title: Effect of concentration on the photo-orientation and relaxation dynamics of self-assembled monolayers of mixtures of an azobenzene-based triethoxysilane with octyltriethoxysilane.
abstract: Self-assembled monolayers (SAMs) were prepared from solutions with different proportions of a photoactive, azobenzene-based, silanized derivative of disperse red one (dDR1), and octyltriethoxysilane (OTE), a shorter, nonphotoactive molecule. The in-plane photoinduced orientational ordering of the resulting two component monolayers was monitored via precision measurement of in-plane birefringence using a dedicated high-extinction polarimeter. Measurements of contact angle, absorption, and birefringence show that introduction of OTE into the dDR1 deposition solution produces a continuous reduction of the surface density of dDR1 in the SAM, enabling the study of photowriting and relaxation dynamics in monolayers ranging from 100% dDR1 to samples where the dDR1 coverage is about 35%. The orientational dynamics depend strongly on the areal density of dDR1. As the fractional area of dDR1 is reduced, the rates of photowriting, photoerasing, and thermal relaxation increase, and the local orientational confinement of the molecules becomes more heterogeneous.
authors.affiliation: Department of Physics and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, United States.
authors.forename: Guanjiu
authors.initials: G
authors.lastname: Fang
authors.forename: Nathan
authors.initials: N
authors.lastname: Koral
authors.forename: Chenhui
authors.initials: C
authors.lastname: Zhu
authors.forename: Youngwoo
authors.initials: Y
authors.lastname: Yi
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Glaser
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Maclennan
authors.forename: Noel A
authors.initials: NA
authors.lastname: Clark
authors.forename: Eva D
authors.initials: ED
authors.lastname: Korblova
authors.forename: David M
authors.initials: DM
authors.lastname: Walba