Editing Smart glass (section)

=== Phase-changing polymer (PCP) ===
Phase-changing polymer (PCP) shows reversible [[phase transition]] between amorphous and semicrystalline states.<ref>{{Cite journal |last1=Liu |first1=Ying |last2=Fan |first2=Jiacheng |last3=Plamthottam |first3=Roshan |last4=Gao |first4=Meng |last5=Peng |first5=Zihang |last6=Meng |first6=Yuan |last7=He |first7=Mingfei |last8=Wu |first8=Hanxiang |last9=Wang |first9=Yufeng |last10=Liu |first10=Tianxi |last11=Zhang |first11=Chao |last12=Pei |first12=Qibing |date=2021-09-28 |title=Automatically Modulated Thermoresponsive Film Based on a Phase-Changing Copolymer |url=https://pubs.acs.org/doi/10.1021/acs.chemmater.1c01389 |journal=Chemistry of Materials |language=en |volume=33 |issue=18 |pages=7232–7241 |doi=10.1021/acs.chemmater.1c01389 |s2cid=239653077 |issn=0897-4756|url-access=subscription }}</ref> This change of phase is dominated by temperature change in thermochromic smart glass application, making it completely automatic at no electricity cost. The structure of PCP often consists of two major components: a phase-changing component polymer (let's call it P1) crosslinked with another polymer (P2) which is strongly phase-separated from the former due to different [[Hydrophile|hydrophilicity]]. Therefore, P1 and P2 are able to form micron-level phase separation after curing. When the temperature is below the phase-transition temperature (Tp) of P1, P1 is semi-crystalline and its [[refractive index]] matches with that of P2, thus making the whole structure transparent to visible light.<ref name=":0">{{Cite journal |last1=Xie |first1=Yu |last2=Guan |first2=Fangyi |last3=Li |first3=Zhou |last4=Meng |first4=Yuan |last5=Cheng |first5=Jiang |last6=Li |first6=Lu |last7=Pei |first7=Qibing |date=August 2020 |title=A Phase‐Changing Polymer Film for Broadband Smart Window Applications |url=https://onlinelibrary.wiley.com/doi/10.1002/marc.202000290 |journal=Macromolecular Rapid Communications |language=en |volume=41 |issue=16 |pages=2000290 |doi=10.1002/marc.202000290 |pmid=32691931 |s2cid=220669546 |issn=1022-1336|url-access=subscription }}</ref> When the temperature goes above Tp, P1 melts and transitions into amorphous phase which exhibits a large refractive index mismatch with P2, resulting in an opaque appearance.<ref name=":0" /> By smartly selecting the material for P1, a reversed effect of transmittance switch can be observed. For example, if at below Tp the refractive index of the semi-crystalline P1 dismatches that of P2, the film then is opaque; if the amorphous P1 matches P2 with respect to refractive index at above Tp, then the film is transparent at the elevated temperature. One signature application would be that, PCP be coated on the glass window of a warehouse where PCP becomes opaque during hot days to block excessive radiation and cools the room down, thus saving energy from running an air conditioner.<ref>{{Cite book |date=2019 |title=Handbook of Energy Efficiency in Buildings |url=https://doi.org/10.1016/C2016-0-02638-4 |doi=10.1016/c2016-0-02638-4|isbn=9780128128176 |s2cid=237077843 }}</ref>