An experimental instrument has been developed utilizing Brewster angle reflectometry and Maxwell displacement current (MDC) measurement techniques, which are ascribed to the linear and spontaneous polarization, respectively, to investigate orientational order of Langmuir monolayers at an air-water interface. This system has been demonstrated to be sensitive in detecting the orientational order parameters S1 and S2 simultaneously [Sn is defined as the thermodynamic average of Legendre polynomials of nth rank, Sn=Pn(cosθ)]. Using this system in conjunction with a previously established system utilizing second harmonic generation and MDC, which is capable of detecting the orientational order parameters S1 and S3 simultaneously, all three orientational order parameters S1, S2, and S3 can be obtained for Langmuir monolayers. An experiment using the newly developed instrument was conducted on a monolayer comprised of 4-octyl-4-n-cyanobiphenyl (8CB) molecules to demonstrate the capability of detecting the orientational order parameters S1 and S2 during monolayer compression.

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