KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 https://bestjournal.
id/index.
php/kovalen Hydrophobicity Properties of Silica-Dimethylsilicone Oil-Stearic Acid Based Materials Applied as Waterproof Coating Materials Joko Suryadi1A.
Annisa Sri Rahmawati1.
Derina Maulinda1.
Ndaru Dwiyatmoko Mukti2.
Andhika Putera Utama2.
Haryadi1 .
Department of Chemical Engineering.
Politeknik Negeri Bandung .
Production Steam Field.
PT Geo DIPA Energi Unit Dieng Abstract.
Geothermal solid waste is one of the byproduct materials from the geothermal energy process.
The silica extracted from this solid waste can be utilized as a raw material for waterproof coatings.
The waterproof or hydrophobic properties in this study have been studied with a formulation of silica, stearic acid, and dimethyl silicone oil.
The technique of extracting silica from geothermal waste is carried out using the sol-gel method.
Preparation of hydrophobic materials is carried out by mixing silica with stearic acid at a ratio of 1:3, 1:5, and 1:7 on a mass basis with the addition of dimethyl silicone oil as an emulsifier.
The hydrophobic silica-dimethyl silicone oil-stearic acid materials were synthesized and characterized by functional group analysis using FTIR.
The best hydrophobic properties are shown in a ratio of silica and stearic acid of 1:5.
On a glass substrate, the silica-dimethyl silicone oil-stearic acid coating produced a contact angle of 110.
2 A.
On a fabric substrate, the coating exhibited a superhydrophobic phenomenon with a contact angle of 153.
7 A.
Keywords: superhydrophobic, water repellent coating, stearic acid, silica Abstrak.
Limbah padat geotermal merupakan salah satu material hasil samping dari proses pengolahan energi yang bersumber dari panas bumi.
Kandungan silika dalam limbah padat ini dapat dimanfaatkan dengan cara diekstrak dan direkayasa, salah satunya adalah sebagai bahan baku pelapis anti-air pada permukaan material.
Sifat anti-air atau hidrofobisisitas dalam penelitian ini telah dipelajari dengan formulasi antara silika, asam stearat dan dimetilsilicone oil.
Metode ekstraksi silika dari limbah geotermal dilakukan dengan metode sol-gel.
Pembuatan material hidrofobik dilakukan dengan pencampuran antara silika dengan asam stearat pada perbandingan 1:3.
1:5.
dan 1:7 berbasis massa dengan ditambahkan dimetilsilicone oil sebagai emulsifier.
Hasil yang didapatkan adalah material hidrofobik silika-dimetilsilicone oil-asam stearat mampu disintesis dengan karakteristik yang ditunjukkan dari analisis gugus fungsi dengan FTIR.
Sifat hidrofobik terbaik ditunjukkan pada perbandingan silika dan asam stearat 1:5.
Pada substrat kaca, pelapis silika-dimetilsilicone oil-asam stearat menghasilkan sudut kontak sebesar 110,2A.
Pada substrat kain, pelapis dapat menunjukkan fenomena superhidrofobik dengan nilai sudut kontak sebesar 153,7A.
Kata kunci: superhidrofobik, pelapis anti air, asam stearat, silika Received: March 6, 2026.
Accepted: April 25, 2026 Citation: Suryadi.
Rahmawati.
Maulinda.
Mukti.
Utama.
, and Haryadi.
Hydrophobicity Properties of SilicaDimethylsilicone Oil-Stearic Acid Based Materials Applied as Waterproof Coating Materials.
KOVALEN: Jurnal Riset Kimia, 12.
, 23-33.
INTRODUCTION
a depth of 2000 m which passes through lava In geothermal energy processing, the flows in volcanic areas.
In practice, the process geothermal well drilling process is carried out to involves the flow of geothermal fluids that contain a lot of silicic acid at high temperatures.
Corresponding author E-mail: joko.
suryadi@polban.
The cooled silicic acid will settle on the walls of the geothermal well pipe as solid SiO2 (Gallup https://doi.
org/10.
22487/kovalen.
2477-5398/ A 2026 Suryadi.
, et al.
This is an open-access article under the CC BY-SA license.
KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 Suryadi.
, et al.
