Vuoriluoto Maija, Orelma Hannes, Johansson Leena-Sisko, Zhu Baolei, Poutanen Mikko, Walther Andreas, Laine Janne, Rojas Orlando J
Biobased Colloids and Materials group (BiCMat), Department of Forest Products Technology, School of Chemical Technology, Aalto University , FI-00076, Espoo, Finland.
VTT, Technical Research Centre of Finland , Biologinkuja 7, P.O. Box 1000, FIN-02044 VTT, Finland.
J Phys Chem B. 2015 Dec 10;119(49):15275-86. doi: 10.1021/acs.jpcb.5b07628. Epub 2015 Nov 25.
Block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) with varying block sizes were synthesized by consecutive reversible addition-fragmentation chain transfer (RAFT) polymerization and then exposed to cellulose substrates with different anionic charge density. The extent and dynamics of quaternized PDMAEMA-b-POEGMA adsorption on regenerated cellulose, cellulose nanofibrils (CNF), and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF) was determined by using electromechanical and optical techniques, namely, quartz crystal microbalance (QCM-D) and surface plasmon resonance (SPR), respectively. PDMAEMA-b-POEGMA equilibrium adsorption increased with the anionic charge of cellulose, an indication of electrostatic interactions. Such an observation was further confirmed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Depending on their architecture, adsorption on TOCNF of some of the PDMAEMA-b-POEGMA copolymers produced a significant reduction in QCM frequency, as expected from large mass uptake, while surprisingly, other copolymers induced the opposite effect. This latter, remarkable behavior was ascribed to coupled water expulsion from the interface upon charge neutralization of anionic surface sites with adsorbing cationic polymer segments. These observations were further investigated with SPR and QCM-D measurements using deuterium oxide solvent exchange to determine the amount of coupled water at the TOCNF-block copolymer interface. Finally, random copolymers with similar composition adsorbed to a larger extent compared to the respective block copolymers, revealing the effect of adsorbed loops and tails as well as hydration.
通过连续可逆加成-断裂链转移（RAFT）聚合反应合成了具有不同嵌段尺寸的聚（甲基丙烯酸2-（二甲氨基）乙酯）（PDMAEMA）和聚（聚乙二醇甲醚甲基丙烯酸酯）（POEGMA）的嵌段共聚物，然后将其暴露于具有不同阴离子电荷密度的纤维素底物上。使用机电和光学技术，即石英晶体微天平（QCM-D）和表面等离子体共振（SPR），分别测定了季铵化的PDMAEMA-b-POEGMA在再生纤维素、纤维素纳米原纤（CNF）和（2,2,6,6-四甲基哌啶-1-氧基）（TEMPO）氧化纤维素纳米原纤（TOCNF）上的吸附程度和动力学。PDMAEMA-b-POEGMA的平衡吸附量随纤维素的阴离子电荷增加而增加，这表明存在静电相互作用。原子力显微镜（AFM）和X射线光电子能谱（XPS）进一步证实了这一观察结果。根据其结构，一些PDMAEMA-b-POEGMA共聚物在TOCNF上的吸附导致QCM频率显著降低，这正如大量质量吸收所预期的那样，然而令人惊讶的是，其他共聚物却产生了相反的效果。后一种显著行为归因于随着吸附的阳离子聚合物链段使阴离子表面位点电荷中和，界面处耦合水的排出。使用重水溶剂交换的SPR和QCM-D测量进一步研究了这些观察结果，以确定TOCNF-嵌段共聚物界面处耦合水的量。最后，与相应的嵌段共聚物相比，具有相似组成的无规共聚物吸附程度更大，这揭示了吸附环和尾以及水合作用的影响。
