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Differentiating bonding and caging in a charged colloid system through rheological measurements.
Zong, Yiwu; Yuan, Guangcui; Zhao, Chuanzhuang; Han, Charles C.
Afiliação
  • Zong Y; State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of Polymer Science and Materials, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, CAS, Beijing 100190, China.
J Chem Phys ; 138(18): 184902, 2013 May 14.
Article em En | MEDLINE | ID: mdl-23676069
The linear and nonlinear rheological measurements were utilized to study the mechanical response of concentrated mixtures of colloidal particles with opposite charges. The particle volume fraction (Φ) spans the region from low volume fraction (Φ = 0.18) gel to high volume fraction (Φ = 0.53) glass. In the linear viscoelastic region, the storage moduli G' exhibits deferent Φ dependence at low and high Φ's. It follows a power law relationship as G' ~ Φ(6.2±0.2) for Φ < 0.46, and follows an exponential relationship as G' ~ exp[(13.8 ± 0.6)Φ] for Φ ≥ 0.46. The difference can be taken as a distinction between a colloidal gel and an attractive glass (or dense gel) for the present system. The loss moduli G" is almost frequency independent within the whole experimental frequency range (10(-1)-10(2) rad∕s) for colloidal gel, and G" exhibits a weak minimum for attractive glass. In the nonlinear large amplitude rheological measurement, samples with Φ < 0.46 show one-step yielding, and samples with Φ ≥ 0.46 exhibit two-step yielding which is in agreement with numerous experiments in attractive glassy systems. The first yielding is due to the breaking of short range interactions which bond the interconnected clusters or local clusters, while the second yielding is attributed to the breaking of long range interaction, normally the caging forming or glass forming interactions. The qualitative distinction between attractive glass and gel in terms of their yielding behavior is consistent with the linear rheological results. The particle-particle interactions were modulated by salt concentration. It was found that, when the attraction interaction is enhanced, both yielding points in attractive glass shift to higher strain amplitude and the gap between the two yielding points become more separated.

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Tipo de estudo: Qualitative_research Idioma: En Revista: J Chem Phys Ano de publicação: 2013 Tipo de documento: Article País de afiliação: China

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Tipo de estudo: Qualitative_research Idioma: En Revista: J Chem Phys Ano de publicação: 2013 Tipo de documento: Article País de afiliação: China