Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, D-01069 Dresden, Germany.
Langmuir. 2012 Feb 21;28(7):3439-48. doi: 10.1021/la204230a. Epub 2012 Feb 7.
Temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) brushes with different molecular weights M(n) and grafting densities σ were prepared by the "grafting-to" method. Changes in their physicochemical properties according to temperature were investigated with the help of in situ spectroscopic ellipsometry and in situ attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. Brush criteria indicate a transition between a brush conformation below the lower critical solution temperature (LCST) and an intermediate to mushroom conformation above the LCST. By in situ ellipsometry distinct changes in the brush layer parameters (wet thickness, refractive index, buffer content) were observed. A broadening of the temperature region with maximum deswelling occurred with decreasing grafting density. The brush layer properties were independent of the grafting density below the LCST, but showed a virtually monotonic behavior above the LCST. The midtemperature ϑ(half) of the deswelling process increased with increasing grafting density. Thus grafting density-dependent design parameters for such functional films were presented. For the first time, ATR-FTIR spectroscopy was used to monitor segment density and hydrogen bonding changes of these very thin PNIPAAm brushes as a function of temperature based on significant variations of the methyl stretching, Amide I, as well as Amide II bands with respect to intensity and wavenumber position. No dependence on M(n) and σ in the wavenumber shift of these bands above the LCST was found. The temperature profile of these band intensities and thus segment density was found to be rather step-like, exceeding temperatures around the LCST, while the respective profile of their wavenumber positions suggested continuous structural and hydration processes. Remaining buffer amounts and residual intermolecular segment/water interaction in the collapsed brushes above the LCST could be confirmed by both in situ methods.
采用“接枝到”方法制备了具有不同分子量 M(n) 和接枝密度 σ 的温敏聚 N-异丙基丙烯酰胺（PNIPAAm）刷。借助原位光谱椭圆测量法和原位衰减全反射傅里叶变换红外（ATR-FTIR）光谱研究了它们随温度的物理化学性质变化。刷状标准表明，在较低临界溶液温度（LCST）以下，刷状构象与在 LCST 以上的中间至蘑菇形构象之间存在转变。通过原位椭圆测量法，观察到刷层参数（湿厚度、折射率、缓冲含量）发生明显变化。随着接枝密度的降低，最大溶胀的温度区域变宽。在 LCST 以下，刷层性质与接枝密度无关，但在 LCST 以上呈几乎单调的行为。溶胀过程的中温 ϑ(半)随接枝密度的增加而增加。因此，提出了这些功能薄膜的接枝密度依赖性设计参数。首次使用 ATR-FTIR 光谱监测这些非常薄的 PNIPAAm 刷的链段密度和氢键变化作为温度的函数，基于甲基伸缩、酰胺 I 和酰胺 II 带相对于强度和波数位置的显著变化。在 LCST 以上，这些带的波数位移与 M(n)和 σ 无关。发现这些带的强度（即链段密度）的温度分布相当阶跃状，超过 LCST 周围的温度，而它们的波数位置的相应分布则表明连续的结构和水合过程。在 LCST 以上的塌陷刷中，可以通过原位方法确认剩余的缓冲量和残留的分子间链段/水相互作用。