& von Hirtz, 2015.
Svavarsson et al.
, 2.
The this study will be applied to a wider range of solid silica has no use value in the geothermal substrates, such as glass and polyester fabrics.
energy extraction process, so it is considered waste in geothermal power generation units.
The utilization of silica waste converted MATERIAL AND METHODS Materials into silica has been carried out in the fields of The raw materials used were solid construction, forensics, textiles, bioanalysis, geothermal waste samples from PT.
Geo Dipa adsorbents, and as a catalyst (Gupta, 2020.
Energi Dieng unit.
The reagents used in the Irshad & Rahul, 2017.
Jenie et al.
, 2020.
Naat, study had pro analysis levels, namely sulfuric Paramitha et al.
, 2019.
Untoro et al.
acid, nitric acid, hydrochloric acid, sodium The wider utilization of silica is by modifying its hydrophobic properties so that it reagents in the synthesis of silica and coatings can be applied as a coating material (Crucho, included dimethylsilicone oil (DSO) from Shin- Ghodrati et al.
, 2023.
Taurino et al.
etsu Japan, ethanol at technical levels, and Silica-based coating materials then distilled water.
continue to develop, especially in the use of Instrumentation Supporting Characterization of the silica layer includes techniques on silica, resulting in hydrophobic the morphology of the hydrophobic silica layer characteristics of the coating material that in the substrate using the image method from reach superhydrophobic levels (Al-Husseny et the results of the Zeiss Scanning Electron , 2022.
Ismail et al.
, 2021.
Jiang et al.
, 2025.
Microscopy (SEM) with a magnification of Latthe & Rao, 2012.
Sutar et al.
, 2020.
20,000 times, the presence of functional groups Sutar et al.
, 2.
Hydrophobic agents using the Shimadzu Prestige 21 Fourier commonly used in the synthesis of hydrophobic Transform materials are derivatives of silane compounds.
Contact angle to see the level of which are still relatively expensive and difficult hydrophobicity of silica with the substrate using to obtain.
the Oppo 12 cellphone camera with data In this study, an alternative to hydrophobic agents, stearic acid, is used, which is more Infrared (FTIR) processing using ImageJ and Microsoft Excel widely available.
The use of stearic acid as a hydrophobic agent has been used as a bitumen Procedure coating and is superhydrophobic (Ismail et al.
The research work procedure is divided The use of stearic acid as a hydrophobic into four steps that consist of raw material agent has also been implemented on the preparation, silica synthesis, coating on the surface of printed circuit boards (PCB.
and substrate, and characterization of the coating produces a superhydrophobic coating (X.
Li et product on the substrate.
, 2.
Based on the research that has been Raw material preparation done, the manufacture of superhydrophobic materials based on geothermal waste silica in The homogenized in size to 325 mesh using a sieve shaker, which is then leached with 25% sulfuric KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 Suryadi.
, et al.
The leaching product is then filtered and determine the average particle size and the dried to be processed to the silica synthesis distribution pattern.
RESULT AND DISCUSSION
Silica synthesis The procedure for silica synthesis using the sol-gel method follows the reference (Ismail Raw Material Preparation Geothermal solid waste in the form of et al.
, 2.
lumps is mechanically ground to obtain a Coating materials preparation smaller size.
Screening with a sieve shaker with The coating step of the glass substrate is a size of 325 mesh aims to obtain a uniform carried out by adding a hydrophobic agent of particle size of raw materials.
The raw materials stearic acid to silica.
The addition of DSO is that have been uniformly processed by the carried out in a constant amount to the three leaching method using 25% sulfuric acid aim to Technically, the composition of the remove metal oxide compounds contained in coating material is stated in Table 1.
the solid raw material sample and only leave Table 1.
Composition of silica, stearic acid, and DSO hydrophobic silica-DSO-stearic acid Number Code Silica .
Stearic acid .
DSO .
silica compounds that are insoluble in acid The reaction of metal oxides that can dissolve in sulfuric acid follows reactions .
3H2SO4.
Ie 6H 3SO42.
26H 3SO4 X2O3 Ie X2(SO.
