Particle size is one of the most critical parameters influencing the behavior, performance, and quality of materials across industries. From pharmaceuticals and paints to metallurgy and food systems, particle size directly impacts properties such as flowability, dissolution, stability, and even appearance.
In a recent technical session hosted through Venture Center Analytical Services, the fundamentals of particle size analysis (PSA) were explored in depth. The session focused on how particle size is defined, why it is not always a single measurable quantity, and how different analytical techniques—sedimentation, static light scattering, and dynamic light scattering—are used to characterize particles across size ranges.
This article presents a structured, technical walkthrough of those concepts and techniques.
From Venture Center’s “Only One Analytical Technique” Talk Series with Mr. Manoj Bhataria, Seasoned Analytical Scientist
Why Particle Size Matters Across Applications
Particle size plays a critical role in determining both material performance and process behavior. Key impacts include:
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Flowability: Larger, more spherical particles tend to flow better than irregular particles
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Dissolution: Smaller particles dissolve faster in solutions or suspensions
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Viscosity: Smaller particles can increase viscosity compared to larger ones
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Stability: Smaller particles can improve suspension stability, often alongside zeta potential
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Compaction behavior: Important in processes such as sintering in metallurgy
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Appearance: Color and gloss in paints, and appearance in cosmetics, are influenced by size
Applications span multiple industries:
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Paints and pigments (gloss, reflectivity)
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Food products (color, flavor, texture)
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Cement and construction (hydration, strength)
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Pharmaceuticals (efficacy, delivery behavior)
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Cosmetics (appearance, shelf life)
Particle size is therefore widely used as a quality and performance indicator.
What Is “Particle Size”? Why a Single Number Is Not Always Enough
In ideal cases, particles may be spherical and uniform, making it easy to assign a single size value. However, real-world particles are often:
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Irregular in shape
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Anisotropic (different dimensions)
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Distributed across a range of sizes
This makes it difficult to define size using a single number.
To address this, particle size analysis uses the concept of Equivalent Spherical Diameter (ESD):
A particle is assigned the diameter of a sphere that exhibits the same physical behavior as the particle being measured.
Instead of measuring “size” directly, instruments measure a property related to size, such as:
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Passage through a sieve aperture
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Sedimentation rate
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Scattered light intensity
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Displaced volume
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Projected area (imaging)
Particles that behave similarly in a given measurement are treated as having the same size.
Classification of Particle Size Analysis Techniques
Particle size analysis techniques differ based on:
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Measurement principle
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Size range
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Sample type (wet vs dry)
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Data output (intensity, volume, number distributions)
Common techniques include:
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Sieving (coarse particles)
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Sedimentation (gravity or centrifugation)
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Static light scattering (laser diffraction / Mie scattering)
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Dynamic light scattering (DLS)
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Electrical sensing zone
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Imaging (microscopy, SEM, TEM)
No single technique can cover all particle types and size ranges. Selecting the appropriate method depends on the sample and application requirements.
Sedimentation-Based Particle Size Analysis
Sedimentation techniques measure how particles settle in a fluid under gravity or centrifugal force.
Principle
Particles settle at a velocity determined by:
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Particle size
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Density difference between particle and fluid
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Fluid viscosity
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Gravitational force
Larger and denser particles settle faster, while smaller particles take longer. At steady conditions, particles reach Stokes velocity (terminal velocity).
Measurement Approach
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Measure time taken for particles to travel a known distance
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Use known parameters (viscosity, density difference, gravity)
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Solve for particle diameter
Practical Considerations
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Gravity-based sedimentation can take very long times for small particles
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Centrifugation increases effective gravitational force, reducing analysis time
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Detectors may be optical or X-ray depending on particle properties
Capabilities
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Wide size range (nanometers to hundreds of microns)
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High resolution for closely spaced particle sizes
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Suitable for broad distributions
Limitations
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Time-consuming for small particles
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Dependent on density and viscosity parameters
Static Light Scattering (Laser Diffraction / Mie Scattering)
Static light scattering measures particle size based on how particles scatter light at different angles.
