group meeting 10_25

1. Photo-Reversible Liquid Crystal Alignment using Azobenzene-Based Self-Assembled Monolayers: Comparison of the Bare Monolayer and Liquid Crystal Reorientation DynamicsGuanjiu Fang, Yue Shi, Joseph E. Maclennan, and Noel A. Clark Figure 3. Liquid crystal alignment by azo-SAMs. Schematic illustration of liquid crystal alignment by azo-SAMs: chromophores, initially with random orientational distribution (a), orient perpendicular to the polarization direction P of the exciting light shown in blue during photobuffing (b), and liquid crystal molecules oriented approximately parallel to the chromophores (c). The optical textures of the liquid crystal cell viewed between crossed polarizers: with a uniformstate (d) when actinic light polarization P^R and a twisted state (e) when P ) R. This cell, composed of a rubbed nylon surfacewith a rubbing direction (R) and an azo-SAMsurface, is 5 μmthick, and is filledwith E31.The exciting light for this experiment is UV radiation centered at 365 nm.

2. Self-Assembly and Dual-Stimuli Sensitivities ofHydroxypropylcellulose-graft-poly(N,N-dimethylaminoethylmethacrylate)Copolymers in aqueous SolutionLin Ma,†,‡ Ruigang Liu,*,† Junjun Tan,†,‡ Deqian Wang,†,‡ Xin Jin,†,‡ Hongliang Kang,† Min Wu,§and Yong Huang*,†, The self-assembly and pH- and thermo-sensitivities properties of hydroxypropyl cellulose-graft-poly(N,N-dimethylaminoethylmethacrylate) (HPC-g-PDMAEMA) copolymers in aqueous solutions were investigated by transmittance, dynamic light scattering (DLS), and 1H NMR spectroscopy. Micelles with different structure can be formed by varying either pH value or temperature. At low pH, e.g., 3.0, the HPC backbone of the copolymer collapse to form the core of micelles stabilized with protonated PDMAEMA side chains on the surface of the micelles upon heating. At the medium pH, e.g., 8.1, both HPC backbone and PDMAEMA side chains collapse upon heating to form unstable aggregates. At high pH, e.g., 12.3, PDMAEMA side chains collapse first to form the core of micelles stabilized with HPC chains upon heating. Further heating the copolymer solution at this pH leads to the aggregation of the micelles due to the collapse of the shell HPC chains. The thermal sensitivity of the HPC-g-PDMAEMA copolymers is reversible.

3. Influence of Molecular Ordering on Electrical and Friction Properties of ω-(trans-4-Stilbene)Alkylthiol Self-Assembled Monolayers on Au (111) The electrical and friction properties of ω-(trans-4-stilbene)alkylthiol self-assembled monolayers (SAMs) on Au(111) were investigated using atomic force microscopy (AFM) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The sample surface was uniformly covered with a molecular film consisting of very small grains. Well ordered and flat monolayer islands were formed after the sample was heated in nitrogen at 120 C for 1 h. While lattice resolved AFM images revealed a crystalline phase in the islands, the area between islands showed no order. The islands exhibit substantial reduction (50%) in friction, supporting the existence of good ordering. NEXAFS measurements revealed an average upright molecular orientation in the film, both before and after heating, with a narrower tilt-angle distribution for the heated film. Conductance-AFM measurements revealed a 2 orders of magnitude higher conductivity on the ordered islands than on the disordered phase. We propose that the conductance enhancement is a result of a better π-π stacking between the trans-stilbene molecular units as a result of improved ordering in islands.

4. Particle Capture via Discrete Binding Elements: Systematic Variations in Binding Energy for Randomly Distributed Nanoscale Surface FeaturesSurachateKalasin,† SurangkhanaMartwiset,‡ E. Bryan Coughlin,† and Maria M. Santore*,† Figure 1. (A) Schematic demonstrating the redistribution of cationic adhesive functionality (red) on a repulsive negative surface (blue) through changes in the size of nanoscopic cationic patches. The series keeps the amount of the cationic functionality on the surface constant. In the limit of extremely small cationic functionality compared with all other length scales, the average (or mean field) surface characteristics are relevant. Negative microparticles adhere to surfaces with larger patches and the same overall cationic functionality but are non adherent on the mean field surface or surfaces with small clusters of charge. (Β) Effective electrostatic contact area (zone of influence) determined by the Debye length. The radius of the zone of influence, Rzoi = 2 (κ-1Rp)1/2 = 63.25 nm,for the ionic conditions in this study.

5. Mixed, Multicompartment, or Janus Micelles? A Systematic Study of ThermoresponsiveBis-Hydrophilic Block TerpolymersAndreas Walther,*,†,‡ Christopher Barner-Kowollik,§ and Axel H. E. M€uller*Langmuir 2010, 26(14), 12237–12246 We present a systematic investigation of the extent of compartmentalization in micelles formed by a series of bishydrophilic block terpolymers with two outer water-soluble segments. The corona blocks are constructed from poly(ethylene oxide) (PEO) and the thermoresponsive poly(N-isopropyl-acrylamide) (PNiPAAm). The fraction of PNiPAAm is varied to establish its influence on the supramicellar aggregation and corona phase behavior. We demonstrate that—when the collapse of PNiPAAm is triggered—a clustering of micelles into superstructures only occurs when the contour length of the thermoresponsive block is longer than that of the PEO chains. The volume fractions play a minor role. The extent of superstructure formation increases with the amount of heating cycles, pointing to a rearrangement of micelles with a mixed corona into a phase-segregated corona. The collapse of PNiPAAm is exploited to artificially raise the incompatibility and drive phase segregation. A uniform population of biphasic Janus micelles cannot be obtained. After repeated heating cycles, the mixture consists of a range of multicompartment architectures, whose patch distribution can be derived from aggregate structures found in cryo-TEM obtained at high temperature. In the last section, we relate our results to previously studied systems and attempt to derive some generalities. First, we try to answer the question of how likely it is in terms of thermodynamics to obtain truly self assembled Janus micelles. Furthermore, our results can provide an estimation for the volume ratio or/and block lengths required in micelles composed out of two corona blocks to induce supramicellar aggregation when a hydrophilic-tohydrophobic phase transition is triggered in one of the blocks.

6. Microphase Separation in Mixed Monolayers of DPPG with a Double Hydrophilic Block Copolymer at the Air-Water Interface: A BAM,LSCFM, and AFM StudyRute I. S. Rom~ao,† Quirina Ferreira,‡ Jorge Morgado,‡,§ Jose M. G. Martinho,§,Amelia M. P. S. Gonc-alves da Silva*