Multi-stimulus responsive weak polyelectrolyte brushes were grafted by surface-initiated atom transfer radical polymerization from spherical silica nanoparticles across a wide range of grafting densities approaching the limit of close packing of grafting sites: a regime not previously explored in the brush swelling literature. Brushes consisted of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) homopolymers or poly(2-(dimethylamino)ethyl methacrylate)- r -poly(4-metharyloyloxyazobenzene) random copolymers P (DMAEMA- r -MOAB) and were subjected to pH-, temperature-, and photoisomerization-induced swelling and deswelling. Homopolymer brushes were prepared at grafting densities ranging from 0.12 to 1.4 nm −2 and number average degrees of polymerization ranging from 300 to 1200. Two copolymer brushes with 8 mol% and 13 mol% of the nonionizable, photoresponsive MOAB units were compared with homopolymer brushes prepared at similar grafting densities and degrees of polymerization. Dynamic light scattering was used to measure the hydrodynamic radius of grafted nanoparticles, and thus brush thickness, in water. Brush swelling in response to increased DMAEMA protonation followed a single scaling behavior across the full range of degrees of polymerization and grafting densities. Incorporating azobenzene-containing MOAB comonomers introduced a modest photoresponsive control of brush swelling and decreased the brush thickness relative to the comparable PDMAEMA homopolymer brush, without affecting the scaling with respect to protonation. PDMAEMA brushes exhibited a pH-dependent lower critical solution temperature behavior, resulting in a thermal collapse of up to 50% upon heating. This work demonstrates that scaling behaviors previously tested at low grafting densities hold for extremely high grafting densities and that they are unaffected by moderate nonionizable comonomer content.

中文翻译：

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多响应球形聚电解质刷在广泛的接枝密度范围内膨胀

多刺激响应弱聚电解质刷是通过表面引发的原子转移自由基聚合从球形二氧化硅纳米粒子在接近接枝位点紧密堆积极限的广泛接枝密度接枝的：以前在刷膨胀文献中没有探索过这种机制。刷子由聚（2-（二甲氨基）甲基丙烯酸乙酯）（PDMAEMA）均聚物或聚（2-（二甲氨基）甲基丙烯酸乙酯）-r-聚（4-甲基酰氧基偶氮苯）无规共聚物P（DMAEMA-r-MOAB）组成，并受到pH 值、温度和光异构化引起的溶胀和消溶胀。均聚物刷制备的接枝密度范围为 0.12 至 1.4 nm -2，数均聚合度范围为 300 至 1200。两种共聚物刷具有 8 mol% 和 13 mol% 的非离子化，将光响应 MOAB 单元与在相似接枝密度和聚合度下制备的均聚物刷进行比较。动态光散射用于测量接枝纳米粒子的流体动力学半径，从而测量水中的刷子厚度。响应于 DMAEMA 质子化增加的刷子膨胀遵循在整个聚合度和接枝密度范围内的单一结垢行为。结合含偶氮苯的 MOAB 共聚单体引入了对刷子膨胀的适度光响应控制，并相对于可比较的 PDMAEMA 均聚物刷子降低了刷子厚度，而不影响质子化方面的结垢。PDMAEMA 刷子表现出依赖于 pH 值的较低临界溶液温度行为，导致加热时热塌陷高达 50%。