Principle
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A laser beam passes through a particle suspension or dry sample
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Particles scatter light at multiple angles
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Intensity vs angle pattern is measured
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Mathematical models (Fraunhofer or Mie theory) are used to calculate size
Instrument Design
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Multiple detectors placed at different angles
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CCD arrays for small-angle detection
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Fixed-angle or variable-angle configurations
Key Features
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Can handle both wet and dry samples
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Fast measurement
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Suitable for large particle sizes (up to hundreds of microns or more)
Important Considerations
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Fraunhofer model works well for larger particles (> ~50 microns)
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Mie theory required for smaller particles
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Requires knowledge of optical properties for accurate results
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Maintaining suspension for large particles is challenging
Limitations
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Reduced accuracy at very small sizes
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Requires careful model selection
Dynamic Light Scattering (DLS)
Dynamic light scattering measures particle size based on Brownian motion in suspension.
Principle
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Particles undergo random motion in liquid
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Laser light scatters from moving particles
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Scattered intensity fluctuates over time
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Correlation analysis extracts diffusion coefficient
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Particle size is calculated as hydrodynamic diameter (Dh)
Key Characteristics
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Measures time-dependent intensity fluctuations
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Uses autocorrelation function
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Applies Stokes-Einstein relationship
Instrument Setup
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Laser source
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Sample cuvette
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Detector (PMT or APD)
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Measurement at a single angle (e.g., 90°, backscatter, or low angle)
Strengths
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Very fast measurement (seconds to minutes)
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High precision and reproducibility
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No calibration required
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Suitable for very small particles (nanometer scale)
Limitations
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Poor resolution for multimodal distributions
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Strong bias toward larger particles (intensity ∝ diameter⁶)
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Sensitive to contamination and sample preparation
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Not suitable for dry powders
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Requires particles to remain in Brownian motion
Practical Insight
Even a small number of large particles can dominate the signal and mask smaller particles.
Choosing the Right Particle Size Analysis Techniques: No Single Solution
An important takeaway from the session is that:
No single particle size analyzer can meet all requirements.
An “ideal” particle size analysis instrument would:
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Cover all size ranges
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Have perfect accuracy and resolution
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Deliver instant results
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Work for all sample types
Such an instrument does not exist.
Instead, selection depends on:
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Particle size range
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Sample type (dry vs suspension)
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Distribution width
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Industry requirements
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End-use expectations
Mismatch between technique and application can lead to misleading results.
Comparative Insights Across Particle Size Analysis Techniques
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Sedimentation: Highest resolution, excellent for broad distributions
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Static light scattering: Fast, versatile, works with dry and wet samples
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DLS: Best for nanoscale particles, fast but limited for complex distributions
Each technique defines “size” differently (Stokes diameter vs hydrodynamic diameter vs optical equivalent), so results are not always directly comparable.
Conclusion
Particle size analysis is not a single technique but a collection of methods, each based on different physical principles and suited to different sample types. Understanding how each technique defines and measures size is essential for selecting the right method and interpreting results correctly.
Whether using sedimentation, light scattering, or diffusion-based approaches, the key lies in aligning the technique with the sample, the size range, and the application objective. When done correctly, particle size analysis becomes a powerful tool for controlling material performance and ensuring product quality across industries.
Particle Size Analysis at Venture Center
Venture Center provides access to analytical workflows that support particle characterization across techniques and applications. As part of Venture Center’s open-access ecosystem, the facility enables startups, researchers, and industry users to evaluate particle size using appropriate methods based on their specific sample and application requirements.
The emphasis is on method selection, practical applicability, and correct interpretation, ensuring that particle size data supports real-world decision-making rather than just measurement.
Book our particle size analysis services today.