. 

Overview of Sol-Gel Science 

and Technology 

by Sandra K. Young 

Approved for public release; distribution is unlimited. 
The findings in this report are not to be construed as an 

official Department of the Army position unless so 

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Citation of manufacturer’s or trade names does not 

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Destroy this report when it is no longer needed. Do not 

return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-2650 Tanmrv2002 

Overview of Sol-Gel Science 

and Technology 

Sandra K. Young 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
Abstract 

Sol-gel science and technology continues to interest researchers decades after 

its discovery. The reaction is easy to perform, does not require special conditions 

(can be done on the bench top in a beaker), and does not require high 

temperatures. The sol-gel reaction consists of a series of simple hydrolysis and 

condensation reactions. This reaction can be influenced by several factors: 

quantity of acid catalyst, amount of water used, incorporation of a network 

modifier, and varying solvent effects. This work presents an overview of sol-gel 

science and technology, discusses the advantages of sol-gel reactions, and 

describes the factors that can influence changes in the final sol-gel material. 

ii 
Acknowledgments 

I ’ 

The author would like to thank Dr. Nora Beck Tan and Dr. Steven M&night, 

who encouraged and continue to encourage independent scientific pursuits in 

the polymers field, which led to some in the sol-gel field, and acknowledge the 

support of the polymers branch in continuing research in the area of sol-gel 

science and technology. 

. . . 

Ill 
. 

INTENTIONALLY Lmr Bum. 

iv 
Contents 

I l 

List of Figures 

1. DOD Interest in Sol-Gel Science and Technology 

2. Global Overview of Silicon-Based Research 

3. Introduction to Sol-Gel Science and Technology 

3.1 

3.2 

3.3 

3.4 

3.5 

Factors Influencing the Sol-Gel Reaction .................................................... 4 

Water-to-A&oxide Ratio ............................................................................... 4 

Type and Amount of Catalyst ...................................................................... 5 

Type of Network Modifier ............................................................................ 6 

Solvent Effects.. .............................................................................................. 

.7 

Acknowledgments . . . 

111 

vii 

1 

1 

2 

4. s-ary 8 

5. References 9 

Distribution List 11 

Report Documentation Page 13 

V 
Vi 
List of Figures 

Figure 1. Potential applications for polymer material modification 

utilizing in situ sol-gel processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Figure 2. Colloidal network formation in sol-gel materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Figure 3. Sol-gel general reaction scheme . . . . . . . . . . . . ..*..................................................... 3 

Figure 4. Hydrolysis mechanism for a tetraalkoxysilane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Figure 5. Effect of catalyst on hydrolysis and condensation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Figure 6. Effect of pH on hydrolysis and condensation rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Figure 7. Condensation mechanism for a tetrafunctional silicate. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Vii 
. . . 

vu1 
1. DOD Interest in Sol-Gel Science and Technology 

Along with the demand for new technologies, new processing techniques, and 

novel nanomaterials, there has been an increased interest in investigating sol-gel 

science and technology. The Department of Defense (DOD) community is 

looking at sol-gel science to produce high-performance materials for low gravity 

and high impact, possessing properties such as increased toughness, strength, 

and thermal stabilities, and decreased sensitivity to shock. These materials 

encompass applications from membranes for fuel cells or water purification, to 

composites for space vehicles or planes, to encapsulated nanomaterials for 

energetics. Researchers are finding that sol-gel science is a straightforward 

technique that many scientists have been using to produce inorganic and 

organic-inorganic materials. 

2. Global Overview of Silicon-Based Research 

Silicon is the second most abundant element on earth, exceeded only by oxygen 

[l]. Silicon-containing compounds, in a variety of compositions, account for over 

90% of the earth’s land mass 11, 21. The earth’s crust alone consists of 25.7% 

silicon, by weight. Silicon is not found free in nature, but occurs chiefly as an 

oxide and as silicates [l]. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, 

and opal are some of the forms in which the oxide appears [l]. It is through this 

natural abundance of silica as a source of raw materials, in addition to its 

inherent high thermal stability and high mechanical strength, that has drawn 

increased emphasis on practical applications of silicon-based materials in the 

research and development of high-performance and functional materials. 

