Surface Analysis & Modification

Physical and chemical analysis of material surfaces is critical to understanding how they interact with the process environment or at the interface where two different materials come into contact. Wet chemical surface analysis techniques provide the tools to explore the surface and subsurface chemistry of solid materials. At BOC Sciences, our skilled staff has a range of surface analysis techniques ideal for solving your specific problem. Any analytical requirements or process issues will be evaluated for quick turnaround, and practical interpretation of results before selecting the appropriate technique or range of techniques and the ideal sample preparation method.

Surface Analysis

Surface Tension Measurement

The wettability of a surface or the surface tension of a liquid has become a key factor in product performance and a mandatory consideration in the manufacturing process. We are able to accurately measure contact angle and surface tension of liquids, as well as dynamic contact angle, powder contact angle, surface free energy, interfacial tension and critical micelle concentration. A deeper understanding of surface chemistry can also be gained by combining contact angle measurements with other surface analysis techniques from BOC Sciences Lab Services.

Crosslink Density Determination

Crosslinking is the process by which a bond is formed between one polymer chain and another one. This process can be initiated accidentally or intentionally by heat, pressure, changes in pH, etc. Cross-linking bonds affect the physical properties of the polymer and make the polymer more beneficial for various applications. The crosslink density of a polymer is defined as the density of crosslinked bonds in a polymer and is used as an excellent quality control method for polymer crosslinking. Our chemists use ASTM-D2765 as a method guide to determine the crosslinking density of polymers, and our quick and easy wet chemical analysis procedure can be applied to most of polymer materials.

• First, the gel content and swell ratio for a known mass of polymer is determined after extraction in an appropriate solvent at a specific temperature for a specific time
• Then, the material is removed from the solvent and reweighed before and after drying
• Finally, the less material that is extracted, the less the material swells, then the higher the crosslink density

Surface Analysis Modification

Wet chemical methods involve a reaction between the surface to be modified and the compound in solution. Surface modified by wet chemical methods indicate a significant increase in roughness and hydrophobicity/hydrophilicity, depending on the application. A typical example is the hydrolysis of polyesters, where water reacts with the ester groups and produces hydrophilic polar groups. Ammonolysis is another typical example of a reaction in which hydrophobic groups can be replaced by more hydrophilic amine groups.

• Polyester hydrolysis

During polyester hydrolysis, the cleavage of ester bonds creates carboxyl and hydroxyl groups in the very surface degraded polymer, which will contribute to the hydrophilization of the mat. However, hydrolysis with water only is too slow, so dilute acids or bases are used to accelerate the reaction. Materials modified by wet chemical methods are shown to exhibit increased hydrophilicity, water absorption and permeability to water.

• Aminolysis

In some cases, two or more wet chemical methods can be combined to achieve the desired wettability, such as the recent widespread use of aminolysis. The amine groups on the surface produced by the first treatment are used to absorb [Ag(NH₃₎₂]⁺ ions and the Ag nanoclusters are immobilized by electroplating techniques. The surface has a rough surface due to the presence of nanoparticles, leading to superhydrophobicity with high contact angle values and low values of contact angle hysteresis. Ammonolysis was also used to induce cross-linking of the electrospun PSMA mats by treating their maleic anhydride groups in hydrazine or ethylenediamine solutions. Untreated PSMA fibers showed heterogeneous wettability, while mats treated with hydrazine or ethylenediamine presented higher water absorption capacity, indicating that the hydrophilization by wet chemical methods was effective.

Figure 1. Aminolysis-based surface modification of polyesters for biomedical applications. (Zhu, Y.; et al. 2013)

Surface Functionalization

• Explore different methods of soft chemical synthesis in liquid solutions and study/optimize reaction mechanisms
• Attachment of species formed in solution to various supports (silicon, glass, stainless steel, metals, polymers, textiles ...) onto them and prospect/develop derived surface functions

Figure 2. Schematic illustration of (a) preparing liquid metal particles, and (b) surface modification of the liquid metal particles. (Bark, H.; Lee, P. S. 2021)