Department of Materials Science and Engineering, Clemson University , Clemson, South Carolina 29634, United States.
Microphotonics Center and Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
ACS Nano. 2016 Dec 27;10(12):10716-10725. doi: 10.1021/acsnano.6b06044. Epub 2016 Oct 20.
We have fabricated gradient-grafted nanofoam films that are able to record the presence of volatile chemical compounds in an offline regime. In essence, the nanofoam film (100-300 nm thick) is anchored to a surface cross-linked polymer network in a metastable extended configuration that can relax back to a certain degree upon exposure to a chemical vapor. The level of the chain relaxation is associated with thermodynamic affinity between the polymer chains and the volatile compounds. In our design, the chemical composition of the nanofoam film is not uniform; therefore, the film possesses a gradually changing local affinity to a vapor along the surface. Upon vapor exposure, the nonuniform changes in local film morphology provide a permanent record or "fingerprint" for the chemical event of interest. This permanent modification in the film structure can be directly detected via changes not only in the film surface profile but also in the film optical characteristics. To this end, we demonstrated that sensing/recording nanofoam films can be prepared and interrogated on the surfaces of optical waveguides, microring optical resonators. It is important that the initial surface profile and structure of the nanofoam film are encrypted by the distinctive conditions that were used to fabricate the film and practically impossible to replicate without prior knowledge.
我们制备了梯度接枝纳米泡棉薄膜，能够在离线状态下记录挥发性化合物的存在。从本质上讲，纳米泡棉薄膜（100-300nm 厚）锚定在表面交联聚合物网络中，处于亚稳态扩展构型，在暴露于化学蒸气时可以在一定程度上松弛。链松弛的程度与聚合物链与挥发性化合物之间的热力学亲和力有关。在我们的设计中，纳米泡棉薄膜的化学成分不均匀；因此，薄膜沿表面具有逐渐变化的局部对蒸气的亲和力。在蒸气暴露时，局部薄膜形貌的不均匀变化为感兴趣的化学事件提供了永久记录或“指纹”。这种薄膜结构的永久改变可以通过不仅在薄膜表面轮廓而且在薄膜光学特性方面的变化直接检测到。为此，我们证明了可以在光波导、微环光谐振器的表面上制备和检测用于感测/记录的纳米泡棉薄膜。重要的是，纳米泡棉薄膜的初始表面轮廓和结构由用于制备薄膜的独特条件加密，并且在没有事先知识的情况下几乎不可能复制。