Silicon-based research has drawn much attention in recent years, with targeted 

conferences such as the University Pierre et Marie Curie hosting proceedings on 

hybrid organic-inorganic materials [3], the National American Chemical Society 

hosting symposia on silicones and silicone-modified materials [4], and McMaster 

University organizing an annual organosilicon symposium [5]. In addition, 

publications such as the Journal of Sol-GeI Science and Technology, Chemistry of 

Maferials, and the Journal ofNon-Crysfulline Solids contain a significant number of 

articles that focus on the research of silicon compounds. These conferences and 

journals highlight much of the major silicon-based research generated 

in academia and industry. Research involving reactive silicone chemistry 

includes production of pure silicon to semiorganics, ring-opening and 

atom transfer polymerizations, hydrosilylation, polymerizations with controlled 

1 
stereochemistry, and condensation reactions. These reactions with silicones 

produce a wide range of materials which encompass the major areas of 

silicon-based research and chemistry: polymers, elastomers, interpenetrating 

networks, reinforcing fillers, membranes, microlithography, photoinitiation, 

high-performance polymers, and sol-gel-derived ceramic precursors. 

3. Introduction to Sol-Gel Science and Technology 

While it was studied earlier, sol-gel chemistry has been investigated extensively 

since the mid-1970s, when sol-gel reactions were shown to produce a variety of 

inorganic networks that can be formed from metal a&oxide solutions [6]. 

Through sol-gel processing, homogeneous, high-purity inorganic oxide glasses 

can be made at ambient temperatures rather than at the very high temperatures 

required for conventional formation of glasses. Various products, such as 

molded gels [7,8], spun fibers [9, lo], thin films [ll-131, molecular cages [14,15], 

and xerogels [16] have been developed for utility in such areas as gas separations 

[12,17], elastomers [lS, 191, coatings [20,21], and laminates [17,22]. It is through 

the inorganic compound incorporation into organic polymers that a wide variety 

of property modifications can be achieved (see Figure 1). 

f Increased T 

/T / A 

High Performance Polymers 

’ / 1 \ ( Degradation u 

Multiphasic Polymers 

Figure 1. Potential applications for polymer material modification utilizing in sihr 

sol-gel processes. 

The sol-gel chemical process is self-described in the definition of a sol, a gel, and 

a summary of the process in which a sol evolves into a gel [23] (see Figure 2). A 

sol is a colloidal dispersion of small particles in a liquid; a gel is usually a 

2 
Figure 2. Colloidal network formation in sol-gel materials. 

substance composed of a continuous network encompassing a continuous liquid 

phase [24, 251. Sol-gel reactions promote the growth of colloidal particles (sol) 

and their subsequent network formation (gel) through the hydrolysis and 

condensation reactions of inorganic a&oxide monomers. The precursors for 

synthesizing these colloids consist of a metal or metalloid element surrounded 

by various reactive ligands. Metal alkoxides are most popular because they react 

readily with water. The most widely used metal alkoxides are the alkoxysilanes, 

such as tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS). However, 

other alkoxides such as aluminates, titanates, zirconates, and borates are also 

commonly used in the sol-gel process, either alone or in combination with other 

alkoxides such as TEOS. 

To more fully understand the sol-gel chemical process, the sol-gel reaction must 

be examined. Sol-gel reactions are a series of hydrolysis and condensation 

reactions of an alkoxysilane, which proceed according to the reaction scheme 

shown in Figure 3. Hydrolysis is initiated by the addition of water to the TEOS 

solution under acidic, neutral, or basic conditions. 

-4 i--GR + HCH 

Alkoxysilane 

Hvtko+is L 

s i--OH + RCH 

Restaification 

-1 

Silarol Alcohol 

Waier 

d -$L---Ai--- + HOH 

l+qdmlysis 

SilAnol 

, I 

siloxane Water 

d i-OH + -4 Alcobl 

ConQmafion 

-1 

i-OR - - -Jidi--.-- + ROH 

AlCOb~Si.5 I I 

Siim01 AlkOXpilXE Siloxane Akchol 

(1) 

(24 

(2b) 

Figure 3. Sol-gel general reaction scheme. 

3 
In the first step, hydrolysis, a silanol group is generated (Figure 3, reaction [l]). 

As only acid catalysis is used in this research, discussions of the sol-gel reactions 

will refer to acid catalysis only [25]. A positive charge develops on the 

alkoxysilane through the attack of an acid catalyst. The alkoxysilane then is 

hydrolyzed in an Sn2-type reaction, forming a silanol moiety. This is discussed 

more thoroughly in section 3.3, which deals with type and amount of catalyst. 

