The Science of Particle Size & Stability in Coatings

In this interview, Dr. Beverly Barnum and Weichen Gan from Bettersize Instruments share their expertise on particle characterization and its impact on the performance of inks, paints, and coatings

Can you please introduce yourselves and tell us about your current role at Bettersize Instruments? 

Dr. Beverly Barnum:

I am Dr. Beverly Barnum, a senior application scientist at Bettersize Instruments. I earned my Bachelor of Science degree in chemistry from California State University and later completed a Ph.D. in organic chemistry at the University of Pennsylvania. My passion lies in innovative problem-solving, and I am committed to advancing technological solutions in my field.

Weichen Gan:

My name is Weichen Gan, and I am an application scientist at Bettersize Instruments. I received my bachelor’s degree in material science and engineering from Harbin Institute of Technology and went on to earn a master’s degree in the same field from the University of Florida. Since joining Bettersize, I have been focusing on characterizing the physical properties of inorganic materials and providing relevant solutions to support our work.

Inks, paints, and coatings are widely used across various industries. Can you explain their primary applications and how they differ from one another? 

Dr. Beverly Barnum:

Inks, paints, and coatings are used in a wide range of applications, from printing and writing instruments to art, automotive finishes, industrial machinery, and protective coatings for buildings. While they share some similarities, each serves a distinct purpose.

• Inks are liquid or paste substances used primarily for writing, printing, and drawing. They consist of pigments, solvents, and other components that create a stable and workable medium.
• Paints add color, protection, and sometimes texture to surfaces. Whether used for artistic expression, home décor, or industrial applications, paints are typically made of pigments suspended in a liquid medium that includes a binder, solvent, and additives.
• Coatings are similar to paints but are often formulated for specific functional purposes beyond aesthetics. They enhance surfaces with protective, decorative, or performance-related properties. Examples include varnishes, lacquers, and enamels, commonly used in industries like automotive, aerospace, and construction.

Despite their differences, inks, paints, and coatings all serve to impart color, protection, and functional properties to surfaces. Their effectiveness depends on the proper dispersion of pigments to ensure uniform color and performance. Stability is key—preventing settling, clumping, or degradation is essential for maintaining quality.

Pigments play a central role in all three, as they determine color by absorbing specific wavelengths of light. They are stable at normal temperatures and have high tinting strength, meaning only a small amount is needed to achieve vibrant color when mixed with a carrier.

What is a particle, and how does it relate to materials such as inks, paints, and coatings?

Dr. Beverly Barnum: 

A particle is a small unit of matter with defined physical properties, such as mass, volume, and shape. Particles can vary widely in size and composition, ranging from subatomic particles like electrons and protons to larger particles like grains of sand.

In the context of materials such as inks, paints, and coatings, particles typically refer to the small solid components, such as pigments and fillers, that are dispersed within a liquid or solid medium to impart specific properties to the final product. Common materials include carbon black, titanium dioxide, and both organic and inorganic pigments. 

Several key particle parameters influence the performance and quality of inks, paints, and coatings. Particle size refers to a single value representing the diameter of an individual particle, while particle size distribution describes the proportion of particles of different sizes within a sample.

Rather than focusing on a single particle’s size, particle size distribution provides information about the range, ratio, and pattern of particle sizes within a sample, often represented graphically. This distribution significantly impacts the performance and quality of the final material. Particle shape refers to the geometric characteristics of individual particles, including form, roundness, and aspect ratio.

These characteristics affect how particles interact with each other and with the surrounding medium, influencing material properties and performance. Common particle shapes include spherical, plate-like, elongated, and irregular forms.

Image Credit: Muzi pear studio/Shutterstock.com

How does analyzing particle shapes help in optimizing the performance of inks, paints, and coatings? 

Dr. Beverly Barnum: 

Analyzing particle shape helps in understanding and optimizing factors such as dispersion, stability, optical properties, and mechanical strength of the final product. Surface area refers to the total exposed outer surface of a particle or group of particles, measuring the amount of surface available for interaction with other substances.

It is directly related to particle size, meaning smaller particles have a larger surface area per unit mass compared to larger particles. This is often referred to as specific surface area.

Porosity refers to the proportion of empty spaces or voids between particles within a material and is a key factor in determining how well particles pack together. It is directly related to particle size distribution.

Density refers to the mass of a particle per unit volume and influences the behavior and performance of particles in various applications. Density can be classified into two types. True density is the mass of the particle divided by its actual volume, excluding any pores or voids within the particle. Bulk density is the mass of a collection of particles divided by the total volume they occupy, including the spaces between particles.

