Second-harmonic scattering in aqueous urea solutions: evidence for solute clusters?

Martin R Ward, Stanley W Botchway, Andrew D Ward, Andrew J Alexander

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Measurements of second-harmonic scattering (SHS) from concentrated aqueous solutions of urea are reported for the first time using scanning microscopy. SHS signal was measured as a function of solution concentration (C) over a range of saturation conditions from undersaturated (S = 0.15) to supersaturated (5 = 1.86), where S = C/C(sat) and C(sat) is the saturation concentration. The results show a non-linear increase in SHS signal against concentration, with local maxima near S = 0.95 and 1.75 suggesting a change in solution structure near these points. Rayleigh scattering images indicate the presence of particles in nearly saturated (S = 0.95) urea solutions. Time-dependent SHS measurements indicate that signals originate from individual events encountered during scanning of the focal volume through the solution, consistent with second harmonic generation (SHG) from particles. SHG from aqueous dispersions of barium titanate (BaTiO3) nanoparticles with diameters <200 nm, showed signals approximately 20 times larger than urea solutions. The results suggest the existence of a population of semi-ordered clusters of urea that changes with solution concentration.

LanguageEnglish
Pages441-454
Number of pages14
JournalFaraday Discussions
Volume167
DOIs
Publication statusPublished - 17 Jun 2013

Fingerprint

ureas
Urea
solutes
Scattering
harmonics
scattering
Harmonic generation
harmonic generations
saturation
scanning
Scanning
Saturation (materials composition)
Rayleigh scattering
barium
Dispersions
Nanoparticles
Microscopy
Microscopic examination
aqueous solutions
microscopy

Keywords

  • barium compounds
  • urea
  • microscopy, fluorescence
  • nanoparticles
  • scattering, radiation
  • titanium

Cite this

Ward, Martin R ; Botchway, Stanley W ; Ward, Andrew D ; Alexander, Andrew J. / Second-harmonic scattering in aqueous urea solutions : evidence for solute clusters?. In: Faraday Discussions. 2013 ; Vol. 167. pp. 441-454.
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Second-harmonic scattering in aqueous urea solutions : evidence for solute clusters? / Ward, Martin R; Botchway, Stanley W; Ward, Andrew D; Alexander, Andrew J.

In: Faraday Discussions, Vol. 167, 17.06.2013, p. 441-454.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Second-harmonic scattering in aqueous urea solutions

T2 - Faraday Discussions

AU - Ward, Martin R

AU - Botchway, Stanley W

AU - Ward, Andrew D

AU - Alexander, Andrew J

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AB - Measurements of second-harmonic scattering (SHS) from concentrated aqueous solutions of urea are reported for the first time using scanning microscopy. SHS signal was measured as a function of solution concentration (C) over a range of saturation conditions from undersaturated (S = 0.15) to supersaturated (5 = 1.86), where S = C/C(sat) and C(sat) is the saturation concentration. The results show a non-linear increase in SHS signal against concentration, with local maxima near S = 0.95 and 1.75 suggesting a change in solution structure near these points. Rayleigh scattering images indicate the presence of particles in nearly saturated (S = 0.95) urea solutions. Time-dependent SHS measurements indicate that signals originate from individual events encountered during scanning of the focal volume through the solution, consistent with second harmonic generation (SHG) from particles. SHG from aqueous dispersions of barium titanate (BaTiO3) nanoparticles with diameters <200 nm, showed signals approximately 20 times larger than urea solutions. The results suggest the existence of a population of semi-ordered clusters of urea that changes with solution concentration.

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KW - scattering, radiation

KW - titanium

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