Adrian Carrera
When discussing advanced polymers and composite bearing materials you’ll often hear terms like hydrophilic, hydrophobic, oleophilic, oleophobic, and hygroscopic. These terms describe how materials interact with water, oils, and humidity, and they play a critical role in bearing performance.
At TriStar Plastics, our engineers consider these properties during material selection and component design, especially for applications exposed to moisture, oils, chemicals, or sanitation cycles.
Let’s define each term and explain why it matters in real-world engineering applications.
Hydrophilic
Hydrophilic materials absorb or bond with water at the molecular level.
- “Hydro” = water
- “Philic” = attracted to
A hydrophilic material will:
- Attract water
- Allow moisture to spread across its surface
- Potentially swell or change properties in wet environments
In bearing applications, hydrophilic behavior can be undesirable, as absorbed moisture may increase friction, alter dimensional stability, and reduce load-carrying capacity.
Hydrophobic
Hydrophobic materials repel water rather than absorbing it.
- “Hydro” = water
- “Phobic” = repelling
Hydrophobic materials:
- Resist water penetration
- Maintain dimensional stability in wet or washdown environments
- Are ideal for marine, food processing, and outdoor applications
Many self-lubricating polymer bearings are intentionally hydrophobic, helping them outperform metal bearings in wet, corrosive, or submerged conditions.
Oleophilic
Oleophilic materials attract and absorb oils and nonpolar liquids.
- “Oleo” = oil
- “Philic” = attracted to
Oleophilic behavior may be beneficial when:
- Oil retention is desired
- A lubricating film needs to be maintained
However, in dusty or dirty environments, oleophilic materials may trap contaminants, accelerating wear.
Oleophobic
Oleophobic materials repel oils and nonpolar liquids.
Oleophobic properties:
- Prevent oil absorption
- Reduce contamination buildup
- Support cleaner operation
Oleophobic behavior is especially valuable in food, pharmaceutical, and cleanroom environments, where grease or oil contamination is unacceptable.
Hygroscopic
Hygroscopic materials absorb moisture from the air without chemically bonding to it.
Key characteristics:
- Actively attract humidity
- Can change size or weight over time
- May require controlled storage conditions
In bearing design, hygroscopic behavior must be carefully managed, as humidity absorption can:
- Affect press fit
- Change running clearance
- Influence long-term wear behavior
Important Clarification: Water vs. Oil Behavior
Water itself is hydrophilic, meaning it readily mixes with more water.
Oils and fats are generally hydrophobic, which is why oil and water separate into layers rather than mixing.
Understanding this distinction helps engineers predict how bearing materials will behave in mixed environments involving moisture, lubrication, or cleaning agents.
Expert Note from TriStar: Material interaction with water, oil, and humidity is a critical but often overlooked design variable. Our engineers evaluate hydrophobicity, oleophobicity, and hygroscopic behavior alongside load, speed, and temperature to ensure bearings maintain clearance, stability, and performance throughout their service life.
Why These Properties Matter in Bearing Design
These material characteristics directly influence:
- Moisture resistance
- Corrosion prevention
- Lubrication behavior
- Dimensional stability
- Sanitation and regulatory compliance
Selecting the wrong surface chemistry can undermine even the best bearing design. Selecting the right one can eliminate grease, reduce maintenance, and extend service life.
A Note on Terminology
- “Philic” means loving or attracted to
- “Phobic” means repelling or resistant to
These suffixes are widely used in materials science to describe how substances interact with their environment, not emotional responses.
Learn More
There’s much more to explore when it comes to modifying materials to enhance or suppress these properties.
If you need help:
- Selecting a bearing material for wet or oily environments
- Understanding moisture absorption and press fit implications
- Designing for sanitation or clean operation
Reach out to TriStar’s engineering experts for application-specific guidance.