How do particle size and shape affect the hiding power and color strength of inks, paints, and coatings? 

Dr. Beverly Barnum: 

Hiding power, or opacity, refers to the covering ability of a coating. Smaller particles have a larger surface area-to-volume ratio, which allows them to scatter light more effectively. This increased scattering enhances the hiding power of the coating, making it more effective at covering the surface.

Optimized particle size distribution, with a mix of larger and smaller particles, improves hiding power by maximizing light scatter and filling gaps in the coating. Smaller particles also tend to enhance hiding power by increasing light scattering, while larger particles contribute less to opacity.

Proper optimization of particle size distribution is key to achieving the desired level of hiding power in inks, paints, and coatings. Particle size and shape influence also affect the color strength of inks, paints, and coatings by affecting light absorption and scattering.

Color strength refers to the intensity of color a pigment can impart to a material and is directly related to particle size.

Well-dispersed fine particles provide better color consistency and hiding power, resulting in a vibrant color appearance. In contrast, larger, poorly dispersed particles scatter light less effectively, leading to weaker color strength and a more muted or dull appearance.

Spherical particles provide smooth and uniform dispersion, contributing to consistent color strength, while irregularly shaped particles scatter light in multiple directions, which can enhance color strength.

A well-balanced distribution of particle sizes and shapes enhances color strength by maximizing light absorption and scattering, resulting in more vibrant and intense colors. Particle size analyzers, such as laser diffraction instruments, can be used to measure particle size distribution and correlate it to color strength.

How do particle size and shape impact other characteristics of inks, paints, and coatings? 

Dr. Beverly Barnum: 

Particle size and shape can also affect various other properties of inks, paints, and coatings. In terms of viscosity, smaller particles have a higher surface area, increasing viscosity, which influences the ease of application and leveling. Irregular shapes also increase interactions with the surrounding fluid, leading to higher viscosity.

In mechanical properties, smaller particles enhance smoothness and durability, while irregular shapes improve mechanical interlocking, which enhances adhesion and scratch resistance. For durability, smaller particles fill voids effectively, creating denser and more durable materials, whereas irregular shapes improve wear resistance and the ability to withstand mechanical stress.

In terms of weathering, smaller particles provide better coverage and protection against environmental factors, while irregular shapes enhance resistance to moisture and UV radiation.

What is zeta potential, and how does it relate to the stability of colloidal suspensions in inks, paints, and coatings? 

Dr. Beverly Barnum: 

Zeta potential is not a property of the particle itself but rather a property of the system, which includes both the particle and the dispersion medium. It is a measure of the electrical potential at the slipping plane of the particle within the medium and indicates the degree of electrostatic repulsion or attraction between particles.

A high zeta potential means strong electrostatic repulsion, like the repulsion between magnetic poles. This repulsion helps prevent agglomeration and ensures stable dispersion. Zeta potential is a critical parameter for understanding and controlling the stability of colloidal suspensions, such as those found in inks, paints, and coatings.

What are some key factors that affect zeta potential?

Dr. Beverly Barnum: 

Several factors affect zeta potential. The pH of the suspension can alter the surface charge of the particles, influencing their electrostatic interactions. The ionic strength of the solution and the type of electrolyte ions present can also modify zeta potential by compressing the electrical double layer around the particles.

Temperature also plays a role by affecting the viscosity and dielectric constant of the medium, as well as the diffusion and mobility of ions in the suspension.

Particle concentration can lead to particle-particle interactions, which has been found to influence the overall zeta potential. Additionally, the presence of surfactants or polymers, the properties of the solvent, and surface modifications of the particles can alter their surface charge, thereby affecting the zeta potential.

How can manufacturers optimize zeta potential to ensure stable dispersions in inks, paints, and coatings? 

Dr. Beverly Barnum: 

Manufacturers can optimize zeta potential by adjusting pH and conductivity to achieve the optimal electrostatic balance for stable dispersions. The use of dispersing agents, such as surfactants and stabilizers, enhances electrostatic or steric repulsion between particles, further preventing aggregation.

Ensuring stability in formulations is essential to prevent settling, agglomeration, and flocculation, which helps maintain product properties throughout storage and application. Proper control of zeta potential and stability ensures that each batch maintains uniformity, performance, and quality, minimizing variations and defects.

What are some of the key formulation challenges in developing high-quality inks, paints, and coatings? 

Dr. Beverly Barnum: 

Developing high-quality inks, paints, and coatings involves addressing several formulation challenges. One challenge is achieving consistent particle size distribution. Smaller particles may aggregate, forming large clusters that affect performance.

