Phase Transitions in the Anchored Organic Bilayers of Long-Chain Alkylammonium Lead Iodides (C_nH_2n+1NH₃)₂PbI₄; n = 12, 16, 18

Abstract

The single perovskite slab alkylammonium lead iodides (C n H2 n +1NH3)2PbI4, n = 12, 16, 18, display two phase transitions, just above room temperature, associated with changes in the alkylammonium chains. We have followed these two phase transitions using scanning calorimetry, X-ray powder diffraction, and IR and Raman spectroscopies. We find the first phase transition to be associated with symmetry changes arising from a dynamic rotational disordering of the ammonium headgroup of the chain whereas the second transition, the melting of the chains in two dimensions, is characterized by an increased conformational disorder of the methylene units of the alkyl chains. We examine these phase transitions in light of the interesting optical properties of these materials, as well as the relevance of these systems as models for phase transitions in lipid bilayers.

Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR

“…Therefore, it is reasonable to assume that there were several different organic phase states in the interlayer. Vibrational spectroscopies provide a powerful and quantitative local probe of the structure and dynamics in the alkylammonium chains [14], this will be help of us a molecular level understanding the microcosmic environment in the confined organic phase. 6 …”

Raman spectroscopic study of organo‐montmorillonites

“…10 Raman spectroscopy in the C-H stretching modes has been extensively used to characterized amine chain conformations. 14 Figure 2 shows the Raman spectra of HDTMAB surfactant recorded at room temperature and liquid nitrogen temperature. The band positions and their assignments are given in Table 1.…”

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Naturally Self-Assembled Nanosystems and Their Templated Structures for Photonic Applications

“…Therefore, nano-/microstructuring using templates such as artificial polymer opals and liquid crystal is a whole new class of research. These micro-/nanostructures have potential applications such as tunable plasmonic bandgaps [116], novel types of liquid crystal displays [117], and nanolaser cavities [118]. These macroporous materials are already available in the market as surface enhanced Raman scattering (SERS) devices [119].…”