Surface zeta potential in industrial application

Certain processes (e.g., dyeing, along with brightness and finishing operations) are strongly related to textile surface properties and to interactions with the environment. You can use the surface zeta potential to monitor and characterize the functionalizing of textiles – which is done to create impregnated wipes for hygiene or bactericidal and insecticidal curtains – and as an indicator for the cleaning effectiveness of laundry detergents and softeners.

For laundry to be successfully washed, textiles have to adsorb detergents and fabric softeners. Adsorption and desorption processes are strictly related to the interfacial interactions between the aqueous bath and the textile (1). Zeta potential change can be used to monitor these adsorption and desorption kinetics.

The graph displays the zeta potential over pH of an untreated textile blend composed of 70% cotton and 30% modacrylic fibre before and after adsorption of a quaternary ammonium (quat) or a softener. After adsorption of detergents (quaternary ammonium, softener), the IEP shifts from an initially acidic pH towards a basic pH. This indicates a change of the chemical behavior of the fabric after adsorption. 

• Relevance of zeta potential analysis for textiles

Although you can find polymers being used in various industrial applications, their inert surface can be a constraint. Modifying or activating the polymer surface prior to further processing, however, lets you enhance a material’s wettability, printability, or adhesion. Surface zeta potential measurements can correlate changes in the charging behavior at the solid-liquid interface with the degree of surface activation. This gives you a quantitative view of surface modifications and a reproducible quality of products.

The graph shows low-density polyethylene (LDPE) foils that were surface-activated by UV light irradiation and exposed to sulfur dioxide (SO₂). The graph compares the pH-dependent zeta potential of the untreated foil with a surface-activated one. You can see significant changes in both the IEP and the zeta potential. The inert surface of the untreated foil marked by an IEP at pH 4 changes dramatically. The IEP shifts to pH 2, and the final absolute zeta potential decreases in magnitude indicating a chemically modified surface. 

• From Inert to Active – Polymer Surface Activation Characterized by the Zeta Potential

In healthcare, medical devices are everyday items for administrating drugs and life-saving treatments. It’s vital that syringes, catheters, heart valves or stents, and many other instruments, perform well. Surface characterization and modification (e.g., coatings) can optimize how you use medical devices. Zeta potential measurements help you characterize surface properties, evaluate coatings and cleaning efficiencies, and monitor how well bioactive substances or components are adsorbed.

Take the example of syringes. They are either prefilled or empty and are used every day to administer particular drugs. The inner surface of the syringe is in contact with the applied substance. Adsorption and any reactivity with the inner surface need to be avoided in order to guarantee efficiency and safety of the applied substance.

This graph shows the comparison of the pH-dependent zeta potential of polymer and glass syringe barrels. Here, siliconized glass barrels behave very similarly to polymer barrels, with an IEP at pH 4 and a highly negative zeta potential in the acidic range. For glass barrels without silicone coating, the IEP shifts to pH 2.3, revealing the efficient removal of the silicone layer.

• Zeta potential studies on the surface treatment of prefilled syringe barrels

To test the cleaning efficiency, a silicon wafer with a silicon nitride top layer was exposed to different etching protocols. This is shown in the graph. The pH dependence of the zeta potential clearly shows the difference between the as-received silicon nitride wafer (SiN untreated) and a silicon wafer with native silicon oxide coating (SiO). When rinsed with diluted hydrofluoric acid (HF), the isoelectric point of the silicon nitride wafer gets shifted towards a higher pH. Treating it with hydrofluoric acid removes the partial oxidation layer that develops on the surface of silicon nitride during storage. Oxidation with Piranha solution prior to the rinse with hydrofluoric acid shifts the isoelectric point even further towards a higher pH. This treatment is used to remove organic contaminants that protect the as-received silicon nitride wafer from attack by hydrofluoric acid. Surface zeta potential thus helps monitor the effect of different cleaning strategies

• Relevance of Zeta Potential for Wafer-Particle Interaction during the CMP Process

Biomaterials are substances or materials that have been engineered to interact with biological systems. They are designed for medical or therapeutic purposes such as replacing a tissue function or a piece of bone in the body. Due to this, biocompatible materials need to be engineered and optimized. Here, surface characterization and modification both play major roles in minimizing the health risks of various products (e.g., implants). The adsorption kinetics of proteins on an implant’s surface are the first step for cell growth – and thus biocompatibility – making their analysis of major interest as well

A typical biomaterial is titanium, which is used to make artificial joints and dental implants. The graph shows a comparison of the pH-dependent zeta potential of untreated and coated titanium discs. The untreated titanium (cp Ti) has an IEP of 3.6 and a highly negative absolute zeta potential in the physiological pH. When exposed to a protein solution of bovine serum albumin (cp Ti+BSA), however, the titanium surface attracts this globular protein, and the zeta potential reveals the changes in the surface charge. Here, you can see a significant shift in the IEP to 5 and a decrease in the absolute zeta potential magnitude, which demonstrates what an efficient coating can do.

• Race for the Surface: Surface Zeta Potential Analysis of Implants

Cosmetics change the surface properties of hair and skin. Throughout the day, both of these are exposed to water, light, heat, and even pollutants. Hair needs to be cleaned and softened without destroying its structure or irritating the scalp. Monitoring these processes with surface zeta potential studies based on streaming potential technology lets you evaluate the efficiency and quality of cleaning reagents and cosmetic products.

Shampoo, conditioner, and rinsing cycles all influence hair. By determining the streaming potential of these, you can monitor their influence over time.

Applying shampoo decreases the absolute streaming potential, which reveals the change in surface chemistry of the hair sample. This is reversed with a rinsing cycle. In contrast, applying conditioner decreases the streaming potential magnitude and reverses the charge. This change is not reversed by rinsing, indicating the conditioner’s excellent efficiency.

• The beauty and the zeta potential - Determine formulation stability and behavior of cosmetic products