Small-Angle Neutron Scattering Study of Interplay of Attractive and Repulsive Interactions in Nanoparticle–Polymer System

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• 作者：Sugam Kumar ; Vinod K. Aswal ; Joachim Kohlbrecher
• 刊名：Langmuir
• 出版年：2016
• 出版时间：February 16, 2016
• 年：2016
• 卷：32
• 期：6
• 页码：1450-1459
• 全文大小：539K
• ISSN：1520-5827

文摘

The phase behavior of nanoparticle (silica)–polymer (polyethylene glycol) system without and with an electrolyte (NaCl) has been studied. It is observed that nanoparticle–polymer system behaves very differently in the presence of electrolyte. In the absence of electrolyte, the nanoparticle–polymer system remains in one-phase even at very high polymer concentrations. On the other hand, a re-entrant phase behavior is found in the presence of electrolyte, where one-phase (individual) system undergoes two-phase (nanoparticle aggregation) and then back to one-phase with increasing polymer concentration. The regime of two-phase system has been tuned by varying the electrolyte concentration. The polymer concentration range over which the two-phase system exists is significantly enhanced with the increase in the electrolyte concentration. These systems have been characterized by small-angle neutron scattering (SANS) experiments of contrast-marching the polymer to the solvent. The data are modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The phase behavior of nanoparticle–polymer system is explained by interplay of attractive (polymer-induced attractive depletion between nanoparticles) and repulsive (nanoparticle–nanoparticle electrostatic repulsion and polymer–polymer repulsion) interactions present in the system. In the absence of electrolyte, the strong electrostatic repulsion between nanoparticles dominates over the polymer-induced depletion attraction and the nanoparticle system remains in one-phase. With addition of electrolyte, depletion attraction overcomes electrostatic repulsion at some polymer concentration, resulting into nanoparticle aggregation and two-phase system. Further addition of polymer increases the polymer–polymer repulsion which eventually reduces the strength of depletion and hence re-entrant phase behavior. The effects of varying electrolyte concentration on the phase behavior of nanoparticle–polymer system are understood in terms of modifications in nanoparticle–nanoparticle and polymer–polymer interactions. The nanoparticle aggregates in two-phase systems are found to have surface fractal morphology.