Marine biofouling generally refers to the undesirable adhesion of marine organisms onto objects with the immersion in seawater. Marine biofouling causes the increase of energy consumption and emission of Greenhouse Gas [1
], while it also damages and corrodes the structure of equipment immersed in water bodies, such as shipping vessels and offshore rigs [4
]. These problems reduce production efficiency in related industries [6
] and ultimately harm the development of the economy. Thus, many approaches have been exploited to mitigate fouling and one of the most effective ways is using antifouling coating [7
]. However, the most efficient coatings, tributyl tin (TBT)-based coatings, inhibited marine fouling through the release of toxic substances. That causes imposex, intersex, and sterility for marine organisms, as well as altering shell growth in molluscs [8
]. It has been limited by the International Marine Organization (IMO) in 2001. As an alternative environmentally-friendly antifouling coating, fouling release coatings based on polydimethylsiloxane (PDMS) have long-lasting antifouling efficiency and non-toxic releases [1
]. It has become the focus of the development of new antifouling coatings.
This is a very complex and dynamic process for marine biofouling [10
]. It includes four stages: (1) the formation of a conditioning layer; (2) the settlement of microorganisms; (3) the colonization of algal spores and marine larvae; and (4) the attachment of large organisms [11
]. There are large number of proteins, polysaccharides, and other organic materials in the marine environment, and these organic materials form conditioning layers. Surfaces of objects immersed in seawater will be covered inevitably by the conditioning layer in a short time. Thus, reducing the settlement of microorganisms becomes the primary consideration, and inhibition of this stage can effectively reduce the damage of the follow-up stages. Specifically, it is experimentally confirmed that adhesion is proportional to the value, which is equal to the square root of the product of the elastic modulus (E
) and surface free energy (γ) [14
]. It can be defined as the relative adhesion factor, and it reveals that the low elastic modulus and low surface energy is better able to inhibit marine fouling, especially in microorganisms. In addition, the surface smoothness and thickness of coating also have an impact on the antifouling effect [14
Fouling release coating based on PDMS has low surface energy and low elastic modulus [14
]. These properties minimize the adhesion strength between marine organisms, especially in microorganisms and substrate surfaces, and marine biofouling is easily removed via mechanical cleaning or hydrodynamic during sailing [1
]. More importantly, coating does not release toxic substances. However, this antifouling coating has the following disadvantages [1
]: mechanical damage is susceptible to happen and also displays poor adhesion strength with substrates [16
]. The reason for these disadvantages is in the molecular structure of the polymer. Silicon atom and oxygen atom alternates to form the basic backbone of PDMS: –Si–O–. Distinguishing from the common basic backbone of –C–C–, the molecular chain of PDMS is very flexible, and causes poor mechanical strength of PDMS polymer. In addition, PDMS polymer exhibits non-polarity, and weakens the adhesion with substrates.
In recent years, researchers have made a lot of work to solve the shortcomings of this coating. Most research studies have focused on PDMS-modified material, whereby PDMS is used as a substrate, and other organic materials provide high mechanical properties [17
]. However, it is less on determining the mechanical properties of coating influenced by particle.
As an important part of antifouling coating, in addition to the basic function–coloration and cover, particles also play an important role in enhancing the mechanical properties of coatings [27
]. It is expected that the mechanical properties of coatings based on PDMS will be changed owing to the addition of the particle, thereby likely changing the antifouling performance. However, the influence of particles on coatings based on PDMS has been researched independently [29
]. Further, most studies were limited to changing the additive amount of particles. There is no systematic comparative study for different particles. Particles could not be mixed unlimitedly into PDMS. When it reaches the maximum mixing value, more than this value, particles will precipitate. Further, the value is also an important parameter for comparing and analyzing the effects of different kinds of particles on coatings. Research of maximum mixing value of the particle can also help to determine the effect of the particle on coating properties. Thus, the PDMS coatings reinforced by particles were prepared by a two-stage process in the current study: (1) particles and PDMS were firstly mixed via high speed mechanical agitation to prepare the pre-dispersed slurry; (2) then coating was reacted by pre-dispersed slurry and curing agent under catalytic conditions. A total of seven types of particles were used in this experiment, including barium sulfate, tourmaline, titanium dioxide, nano-silica, fumed silica, nano calcium carbonate, and nano titanium dioxide. The particle size of these particles is from micrometer to nanometer. Further, these particles have been applied in coating industry. For barium sulfate, it was used to improve mechanical properties of coatings [34
]. Tourmaline has the characteristics of releasing negative ions and radiating far infrared rays [29
], and can be applied in the antifouling field and affect the adhesion of fouling organism. Titanium dioxide also has good cover function. For nano particles, the influence of nano effect on marine coatings has also become the focus of research [30
]. Research was performed to analyze the influence factors of the dispersion tolerance. Further, the effects of particle on properties of coatings were also investigated under the condition of dispersion tolerance.