To address this, advanced particle size analyzers are used to monitor and control particle size distribution, while dispersion techniques break up aggregates and ensure uniform particle size.

Another challenge is balancing stability and performance. Environmental factors such as temperature and humidity can affect stability. Stability testing under various conditions helps identify optimal formulations, and the use of compatible stabilizers and performance enhancers ensures long-term product reliability. 

In terms of processing challenges, it can be hard to effectively prevent sedimentation and caking, which is key to ensuring a long shelf life and uniform application. Particles can settle over time, causing component separation, and high-viscosity formulations may form hard lumps that are difficult to redisperse.

Solutions include using thickeners and stabilizers to maintain suspension, controlling viscosity for smooth consistency, and optimizing storage conditions such as temperature and humidity to reduce caking.

Ensuring uniform mixing is another challenge, as uneven distribution of pigments, binders, and additives can impact color and performance, especially in large batches. Mechanical mixers help break up clumps and ensure even distribution, while real-time monitoring techniques assess mixing efficiency and allow for parameter adjustments as needed. 

How do quality control measures help maintain batch-to-batch consistency? 

Dr. Beverly Barnum: 

Maintaining batch-to-batch consistency is critical for product reliability and customer satisfaction. Variability in raw materials and process conditions can lead to differences in color, viscosity, and performance.

To address this, strict quality control measures are implemented, including incoming raw material inspection and testing. Standard operating procedures (SOPs) for production processes ensure consistency, while regular calibration and maintenance of equipment guarantee accuracy and reliability.

How do environmental factors impact product performance, and what solutions can mitigate these effects? 

Dr. Beverly Barnum: 

Environmental factors such as temperature, humidity, and exposure to light can degrade pigments, binders, and additives, leading to changes in color, stability, and performance. To mitigate these effects, environmental testing is conducted to assess product stability under different conditions.

The use of robust formulation additives resistant to environmental factors enhances durability, and optimized packaging protects products from external influences.

What advanced characterization techniques can be used to optimize formulations and quality control? 

Dr. Beverly Barnum: 

Advanced characterization techniques are essential for optimizing formulations and ensuring quality control in inks, paints, and coatings. These methods provide detailed insights into particle properties and formulation performance, helping maintain consistency and effectiveness.

One widely used technique is laser diffraction, which measures particle size distribution to ensure uniformity within a formulation. Dynamic light scattering further refines this analysis by providing precise measurements of fine particles in colloidal systems. To assess electrostatic stability and prevent aggregation, zeta potential measurement helps maintain stable dispersions.

To optimize viscosity and application properties, rheology analysis evaluates flow behavior, ensuring smooth and even application. Electron microscopy offers highly detailed images of particle size, morphology, and surface topography, providing a deeper understanding of structural characteristics.

For long-term stability assessment, static multiple light scattering monitors dispersion stability over time, while image analysis examines particle size, shape, and distribution within the formulation. Finally, Brunauer-Emmett-Teller (BET) analysis measures particle porosity, offering valuable insights into surface area and potential interactions with surrounding materials.

How can formulation parameters be optimized to enhance product performance and consistency? 

Dr. Beverly Barnum: 

Optimizing formulation parameters is key to improving product performance and consistency. This involves fine-tuning composition and processing conditions to achieve the desired properties.

For instance, adjusting pH levels helps optimize zeta potential, which enhances stability and prevents issues like agglomeration and sedimentation. Choosing the right stabilizers ensures proper dispersion and reduces the risk of particle aggregation.

Carefully fine-tuning additive concentrations is also essential. This helps maintain the right balance between performance and stability without compromising either aspect. Achieving the optimal blend of additives improves durability, gloss, and adhesion, resulting in high-quality inks, paints, and coatings.

Can you provide a real-world example of how particle size affected spray paint performance? 

Weichen Gan:

In a case study involving a leading paint provider, frequent nozzle clogging was observed—an issue that was highly unusual. To investigate, the Bettersizer 2600 was used to analyze particle size distribution, revealing the presence of oversized particles. While most particles fell within the correct size range, the distribution curve showed a distinct peak of larger particles, highlighted in the red box.

These oversized particles disrupted the formulation’s uniformity, causing inconsistent flow and clogging. An animation further illustrated how agglomerates formed, leading to nozzle blockages and spray paint failure.

With the help of the Bettersizer 2600, the paint provider was able to quantify and pinpoint the issue, adjust their process, and implement a finer filtration system to eliminate the problem.

What are the key features of Bettersizer 2600 that make it effective for analyzing spray paint quality? 

