Understanding sol–gel transition through a picture. A short tutorial


Investigating and understanding in detail the sol-to-gel transition in inorganic and hybrid systems is a very challenging task. The transition is a critical phenomenon that can only be described with statistical but not thermodynamic models. Graphic schemes, therefore, cannot easily represent such a complicated process. The sol-to-gel transition has been illustrated with the support of several drawings. Representing complex media, such as the sol and the gel, by a scheme, is however quite tricky. Using oversimplified pictures can mislead the comprehension of the process, which is difficult to describe in general terms, as it depends so much on the synthesis and processing conditions. In this short tutorial, a fault-finding discussion based on the most common pictures drawn to illustrate the sol-to-gel transition has been used for a critical description of the process.


  • Sol–gel transition is a critical phenomenon described by statistical models.

  • Description of sol–gel transition through pictures should be done with care, to avoid a misinterpretation of the process.

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  1. 1.

    Innocenzi P (2019) The sol-to-gel transition. Springer briefs in materials. 2nd edn. Springer, the Netherlands

  2. 2.

    Brinker J, Scherer G (1990) Sol–gel science. Academic Press, Boston

  3. 3.

    Wikimedia Commons under the CC BY 4.0 licence. https://en.wikipedia.org/wiki/File:SolGelTechnologyStages.svg

  4. 4.

    PAC, 2007, 79, 1801. (Definitions of terms relating to the structure and processing of sols, gels, networks, and inorganic-organic hybrid materials (IUPAC Recommendations 2007)) on page 1806. IUPAC. Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019) created by S. J. Chalk. https://doi.org/10.1351/goldbook

  5. 5.

    Definition of Xerogel. In Enciclopeda Treccani on line. www.treccani.it/vocabolario/xerogel

  6. 6.

    Matsoukas T (2015) Statistical thermodynamics of irreversible aggregation: the sol-gel transition. Sci Rep 5:8855

    Article  Google Scholar 

  7. 7.

    Flory PJ (1942) Constitution of three-dimensional polymers and the theory of gelation. J Phys Chem 46:132–140

    CAS  Article  Google Scholar 

  8. 8.

    Kricheldorf HR (2013) Paul J. Flory and the classic theory of percolation. In Polycondensation: history and new results, p 35–50. Springer Science & Business Media, Springer, Germany

  9. 9.

    Hench LH, West JK (1990) The sol-gel process. Chem Rev 90:33–72

    CAS  Article  Google Scholar 

  10. 10.

    IUPAC (1997) Compendium of Chemical Terminology. 2nd edn. (the “Gold Book”). Blackwell Scientific Publications, Oxford (Compiled by A. D. McNaught and A. Wilkinson Online version (2019) created by S. J. Chalk). https://doi.org/10.1351/goldbook

  11. 11.

    Rojas G, Estevez M, Vargas S, Rodriguez R (2002) Fractal characterization of silica sol prepared by the sol-gel method: from the sol formation to the flocculation. J Sol–Gel Sci Technol 23:99–105

  12. 12.

    Sacks MD, Sheu RS (1986) Rheological characterization during the sol-gel transition. In: LL Hench, DR Ulrich (eds). Science of ceramic chemical processing. Wiley, New York

  13. 13.

    Sacks MD, Sheu RS (1987) Rheological properties of silica sol-gel materials. J Non Cryst Solids 92:383–396

    CAS  Article  Google Scholar 

  14. 14.

    Winter HH, Mours M (1997) Rheology of polymers near liquid-solid transitions. Adv Polym Sci 134:165–234

    CAS  Article  Google Scholar 

  15. 15.

    Ng LV, Thompson P, Sanchez J, Macosko CW, McCormick AV (1995) Formation of cagelike intermediates from nonrandom cyclization during acid-catalyzed sol-gel polymerization of tetraethyl orthosilicate. Macromolecules 28:6471–6476

    CAS  Article  Google Scholar 

  16. 16.

    Devreux F, Boilot JP, Chaput F, Lecomte A (1990) Sol-gel condensation of rapidly hydrolyzed silicon alkoxides: a joint 29Si NMR and small angle X-ray scattering. Phys Rev A 41:6901–6909

    CAS  Article  Google Scholar 

  17. 17.

    Gits-Leon S, LeFaucheux F, Robert MC (1987) Mass transport by diffusion in a tetramethoxysilane gel. J Cryst Growth 84:155–162

    CAS  Article  Google Scholar 

  18. 18.

    Innocenzi P, Malfatti L, Carboni D, Takahashi M (2015) Sol-to-gel transition in fast evaporating systems observed by in situ time-resolved infrared spectroscopy. ChemPhysChem 16:1933–1939

    CAS  Article  Google Scholar 

  19. 19.

    Innocenzi P, Kidchob T, Bertolo JM, Piccinini M, Guidi MC, Marcelli A (2006) Infrared spectroscopy as an in-situ tool to study the kinetics of processes involved in self-assembly of mesostructured films. J Phys Chem B 110:10837–10841

    CAS  Article  Google Scholar 

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Prof. Luca Malfatti is gratefully acknowledged for critival discussion. Mrs Lavinia Innocenzi for support in drawing the figures.

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Innocenzi, P. Understanding sol–gel transition through a picture. A short tutorial. J Sol-Gel Sci Technol 94, 544–550 (2020). https://doi.org/10.1007/s10971-020-05243-w

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  • Sol-gel transition
  • Sol
  • Gel