The mechanism for reaction 1 is depicted in Figure 4. TEOS is not soluble in 

water. Therefore, hydrolysis is promoted by the addition of organic cosolvents, 

such as alcohols [25] that aid in the thorough mixing of the alkoxide molecules 

with water molecules in solution. 

FAST - R 

Si(OR)4 + H+ k (RO)sSi--i)’ 

‘H (3) 

Figure 4. Hydrolysis mechanism for a tetraalkoxysilane. 

In the second step, the silanol group can undergo condensation with either an 

a&oxide or another silanol group (reaction [2a] or [2b] in Figure 3), which results 

in the formation of strong siloxane linkages and produces either alcohol (ROH) 

or water in situ. As the number of Si-0-Si bridges increases, the siloxane 

particles can aggregate into a sol. This, as shown in Figure 2, consists of the 

formation of small silicate clusters dispersed in solution. Gel formation occurs 

when the sol particles undergo sufficient condensation reactions such that a 

network (a gel) is formed, trapping the aqueous and alcohol by-products. After 

gel-network formation is complete, the by-products are removed by heat and 

vacuum, yielding a vitrified and densified glass network. 

3.1 Factors Influencing the Sol-Gel Reaction 

A number of conditions can influence the hydrolysis and condensation reactions. 

Of these, the most pertinent include water-to-&oxide ratio, type and amount of 

catalyst, type of organic group(s) attached to the silicon atom, and solvent effects 

[25,26]. These factors will now be considered. 

3.2 Water-to-Alkoxide Ratio 

The effect of the water-to-alkoxide ratio for the sol-gel process is such that as the 

ratio increases, so does the SiOz content of the gel. Therefore, for complete 

hydrolysis, there must be at least one mole of water for every alkoxide group. 

Some researchers have gone further to state that if more than one mole of water 

4 
per alkoxide group is used, the reverse reaction, reesterification, will occur 

faster than the forward reaction [25]. However, in a recent article by McCormick 

et al. [271, whose experiments were conducted over a wide range of 

water-to-TEOS ratios, there was no correlation between the wateralkoxide ratio 

and the achievement of complete hydrolysis. The validity of these experiments 

on the effect of water:alkoxide ratio are thought to be accurate because water is 

generated in the reaction in situ and therefore the reaction, once catalyzed, 

self-propagates the hydrolysis. 

3.3 Type and Amount of Catalyst 

One important issue for consideration when deciding the concentration of 

catalyst is whether a precise concentration is needed. In the sol-gel process, 

water is generated in situ through condensation reactions. This makes 

calculation and addition of any precise amount of catalyst difficult. In addition 

to water:TEOS ratio experiments, McCormick et al. [271 synthesized sol-gel films, 

adding a wide range of acid concentrations. Their results indicated no 

correlation between the acid concentration and acid initiation of the sol-gel 

reaction. In the experiments, different acid concentrations were used with each 

sample and, as previously discussed, the condensation reaction caused the in situ 

generation of water. Consequently, this in situ generation of water diluted the 

initial acid concentration in every experiment. However, no differentiation 

between the final sol-gel structures was observed by 2% nuclear magnetic 

resonance (NMR) spectroscopy for the various different overall sol-gel reactions. 

From these experiments, it was determined that only a catalytic amount of acid 

was necessary. Therefore, the reaction, containing this minimum amount of 

catalyst in all experiments, could self-propagate. This may cause a change in the 

kinetics of the reaction but not in the basic structure of the overall network. 

Hydrolysis and condensation reactions of most inorganic a&oxides can be 

carried out without catalyst because of the extremely fast rates of reaction. 

However, alkoxysilanes hydrolyze much more slowly, requiring the addition of 

either an acid or base catalyst (see Figure 5). Acid-catalyzed reactions, having a 

particle nucleation rate-determinin g process, tend to yield more linear-like 

networks due to the fast hydrolysis. Therefore, acid catalyzed systems have a 

less completely formed network of siloxane bonds with a higher concentration of 

unreacted silanols. Base-catalyzed reactions, on the other hand, yield highly 

dense materials due to the longer time that the sol particles have to aggregate 

and arrange themselves in the most thermodynamically stable arrangement. 

This process leaves fewer unreacted silanol groups in the overall network and a 

more highly densified network. 

