Roles of chemical and physical crosslinking on the rheological properties of silica-doped polyacrylamide hydrogels

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• 作者：Vahid Adibnia ; Seyed Mohammad Taghavi ; Reghan J. Hill
• 关键词：Crosslinking ; Gelation ; Gel ; Storage modulus ; Dispersions ; Polyacrylamide ; Nanocomposites
• 刊名：Rheologica Acta
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：56
• 期：2
• 页码：123-134
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Characterization and Evaluation of Materials; Polymer Sciences; Soft and Granular Matter, Complex Fluids and Microfluidics; Mechanical Engineering; Food Science;
• 出版者：Springer Berlin Heidelberg
• ISSN：1435-1528
• 卷排序：56

文摘

This paper examines the nanoparticle (NP) influence on energy storage and dissipation in hydrogel nanocomposites (HNCs). To obtain fundamental insights into mechanical enhancement, a model system involving the in situ free-radical polymerization of acrylamide with bis-acrylamide (bis) and silica NPs is adopted. The loss tangents of the unmodified polymer networks span three orders of magnitude, and the weak attraction between silica and poly(acrylamide) (PA)—as compared to composites with a stronger NP-polymer interaction—makes these HNCs particularly sensitive to systematic variations in (i) NP size and concentration and (ii) monomer and crosslinker concentrations. From the dynamic shear moduli during polymerization, and their spectra at steady-state, silica NPs in PA behave as multi-functional, physical crosslinking centers that increase the storage modulus, particularly in very weakly bis-crosslinked PA (in which NP aggregates are proposed to form elastically effective clusters). The loss modulus for HNCs reflects adsorption/desorption and friction at the NP surfaces, varying with the NP, monomer and crosslinker concentrations. Silica NPs were also found to slow the polymerization and crosslinking of acrylamide according to the specific NP surface area (set by the NP size and concentration), suggesting that silica NPs reduce the free-radical concentration.