Ultra-low fouling
Consequently, a necessity for anti-fouling surfaces has arisen in many fields: blocked pipes inhibit factory productivity, biofouling increases fuel consumption on ships, medical devices must be kept sanitary, etc.
To be considered effective, an ultra-low fouling surface must be able to repel and withstand the accumulation of detrimental aggregates down to less than 5 ng/cm2.
[1] A recent surge of research has been conducted to create these surfaces in order to benefit the biological, nautical, mechanical, and medical fields.
However, PDMS coating's hydrophobicity [3] causes any adsorbed particles to increase the surface energy, easing adhesion[4] and ultimately defeating the purpose.
[3] In aqueous environments the alternative is to use high-energy hydrophilic coatings; whose chains become hydrated by the surrounding water and physically bar adsorbates.
[1] The length of the chains is easily manipulated by varying the degree of polymerization by changing the ratio of initiator to monomer.
[8] SPRs used in this type of experimentation have a detection limit of 0.3 ng/cm2 for nonspecific protein adsorption[9] allowing for the identification of a surface which is capable of achieving ultralow fouling (<5 ng/cm2).
From the measured change in RI the ability of an adsorbate molecule to bind to the surface of a material can be determined by where
Also measured by ellipsometry, a film thickness too small or too large results in increased protein adsorption, indicating that some optimal value unique to the surface must be reached to achieve ultra-low fouling.
[1] The effect of film thickness and RI on nonfouling properties can be better studied by varying the water content of the solution.
[1] However, when the water concentration is too high, film thickness is decreased due to increased radical recombination of the polymer chain.
Sustainable alternatives like topographically modified cellulose are also of high interest due to recyclability and low cost.
Superhydrophobic xerogels made from silica colloids have been shown to reduce bacterial adhesion, specifically S. aureus and P.
[14] The non-fouling applications of these polymers and superhydrophobic coatings is of substantial importance to the field of medical devices.
Traditionally, marine biofouling has been prevented through use of biocides: substances that deter or eliminate organisms upon contact.
Emerging regulations by the International Maritime Organization (IMO) have all but ceased application of biocides, causing a rush to research environmentally friendly ultra-low fouling materials.
Toxic copper, iron, and zinc oxide pigments are mixed with rosin derivative binders to produce both water-soluble matrix paints, which are adhered to surfaces with bituminous-based primers.
In contrast, insoluble matrix paints must use higher molecular weight binders: acrylics, vinyl polymers, chlorinated rubbers, etc.
The most effective metallic variation utilized is tributyltin (TBT) water-soluble self-polishing paint, whose effectiveness in 1999 was estimated to save close to $US 2400 million and coat 70% of commercial ships: However TBT, copper, zinc, and all other heavy metal coatings have been outlawed by the IMO.
[16] Fouling-release properties have also been reportedly improved via attachment of quaternary ammonium salts to the polymer backbone.
Alloys of nickel and copper have also been shown to resist corrosion and pitting, which is of interest in piping systems for mechanical application, specifically in the offshore oil industry.
