Length scale hierarchy in sol, gel, and coacervate phases of gelatin

Biswaranjan Mohanty, V. K. Aswal, J. Kohlbrecher, H. B. Bohidar

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Abstract

Length scale hierarchy in gelatin sol, gel, and coacervate (induced by ethanol) phases, having same concentration of gelatin in aqueous medium (13% w/v), has been investigated through small angle neutron scattering and rheology measurements. The static structure factor profile, I(q) versus wave vector q, was found to be remarkably similar for all these samples. This data could be split into three distinct ç-regimes: the low-? regime, Iex(q) = Iex(0)/(1-q2ζ2)2 valid for q < 3Rg -1; the intermediate q-regime, I(q) = I(0)/(1+q2ξ2) for 3Rg -1 < q < ξ-1; and the asymptotic regime, I(q) = (c/q) exp(-R c 2q2/2) for q >ξ-1i. Consequently, three distinct length scales could be deduced from structure factor data: (a) inhomogeneity of size, ζ= 20 ±1 nm for all the three phases; (b) average mesh size, ξ0 = 2.6 ±0.2 nm for sol and gel, and smaller mesh size, ξos = 1.2 ±0.2 nm for coacervate; and (c) cross section of gelatin chains, Rc= 0.35 ±0.04 nm. In addition, the structure factor data obtained from coacervating solution analyzed in the Guinier region, I(q) = exp(-q 2Rg 2/3), yielded value of typical radius of gyration of clusters, Rg ≈69 nm that indicated existence of triple-helices of length, L ≈239 nm; (d) Frequency and temperature sweep measurements conducted on coacervate samples revealed two other length scales: (e) viscoelastic length, ξve= 14 ±2 nm and (f) correlation length at melting, ξT = 500 ±70 nm. Thus, existence of six distinct length scales, (a-f), ranging from 1.2 to 500 nm has been established in the coacervate phase of gelatin-ethanol-water system. Results are discussed within the framework of Landau-Ginzburg treatment of dynamically asymmetric systems (Prog Theor Phys 1977. 57. 826: Phvs Rev A 1991, 44, R817; J Phys II (France) 1992, 2, 1631).

Original languageEnglish
Pages (from-to)1653-1667
Number of pages15
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume44
Issue number12
DOIs
Publication statusPublished - 15 Jun 2006
Externally publishedYes

Keywords

  • Biopolymer
  • Hydrogels
  • Neutron scattering
  • Polyelectrolyte
  • Rheology

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