3 H2O .
The residue from the leaching process in the form of solids containing concentrated silica Coating to glass and polyester fabric is dried to remove water content at a The next step is stirring and heating at 60 material residue is obtained with a lighter color AC until the silica, hydrophobic agent, and DSO before undergoing the leaching process.
This is are perfectly mixed.
The contacting process of in accordance with reaction .
where sulfuric the mixture with the substrate, which is acid can dissolve metal oxides into sulfate prepared by the dip coating method.
compounds that are soluble in aquadest temperature of 105 AC.
Visually, the raw (Silviana et al.
, 2.
Particle size distribution analysis The particle size distribution of the Silica Synthesis synthesized silica was analyzed using ImageJ Silica synthesis is carried out by the sol-gel SEM micrographs were processed by method, where the preparation goes through setting the scale and applying thresholding to the sol phase stage, which produces sodium distinguish individual particles.
The diameters silicate sol and pH value adjustment with acid of random particles were measured to obtain so that silica is produced in the gel phase.
The reaction that occurs follows the reaction measurement data were then exported and between silica and NaOH, which produces plotted as a histogram using Veusz software to sodium silicate and water.
The KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 Suryadi.
, et al.
SiO2.
2NaOH.
Ie Na2SiO3.
H2O.
and stearic acid is hydrophobic.
To overcome this problem, dimethyl silicone oil (DSO) is used After sodium silicate is formed, the addition as an emulsifier.
The interaction between the of nitric acid aims to form a silica compound that silica-DSO-stearic acid system is illustrated in has a silanol group.
Si(OH)4, and with drying.
Figure 1.
the Si(OH)4 compound forms a white solid The interaction that occurs between the (Ismail et al.
, 2.
The reaction that occurs in hydroxyl group on silica and the hydroxyl group the formation of Si(OH)4 is written in reaction on DSO is a hydrogen bond.
Stearic acid added .
to the silica-DSO system has formed a covalent Na2SiO3.
2HNO3.
H2O.
Ie 2NaNO3.
bond between the hydroxyl group of the Si(OH)4.
carboxylic group of stearic acid and the .
In the synthesis process of silica, the hydroxyl group on DSO (X.
Li et al.
, 2.
The sonication treatment aims to help homogenize interaction of the three components causes the the sol phase formed between silica and NaOH silica/DSO/stearic so that it reacts perfectly.
The use of ethanol in hydrophobic from the carbon chain in the alkyl the manufacture of silica aims to form silanol group of the stearic acid compound and on the groups more quickly due to the presence of other side is hydrophilic which can be bound to hydroxyl groups from ethanol and is followed by the substrate because it contains abundant the condensation process of silanol groups into hydroxyl groups.
condensed silica compounds as stated in reaction .
(Ismail et al.
, 2.
Si(OH)4 Si(OH)4 Ie (HO)3-Si-O-Si-(OH)3 H2O The centrifugation process aims to finalize the formed silica compound sediment so that it is separated from its filtrate.
Dry silica .
still contains silanol groups that are needed for the preparation of hydrophobic materials.
Coating of Substrate Hydrophobic Material The first step in coating hydrophobic Hydrophobic silica is made by mixing synthetic silica with an agent that forms hydrophobic properties, namely stearic acid.
this study, variations in the amount of stearic Figure 1.
Interaction between silica.
DSO, and stearic acid in a system of hydrophobic material acid were carried out to see the effectiveness in The hydrophobic material coating stage forming hydrophobic properties in materials on the substrate is carried out by heating and with silica as the raw material.
In order to form dip coating methods.
Heating at a temperature a hydrophobic compound, an emulsifier is of 60 AC and stirring aims to make the needed because silica tends to be hydrophilic hydrophobic silica system homogeneous and in KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 Suryadi.
, et al.
a liquid phase.
The dip coating and drying bonds cause the formation of agglomerates that treatment at a temperature of 180 AC aims to vary in size from one silica compound to ensure that the coating material adheres to the substrate evenly and perfectly (R.
Sutar et , 2.
the silica-DSO-stearic acid coating system was Characteristics of Silica and Hydrophobic Coatings The initial characterization of silica is observing morphology and determining the particle size using the Scanning Electron Microscopy Characterization of the functional groups of (SEM) The carried out by interpreting the spectra produced FTIR The synthesized silica are used as a comparison, as shown in Figure 3.
