphere, known as an evanescent light field. When nanoparticles come within range of this field, they distort its wavelength, effectively changing its color. Monitoring these color changes allows scientists to use the WGRs as a sensor; previous research groups have used them to detect individual virus particles in solution, for example. But at OIST’s Light-Matter Interactions Unit, scientists saw they could improve on previous work and create even more sensitive designs. The study is published in Optica.

Today, Dr. Jonathan Ward is using WGRs to detect minute particles more efficiently than ever before. The WGRs they have made are hollow glass bubbles rather than balls, explains Dr. Ward. “We heated a small glass tube with a laser and had air blown down it – it’s a lot like traditional glass blowing”. Blowing the air down the heated glass tube creates a spherical chamber that can support the sensitive light field. The most noticeable difference between a blown glass ornament and these precision instruments is the scale: the glass bubbles can be as small as 100 microns– a fraction of a millimeter in width. Their size makes them fragile to handle, but also malleable.

Working from theoretical models, Dr. Ward showed that they could increase the size of the light field by using a thin spherical shell (a bubble, in other words) instead of a solid sphere. A bigger field would increase the range in which particles can be detected, increasing the efficacy of the sensor. “We knew we had the techniques and the materials to fabricate the resonator”, said Dr. Ward. “Next we had to demonstrate that it could outperform the current types used for particle detection”.


A diagram showing the new WGR experiments. Test particles (shown here in green) are passed through a light field, which distorts the light wavelength, which can be used to detect the particles.


To prove their concept, the team came up with a relatively simple test. The new bubble design was filled with a liquid solution containing tiny particles of polystyrene, and light was shined along a glass filament to generate a light field in its liquid interior. As particles passed within range of the light field, they produced noticeable shifts in the wavelength that were much more pronounced than those seen with a standard spherical WGR.

With a more effective tool now at their disposal, the next challenge for the team is to find applications for it. Learning what changes different materials make to the light field would allow Dr Ward to identify and target them, and even control their activity.

Despite their fragility, these new versions of WGRs are easy to manufacture and can be safely transported in custom made cases. That means these sensors could be used in a wide verity of fields, such as testing for toxic molecules in water to detect pollution, or detecting blood borne viruses in extremely rural areas where healthcare may be limited.

For Dr. Ward however, there’s always room from improvement: “We’re always pushing to get even more sensitivity and find the smallest particle this sensor can detect. We want to push our detection to the physical limits.”
By Andrew Scott

The objective of this work is to improve the structural characteristics of hollow glass microsphere filled epoxy syntactic foam composites with little voids content and improved hollow glass microsphere dispersion in the composite.

A modified degassing technique has been introduced during resin casting process of the hollow glass microsphere filled syntactic foam composites. The effect of hollow glass microsphere content volume fractions (5–25%) on the degassing techniques was examined. The syntactic foam composites were characterized by analysing structural morphology using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy(TEM), and density measurements (theoretical and experimental).

Less than 5% void content has been achieved in this study. This resulted in improved tensile and dynamic mechanical properties (DMA).

Hollow glass microspheres are increasingly being used in the construction of energy-efficient building structures by several constructors, designers, and building owners. The product is extensively accepted to be utilized in coatings in order to achieve high overall solar reflectance within building coatings. These coatings have the capability to reflect solar energy back into the atmosphere, which is achieved by utilizing conventional fillers like calcium carbonate, and titanium oxide among others.

Increasing adoptionof titanium oxide coated hollow glass microspheres.

Increasing application scope in paints and coatings.

Growing product consumption across Asia-Pacific.

In order to give full play to the effect of hollow glass microspheres, it is necessary to ensure that the hollow structure remains intact during the addition process. The strong shear in the twin-screw extruder can easily break the glass beads. Once the hollow glass beads are broken, they will become glass fragments with a density of 2.5g/cm3, which cannot achieve weight reduction. This is also the main reason why many application products did not achieve the desired effect in the initial stage of the experiment.
Therefore, how to reduce the breakage rate of microbeads in the twin-screw extruder granulation process is the key to the excellent performance of hollow glass microbeads.
Specifically, it can be considered from the extruder thread combination, feeding and pelletizing method, main engine speed, and compressive strength of microbeads.

