Langmuir and Langmuir−Blodgett Films of Side-Chain Liquid-Crystalline Poly(maleic acid-alt-1-alkene)s

Abstract

Langmuir layers of side-chain liquid-crystalline poly(maleic acid-alt-1-alkene)s (SCLCPs) with biphenyl mesogens were studied on water subphases but were also transferred by the use of the Langmuir-Blodgett technique. Brewster angle microscopy showed that the SCLCPs with methoxybiphenyl mesogens strongly aggregate on the water subphase and form islands, which merge upon compression. In contrast, SCLCPs with cyanobiphenyl mesogens spread nicely and compression of these polymers resulted in the formation of triple layers. Langmuir monolayers of SCLCPs with methoxybiphenyl mesogens show Z-type transfer. Atomic force microscopy and X-ray reflectivity measurements of the resulting Langmuir-Blodgett monoand/or multilayers indicate that the side chains of these polymers are possibly tilted. The multilayers have a double layer periodicity, which requires a reorientation of the side chains during or after transfer. Annealing of these Langmuir-Blodgett films resulted in an increase of the mean film thickness and a more uniform d spacing within the multilayer. With atomic force microscopy droplets were observed on top of the multilayer, indicating dewetting of the upper layers.

Langmuir−Blodgett Films of Preformed Polymers Containing Biphenyl Groups

“…The length of the spacer chain is also found to have some effect; by comparing 1 with 2 , 3 with 4 , or 7 with 10 it is apparent that the longer spacer polymers give lower areas per repeat unit suggesting tighter packing. This could be due to the bulky biphenyl unit being at a larger distance from the backbone, not effecting its packing, or the longer, more flexible spacer allowing better ordering within the monolayer, similar to findings by other workers …”

“…This is in contrast to the behavior of fatty acid monolayers, indicating again that it is the nature of the polymer backbone at the air−water interface that is the dominant factor in monolayer behavior. The areas per repeat units and isotherm shapes are similar to those obtained for maleic acid copolymers previously reported . For almost all the polymers, the isotherms become very steep at pressures of more than 5 mN m -1 , probably because a tightly packed structure is being formed.…”

“…For almost all the polymers, the isotherms become very steep at pressures of more than 5 mN m -1 , probably because a tightly packed structure is being formed. The isotherms are fairly featureless otherwise, except for polymer 8 , which has a kink at 25 mN m -1 , which could indicate that at lower pressures there is some interaction between the hydrophilic ester group adjacent to the biphenyl unit and the water surface, a similar interaction being noted by other workers for polymers containing cyanobiphenyl groups . This did not occur for similar polymers 6 and 7 , probably because these have much shorter and less flexible spacer chains.…”

“…Similar measurements give the calculated angles between the side chain and the substrate for the other material; see Table . Tilting of biphenyl-containing side chains has also been observed for maleic acid copolymers 4 Proposed structure of the bilayer of polymer 1 . 3 Modeling of Polymer Spacing thickness of side chain bilayer(nm)polymerX-rayCPKangle of side chain to substrate (deg) 1 0.66 1.10 37 2 0.89 1.40 39 3 1.35 1.86 47 4 1.54 2.51 38 5 1.58 2.60 37 6 0.80 1.62 30 7 1.36 2.08 41 8 1.14 2.10 33 9 1.44 2.02 45 10 1.65 2.72 37 …”

“…Maleic anhydride can copolymerize with a wide variety of olefins; therefore, a range of olefins derived from commercial liquid crystals were synthesized and shown to form monolayers and deposit to form LB films suitable for use as waveguides . This class of polymer has also been incorporated as spacer layers combined with various chromophores in nonlinear optical devices. , Besides our work, a series of liquid crystalline maleic acid copolymers containing biphenyl and cyanobiphenyl units has also been studied as monolayers and one of them deposited as a multilayer …”