The FTIR characteristic absorption at 470.
63 cm .
obtained from SEM analysis show that the morphology of the silica particles is round, with characteristic absorption of Si-O-Si bend agglomeration occurring in several parts.
The (Loganathan et al.
, 2013.
Mujiyanti et al.
, 2.
particle sizes obtained from the SEM image Absorption at wave number 956.
70 cm-1 shows approach show that silica particles have a size the presence of the vibration of Si-OH, which is distribution below 1 m, and the largest characteristic of the silanol group in silica distribution is in the range of 200-250 nm, as compounds (Alattar, 2021.
Cui et al.
, 2.
shown in Figure 2.
The characteristic of silica, which is still hydrophilic, is shown in absorption at wave 78 cm-1 as absorbed H2O (K.
Li et al.
, 2.
In addition, the characteristic absorption at wave number 3455.
22 cm -1 shows the presence of a hydroxyl group (-OH), which strengthens the hydrophilic nature of silica used as raw material.
The FTIR spectrum of the silica-DSOstearic characteristics indicating chemical interactions DSO.
Absorption at wave numbers 466.
67 cm-1.
46 cm-1.
50 cm-1 indicates the Figure 2.
Silica size distribution after data processing with ImageJ and Veusz 2 software.
The distribution of particle sizes shows characteristics of silica identity functional groups, namely Si-O-Si bends (Loganathan et , 2.
that the sizes of silica synthesized using the sol- The covalent bonds found in the DSO gel method are of various sizes.
This is because compound are shown in the absorption the silica form is still in the form of a silanol compound with the characteristic of having absorption characteristic of Si-C (Cui et al.
hydroxyl bonds on its surface.
These hydroxyl The alkyl groups in stearic acid are cm-1.
KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 Suryadi.
, et al.
shown in absorption at various wavenumbers.
86 cm-1.
37 cm-1.
The absorption that appears at 719.
45 cm -1 2960 cm-1.
In addition, the absorption at shows the bend in the C-H group of alkanes 76 cm-1 reinforcing the presence of C-H (Mohrig et al.
, 2.
The presence of the C-H group absorption in alkane (Mujiyanti et al.
Yuan et al.
, 2.
Figure 3.
FTIR spectra of silica-DSO-stearic acid in the hydrophobic material system The chemical interaction in the silica- The inversion of the hydrophilic properties DSO-stearic acid system is demonstrated by of the silica raw material used to become a the presence of a new absorption formed at a hydrophobic material was initially indicated by sharp wavenumber at 1020.
34 cm as a C-O the loss of absorption of 1631.
78 cm-1, which is alkoxy group.
This group is formed due to the characteristic of the absorption of water (K.
breakdown of the hydroxyl group in stearic acid Li et al.
, 2.
and covalently bonded with Si in DSO, and Visualization of the water contact angle on forms a Si-O-(C=O)- bond.
The carbonyl group the substrate surface that has been coated with in stearic acid is stated in the new wave number silica-DSO-stearic acid is a parameter that absorption at 1703.
14 cm .
From indicates the hydrophobicity of the material The FTIR spectra, it can be stated that the observations at various ratios of silica and interaction between silica-DSO-stearic acid is stearic acid are stated in Figure 4.
indicated to occur as a covalent bond or a The coating material showed the highest hydrogen bond (X.
Li et al.
, 2.
The hydrophobicity symptoms on both glass and polyester fabric substrates with an optimal strengthened by the absorption of the hydroxyl mass ratio of silica and stearic acid of 1:5.
The group wave number, which is significantly hydrophobic phenomenon of the silica-DSO- reduced to 3435.
22 cm in the silica spectrum.
stearic acid system coating is due to the This indicates that the hydroxyl group is presence of long chains of alkyl contained in the reduced due to the formation of a sharper Si-O hydrophobic agent stearic acid facing the group at 800.
46 cm .
surface (X.
Li et al.
, 2.
Superhydrophobic Suryadi.
, et al.
KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 properties in observations were shown in Chemically, the hydroxyl groups on the coatings applied to the surface of polyester silica surface interact with the free oxygen- fabrics (Liu et al.