01 . Adjustment of twin screw thread combination



In a twin-screw extruder, the shear force of the screw on the material makes the filler evenly dispersed. The spherical shape of the microbeads is easier to disperse, and excessive shear force can easily cause them to break. Therefore, the angle of the thread block of the meshing section should be adjusted, and the shear force should be reduced according to the low shear design. The specific adjustment method is as follows (real shot by St. Wright Laboratory):







After improving the thread combination
Comparison of crushing rates caused by different feeding methods and granulation methods




02. Adjustment of feeding method
To better reduce the bead breakage rate, you should:
1) Select side feeding to reduce the chance of microbeads being sheared in the screw.
2) Select long particles for granulation to reduce the damage of strong mechanical force during granulation.
After improving the thread combination
Comparison of crushing rates caused by different feeding methods and granulation methods





1. Sanlight HS46, compressive strength: 16000psi, D90 (typical value) 30μm, specific gravity 0.46g/cm3.
2. Sanlight HL60S, compressive strength: 18000psi, D90 (typical value) 55μm, specific gravity 0.60g/cm3.

03. The influence of the rotational speed of the twin-screw machine
When the rotation speed is high, the shear force on the material is greater, which makes the microbeads more easily broken. Therefore, under the premise of ensuring the production process, reduce the speed and reduce the shear force of the screw.
After improving the thread combination, long particle granulation and side feeding conditions
Comparing the crushing rate caused by different screw speeds




When the content of microbeads is about 10wt%, the crushing rate of microbeads increases with the increase of screw speed, and the crushing rate rises to 7.23% at 400r/min.

04. Common problems and solutions






1) What is the normal breakage rate of microbeads during extrusion?
Due to the problem of the processing method, the microbeads will have a certain breakage rate during the extrusion process.

Adjust the screw combination, add microbeads to the side feed, granulate long particles, and the crushing rate can be controlled at 2-3%.

2) Does the addition of microbeads affect the resin processing performance?
Microbeads are an inorganic powder filler, similar to other inorganic fillers, which can improve the heat resistance of the resin after adding. Therefore, the processing temperature is increased.

1. The extruder is at the original processing temperature;
2. Add a small amount of lubricant to the formula to solve.

3) After the microbeads are fed from the side, how to ensure the uniformity of feeding?
1. Side feeding chooses twin-screw forced feeding;
2. A stirring rod should be added to the side feeding to prevent microbeads from “bridging” and ensure uniform feeding.
4) Will the mechanical properties of the resin drop significantly after adding microbeads?
Part of the impact performance will be sacrificed after adding microbeads, but part of the flexural modulus can be improved.

ways to improve:
1. Add a small amount of toughening agent;
2. Modify the surface of the microbeads with a coupling agent to improve the binding properties of the microbeads and the resin.
In addition, the compatibility of hollow glass microspheres with resin is not good, and the interfacial adhesion between resin and glass microsphere material will become poor, which will greatly reduce the performance of hollow glass microspheres, so improve the interfacial adhesion between them. Compatibility is very important.

Commonly used methods to improve compatibility include:
(1) Add compatibilizer: use coupling agent or maleic anhydride graft resin to improve the interface adhesion between the two;
(2) Surface etching: using acid and alkali to produce a large number of defects on the surface of the microbeads, at this time, the resin will be filled into the defect gap to achieve a stable effect;
(3) Surface modification: Through the reaction of strong oxidants and or acid-base and SiO, compatible functional groups such as silicon carboxyl groups and hydroxyl groups are generated; these functional groups can also be modified, and these modified functional groups can be grafted, polymerization and other reactions. Thereby improving the interfacial adhesion.

FROM: Eighth Element Plastic Edition

Hollow glass microspheres are industrially useful lightweight materials that exhibit high mechanical performance and are flexible. These are used as reinforcing materials in a polymer matrix to produce lightweight composites. According to Researcher, the global hollow glass microspheres market is expected to witness a moderate growth rate during the forecast period. Product innovations and technological advancements in the hollow glass microspheres industry are going to drive the global market. Moreover, growth in multiple other applications such as plastics, paints, and life sciences further pushes the market growth.

Of the many fillers now available to composites manufacturers, hollow glass microspheres, also called micro-balloons, are the most versatile.Microspheres pack a lot of functionality into a tiny package. Hollow glass microspheres can be produced by processing perlite that is a common volcanic glass.

