Polymer adsorption
A polymer is a large molecule composed of repeating subunits bound together by covalent bonds.
[3] The intermolecular forces between the large polymer molecules are difficult to calculate and cannot be determined as easily as non-polymer surface molecular interactions.
Some examples of polymer surfaces include: polyvinyl chloride (PVC), nylon, polyethylene (PE), and polypropylene (PP).
[3] The adsorption process can be characterized by determining what amount of the ions or molecules are adsorbed to the surface.
To measure the thermodynamics of polymer surfaces, contact angles are often used to easily obtain useful information.
The thermodynamic description of contact angles of a drop of liquid on a solid surface are derived from the equilibrium formed between the chemical potentials of the solid–liquid, solid–vapor, and liquid–vapor interfaces.
The Langmuir equation states that for the adsorption of a molecule of adsorbate A onto a surface binding site S, a single binding site is used, and each free binding site is equally likely to accept a molecule of adsorbate:[1] where: The equilibrium constant for this reaction is then defined as:[1] The equilibrium constant is related to the equilibrium surface coverage θ, which is given by:[1] where: Because many polymers are composed of primarily of hydrocarbon chains with at most slightly polar functional groups, they tend to have low surface energies and thus adsorb rather poorly.
For example, many applications utilize polymers as structural components, but which degrade rapidly when exposed to weather or other sources of wear.
However, the poor adhesive properties of nonpolar polymers makes it difficult to adsorb the protective coating onto its surface.
These types of problems make the measurement and control of surface energies important to development of useful technologies.
Because the physisorption energy is so low for these types of materials, chemisorption is used to form covalent bonds between the polymer coating and the surface of the object (such as a pan) which holds it in place.
Because the relative magnitudes of chemisorption processes are generally much greater than magnitudes of physisorption processes, this forms a strong bond between the polymer and the surface it is chemically adhered to, while allowing the polymer to retain its physisorption characteristics toward other materials.
Protein adsorption can lead to blood clots, the foreign-body response and ultimately the degradation of the device.
[12] By applying a thin monolayer coating of PEG, protein adsorption is prevented at the device site.
[14] Devices that fail to be hemocompatabile run the risk of forming a thrombus, proliferation and compromising the immune system.
By choosing to use hydrophilic polymer coatings, protein adsorption decreases and the chance of negative interactions with the blood diminishes as well.
These advanced composites can be made using many different methods including prepreg, resin, infusion, filament winding and pultrusion.
FRPs respond linear-elastically to axial stress, making them a great material to hold a load.
FRPs are usually in a laminate formation with each lamina having unidirectional fibers, typically carbon or glass, embedded within a layer of light polymer matrix material.
Polytetrafluoroethylene (PTFE) is a polymer used in many applications including non-stick coatings, beauty products, and lubricants.
Carbon-fluorine bonds cause PTFE to be a low-friction material, conducive in high temperature environments and resistant to stress cracking.
