TY - JOUR
T1 - Specific anion effects on the hydration and tribological properties of zwitterionic phosphorylcholine-based brushes
AU - Yu, Yunlong
AU - Yao, Yongchao
AU - van Lin, Simone
AU - de Beer, Sissi
N1 - Elsevier deal
PY - 2019/3/1
Y1 - 2019/3/1
N2 - Polymer brushes are known to form highly efficient lubricating layers for a broad range of contacting surfaces in water. Here we focus on brushes of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) polymers that are end-anchored to the substrate at a high density. We show that the friction coefficient, which is measured upon sliding atomic force microscopy colloid probes on PMPC brushes at different normal loads, decreases when salts are added (1 M sodium fluoride (NaF), sodium chloride (NaCl), sodium iodide (NaI), cesium chloride (CsCl) and cesium iodide (CsI)). Interestingly, we observe that the reduction in the friction coefficient increases with increasing anionic size in the solution, while the size of the cation has no measureable effect. We relate the reduction in the friction coefficient to a decrease in the compliance of the brush. In pure water the brush is swollen and soft, resulting in a large contact area between colloids and brushes and, therefore, a relatively “high” friction coefficient. In salt solutions, the stiffness of the brush increases with increasing anionic size resulting in a lower contact area and, therefore, lower friction coefficient.
AB - Polymer brushes are known to form highly efficient lubricating layers for a broad range of contacting surfaces in water. Here we focus on brushes of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) polymers that are end-anchored to the substrate at a high density. We show that the friction coefficient, which is measured upon sliding atomic force microscopy colloid probes on PMPC brushes at different normal loads, decreases when salts are added (1 M sodium fluoride (NaF), sodium chloride (NaCl), sodium iodide (NaI), cesium chloride (CsCl) and cesium iodide (CsI)). Interestingly, we observe that the reduction in the friction coefficient increases with increasing anionic size in the solution, while the size of the cation has no measureable effect. We relate the reduction in the friction coefficient to a decrease in the compliance of the brush. In pure water the brush is swollen and soft, resulting in a large contact area between colloids and brushes and, therefore, a relatively “high” friction coefficient. In salt solutions, the stiffness of the brush increases with increasing anionic size resulting in a lower contact area and, therefore, lower friction coefficient.
KW - UT-Hybrid-D
KW - Atomic force microscopy
KW - Friction
KW - Hofmeister series
KW - Polymer brush
KW - Adhesion
UR - http://www.scopus.com/inward/record.url?scp=85059677374&partnerID=8YFLogxK
U2 - 10.1016/j.eurpolymj.2019.01.013
DO - 10.1016/j.eurpolymj.2019.01.013
M3 - Article
AN - SCOPUS:85059677374
SN - 0014-3057
VL - 112
SP - 222
EP - 227
JO - European polymer journal
JF - European polymer journal
ER -