The most obvious benefit of the hollow microsphere is its potential to reduce part weight, which is a function of density. Compared to traditional mineral-based additives, such as calcium carbonate, gypsum, mica, silica, and talc, hollow glass microspheres have much lower densities. Densities and crush ratings, however, vary dramatically across product lines. The market is expected to continue to be driven by the ongoing product developments in the hollow glass microsphere industry.

As the search continues for lower material costs, without sacrificing performance or processability, glass bubbles are getting more attention. Reducing density with additives is not new, but bubbles are showing advantages.

As the search continues for lower material costs, without sacrificing performance or processability, glass bubbles are getting more attention. Reducing density with additives is not new, but bubbles are showing advantages.

Resin compounder Noble Polymers (Grand Rapids, MI), a subsidiary of manufacturer Cascade Engineering, has developed a low-density resin formulation that reduces the weight of parts molded of TPO (thermoplastic polyolefin) by up to 20%. It’s a masterbatch bulk resin additive that incorporates hollow glass bubbles to displace resin and reduce part density in molded, thermoformed, and extruded products.

“Mandated standards for Corporate Average Fuel Economy (CAFE), along with the drive to reduce industrial emissions and achieve more sustainable production methods, have led to a growing demand for enhanced TPO production methods,” says Tim Patterson, Noble Polymers business unit manager. “Glass bubble additives in our masterbatch material displace hydrocarbon-based resin content and lighten parts to help cut transport fuel consumption.

“Use of density-reducing agents for filled TPO raw material is not a new concept,” Patterson continues. “While various filler materials have been used to reduce TPO part density, glass bubbles have significant process and resin displacement advantages over alternate fillers. We’ve found that the addition of glass bubbles yields secondary benefits to TPO components as well, including improved part stiffness, greater dimensional stability, and reduced shrinkage.”

Patterson says traditional resin-displacement mineral fillers such as cenospheres, asbestos particulate, chopped glass fiber, and calcium carbonate (CaCO3) have considerably less volume per unit weight than glass bubbles. For example, 1 kg of typical glass bubble material has a volume of 1666.7 cm3, while the equivalent weight of CaCO3 displaces only 370.4 cm3. Thus its resin displacement potential per unit of weight is only a fraction of that of glass bubbles.

Glass bubble selection
Wang says the class of bubbles selected for a masterbatch depends on the end use of the TPO component. For example, the pressures involved in TPO molding require glass bubbles with elevated crush strength. Glass bubble strength is generally proportional to density, and thus lower-strength bubbles are less dense, and offer greater potential for TPO weight reduction than thicker-walled, higher-strength bubbles.

According to Wang, bubble size impacts TPO surface finish as well as stress transmission through the composite, with smaller bubbles contributing to more favorable impact and tensile properties. “In general, higher-strength bubbles are required for injected molded interior and exterior automotive components, and other industrial components,” says Wang.

Noble’s development work shows that mold shrinkage in a TPO part is inversely proportional to the volume percentage of glass bubbles in the mix. The modulus (stiffness) of a part also increases in proportion to the ratio of glass bubbles to resin. The positive attributes of increased stiffness and heat distortion temperature (HDT) as well as decreasing coefficient of linear thermal expansion (CLTE), shrink, warp, and sink marks continue to improve as the percentage of glass bubbles in the resin mix rises. Tensile strength, elongation, and impact strength tend to decrease as well. Complementary additives in the masterbatch can modify these values to some degree.

“In general, plastics are flexible and experience ductile failure under stress, while glass adds stiffness but is more prone to brittle breakage,” said Wang. “It is possible to improve TPO impact strength by adding an impact modifier to the masterbatch that reduces potential for brittle failure while maintaining the stiffness advantage.”

According to Wang, the concentration of glass bubbles in a masterbatch additive mix varies, but can be as much as 50% by weight, depending on customer requirements. Finished parts made using this masterbatch glass bubble concentration will be 20% or more lighter than resin-only parts.

“Process tests show that a Noble masterbatch formulation with glass bubbles can cut TPO injection molding production time as much as 20%,” says Wang. “This benefit is apparently related to changes in thermal properties that result from displacing resin with hollow glass (reduced mass), and the resulting time savings are concentrated primarily during the cooling period.”