, 2.
This is due to the containing groups of the polyester fibers strong interaction between the hydroxyl groups through hydrogen bonding and Van der Waals on silica and the surface of polyester fabrics, forces, ensuring strong adhesion of the primer which contain abundant carboxyl groups.
In this system, dimethyl silicone oil (DSO) facilitating the uniform attachment of stearic acidAithe primary hydrophobic agentAionto the silica particles.
At a 1:3 ratio, the concentration of stearic acid is already sufficient to saturate the available active sites on the silica surface, forming a dense and well-ordered hydrophobic As the ratio increases to 1:5, the system reaches a chemical saturation point where the hydrophobic tails are closely packed, leaving no significant residual or unbound stearic acid.
The integration of silica particles into the micro-scale This promotes air pockets are trapped within the fabric's pores beneath the water droplet.
Since the optimal surface coverage and hierarchical morphology are already effectively established at both 1:3 and 1:5 ratios, any additional stearic acid does not significantly lower the surface energy or alter the air-trapping capability.
Figure 4.
Contact angle of hydrophobic material on the glass substrate .
and polyester fabrics .
in various ratios between silica and stearic The interactions that occur can be in the form of hydrogen bonds because, according to The experimental results demonstrated its function, the coating material does not react that the contact angles for silica-to-stearic acid with the substrate material, which produces by- ratios of 1:3 and 1:5 on polyester fabric substrates were nearly equivalent, showing properties on the substrate is observed over only marginal differences.
This phenomenon time as presented in Figure 5.
The can be explained by both chemical synergetic effects and the physical morphology of the KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 Suryadi.
, et al.
to maintain hydrophobic properties because the interaction between the glass surface and the A significant anomaly was observed in the 1:7 silica-to-stearic acid ratio, where the initial contact angle at minute 0 was markedly lower than that of other ratios, as illustrated in Figure This performance can be attributed to the excessive The molecules creates a steric hindrance effect that disrupts the effective interaction between the silica particles and the polyester substrate (Wang et al.
, 2.
This hindrance prevents the silica from anchoring securely to the fabric fibers, thereby inhibiting the formation of a Figure 5.
Contact angle stability as a function of time for hydrophobic materials on glass (A) and polyester fabric (B) at different silica-to-stearic acid ratios.
In observing the stability of hydrophobic properties, it was found that both substrates were able to maintain hydrophobic properties on a minute scale and continued to decrease as indicated by the contact angle value over time.
This is because the interaction caused by the substrate and coating is only able to maintain hydrophobic properties on a certain time scale.
The factor that causes the short interaction between the substrate and the coating is that the interaction that occurs between the two is still limited to physical interactions.
On polyester fabric substrates, hydrogen bonds can occur between hydroxyl groups on silanol and carboxyl on the substrate.
On glass substrates the instability of hydrophobicity is caused by the adhesion force of the glass surface with the coating material.
Therefore, coatings on glass substrates tend not to be able stable hydrophobic network.
Furthermore, perspective, the excess stearic acid acts as a redundant organic phase that submerges the Instead necessary hierarchical roughness, the surplus acid fills the interstitial spaces between fibers and silica, resulting in a relatively smooth, waxy This loss of surface roughness prevents the entrapment of air pockets, causing the system to fail in achieving the CassieBaxter state required for superhydrophobicity (Maghsoudi et al.
, 2.
Consequently, even at the initial contact .
, the material exhibits a significantly lower contact angle as the water droplet interacts with a more uniform organic layer rather than a roughened, airtrapping interface.
CONCLUSION
Silica can be extracted from geothermal solid waste by the sol-gel method with a variety KOVALEN: Jurnal Riset Kimia, 12.
, 2026: 23-33 Suryadi.
, et al.
of sizes distributed at sizes below 1 m.
The silica-DSO-stearic acid-based optimally hydrophobic at a silica and stearic acid ratio of 1:5.
The waterproof coating shows superhydrophobic symptoms on the polyester fabric substrate with a contact angle value of 7 A.
The stability of the best hydrophobic coating with the contact angle measurement method against time is also shown in the silica
and stearic acid ratio at a 1:5 ratio on the fabric
ACKNOWLEDGMENT