pH is one of the most important chemical parameters in materials science and quality control. It is directly related to the concentration of hydrogen ions (H⁺) in a solution or emulsion and provides information about its acidity or base content. Understanding and controlling pH is crucial not only for basic research but also for the food, pharmaceutical, chemical, cosmetic, oil and gas, and agricultural industries.
Emulsions are multiphase systems consisting of a mixture of two immiscible liquids (e.g., oil and water) and are extremely sensitive to changes in pH. pH fluctuations can lead to instability, sedimentation, and even changes in functional properties.
Defoamer emulsion Momentive SAG 1572
Determination of pH value
The pH value refers to the concentration of hydrogen ions and is defined as the negative logarithm of the hydrogen ion concentration:
pH = −log[H+]pH = -\log [H^+]
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pH < 7: acidic environment
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pH = 7: neutral environment
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pH > 7: alkaline environment
The index is normally measured in the range of 0 to 14, but in some concentrated solutions it may exceed this range.
Understanding the pH of an emulsion
Emulsions typically consist of a water phase and an oil phase. pH plays a key role in these systems:
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Emulsion stability: Changes in pH can affect the surface charge of emulsion droplets and cause coalescence or phase separation.
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Surfactant activity: The effectiveness of surfactants depends heavily on pH. Some surfactants are only stable in acidic or alkaline environments.
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Environmental compatibility: In the pharmaceutical and cosmetics industries, the pH value must be close to the natural pH value of the skin or body to avoid irritation.
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Final product quality: In the food industry, pH changes can affect the color, taste, and even nutritional value of a product.
The importance of pH in different industries
1. Food industry
pH control is crucial in the production of dairy products, beverages, sauces, and jams. For example:
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A low pH value prevents bacterial growth.
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In dairy products, pH changes can lead to protein coagulation and texture changes.
2. Pharmaceutical and cosmetic industry
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The pH value of creams and lotions should be close to the pH value of your skin (approx. 5.5).
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In pharmaceuticals, the pH value influences the solubility and absorption of drugs in the body.
3. Chemical industry
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In the production of paints and resins, the pH value plays an important role in product stability.
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In chemical processes, the pH value can change the course of a reaction.
4. Oil and gas industry
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Controlling the pH of oil emulsions is important to prevent corrosion and deposits.
5. Agriculture
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The nutrient solution for hydroponics should have a suitable pH value (5.5–6) to improve the uptake of nutrients by the plant roots.
How to measure pH
1. Sunflower paper
This method is simple and inexpensive, but not accurate and can only indicate a specific level of acidity or alkalinity.
2. pH indicator paper (pH strips)
It has a larger chromatographic range than litmus paper and offers a more precise range (usually accurate to 0.5 pH units).
3. Indicator solutions
For example, phenolphthalein and methyl orange change their color within a certain range.
4. Digital pH meter
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The most accurate method is pH measurement.
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It uses a glass electrode that reacts to H⁺ ions .
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It is capable of calibrating and performing measurements in various solutions and emulsions.
Factors that influence the pH of a solution or emulsion
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Chemical composition: presence of acids, bases and salts.
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Room temperature: Increasing temperature affects the dissociation constant of ions.
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Surfactant concentration: The type and concentration of the surfactant determine the surface charge of the emulsion droplets.
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Shelf life: Over time, pH changes may occur due to chemical reactions or microbial growth .
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Additives: Preservatives, flavors, or bioactive ingredients can cause pH changes.
pH control and regulation
To maintain the quality of a solution or emulsion, the following methods are commonly used:
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Adding a buffer: A mixture of a weak acid and its conjugate base that reduces pH changes.
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Use a pH adjuster such as citric acid, lactic acid, sodium hydroxide or carbonate.
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Continuous monitoring: In sensitive industries, pH values are continuously monitored using online sensors.
pH standards and guidelines
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ASTM E70: Standard Test Method for Acidity of Aqueous Solutions.
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ISO 4316: Guide to pH measurement in various industries.
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FDA regulations: In the food and pharmaceutical industries, pH ranges must meet FDA requirements.
Problems of pH measurement in emulsions
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Heterogeneity of the system: The presence of two phases (water and oil) makes it difficult to carry out accurate measurements.
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Electrode contamination: Oil droplets can contaminate the surface of the pH meter electrode.
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Influence of temperature: Temperature changes can sometimes occur more quickly in emulsions than in simple solutions.
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Limited stability: Chemical or microbiological changes can cause the pH to change over time.
Best practices for pH management of emulsions
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Use a suitable buffer solution to stabilize the pH.
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Calibrate your pH meter regularly with standard solutions.
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Accelerated tests were conducted to investigate pH changes over time.
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Pay attention to the pH of the product to ensure it is compatible with the end use (for example, the pH of cosmetics is close to the pH of the skin).
Finally
pH is a key parameter in the quality control of solutions and emulsions. It not only determines the acidity or alkalinity of the medium, but also plays a crucial role in the stability of the system, the effectiveness of surfactants, environmental compatibility, and the quality of the final product.
A thorough understanding of pH, the selection of appropriate measurement methods, and the application of pH monitoring and adjustment methods can contribute to improving the stability, safety, and quality of industrial production.