Weichen Gan:

Bettersizer 2600 is an award-winning laser diffraction particle size analyzer that was recognized at the 2024 i-NOVO Awards. It offers exceptional measurement capabilities with a modular design that accommodates both paint suspensions and pigment dry powders. With a unique optical design, it covers a wide particle size range, measuring from 0.02 to 2600 microns with wet dispersion and 0.1 to 2600 microns with dry dispersion.

In addition, the Bettersizer 2600 measures particle shape, which is another crucial factor in spray paint performance. The powerful PIC-One image analysis module provides dynamic imaging capabilities, covering particles from 2 to 3500 microns. This versatility is achieved through the combination of laser diffraction for rapid size analysis and dynamic imaging for detailed shape characterization.

How does the Bettersizer 2600 improve upon traditional particle size measurement methods? 

Weichen Gan:

Traditional methods like sieving and filtering have played a crucial role in paint production for many years.

Sieving offers a systematic and reliable way to separate particles, but it comes with challenges—especially when working with fine materials around 40 microns or smaller. Limitations in mesh size and the tendency of particles to clump together can make it difficult to achieve precise separation. As a result, sieving may fall short when it comes to delivering the accuracy needed for modern paint formulations.

The Bettersizer 2600 provides a more advanced solution for particle size analysis. It enables precise measurement and control of particle size distribution, ensuring consistent spray paint quality while reducing common defects.

Unlike sieving, which, while systematic, lacks precision, the Bettersizer 2600 offers highly reliable measurements backed by detailed statistical data from a large sample of particles. This level of accuracy enhances quality control and helps optimize paint formulations more effectively.

How does the BeNano series contribute to evaluating ink quality through zeta potential testing? 

Weichen Gan:

The BeNano series plays a critical role in assessing ink quality by analyzing zeta potential, which directly affects nanosized pigment dispersibility and stability. In ink formulation, maintaining stable dispersion is essential to prevent clogging, ensure consistent color output, maintain the correct ink viscosity, improve print resolution, and extend shelf life.

Instability in dispersions can lead to sedimentation, viscosity changes, and flocculation, which negatively impact ink performance. The BeNano instrument helps analyze suspension stability, allowing for targeted adjustments to optimize ink formulations.

Can you provide an example of how BeNano has been used in ink analysis? 

Weichen Gan:

A nano pigment ink sample was put to the test using the BeNano instrument, which measured a zeta potential of around 30 millivolts. This showcased BeNano’s accuracy in analyzing complex ink formulations packed with nanosized pigments.

Knowing the zeta potential makes it easier to fine-tune ink stability. Take water-based inks, for example—tweaking the pH with acids or bases changes the surface charge of pigment particles. Adding salts can also adjust the ionic strength, affecting the double layer around the particles and helping to keep the dispersion stable.

What makes BeNano a reliable instrument for nanoparticle and zeta potential analysis? 

Weichen Gan:

The BeNano is built for precision and versatility in nanoparticle and zeta potential analysis. It delivers accurate zeta potential measurements, even in samples with low electrophoretic mobility—something that can be especially tricky to analyze.

For a more in-depth look at zeta potential across different pH levels, the BAT-1 autotitrator integrates seamlessly with BeNano, making comprehensive analysis easier. Plus, with DLS backscattering technology, BeNano can measure particles as small as 0.3 nanometers and handle concentrations of up to 40 %, giving it impressive range and flexibility.

How do you analyze the stability of coatings and other suspension systems? 

Weichen Gan:

Stability in coatings and suspension systems depends on multiple factors, including steric hindrance, particle size, density, viscosity, pH range, and temperature. To analyze stability effectively, we use Static Multiple Light Scattering (SMLS), a powerful, non-destructive, simple, and fast technique.

SMLS works by shining a light source onto the sample, with detectors collecting the resulting scattered light. The optical system scans across the sample, gathering optical signal data over time.

SMLS instruments typically provide both transmitted and backscattered optical signals. Since coatings are often opaque, transmitted light signals tend to be weak, making backscattered light the preferred metric for analyzing coating stability. 

The SMLS instrument records two types of data: raw data and delta data. Raw data represents the original, unprocessed signal detected by forward or backward detectors and serves as a baseline for comparison. Delta data, on the other hand, quantifies changes in the sample over time by calculating the difference between subsequent scans and the initial reference scan.

This allows us to track the evolution of the sample structure. For example, when analyzing sedimentation, delta data shows a characteristic pattern where backscattered light increases at the bottom of the sample while decreasing at the top. This indicates that particle concentration at the top is decreasing while it is increasing at the bottom, confirming that sedimentation is occurring.