Acid catalysis, used in this research, increases the rate of the hydrolysis reaction, 

as shown in Figure 4. In the first step (Figure 4, equation [3]), hydrolysis occurs 

5 
High Rate of Condensation High Rate of Hydrolysis 

* Rapid Gelation 

* Growth Rate Determining 

Process 

* Slow Gelation 

* Nucleation Rate Determining 

Process 

Figure 5. Effect of catalyst on hydrolysis and condensation. 

through the protonation of the oxygen atom of the alkoxy group due to the 

presence of extra electrons. This causes a shift in the electron cloud of the Si-0 

bond toward the oxygen, resulting in a positive charge on the silicon atom 1281. 

In the rate-determinin g step (Figure 4, equation [4]), oxygen from the water 

attacks the silicon atom, which has low electron density. This results in the 

formation of a pentacoordinate transition state in which partial positive charges 

are developed. Steric effects, such as the presence of bulky and/or long alkyl 

substituents, will affect the rate of the hydrolysis reaction by hindering the 

inversion of the Sn2 transition state [28]. 

Several pH-dependent rate profiles have also been reported for the hydrolysis 

and condensation reactions, where it has been found that reaction rates are 

largely dependent on pH (see Figure 6) [24,25,29,30]. For instance, at pH = 7, 

molecular hydrolysis occurs at a slow rate, while molecular condensation occurs 

at a fast rate. It is this inverse relationship between the rates of the hydrolysis 

and condensation reactions that must be taken into account in controlling the 

kinetics of the reaction and therefore controlling the ultimate network structure. 

3.4 Type of Network Modifier 

When TEOS is commix ed with a silicon a&oxide comonomer containing organic 

groups directly bonded to the silicon atom, organically modified silicates 

(ORMOSILs) are created. The result of synthesizing ORMOSILs is to modify the 

network connectivity. Organic groups cause coordination centers with 

6 
PH 

Figure 6. Effect of pH on hydrolysis and condensation rates. 

functionality less than four and influence the reactivity of the alkoxy groups and 

therefore the connectivity of the sol-gel network in two ways. (1) Formation of 

siloxane bonds requires the diffusion of partially hydrolyzed molecules. The 

larger the alkyl group attached to the silicone, the slower the rate of diffusion 

and therefore the less interconnection within the network. (2) It is also reported 

that larger alkyl groups produce polymers with higher surface area [25]. Larger 

surface area allows for higher unreacted oxide concentration in the gels. This 

produces a branching effect in the sol-gel network. In addition to these two 

points, it was previously discussed that steric effects, such as the presence of 

bulky and/or long alkyl substituents, will affect the rate of the hydrolysis 

reaction by hindering the inversion of the Sn2 transition state [28]. ORMOSILs 

will be discussed in more detail in a subsequent technical report on organicinorganic nanocomposites. 

3.5 Solvent Effects 

The effect of solvents on hydrolysis and condensation reactions is not usually 

discussed primarily because solvents other than water and simple alcohols, 

which are produced internally, are not often used. However, addition of external 

solvents can have an important effect on controlling hydrolysis and condensation 

rates. These solvents, excluding the usual water and alcohol cosolvent, are called 

drying chemical control additives (DCCAs) and include tetrahydrofuran, 

formamide, dimethylformamide, and oxalic acid. These solvents can be used in 

addition to alcohol in order to promote slow drying of the silica monolithic gel 

[25,28]. In bulk films, slow drying is necessary to prevent cracking of the film. 

Condensation rates may be dramatically affected by solvent type (see Figure 7). 

Condensation, via acid catalysis, is proposed to go through a two-step Sn2 

mechanism. 

7 
(5) 

Wh WW x H i P OH 

+ + tRWWW2 - (RO)#i-O-Si(OR)2 + H+ + H20 (6) 

H’ ?H 

Figure 7. Condensation mechanism for a tetrafunctional silicate. 

Protic solvents seemingly have little or no effect on condensation rates. Polar 

aprotic solvents, such as those previously mentioned, solvate the protonated 

silanol (Si-OHz+). The cation is solvated by orienting the negative end of the 

polar aprotic around the cation and by donating unshared electron pairs to the 

vacant orbitals of the cation. This process stabilizes the transition state and 

increases the rate of condensation. Use of DCCAs can be an advantage for solgel reactions within a membrane template. A DCCA will allow molecular 

diffusion but will delay the reaction, resulting in inorganic uniformity through 

the template. Without a DCCA, the overall reaction rate is high in relation to the 

slow diffusion process; therefore, the ultimate geometrical distribution of the 

silicate phase will be highly nonuniform. 

