Water Repellent

Whether decorative, protective or functional, coatings must contend with water in the environment. A problem distinct from the issue of wet adhesion and hydrolytic stability of coatings is controlling the interaction of water with a coated surface. Very often the descriptors hydrophobic or hydrophilic are applied to coated surfaces. Although the terms hydrophobic and hydrophilic are casually used, they are usually not defined. A growing number of applications ranging from architectural coatings to aortic stents require precise control and, therefore, precise definition of substrate interaction with water. Silanes are playing an increasing role in controlling the interaction of water with a surface. Silanes are silicon chemicals that possess a hydrolytically sensitive center that can react with inorganic substrates such as glass to form stable covalent bonds and organic substitution that alters the physical interactions of treated substrates (Figure 1). Different than most additives, which have a limited performance range, they can achieve surface properties ranging from hydrophobic to hydrophilic. They may be a sole active ingredient or a component in a coatings formulation, controlling the interaction of water over a broad spectrum of requirements. In order to understand how silanes can affect hydrophobicity and hydrophilicity, it is important to understand some of the fundamentals of the interaction of water with surfaces.

A NEWLY prepared stearyl alcohol / poly (N-vinyl-2-pyrrolidone).(SA/PVP) hybrid emulsion was used, as a water repellent finish, alone or in combination with some phenolic compounds namely tertiary butyl hydroquinone (TBHQ), curcumin and vanillin, in easy care finishing formulations. The results obtained reveal that: i) finishing fabric samples with different concentrations of the hybrid emulsion in absence of the aforementioned phenolic compounds, significantly enhances fabric weight, tensile strength, stiffness, water repellency, antibacterial, water vapor resistance and thermal resistance properties along with a gradual decrease in the resilience, surface roughness and air permeability of treated fabric, ii) using the hybrid emulsion with the above phenolic compounds efficiently enhances the storage life of the emulsion and upgrades the antibacterial properties of treated fabric, iii) addition of vanillin provides the finished fabric with pleasant scent, curcumin upgrades the UV protection property of treated fabric and TBHQ slightly enhances tensile strength, surface roughness, air permeability, water vapor resistance and thermal resistance along with a reduction in the resilience of treated fabric, and iv) the prepared hybrid emulsion, whether in absence or presence of TBHQ, can be used as extender for fluorocarbon textile finishes.

The wetting of solid surfaces by water droplets is ubiquitous in our daily lives as well as in industrial processes.
In the present research work, water repellent porous silica films are prepared on glass substrate at
room temperature by sol–gel process. The coating sol was prepared by keeping the molar ratio of methyltriethoxysilane
(MTES), methanol (MeOH), water (H2O) constant at 1:12.90:4.74, respectively, with 2 M
NH4OH throughout the experiments and the molar ratio (M) of MTES/Ph-TMS was varied from 0 to 0.22.
A simple dip coating technique is adopted to coat silica films on the glass substrates. The static water contact
angle as high as 164 and water sliding angle as low as 4 was obtained for silica film prepared from
M = 0.22. The surface morphological studies of the prepared silica film showed the porous structure with
pore sizes typically ranging from 200 nm to 1.3 lm. The superhydrophobic silica films prepared from
M = 0.22 retained their superhydrophobicity up to a temperature of 285 C and above this temperature
the films became superhydrophilic. The porous and water repellent silica films are prepared by proper
alteration of the Ph-TMS in the coating solution. The prepared silica films were characterized by surface
profilometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier
Transform Infrared (FT-IR) spectroscopy, humidity tests, chemical aging tests, static and dynamic water
contact angle measurements.

Bu çalışmada, öncelikle nanomalzemelerin yapı üretiminde ve mimaride kullanımları ele alınmış olup sonrasında yapı malzemelerinde en çok kullanılan nanomalzeme türleri belirtilmiştir. Daha sonra dünyada özellikle son yıllarda çeşitli ülkelerde yapılmış çalışmalar ışığında nanomalzemelerin, yapı malzemesi yüzeylerine su iticilik kazandırmak için nanokompozit malzeme olarak kullanılması incelenmiştir. Son olarak nanomalzemelerin, çevresel etkileri ve sağlık açısından risk durumları değerlendirilmiştir.

As a result of a multi-year conservation/restoration program for the gardens of the National Palace of Queluz in Portugal, the opportunity to evaluate the long-term performance of conservation interventions on the marble statues that decorate these Baroque gardens was presented. The observations have shown that although water repellents may reduce the rate of biocolonization on the statues and vases they strongly influence re-colonization patterns. In general, unsightly streaking develops which can be attributed to the formation of preferential water paths. The latter will favour biological colonization and eventually, be literally etched into the stone. It would appear that the application of higher amounts of a water repellent, and in solution rather than in an aqueous emulsion, enhances the appearance of streaking on these marble elements. Further research is needed to elucidate these observations. A practical solution to the problem presented by these decorative elements was found by regular application of a biocide, since this can be applied locally by maintenance personnel, while water repellents require a professional application.

Surface wettability, as one of the most crucial properties of solid surface, is a very common interface phenomenon in
our daily life and nature. The authors obtained water-repellent porous silica microbowl-like structure by controlled
sol-gel method with tetraethaoxysilane (TEOS) as a precursor and 3,3,3-trifluropropyltrimethoxysilane (TFPTMOS)
as a coprecursor. The water-repellent properties of the coatings were raised with increasing molar ratio (M) of
TFPTMOS/TEOS. The prepared silica coatings showed water-repellent behavior with water contact angle of 136 ± 3°
and sliding angle of 18 ± 1° without any posthydrophobization. In conclusion, the wetting properties were dependent
on the micro-/nano-structure and the chemical composition of the coatings.

Development of the solid surfaces with waterrepellent
and self-cleaning ability has attracted much
research interest in recent years. In the present research
work, we have prepared water repellent silica coatings on
glass at room temperature (*27 C) by sol gel process and
surface silylation technique. Coating sol was prepared by
keeping the molar ratio of tetramethoxysilane (TMOS),
methanol (MeOH) and water (H2O) constant at
1:12.36:4.25, respectively, with 0.01 M NH4F. The dip
coated silica films were surface silylated using two different
silylating agents namely hexamethyldisiloxane
(HMDSO) and hexamethyldisilazane (HMDZ). The
HMDSO and HMDZ in hexane solvent were varied from 0
to 1 vol.% and silylation period was varied from 1 to 3 h.
The HMDSO and HMDZ modified films showed dense and
porous surface morphology, respectively. The HMDSO
modified silica films showed static water contact angle of
122 whereas HMDZ modified films showed 165. The
HMDZ modified films displayed the extreme water repellency
comparing with that of lotus leaves. The silica films
were characterized by surface profilometer, scanning
electron microscopy, transmission electron microscopy,
Fourier transform infrared microscopy, thermal and chemical aging tests, optical transmission and static water
contact angle measurements.