Chifukwa chiyani PTFE imatha kupirira kutentha kwambiri?

Choyamba ndi chifukwa chakuti malo ake osungunuka ndi pafupifupi madigiri 327 Celsius, omwe ndi apamwamba kwambiri kuposa a PE (~ 130) ndi PVDF (~ 177) omwe ali ndi zofanana. Chinthu chofunika kwambiri chomwe chimatsimikizira malo osungunuka ndi mphamvu pakati pa unyolo ndi mamolekyu a unyolo. , ngakhale fluorine ali mkulu electronegativity, koma kuchokera kapangidwe mankhwala a PTFE, dipole mphindi anathetsedwa wina ndi mzake, choncho si polar zinthu ndipo samatulutsa zoonekeratu lolunjika mphamvu, kutanthauza kuti kubalalitsidwa mphamvu ndi zotsatira zazikulu Choncho. , ndizomveka kunena kuti malo osungunuka a PTFE sayenera kukhala apamwamba kwambiri kuposa a PE, koma kuchuluka kwa ma elekitironi a fluorine kumapangitsa kuti maatomu a fluorine okonzedwa bwinowa akhale ndi mgwirizano wotsutsana komanso wolepheretsa steric block, kotero kuti ma molecular chain conformation imapereka mawonekedwe a spirochete, m'malo mwa mawonekedwe a zigzag omwe amapezeka m'ma polima odzaza, omwe amathandizira kusungika bwino kwa maunyolo a molekyulu kuti apange makhiristo, komanso kuchepetsa mtunda wolekanitsa pakati pa maunyolo osungidwa kumachulukitsa mphamvu zapakati ndipo motero kumawonjezera kusungunuka. .

Chachiwiri ndi kukhazikika kwa PTFE pa kutentha kwakukulu. Kwa ma polima, chimodzi mwazifukwa zazikulu zakuwonongeka kwa magwiridwe antchito ndi kawopsedwe ndikuwonongeka kwa zomangira kukhala mamolekyu ang'onoang'ono. Popeza zomangira za CF ndizokhazikika kwambiri, zomangira za CC pagawo lalikulu la unyolo Kunena zoona, zimakhala zosavuta kusweka, koma chifukwa cha kukhalapo kwa CF, zimapanga hyperconjugation zotsatira pa CC yake yapafupi (anti-bonding orbital of CF ndi kulumikizana kwa orbital kwa CC), komwe kumapangitsanso kukana kwakukulu kwa unyolo kutentha / kuwala. Panthawi imodzimodziyo, mphamvu ya hyperconjugation imabweretsa mphamvu yochepa ya ortho position (gauche) kusiyana ndi anti position (anti), yomwe imafotokozanso chifukwa chake ngakhale pali electrostatic repulsion pakati pa fluorine, amakhudzidwabe ndi mphamvu zomwe zingatheke. Ubwino wa maatomu a fuloroni ndi wochepetsedwa kuti maatomu a fluorine azitha kukonzedwa bwino kwambiri mu PTFE.

Ma atomu a fluorine omwe amakonzedwa bwino kwambiri amakhala ndi mawonekedwe athunthu a octahedral, kotero sali opereka ma elekitironi abwino kapena olandila ma elekitironi. Amakulunga mwamphamvu unyolo waukulu womwe umakhala wosalimba kwambiri pakati, ngati kupanga filimu yoteteza. Kulimbana ndi kuukira kwamankhwala, kupatsa PTFE kukana kwambiri kwamankhwala. Chotsatira china cha dongosolo lolimba ndi mphamvu yotsika pamwamba, kotero kuti PTFE ilibe zokopa zambiri ku mamolekyu akunja, chifukwa chake siimamatira.