Sol-gel particle growth studied using fluorescence anisotropy: An alternative to scattering techniques

Birch, David J. S.; Geddes, Chris D.

doi:10.1103/physreve.62.2977

Cited by 49 publications

(67 citation statements)

References 14 publications

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“…Our previous analysis of R(t) 9,10 for silica hydrogels and that of Narang and co-workers 7 on TMOS showed that the best description was provided by two rotational correlation times τ r1 and τ r2 in the form where R 0 is the initial anisotropy. We interpret f as the fraction of fluorescence due to probe molecules bound to silica particles and hence 1 -f is the fraction due to free dye in the sol.…”

Section: Theorymentioning

confidence: 96%

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1- and 2-Photon Fluorescence Anisotropy Decay in Silicon Alkoxide Sol−Gels: Interpretation in Terms of Self-assembled Nanoparticles

2002

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We have studied the one-and two-photon induced fluorescence anisotropy decay of rhodamine 6G (R6G) during polymerization of tetramethyl orthosilicate (TMOS) approaching the sol-to-gel transition, a time denoted t g , using time-correlated single-photon counting and femtosecond Ti:sapphire laser excitation. A biexponential decay of fluorescence anisotropy is observed at all times. We propose a different interpretation to the widely accepted view, that fluorescence anisotropy reports solely on molecular viscosity in sol-gels. We think our results are consistent with the presence of both free dye and dye bound to nm-size silica particles rather than just the coexistence of different discrete viscosity domains as reported previously. A corollary of our interpretation is that the microviscosity changes very little from that of the initial bulk sol throughout the sol-gel polymerization. Nanometer-size particles are known from small angle scattering studies to be precursors to gelation in sol-gels over a wide range of conditions and our interpretation might prove to be an important step toward understanding the self-assembly mechanisms of silicon alkoxide based materials at the molecular level. According to our measurements and interpretation, for TMOS at pH 2.3 for example, primary silica particles of ≈0.8-nm mean radius grow by monomer-monomer or monomer-cluster addition to produce larger structures ≈1.1-nm mean radius after one month.

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Section: Theorymentioning

confidence: 96%

“…7,9,10 Multiphoton excitation increases the initial value of the fluorescence anisotropy, R 0 , and hence the dynamic range over which rotations are observed. This is particularly useful when the fluorescence lifetime is significantly less than the rotational correlation time, as is the case here.…”

Section: Theorymentioning

confidence: 99%

1- and 2-Photon Fluorescence Anisotropy Decay in Silicon Alkoxide Sol−Gels: Interpretation in Terms of Self-assembled Nanoparticles

2002

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“…The control of the structure has been achieved by the selection of starting materials, pH control of the solvent, solvent exchange during polymerization stage, and aging [7,8,9].…”

Section: Introductionmentioning

confidence: 99%

Structural anisotropy of silica hydrogels prepared under magnetic field

2008

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Birefringence measurements have been carried out on the Pb-doped silica hydrogels prepared under various magnetic fields up to 5T. The silica gels prepared at 5T were used as a medium of crystal growth of PbBr2, whose result implied the structural anisotropy; an aligned array of crystallites was obtained by transmission electron microscopy. While the samples prepared at 0, 1, and 3T have no birefringence, we found that the samples have negative birefringence on the order of magnitude 10 −6 as if the direction of the magnetic field is the optic axis of a uniaxal crystal. To the authors' knowledge, the birefringent silica hydrogels were obtained by gelation under magnetic field for the first time. Also, scanning microscopic light scattering experiments have been performed. The results indicate that the characteristic length distribution for birefringent samples is narrower than that for non-birefringent ones.

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“…[15][16][17] When this experimental method is used, it has been shown 18 that glycerol as an organic polyhydroxy compound (as in the case of our tri(n-butyl)amine/citric acid system) significantly suppresses the rate of silica particle growth in aqueous systems (in this context, see also ref 19).…”

Section: Discussionmentioning

confidence: 96%

Behavior of Tri(n-butyl)ammonium Bis[citrato(3−)-O¹,O³,O⁶]silicate in Aqueous Solution: Analysis of a Sol−Gel Process by Small-Angle Neutron Scattering

et al. 2005

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The racemic hexacoordinate silicon(IV) complex tri(n-butyl)ammonium bis[citrato(3−)-O 1 ,O 3 ,O 6 ]silicate (1) was synthesized by treatment of Si(OMe) 4 with 2 molar equiv of citric acid and 2 molar equiv of N(n-Bu) 3 . The corresponding germanium analogue, tri(n-butyl)ammonium bis[citrato(3−)-O 1 ,O 3 ,O 6 ]germanate (5; structurally characterized by single-crystal X-ray diffraction), was obtained analogously, starting from Ge(OMe) 4 . Upon dissolution in water, the λ 6 Si-silicate dianion of 1 hydrolyzes spontaneously (formation of Si(OH) 4 and citric acid), whereas the λ 6 Ge-germanate dianion of 5 was found to be stable in water. Aqueous "solutions" of 1, with concentrations that are significantly higher than the saturation concentration of Si(OH) 4 , look absolutely clear over a period of several weeks; however, in reality, these solutions are sols with very small particles that slowly grow with time and finally form a gel that precipitates. This sol−gel process was monitored by small-angle neutron scattering (SANS). For reasons of comparison, an aqueous solution of the hydrolytically stable germanium compound 5 was also studied by the SANS technique.

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Sol-gel particle growth studied using fluorescence anisotropy: An alternative to scattering techniques

Cited by 49 publications

References 14 publications

1- and 2-Photon Fluorescence Anisotropy Decay in Silicon Alkoxide Sol−Gels: Interpretation in Terms of Self-assembled Nanoparticles

1- and 2-Photon Fluorescence Anisotropy Decay in Silicon Alkoxide Sol−Gels: Interpretation in Terms of Self-assembled Nanoparticles

Structural anisotropy of silica hydrogels prepared under magnetic field

Behavior of Tri(n-butyl)ammonium Bis[citrato(3−)-O¹,O³,O⁶]silicate in Aqueous Solution: Analysis of a Sol−Gel Process by Small-Angle Neutron Scattering

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Sol-gel particle growth studied using fluorescence anisotropy: An alternative to scattering techniques

Cited by 49 publications

References 14 publications

1- and 2-Photon Fluorescence Anisotropy Decay in Silicon Alkoxide Sol−Gels: Interpretation in Terms of Self-assembled Nanoparticles

1- and 2-Photon Fluorescence Anisotropy Decay in Silicon Alkoxide Sol−Gels: Interpretation in Terms of Self-assembled Nanoparticles

Structural anisotropy of silica hydrogels prepared under magnetic field

Behavior of Tri(n-butyl)ammonium Bis[citrato(3−)-O1,O3,O6]silicate in Aqueous Solution: Analysis of a Sol−Gel Process by Small-Angle Neutron Scattering

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Behavior of Tri(n-butyl)ammonium Bis[citrato(3−)-O¹,O³,O⁶]silicate in Aqueous Solution: Analysis of a Sol−Gel Process by Small-Angle Neutron Scattering