Temperature- and pH-Responsive Micelles with Collapsible Poly(N-isopropylacrylamide) Headgroups
Temperature- and pH-Responsive Micelles with Collapsible Poly(N-isopropylacrylamide) Headgroups
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DOI：
10.1021/la501861t
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发表时间：
2014-07-15
期刊：
影响因子：
3.9
通讯作者：
Warr, Gregory G.
中科院分区：
文献类型：
--
作者：
FitzGerald, Paul A.;Gupta, Sushen;Warr, Gregory G.
本文研究了通过控制自由基（RAFT）聚合制备的一系列温度和ph响应表面活性剂的胶束形成和相行为。这些C(12)NIPAM(m)表面活性剂由一个十二烷基尾部、一个平均聚合度在7到96之间的聚n -异丙基丙烯酰胺（polyNIPAM）头基和一个可电离羧酸基组成。在非电离状态下，这些表面活性剂在加热到较低的临界溶液温度（LCST）时相分离，该温度随着NIPAM基团长度的减少而降低。这与传统的非离子型聚环氧乙烷表面活性剂的行为一致，但与聚nipam低聚物溶液的行为截然不同。小角中子散射（SANS）表明，这些表面活性剂自组装成胶束，胶束由一个接近球形的疏水性核组成，胶束周围是一个远低于其LCST的“毛茸茸”polyNIPAM壳。在升温后，胶束经历由polyNIPAM外壳坍塌引起的球体到棒状转变，导致头团面积减少。在非电离状态下，在lst处进行脱混，但自由聚合物端上的单个电荷完全抑制相分离，使胶束经历形状变化但保持溶解。
We have studied the micelle formation and phase behavior of a series of temperature- and pH-responsive surfactants prepared by controlled radical (RAFT) polymerization. These C(12)NIPAM(m) surfactants consist of a dodecyl tail, a poly(N-isopropylacrylamide) (polyNIPAM) headgroup with average degrees of polymerization of between 7 and 96, and an ionizable carboxylate group. In the un-ionized state, these surfactants phase separate on warming toward a lower critical solution temperature (LCST), which decreases as the length of the NIPAM group is decreased. This is in agreement with the behavior of conventional nonionic poly(ethylene oxide)-based surfactants but is very different from that of polyNIPAM oligomer solutions. Small angle neutron scattering (SANS) shows that these surfactants self-assemble into micelles consisting of a nearly spherical hydrophobic core surrounded by a "hairy" polyNIPAM shell far below their LCST. Upon warming, the micelles undergo a sphere-to-rod transition induced by the collapse of the polyNIPAM shell, causing a reduction in the headgroup area. In the un-ionized state the demixing follows at the LCST, but a single charge on the free polymer end completely suppresses phase separation, allowing micelles to undergo a shape change but remain dissolved.