Observation of Amplitude Mode Under Dc Electric Field in Smectic-cα* Phase

Linear and nonlinear dielectric spectroscopy under DC electric fields has been performed in the high temperature region of smectic-Cα* phase of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC) to obtain a deeper insight of dynamic properties. It is observed a softening of amplitude mode and ferroelectric mode with increasing the DC field close to the smectic-Cα*-smectic-A(C) phase boundary line. It was seen that the relaxation frequency of the amplitude mode obeys the Curie-Weiss law with respect to the applied electric field

Dielectric Propertiesof Smectic-cα* Phase

DIELECTRIC PROPERTIESOF SMECTIC-Cα* PHASE. Linear and third-order nonlinear dielectric measurements have been performed within the smectic-Cα* phase of antiferroelectric liquid crystal 4-(1-methyl-heptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC). In the low temperature region of smectic-Cα* phase, we observed the hysteresis of dielectric constant in cooling and heating process measurement. From the frequency dispersion measurement, it has been found that the frequency relaxation of antiferroelectric Goldstone mode and ‘low frequency mode', decreased with increasing the temperature until approach the center of the smectic-Cα* phase

EFEK ELEKTROOPTIK NONLINIER PADA FASASMEKTIK-C *

EFEK ELEKTROOPTIK NONLINIER PADA FASASMEKTIK-C *. Telah dilakukan pengukuran elektrooptik untuk mempelajari dinamika molekul kristal cair di sekitar transisi fasa smektik-A-smektik-Cα* kristal cair antiferoelektrik 4-(1-methyl-heptyloxycarbonyl)phenyl 4-octylcarbonyloxybiphenil-4-carboxylate (MHPOCBC). Telah diperlihatkan bahwa dispersi frekuensi dari respon elektrooptik orde kedua sangat tergantung pada sudut antara polarizer dan arah normal lapisan smektik dan anisotropi indeks bias, sedangkan respon linier tidak demikian. Meskipun soft mode pada fasa SmA tidak dapat diamati, pada fasa smektik-Cα* amplitude mode dan ferroelectric mode dapat diamati menggunakan spektroskopi elektrooptik orde kedua. Pada kondisi eksperimen tertentu, kontribusi ferroelectric mode pada spektrum dispersi frekuensi berhasil dikurangi dan amplitude mode dapat diamati dengan jelas. Hasil yang diperoleh didiskusikan dan dianalisis berdasarkan teori fenomenologikal

SIFAT DIELEKTRIK FASA SMEKTIK-Cα* KRISTAL CAIR MHPOBC DALAM MEDAN LISTRIK DC

SIFAT DIELEKTRIK FASA SMEKTIK-Cα* KRISTAL CAIR MHPOBC DALAM MEDAN LISTRIK DC. Telah dilakukan pengukuran tetapan dielektrik kristal cair MHPOBC pada fasa SmA, SmCα* dan SmC* di dalam medan listrik DC. Telah diamati adanya titik trikritikal pada diagram fasa E-T dari kristal cair MHPOBC di sekitar transisi fasa SmA- SmCα* di mana transisi fasa orde kedua berubah menjadi orde pertama. Proses relaksasi baru dengan frekuensi rendah diamati pada fasa SmCα*, yang diyakini berhubungan dengan soft mode

DIELECTRIC PROPERTIESOF SMECTIC-Cα* PHASE

DIELECTRIC PROPERTIESOF SMECTIC-Cα* PHASE. Linear and third-order nonlinear dielectric measurements have been performed within the smectic-Cα* phase of antiferroelectric liquid crystal 4-(1-methyl-heptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC). In the low temperature region of smectic-Cα* phase, we observed the hysteresis of dielectric constant in cooling and heating process measurement. From the frequency dispersion measurement, it has been found that the frequency relaxation of antiferroelectric Goldstone mode and ‘low frequency mode’, decreased with increasing the temperature until approach the center of the smectic-Cα* phase

IDENTIFIKASI FASA FEROELEKTRIK PADA KRISTAL CAIR EP10PBNP

IDENTIFIKASI FASA FEROELEKTRIK PADA KRISTAL CAIR EP10PBNP. Telah dilakukan pengukuran tetapan dielektrik kristal cair 1-ethylpropyl (S)-2-{6-[4-(4’-decyloxyphenyl) benzoyloxyl]-2-naphthyl} propionate (EP10PBNP) untuk mengidentifikasi fasa serta mempelajari dinamika molekulnya di sekitar daerah transisi fasa, yaitu dari fasa smektik-A (SmA) ke fasa lain yang berada di bawah suhu transisi. Dari hasil analisis diperoleh bahwa fasa feroelektrik smektik-C* (SmC*) terbentuk di bawah fasa SmA. Di samping itu, telah diperoleh hubungan antara frekuensi relaksasi dari ferroelectric soft mode dan ferroelectric goldstone mode terhadap suhu. Perubahan frekuensi relaksasi ferroelectric soft mode pada fasa SmA mengikuti hukum Curie-Weiss

Field-induced behaviors near the smectic-A–smectic-Cα* phase transition of an antiferroelectric liquid crystal

We have experimentally and theoretically investigated the electric-field effect on the smectic-A–smectic-Cα* phase transition of an antiferroelectric liquid crystal4-(1-methyl-heptyloxycarbonyl)phenyl 4′-octylcarbonyloxybiphenil-4-carboxylate. From the microscopic observations under electric fields and the measurements of the D-E hysteresis loop and apparent tilt angle, the E (electric field)-T (temperature) phase diagram was established, in which a tricritical point was found. From the dielectric measurements under dc electric fields, a soft mode inducing the transition was observed. Furthermore, we have developed a phenomenological theory under dc fields to analyze the experimental results. The origin of the soft mode observed under fields was clarified and the temperature dependence of the relaxation frequency was obtained by the analyses