In addition to automotive, exploring markets such as building materials, composite materials, sporting goods, and construction applications, where benefits seen include weight reduction, processing improvements, and product design enhancements, according to William Donahue, business manager, Resin System Additives.

And the cost compared with straight TPO? “There is a premium that can be offset by manufacturing improvements, weight reduction, and/or product enhancements,” says Donahue. “The potential cost savings depends upon the density and the cost of the polymer.”

Noble Polymers works with individual customers to determine precise TPO part specifications, and multiple interests are weighted in a staged/gate process to achieve optimum density reduction while meeting necessary physical specifications. The resulting formulas are confidential and proprietary to customers. Patterson estimates that nearly half of the company’s TPO masterbatch customer applications call for some degree of formula customization, while the balance can be met using the company’s standard masterbatch material.


The development of the times has put forward higher requirements for materials, shoes are lighter, cars are more fuel-efficient, plastic products are more environmentally friendly, processing performance is better, cost is lower, and quality is better…
These are the source of material innovation and the driving force of the development of the times. As a new type of functional filler, hollow glass microspheres have gradually come under the spotlight of the material industry, bringing possibilities for more innovations.

Application of hollow glass microspheres in resin system
High-strength, low-density hollow glass microspheres can be used as lightweight additives in a variety of polymers and applications, while maintaining or improving processability and material physical properties, including:
1) Polyolefins, nylon composites and other thermoplastics
2) Thermosetting materials, liquids and pastes
3) Sheet molding and bulk molding composites
4) Elastomers
5) Substitute wood/polymer composites

Performance improvement of hollow glass microspheres for resin systems
The hollow microspheres can withstand processing conditions such as temperature and pressure of blending, injection molding, extrusion and other manufacturing processes. Correct use can improve product quality:

reduce weight
First of all, the density of glass beads is 0.4-0.75g/cm3, which reduces the density of the composite material to achieve the effect of weight reduction. Secondly, due to the hollow characteristics, the use of resin is reduced while meeting the performance; The development of aviation lightweight.

Improved dielectric properties
Since the interior of the glass beads is air, the dielectric constant of the air is 1, which makes the dielectric constant of the hollow glass beads very low as a whole, reducing the loss of high-frequency signals, which is very useful in the 5G industry and autonomous vehicles. .

Improve flow performance
Hollow glass microspheres are tiny spheres that play the role of miniature ball bearings in the resin, and have better fluidity than flake, needle or irregular shaped filler particles. The resulting microsphere effect makes mixing The viscosity of the material decreases, the filling performance is naturally excellent, and the good processing performance can increase the production efficiency by 15% to 20%.

Reduce shrinkage and warpage of products
Since spherical objects are isotropic, filled microbeads can overcome the disadvantage of inconsistent shrinkage rates of different parts caused by orientation, ensure the dimensional stability of the product, reduce warpage, and solve the problem that has always existed in the molding of special-shaped materials and large injection molding products. deformation problem. In addition, hollow glass microspheres are used as fillers to improve the processing speed of filling and modified materials and improve production efficiency.

lower oil absorption
The oil absorption rate of hollow glass microspheres is 0.20~0.60cc/g, because of its spherical structure, the specific surface area per unit volume is lower, and the oil absorption value is lower.

Volume cost is more economical
The density of high-performance hollow glass microspheres is only 1/5~1/2 of the resin density, and only a small amount of hollow glass microspheres can be used to replace other heavier powder materials under the same volume. When considering the cost per unit volume, the weight of the product can be reduced after filling, thereby reducing the amount of the main raw material resin and rubber, and reducing the cost of the product.

Reinforced resin rigidity, sound insulation and noise reduction
Hollow glass microspheres are rigid particles themselves, which can improve the compressive strength and modulus of the material after being added to the resin.
At the same time, because the interior of the glass beads is air, the air thermal conductivity is low, and the porous material will absorb the vibration of the sound wave, thereby reducing the heat and hindering the transmission of the sound wave.

FROM:Eighth Element Plastic Edition

White roof coatings have existed in hot countries for a long time. These coatings help to reflect solar energy back into the atmosphere, rather than heating up the building. To achieve this white finish, pigments and fillers like titanium dioxide and calcium carbonate are used.

This article demonstrates that, with the use of hollow glass microspheres in a coating, one can achieve a high level of total solar reflection with the dry film. This helps to reduce the need for energy-intensive cooling systems.