4. Summary 

Sol-gel science and technology has the potential to make a significant impact in 

modification of the properties of materials. One of the most significant benefits 

of sol-gel science is its use of room temperature conditions and insensitivity to 

the atmosphere. These features will allow its use with various materials, which 

cannot tolerate high temperatures and does not limit the researcher to using 

special precautions, such as a dry box. By assuming the load- and 

thermal-bearing phase in the material, sol-gel materials can increase thermal and 

mechanical properties of composites if the two systems are mixed 

homogeneously on the molecular level. A number of factors, including water 

content, modifiers, and solvent, can be altered in any sol-gel system, modifying 

the connectivity of the network and affeding the properties. 

Several current projects in the polymers branch utilize sol-gel chemistry. These 

include silane epoxies for adhesives, silane urethanes for controlled porosity 

materials for water filtration, silane zeolites for modifying polymer membranes 

for fuel cells or chemical/biological resistant materials, and silsesquioxane 

materials for compatibilizing organic-inorganic composites. It is likely that 

technical reports and peer-reviewed publications will come out of these works in 

the near future. 

8 
5. References 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

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Lide, D. R. (editor). Handbook ofchemisfry and Physics. Boca Raton, FL: CRC 

Press LLC, 1992. 

Wilkes, G. L., H. H. Huang, and R. H. Glaser. Silicon Based Polymer Science. 

Columbus, OH: ACS Publications, 1990. 

Sanchez, C., and F. Ribot (editors). First European Workshop on Hybrid 

Organic-Inorganic Materials. University Pierre et Marie Curie, Paris, France, 

1993. 

215th National American Chemical Society Meeting. Dallas, TX. March 1998. 

31st Organosilicon Symposium. McMaster University, New Orleans, LA. 

<http://www .chemistry. mcmaster.ca/-31SiSymp/>, May 1998. 

Nogami, M., and Y. Moriya. JoumaZ of Non-Crystalline Solids. Vol. 37, 

pp. 191-201,198O. 

Wei, Y., D. Jin, C. Yang, and G. Wei. Journal of Sol-Gel Science & Technology. 

Vol. 7, pp. 191-201,1996. 

Mackenzie, J. D. “Glasses From Melts and Glasses From Gels: A 

Comparison.” Journal of Non-Crystalline Solids, vol. 48, pp. l-10,1982. 

Mascia, L., Z. Zhang, and S. J. Shaw. “Carbon Fibre Composites Based on 

Polyimide/Silica Ceramers: Aspects of Structure-Property Relationship.” 

Composites Part A, vol. 27A, no. 12, pp. 12ll-1221,1996. 

Sakka, S., Y. Tanaka, and T. Kokubo. “Hydrolysis and Polycondensation of 

Dimethyldiethoxysilane and Methyltriethoxysilane as Materials for the 

Sol-Gel Process.” Journal of Non-Crystalline Solids, vol. 82, pp. 24-30,1986. 

Brinker, C. J., R. Shegal, S. L. Hietala, R. Deshpande, D. M. Smith, D. Loy, 

and C. S. Ashley. “Sol-Gel Strategies for Controlled Porosity Inorganic 

Materials.” JoumaI of Membrane Science, vol. 94, pp. 85-102,1994. 

Yoldas, B. E. JoumaZ of Non-CystaZZine Solids. Vol. 112, pp. 419-423,1989. 

, 

13. Schmidt, H. Journal of Non-CystaZZine Solids. Vol. 37, pp. 191-201,198O. 

14. Zusman, R. D., A. Beckman, I. Zusman, and R. L. Brent. Analytical 

BiochemistnJ. Vol. 201, pp. 103-106,1992. 

15. Yakubovich, T. N., Y. L. Zub, and R. Leboda. “Metal Coordination 

Compounds Built Into Polyorganosiloxane Matrices: Hemin.” Russian 

Journal of Coordination Chemistq, vol. 20, no. 10, pp. 761-765,1994. 

9 
16. Hobson, S. T., and K. J. Shea. “Bridged Bisimide Polysilsesquioxane 

Xerogels: New Hybrid Organic-Inorganic Networks.” C%mistry of Materials, 

vol. 9, no. 2, pp. 616-623,1997. 