How is stability quantified in coatings analysis? 

Weichen Gan:

Stability is quantified using the instability index, which is calculated by accumulating the differences between successive scans. These differences are mathematically combined into a single value that represents the overall stability of the sample at a given moment.

A lower instability index (IUS) value, such as 0.5, indicates a stable system, while a higher value, such as 10 or more, suggests significant instability, including sedimentation, flocculation, or delamination.

Can you provide an example of how the instability index is applied? 

Weichen Gan:

In a study of titanium oxide coating samples, the instability index was used to compare the effects of different surfactants. The sample containing 1 % Span 80 showed a rapid increase in instability over time, as indicated by a steeply rising instability index curve.

In contrast, the sample containing 1 % SDS exhibited a relatively flat curve with a low instability index, demonstrating greater stability throughout the one-hour test period. The instability index offers both discrete snapshots of stability at specific moments and an overall view of how the system evolves over time.

What are the limitations of the instability index? 

While the instability index provides a convenient, quantitative assessment of overall stability, it does not specify the exact mechanism of destabilization. It captures numerical values and trends, but it does not indicate whether instability is due to sedimentation, agglomeration, or another process.

For a deeper understanding of the destabilization mechanism, we must analyze the delta data, which provides detailed insights into how and why the system is changing.

Can you tell us about the BeScan Lab's Stability Analyzer and its capabilities? 

Weichen Gan:

BeScan Lab's Stability Analyzer is based on SMLS technology, providing quick and direct stability measurements. It captures subtle variations much faster than the human eye and offers both qualitative and quantitative stability assessments.

This analyzer can recognize a range of unstable phenomena, allowing users to study destabilization kinetics in detail. It is capable of handling various sample types, including films, suspensions, and emulsions, even at high concentrations—up to 95 % by volume, as seen in applications like paints and inks.

In addition, because the BeScan Lab is non-destructive, non-contact, and requires no dilution or shearing, it preserves the integrity of the sample. Its integrated system allows multiple BeScan Lab units to be connected, enabling simultaneous measurement of multiple samples and saving valuable time in the analysis process.

How should one choose between Electrophoretic Light Scattering (ELS) and SMLS for particle characterization? 

Weichen Gan:

Both ELS and SMLS provide valuable insights, but they are suited for different applications.

SMLS is the preferred choice when a comprehensive stability evaluation is needed, as it offers both qualitative and quantitative analysis. It provides a quantitative view of stability dynamics, revealing how quickly a system changes over time and offering insights for optimizing formulations and ensuring product quality.

SMLS is ideal for samples with sufficient volume, typically between four and 25 milliliters, and is well-suited for high-viscosity, highly concentrated samples.

In contrast, ELS is the preferred method when the focus is on electrostatic stabilization. It is ideal for rapid stability evaluations, often providing results in less than a minute. ELS is also beneficial when working with limited sample sizes, as it only requires 0.75 to 1.5 milliliters of sample.

ELS testing can provide valuable information on particle size distribution through a Dynamic Light Scattering (DLS) test. By carefully considering these factors, users can select the most appropriate technique for their specific needs, ensuring the highest possible quality for their products.

How have Bettersize products contributed to success in the paint, ink, and coating industries? 

Weichen Gan:

Bettersize products have played a crucial role in helping leading brands optimize their formulations and achieve high-quality results. Companies in the paint, ink, and coating industries rely on Bettersize instruments for their particle characterization needs.

Whether it is optimizing formulations for vibrant packaging, ensuring precise particle size control for critical pigments in coatings, or addressing challenges in dispersion stability, Bettersize has been a long trusted partner in driving innovation.

The success stories of companies using Bettersize products continue to grow, and we are proud to provide them with the tools necessary to advance their research and production processes.

 

About Beverly Barnum and Weichen Gan

Beverly Barnum, PhD is a Senior Application Scientist at Bettersize Inc. She received her Bachelor of Science degree in Chemistry from California State University and earned her PhD in Inorganic Chemistry from the University of Pennsylvania. Recognized for innovative problem-solving, Dr. Barnum is a highly accomplished scientist committed to advancing technological solutions.

Weichen Gan, MS is an Application Scientist at Bettersize Instruments. He received his Bachelor of Science degree in material science and engineering from Harbin Institute of Technology and earned an MS in material science and engineering from the University of Florida. Since joining Bettersize, Weichen has focused on the characterization of the physical properties of inorganic materials and has helped provide relevant solutions.

 

This information has been sourced, reviewed and adapted from materials provided by Bettersize Instruments Ltd.

For more information on this source, please visit Bettersize Instruments Ltd.