It is worth noting that there are many coating applications possible with this technology and that it is not just restricted to improving the energy efficiency of buildings. Other examples that would benefit from the use of solar heat reflective coatings include caravans, mobile homes, cold storage distribution centres, refrigerated vehicles, oil and gas storage tanks, cryogenic tanks and tankers, and deck coatings.

Total solar emission comprises UV, visible and IR radiation – the latter responsible for heating. In this article, we will show that hollow glass bubbles offer an excellent level of reflection in both the visible and IR regions of the spectrum.

Testing hollow glass microspheres for Total Solar Reflectance when incorporated into a coating
A waterborne coating was formulated for the subsequent TSR testing. Glass bubbles are compared with calcium carbonate on a volume replacement basis. For this study, 22.5% by volume of glass bubbles or calcium carbonate were used.

A Perkin-Elmer spectrophotometer was used to analyse the Total Solar Reflectance of the subsequent coating at 400 microns. hollow glass microspheres outperformed the reference filler (calcium carbonate). Conventionally filled roof coatings absorb over 50% more solar energy compared to systems containing the novel, small particle size glass bubbles. This correlates to impressive temperature reduction. These coatings can also be applied with an airless sprayer, without breakage of the hollow glass microspheres.

How does Total Solar Reflectance correlate with the reflection of heat?
Each coating was painted onto an aluminium panel and exposed to an IR lamp. A thermocouple on the other side of a supporting polystyrene box was monitored over time, to investigate the thermal barrier presented by the coating.

A good correlation is found between Total Solar Reflectance and the level to which heat transfer is reduced through the coating. with a reduction of 10°C when compared to the coating containing only calcium carbonate.

What other benefits can hollow glass bubbles impart to your coating?
Additionally, hollow glass bubbles reduce microcracks forming in the coating, due to the reduction of shrinkage and warpage under temperature fluctuations. These cracks can form thermal bridges through the coating and areas for water infusion, leading to subsequent algae and fungal growth. Glass bubbles reduce crack formation when using nails or screws.

Author: Adam Morgan , Ph.D.

The newest additions hollow glass microspheres offer improved scrub and burnish properties, viscosity control, thermal insulation and sound dampening characteristics, improved performance and other functional properties previously unattainable to paint and coatings formulators.

No one conventional additive can match the multiple performance benefits of hollow glass microspheres. Because they are made of colorless glass they do not discolor light or pastel formulations. Their hollow glass microsphere structure, low density (0.60 and 0.34 g/cc) and small particle size make them ideal for use as extenders for paint formulations.

Paint that is extended with hollow glass microspheres has a lower viscosity than one filled to an equivalent volume with a non-spherical extender. Spherical particles have a low-energy surface that minimizes friction and drag. As a result, an equal volume substitution of these microspheres for irregularly shaped extenders will decrease the coating’s viscosity. Lower viscosity is a significant benefit in offsetting VOC levels in solvent borne paint. Adding microspheres to a high-VOC paint formulation allows formulators to remove some of the solvent and still maintain a viscosity that facilitates application and spreading properties.

With particle sizes considerably finer than previously available, hollow glass microspheres can be used in thin film coatings to improve integrity. Because glass spheres do not absorb resin, more resin is available to create the film. The result is a tighter and more uniform film with improved durability, even under adverse conditions.

Hollow glass microspheres may also be added to improve hiding properties or to replace some of the titanium dioxide (TiO2). The hollow glass microspheres redirect the angle of light, imparting opacity. Depending on the formulation, equivalent tint strength can be achieved with 5%-10% replacement of TiO2.

Magnetic iron oxide coated hollow glass microspheres were developed in response to an identified opportunity in the diagnostic sector. It involved the immobilisation of superparamagnetic iron oxide particles on the surface of a hollow glass sphere using a biological binder molecule.

The superparamagnetic nature of the coating meant that the particles would come to a magnet, but not retain magnetism after release and so would redisperse easily. A thin silica layer on top of the iron oxide helped protect the magentic layer and also provided chemical functionality for the coupling of biological ligands such as antibodies for target capture.

Researchers have successfuly applied hollow glass microsphere to the extraction and quantitation of marine biotoxins from shellfish and have found the material to offer a number of advantages in this area.