17. Mulhaupt, R., U. Buchholz, J. Rosch, and N. Steinhauser. “Progress in 

Synthesis and Application of Segmented Polymers.” Die Angewandte 

Makromoleckulare Chemie, vol. 223, pp. 47-60,1994. 

18. Hashim, A. S., N. Kawabata, and S. Kohjiya. Journal of Non-Crystalline Solids. 

Vol. 5, pp. 211-218,1995. 

19. Mark, J. E. “Novel Reinforcement Techniques for Elastomers.” JoumaZ of 

Applied Polymer Science: Appkd Polymer Symposium, vol. 50, pp. 273-282,1992. 

20. Baumann, F., B. Deubzer, M. Geck, J. Dauth, and M. Schmidt. “Elastomeric 

Organosilicon Micronetworks.” MizcromoZecuZes, vol. 30, no. 24, 

pp. 7568-7573,1997. 

21. Wen, J., and G. L. Wilkes. “Organic-Inorganic Hybrid Network Materials by 

the Sol-Gel Approach.” Chemistry of Materials, vol. 8, pp. 1667-1681,1996. 

22. Chou, H. C., D. A. Wilson, W. Y. Lin, and J. 0. Stoffer. American Chemical 

Society Polymer Preprints. Vol. 36, no. 2, pp. 376-377,1995. 

23. Brinker, C. J., and G. W. Scherer. Sol-Gel Science: The Physics and Chemistry of 

SoI-Gel Processing. New York: Academic Press, Inc., 1990. 

24. Brinker, C. J. The Colloid Chemistry of Silica. Columbus, OH: ACS 

Publications, ch. 18,1994. 

25. Brinker, C. J. “Hydrolysis and Condensation of Silicates: Effects on 

Structure.” Journal of Non-CystaZline Solids, vol. 100, pp. 31-50,1988. 

26. Yoldas, B. E. “Modification of Polymer-Gel Structures.” Journal of 

Non-Crystalline Solids, vol. 63, pp. 145-154,1984. 

27. McCormick, A. V., L. V. Ng, P. Thompson, J. Sanchez, and C. W. Macosko. 

“Formation of Cagelike Intermediates From Nonrandom Cyclization During 

Acid-Catalyzed Sol-Gel Polymerization of Tetraethyl Orthosilicate.” 

Mizcromolecules, vol. 28, pp. 6471~6476,1995. 

28. Hench, L. L., and J. K. West. “The Sol-Gel Process.” Chemical Reviews, 

vol. 90, pp. 33-72,199O. 

29. Schmidt, H., H. Scholze, and A. Kaiser. “Principles of Hydrolysis and 

Condensation Reaction of Alkoxysilanes.” Journal of Non-Crystalline Solids, 

vol. 63, pp. l-11,1984. 

30. Julbe, A., C. Balzer, J. M. Barthez, C. Guizard, A. Larbot, and L. Cot. “Effect 

of Non-Ionic Surface Active Agents on TEOS-Derived Sols, Gels and 

Materials.” Journal of Sol-Gel Science & Technolog?l, vol. 4, pp. 89-97,1995. 

10 
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Overview of Sol-Gel Science and Technology EMATOlA 

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Sandra K. Young 

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3. ABSTRACT(Maximum 200 words) 

Sol-gel science and technology continues to interest researchers decades after its discovery. The reaction is easy tc 

berform, does not require special conditions (can be done on the bench top in a beaker), and does not require high 

emperatures. The sol-gel reaction consists of a series of simple hydrolysis and condensation reactions. This reactior 

an be influenced by several factors: quantity of acid catalyst, amount of water used, incorporation of a network 

nodifier, and varying solvent effects. This work presents an overview of sol-gel science and technology, discusses the 

dvantages of sol-gel reactions, and describes the factors that can influence changes in the fmal sol-gel material. 

1. SUBJECT TERMS 15. NUMBER OF PAGES 

al-gel science and technology, acid catalyst, water content, network modifier, solvent 17 

ffects 16. PRICE CODE 

r. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT 

OF REPORT OF THIS PAGE OF ABSTRACT 

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL 

13 

Standard Fom~ 298 (Rev. 2-89) 

Prescribed by ANSI Std. 239-18 298-102 
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