Polyacrylamides of different molecular weight, charges and dosages allow to control the retention and distribution of nanoparticles (NPs) in composites, and optimise composite properties and functionality. Our aim is to evaluate the effect of high molecular weight (13 MDa) cationic polyacrylamide (CPAM) charge and dosage on SiO₂ (74 nm) NP’s assembly in cellulose nanofibers composites.

Engineered cellulose/SiO₂ composites were investigated by SEM, SAXS and DLS. SEM images show the local area retention of NPs into the cellulose matrix. SAXS provides an average NPs distribution and inter-NPs distance over complete volume of composite. DLS gives the hydrodynamic radius of CPAM adsorbed onto SiO₂ NPs in a suspension.

SAXS analysis reveals a structure conformation made of spherical SiO₂ NPs core of diameter 74 nm surrounded by a CPAM polyelectrolyte shell 2.5 nm thick. Surprisingly, CPAM induced assembly of SiO₂ NPs with constant inter-nanoparticle distance, which is irrelevant of polymer charge density. However, NPs retention in the cellulose fibre network increases with CPAM dosage. The assembly mechanism is governed by the balance of electrostatic and steric forces following CPAM coverage onto NPs and the inter-nanoparticle CPAM bridging conformation. This maintains the constant inter-nanoparticle distance and the assembly of NPs in the cellulose network.

不同分子量，电荷和剂量的聚丙烯酰胺可控制纳米颗粒（NPs）在复合材料中的保留和分布，并优化复合材料的性能和功能。我们的目的是评估纤维素纳米纤维复合物中高分子量（13 MDa）阳离子聚丙烯酰胺（CPAM）的电荷和用量对SiO ₂（74 nm）NP组装的影响。

通过SEM，SAXS和DLS对工程纤维素/ SiO ₂复合材料进行了研究。SEM图像显示了NPs在纤维素基质中的局部保留。SAXS提供了完整复合材料体积上的平均NP分布和NP间距离。DLS给出了悬浮液中吸附到SiO ₂ NPs上的CPAM的流体力学半径。

SAXS分析揭示了由直径为74 nm的球形SiO ₂ NPs核制成的结构构象，该核被2.5 nm厚的CPAM聚电解质壳包围。出乎意料的是，CPAM诱导了具有恒定纳米粒子间距离的SiO ₂ NP的组装，这与聚合物电荷密度无关。但是，NPs在纤维素纤维网络中的保留量随CPAM剂量的增加而增加。CPAM覆盖在NP上后，纳米粒子之间的CPAM桥接构象受静电和空间力平衡的控制。这样可以保持恒定的纳米粒子间距离和纤维素网络中NP的组装。