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1. ​Definition and Solubility

• ​Dyes:
  • ​Solubility: Typically soluble in water or organic solvents, penetrating materials at a molecular level (e.g., textile fibers).
  • ​Application: Applied via adsorption, chemical bonding, or physical diffusion.
• ​Pigments:
  • ​Solubility: Insoluble in media; dispersed as solid particles in carriers (e.g., inks, paints).
  • ​Application: Fixed to surfaces using binders (e.g., resins).

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2. ​Color Performance

• ​Dyes:
  • ​Advantages: Vibrant colors, high transparency; ideal for gradient effects (e.g., silk dyeing).
  • ​Disadvantages: Poor lightfastness; prone to fading under prolonged UV exposure (e.g., some acid dyes).
• ​Pigments:
  • ​Advantages: Strong opacity, excellent lightfastness (e.g., titanium dioxide, phthalocyanine blue); suitable for outdoor coatings and plastics.
  • ​Disadvantages: Less vivid than dyes; particle texture may reduce smoothness.

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3. ​Applications

• ​Dyes:
  • ​Textiles: Coloring cotton, silk, wool (e.g., reactive dyes, direct dyes).
  • ​Biological Staining: Laboratory cell staining (e.g., methylene blue).
• ​Pigments:
  • ​Coatings and Inks: Architectural paints, printing inks (e.g., iron oxide red, carbon black).
  • ​Plastics and Cosmetics: Coloring plastics (e.g., ultramarine), pearlescent pigments in lipsticks and eyeshadows (e.g., mica-titanium).

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4. ​Lightfastness and Durability

• ​Dyes:
  • ​Lightfastness: Most degrade under UV light; UV absorbers may extend lifespan (e.g., automotive interior fabrics).
  • ​Wash Resistance: Reactive dyes form covalent bonds with fibers, offering better wash durability.
• ​Pigments:
  • ​Weather Resistance: Inorganic pigments (e.g., chromium oxide green) resist heat, acids, and bases; used in automotive and industrial coatings.
  • ​Stability: Highly resistant to migration and chemical degradation.

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5. ​Environmental and Safety Considerations

• ​Dyes:
  • ​Risks: Some synthetic dyes contain heavy metals (e.g., azo dyes may release carcinogenic aromatic amines); compliance with OEKO-TEX® standards is critical.
  • ​Trends: Natural dyes (e.g., indigo, madder) are eco-friendly but limited by low yield and high cost.
• ​Pigments:
  • ​Safety: Inorganic pigments may contain heavy metals (e.g., cadmium red), but modern regulations (e.g., EU REACH) restrict their use; organic pigments (e.g., phthalocyanines) are safer.
  • ​Recycling Challenges: Residual particles complicate wastewater treatment.

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6. ​Cost and Processing

• ​Dyes:
  • ​Cost: Simple application but water- and energy-intensive (e.g., indigo dyeing for denim requires multiple rinses).
  • ​Suitability: Ideal for large-scale continuous production.
• ​Pigments:
  • ​Cost: Complex dispersion processes (micron-level grinding) require high equipment investment.
  • ​Suitability: Preferred for high-value products (e.g., automotive paints, premium cosmetics).

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​Conclusion: Choosing the Optimal Option

• ​Choose Dyes When:
  • Vibrant colors and transparency are needed (e.g., scarves, watercolor art).
  • Materials are permeable (e.g., textiles, paper).
• ​Opt for Pigments When:
  • High weather resistance and opacity are required (e.g., exterior paints, plastic toys).
  • Long-term stability in opaque media is critical (e.g., printing inks, automotive coatings).

Modern Trends: Nanotechnology-driven dye-pigment hybrids (e.g., “nanodyes” with enhanced lightfastness) and bio-based pigments (e.g., bacterial pigments) balance performance and sustainability.